From 09172271502d1e2e39a1bb26f574002738aa7f9a Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 18 Jan 2021 12:23:39 +0100
Subject: [PATCH 001/217] Initial POC of general HTML support.

---
 .../src/dataschema.js                         | 193 ++++++++++++++++++
 1 file changed, 193 insertions(+)
 create mode 100644 packages/ckeditor5-content-compatibility/src/dataschema.js

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
new file mode 100644
index 00000000000..dce78f4e9a7
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -0,0 +1,193 @@
+/**
+ * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module content-compatibility/dataschema
+ */
+
+import { capitalize, escapeRegExp } from 'lodash-es';
+
+const DATA_SCHEMA_PREFIX = 'ghs';
+
+const dtd = {
+	'div': {
+		inheritAllFrom: '$block'
+	}
+};
+
+export default class DataSchema {
+	constructor( editor ) {
+		this.editor = editor;
+		this.attributeFilter = new AttributeFilter();
+	}
+
+	allowElement( { name: viewName, attributes = [] } ) {
+		this._defineSchema( viewName );
+		this._defineConverters( viewName );
+
+		if ( !Array.isArray( attributes ) ) {
+			attributes = [ attributes ];
+		}
+
+		for ( const attribute of attributes ) {
+			this.allowAttribute( {
+				name: attribute,
+				elements: [ viewName ]
+			} );
+		}
+	}
+
+	allowAttribute( { name: attributeName, elements = [] } ) {
+		if ( !Array.isArray( elements ) ) {
+			elements = [ elements ];
+		}
+
+		elements.forEach( element => this.attributeFilter.allow( element, attributeName ) );
+	}
+
+	disallowAttribute( { name: attributeName, elements = [] } ) {
+		if ( !Array.isArray( elements ) ) {
+			elements = [ elements ];
+		}
+
+		elements.forEach( element => this.attributeFilter.disallow( element, attributeName ) );
+	}
+
+	* _filterAttributes( elementName, attributes ) {
+		for ( const attribute of attributes ) {
+			const attributeName = attribute[ 0 ];
+
+			if ( this.attributeFilter.isAllowed( elementName, attributeName ) ) {
+				yield attribute;
+			}
+		}
+	}
+
+	_defineSchema( viewName ) {
+		const schema = this.editor.model.schema;
+
+		schema.register( encodeView( viewName ), dtd[ viewName ] );
+	}
+
+	_defineConverters( viewName ) {
+		const conversion = this.editor.conversion;
+		const filterAttributes = this._filterAttributes.bind( this );
+		const modelName = encodeView( viewName );
+
+		conversion.for( 'upcast' ).elementToElement( {
+			view: viewName,
+			model: ( viewElement, { writer: modelWriter } ) => {
+				const attributes = filterAttributes( viewName, viewElement.getAttributes() );
+
+				const encodedAttributes = [];
+				for ( const attribute of attributes ) {
+					encodedAttributes.push( [
+						encodeAttributeKey( attribute[ 0 ] ),
+						attribute[ 1 ]
+					] );
+				}
+
+				return modelWriter.createElement( modelName, encodedAttributes );
+			}
+		} );
+
+		conversion.for( 'downcast' ).elementToElement( {
+			model: modelName,
+			view: viewName
+		} );
+
+		conversion.for( 'downcast' ).add( dispatcher => {
+			dispatcher.on( 'attribute', ( evt, data, conversionApi ) => {
+				if ( data.item.name != modelName ) {
+					return;
+				}
+
+				const viewWriter = conversionApi.writer;
+				const viewElement = conversionApi.mapper.toViewElement( data.item );
+				const attributeKey = decodeAttributeKey( data.attributeKey );
+
+				if ( data.attributeNewValue !== null ) {
+					viewWriter.setAttribute( attributeKey, data.attributeNewValue, viewElement );
+				} else {
+					viewWriter.removeAttribute( attributeKey, viewElement );
+				}
+			} );
+		} );
+	}
+}
+
+class AttributeFilter {
+	constructor() {
+		this._allowedRules = {};
+		this._disallowedRules = {};
+	}
+
+	allow( elementRule, attributeRule ) {
+		this._register( this._allowedRules, elementRule, attributeRule );
+	}
+
+	disallow( elementRule, attributeRule ) {
+		this._register( this._disallowedRules, elementRule, attributeRule );
+	}
+
+	isAllowed( elementName, attributeName ) {
+		const isDisallowed = this._match( this._disallowedRules, elementName, attributeName );
+
+		if ( isDisallowed ) {
+			return false;
+		}
+
+		return this._match( this._allowedRules, elementName, attributeName );
+	}
+
+	_register( rules, elementRule, attributeRule ) {
+		if ( !rules[ elementRule ] ) {
+			rules[ elementRule ] = [];
+		}
+
+		if ( typeof attributeRule === 'string' ) {
+			attributeRule = createWildcardMatcher( attributeRule );
+		}
+
+		rules[ elementRule ].push( attributeRule );
+	}
+
+	_match( rules, elementName, attributeName ) {
+		for ( const rule of this._getMatchingRules( rules, elementName ) ) {
+			if ( rule( attributeName ) ) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+	* _getMatchingRules( rules, elementName ) {
+		for ( const ruleName in rules ) {
+			const matcher = createWildcardMatcher( ruleName );
+
+			if ( matcher( elementName ) ) {
+				yield* rules[ ruleName ];
+			}
+		}
+	}
+}
+
+function createWildcardMatcher( rule ) {
+	const matcher = new RegExp( '^' + rule.split( '*' ).map( escapeRegExp ).join( '.*' ) + '$' );
+	return value => matcher.test( value );
+}
+
+function encodeView( name ) {
+	return DATA_SCHEMA_PREFIX + capitalize( name );
+}
+
+function encodeAttributeKey( name ) {
+	return DATA_SCHEMA_PREFIX + '-' + name;
+}
+
+function decodeAttributeKey( name ) {
+	return name.replace( DATA_SCHEMA_PREFIX + '-', '' );
+}

From f30d3295031c939f4ed7f7470c00e3635dcc49d6 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 18 Jan 2021 12:43:50 +0100
Subject: [PATCH 002/217] Make sure to consume attribute on downcast.

---
 packages/ckeditor5-content-compatibility/src/dataschema.js | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index dce78f4e9a7..a594cacca9a 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -104,6 +104,10 @@ export default class DataSchema {
 					return;
 				}
 
+				if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
+					return;
+				}
+
 				const viewWriter = conversionApi.writer;
 				const viewElement = conversionApi.mapper.toViewElement( data.item );
 				const attributeKey = decodeAttributeKey( data.attributeKey );

From a204ba3e2f562059b51b09cd545aba44855b307d Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 18 Jan 2021 12:56:52 +0100
Subject: [PATCH 003/217] Refactoring.

---
 packages/ckeditor5-content-compatibility/src/dataschema.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index a594cacca9a..b39a116af45 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -34,7 +34,7 @@ export default class DataSchema {
 		for ( const attribute of attributes ) {
 			this.allowAttribute( {
 				name: attribute,
-				elements: [ viewName ]
+				elements: viewName
 			} );
 		}
 	}

From 059edf5cb6033a83e449d836b708666566656880 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 4 Feb 2021 11:14:49 +0100
Subject: [PATCH 004/217] Changed dataschema implementation to use view
 matcher.

---
 .../src/dataschema.js                         | 191 +++++++-----------
 1 file changed, 71 insertions(+), 120 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index b39a116af45..880ce931717 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -1,5 +1,5 @@
 /**
- * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
  * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
  */
 
@@ -8,88 +8,96 @@
  */
 
 import { capitalize, escapeRegExp } from 'lodash-es';
+import Matcher from '@ckeditor/ckeditor5-engine/src/view/matcher';
 
 const DATA_SCHEMA_PREFIX = 'ghs';
+const DATA_SCHEMA_ATTRIBUTE_KEY = 'ghsAttributes';
+
+// "h1", "h2", "h3", "h4", "h5", "h6", "legend", "pre", "rp", "rt", "summary", "p"
+// legend, rp, rt, summary
+
+// Phrasing elements.
+const P = encodeView( [ 'a', 'em', 'strong', 'small', 'abbr', 'dfn', 'i', 'b', 's', 'u', 'code',
+	'var', 'samp', 'kbd', 'sup', 'sub', 'q', 'cite', 'span', 'bdo', 'bdi', 'br',
+	'wbr', 'ins', 'del', 'img', 'embed', 'object', 'iframe', 'map', 'area', 'script',
+	'noscript', 'ruby', 'video', 'audio', 'input', 'textarea', 'select', 'button',
+	'label', 'output', 'keygen', 'progress', 'command', 'canvas', 'time', 'meter', 'detalist' ] );
+
+// Flow elements.
+const F = encodeView( [ 'a', 'p', 'hr', 'pre', 'ul', 'ol', 'dl', 'div', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6',
+	'hgroup', 'address', 'blockquote', 'ins', 'del', 'object', 'map', 'noscript', 'section',
+	'nav', 'article', 'aside', 'header', 'footer', 'video', 'audio', 'figure', 'table',
+	'form', 'fieldset', 'menu', 'canvas', 'details' ] );
 
 const dtd = {
-	'div': {
-		inheritAllFrom: '$block'
-	}
+	section: { inheritAllFrom: '$block', allowContentOf: P, allowIn: F, allowAttributes: [ DATA_SCHEMA_ATTRIBUTE_KEY ] },
+	article: { inheritAllFrom: '$block', allowContentOf: P, allowIn: F, allowAttributes: [ DATA_SCHEMA_ATTRIBUTE_KEY ] }
 };
 
+function remove( source, toRemove ) {
+	return source.filter( item => !toRemove.includes( item ) );
+}
+
 export default class DataSchema {
 	constructor( editor ) {
 		this.editor = editor;
-		this.attributeFilter = new AttributeFilter();
-	}
 
-	allowElement( { name: viewName, attributes = [] } ) {
-		this._defineSchema( viewName );
-		this._defineConverters( viewName );
-
-		if ( !Array.isArray( attributes ) ) {
-			attributes = [ attributes ];
-		}
-
-		for ( const attribute of attributes ) {
-			this.allowAttribute( {
-				name: attribute,
-				elements: viewName
-			} );
-		}
+		this.allowedContent = {};
 	}
 
-	allowAttribute( { name: attributeName, elements = [] } ) {
-		if ( !Array.isArray( elements ) ) {
-			elements = [ elements ];
+	allow( config ) {
+		if ( !config.name ) {
+			return;
 		}
 
-		elements.forEach( element => this.attributeFilter.allow( element, attributeName ) );
-	}
+		const matchElement = getElementNameMatchingRegExp( config.name );
 
-	disallowAttribute( { name: attributeName, elements = [] } ) {
-		if ( !Array.isArray( elements ) ) {
-			elements = [ elements ];
-		}
+		for ( const elementName in dtd ) {
+			if ( !matchElement.test( elementName ) ) {
+				continue;
+			}
 
-		elements.forEach( element => this.attributeFilter.disallow( element, attributeName ) );
+			this._defineSchema( elementName );
+			this._defineConverters( elementName );
+			this._getOrCreateMatcher( elementName ).add( config );
+		}
 	}
 
-	* _filterAttributes( elementName, attributes ) {
-		for ( const attribute of attributes ) {
-			const attributeName = attribute[ 0 ];
-
-			if ( this.attributeFilter.isAllowed( elementName, attributeName ) ) {
-				yield attribute;
-			}
+	_getOrCreateMatcher( elementName ) {
+		if ( !this.allowedContent[ elementName ] ) {
+			this.allowedContent[ elementName ] = new Matcher();
 		}
+
+		return this.allowedContent[ elementName ];
 	}
 
 	_defineSchema( viewName ) {
 		const schema = this.editor.model.schema;
+		const modelName = encodeView( viewName );
 
-		schema.register( encodeView( viewName ), dtd[ viewName ] );
+		schema.register( modelName, dtd[ viewName ] );
 	}
 
 	_defineConverters( viewName ) {
 		const conversion = this.editor.conversion;
-		const filterAttributes = this._filterAttributes.bind( this );
 		const modelName = encodeView( viewName );
 
 		conversion.for( 'upcast' ).elementToElement( {
 			view: viewName,
-			model: ( viewElement, { writer: modelWriter } ) => {
-				const attributes = filterAttributes( viewName, viewElement.getAttributes() );
-
-				const encodedAttributes = [];
-				for ( const attribute of attributes ) {
-					encodedAttributes.push( [
-						encodeAttributeKey( attribute[ 0 ] ),
-						attribute[ 1 ]
-					] );
+			model: ( viewElement, conversionApi ) => {
+				const match = this._getOrCreateMatcher( viewName ).match( viewElement );
+				const attributeMatch = match.match.attributes || [];
+
+				const originalAttributes = attributeMatch.map( attributeName => {
+					return [ attributeName, viewElement.getAttribute( attributeName ) ];
+				} );
+
+				let attributesToAdd;
+				if ( originalAttributes.length ) {
+					attributesToAdd = [ [ DATA_SCHEMA_ATTRIBUTE_KEY, originalAttributes ] ];
 				}
 
-				return modelWriter.createElement( modelName, encodedAttributes );
+				return conversionApi.writer.createElement( modelName, attributesToAdd );
 			}
 		} );
 
@@ -99,7 +107,7 @@ export default class DataSchema {
 		} );
 
 		conversion.for( 'downcast' ).add( dispatcher => {
-			dispatcher.on( 'attribute', ( evt, data, conversionApi ) => {
+			dispatcher.on( `attribute:${ DATA_SCHEMA_ATTRIBUTE_KEY }`, ( evt, data, conversionApi ) => {
 				if ( data.item.name != modelName ) {
 					return;
 				}
@@ -110,88 +118,31 @@ export default class DataSchema {
 
 				const viewWriter = conversionApi.writer;
 				const viewElement = conversionApi.mapper.toViewElement( data.item );
-				const attributeKey = decodeAttributeKey( data.attributeKey );
 
 				if ( data.attributeNewValue !== null ) {
-					viewWriter.setAttribute( attributeKey, data.attributeNewValue, viewElement );
-				} else {
-					viewWriter.removeAttribute( attributeKey, viewElement );
+					data.attributeNewValue.forEach( ( [ key, value ] ) => {
+						viewWriter.setAttribute( key, value, viewElement );
+					} );
 				}
+
+				viewWriter.removeAttribute( DATA_SCHEMA_ATTRIBUTE_KEY, viewElement );
 			} );
 		} );
 	}
 }
 
-class AttributeFilter {
-	constructor() {
-		this._allowedRules = {};
-		this._disallowedRules = {};
-	}
-
-	allow( elementRule, attributeRule ) {
-		this._register( this._allowedRules, elementRule, attributeRule );
-	}
-
-	disallow( elementRule, attributeRule ) {
-		this._register( this._disallowedRules, elementRule, attributeRule );
-	}
-
-	isAllowed( elementName, attributeName ) {
-		const isDisallowed = this._match( this._disallowedRules, elementName, attributeName );
-
-		if ( isDisallowed ) {
-			return false;
-		}
-
-		return this._match( this._allowedRules, elementName, attributeName );
-	}
-
-	_register( rules, elementRule, attributeRule ) {
-		if ( !rules[ elementRule ] ) {
-			rules[ elementRule ] = [];
-		}
-
-		if ( typeof attributeRule === 'string' ) {
-			attributeRule = createWildcardMatcher( attributeRule );
-		}
-
-		rules[ elementRule ].push( attributeRule );
-	}
-
-	_match( rules, elementName, attributeName ) {
-		for ( const rule of this._getMatchingRules( rules, elementName ) ) {
-			if ( rule( attributeName ) ) {
-				return true;
-			}
-		}
-
-		return false;
+function encodeView( name ) {
+	if ( Array.isArray( name ) ) {
+		return name.map( encodeView );
 	}
 
-	* _getMatchingRules( rules, elementName ) {
-		for ( const ruleName in rules ) {
-			const matcher = createWildcardMatcher( ruleName );
-
-			if ( matcher( elementName ) ) {
-				yield* rules[ ruleName ];
-			}
-		}
-	}
-}
-
-function createWildcardMatcher( rule ) {
-	const matcher = new RegExp( '^' + rule.split( '*' ).map( escapeRegExp ).join( '.*' ) + '$' );
-	return value => matcher.test( value );
-}
-
-function encodeView( name ) {
 	return DATA_SCHEMA_PREFIX + capitalize( name );
 }
 
-function encodeAttributeKey( name ) {
-	return DATA_SCHEMA_PREFIX + '-' + name;
-}
+function getElementNameMatchingRegExp( value ) {
+	if ( value instanceof RegExp ) {
+		return value;
+	}
 
-function decodeAttributeKey( name ) {
-	return name.replace( DATA_SCHEMA_PREFIX + '-', '' );
+	return new RegExp( escapeRegExp( value ) );
 }

From 8b1112b00ff6ee7a8fc449cd36342394c62df6ad Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 4 Feb 2021 13:04:57 +0100
Subject: [PATCH 005/217] Refactoring.

---
 .../src/dataschema.js                         | 26 ++++++++++++-------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 880ce931717..026d3ef7710 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -52,18 +52,19 @@ export default class DataSchema {
 
 		const matchElement = getElementNameMatchingRegExp( config.name );
 
-		for ( const elementName in dtd ) {
-			if ( !matchElement.test( elementName ) ) {
+		for ( const viewName in dtd ) {
+			if ( !matchElement.test( viewName ) ) {
 				continue;
 			}
 
-			this._defineSchema( elementName );
-			this._defineConverters( elementName );
-			this._getOrCreateMatcher( elementName ).add( config );
+			this._defineModel( viewName );
+
+			const matcher = this._getMatcher( viewName );
+			matcher.add( config );
 		}
 	}
 
-	_getOrCreateMatcher( elementName ) {
+	_getMatcher( elementName ) {
 		if ( !this.allowedContent[ elementName ] ) {
 			this.allowedContent[ elementName ] = new Matcher();
 		}
@@ -71,21 +72,26 @@ export default class DataSchema {
 		return this.allowedContent[ elementName ];
 	}
 
-	_defineSchema( viewName ) {
+	_defineModel( viewName ) {
 		const schema = this.editor.model.schema;
 		const modelName = encodeView( viewName );
 
+		if ( schema.isRegistered( modelName ) ) {
+			return;
+		}
+
 		schema.register( modelName, dtd[ viewName ] );
+
+		this._defineConverters( viewName, modelName );
 	}
 
-	_defineConverters( viewName ) {
+	_defineConverters( viewName, modelName ) {
 		const conversion = this.editor.conversion;
-		const modelName = encodeView( viewName );
 
 		conversion.for( 'upcast' ).elementToElement( {
 			view: viewName,
 			model: ( viewElement, conversionApi ) => {
-				const match = this._getOrCreateMatcher( viewName ).match( viewElement );
+				const match = this._getMatcher( viewName ).match( viewElement );
 				const attributeMatch = match.match.attributes || [];
 
 				const originalAttributes = attributeMatch.map( attributeName => {

From da9f31d5d58cb8aef2f1e718ef95c6d2a6701ed6 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 10 Feb 2021 09:21:13 +0100
Subject: [PATCH 006/217] Refactored data schema definitions.

---
 .../src/dataschema.js                         | 367 ++++++++++++++----
 .../src/generalhtmlsupport.js                 |  58 +++
 .../tests/dataschema.js                       | 262 +++++++++++++
 .../tests/manual/generalhtmlsupport.html      |  11 +
 .../tests/manual/generalhtmlsupport.js        |  46 +++
 .../tests/manual/generalhtmlsupport.md        |   1 +
 6 files changed, 675 insertions(+), 70 deletions(-)
 create mode 100644 packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
 create mode 100644 packages/ckeditor5-content-compatibility/tests/dataschema.js
 create mode 100644 packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
 create mode 100644 packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
 create mode 100644 packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.md

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 026d3ef7710..8082fce08c8 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -7,100 +7,206 @@
  * @module content-compatibility/dataschema
  */
 
-import { capitalize, escapeRegExp } from 'lodash-es';
+import { escapeRegExp, cloneDeep, uniq } from 'lodash-es';
 import Matcher from '@ckeditor/ckeditor5-engine/src/view/matcher';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
-const DATA_SCHEMA_PREFIX = 'ghs';
 const DATA_SCHEMA_ATTRIBUTE_KEY = 'ghsAttributes';
 
-// "h1", "h2", "h3", "h4", "h5", "h6", "legend", "pre", "rp", "rt", "summary", "p"
-// legend, rp, rt, summary
-
-// Phrasing elements.
-const P = encodeView( [ 'a', 'em', 'strong', 'small', 'abbr', 'dfn', 'i', 'b', 's', 'u', 'code',
-	'var', 'samp', 'kbd', 'sup', 'sub', 'q', 'cite', 'span', 'bdo', 'bdi', 'br',
-	'wbr', 'ins', 'del', 'img', 'embed', 'object', 'iframe', 'map', 'area', 'script',
-	'noscript', 'ruby', 'video', 'audio', 'input', 'textarea', 'select', 'button',
-	'label', 'output', 'keygen', 'progress', 'command', 'canvas', 'time', 'meter', 'detalist' ] );
-
-// Flow elements.
-const F = encodeView( [ 'a', 'p', 'hr', 'pre', 'ul', 'ol', 'dl', 'div', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6',
-	'hgroup', 'address', 'blockquote', 'ins', 'del', 'object', 'map', 'noscript', 'section',
-	'nav', 'article', 'aside', 'header', 'footer', 'video', 'audio', 'figure', 'table',
-	'form', 'fieldset', 'menu', 'canvas', 'details' ] );
-
-const dtd = {
-	section: { inheritAllFrom: '$block', allowContentOf: P, allowIn: F, allowAttributes: [ DATA_SCHEMA_ATTRIBUTE_KEY ] },
-	article: { inheritAllFrom: '$block', allowContentOf: P, allowIn: F, allowAttributes: [ DATA_SCHEMA_ATTRIBUTE_KEY ] }
-};
-
-function remove( source, toRemove ) {
-	return source.filter( item => !toRemove.includes( item ) );
-}
-
+/**
+ * Holds representation of the extended HTML document type definitions to be used by the
+ * editor in content compatibility support.
+ *
+ * Allows to validate additional elements and element attributes using declarative data schema API.
+ *
+ * Data schema is represented by registered definitions. To register new definition, use {@link #register} method:
+ *
+ *		dataSchema.register( {
+ *			view: 'section',
+ *			model: 'my-section',
+ *			schema: '$block'
+ *		} );
+ *
+ * Note that the above code will only register new data schema definition describing document structure
+ * for the given element.
+ *
+ * To enable registered element in the editor, use {@link #allowElement}
+ * method:
+ *
+ *		dataSchema.allowElement( {
+ *			name: 'section'
+ *		} );
+ *
+ * Additionaly, you can allow or disallow specific element attributes:
+ *
+ *		// Allow `data-foo` attribute on `section` element.
+ *		dataSchema.allowedAttributes( {
+ *			name: 'section',
+ *			attributes: {
+ *				'data-foo': true
+ *			}
+ *		} );
+ *
+ *		// Disallow `color` style attribute on 'section' element.
+ *		dataSchema.disallowedAttributes( {
+ *			name: 'section',
+ *			styles: {
+ *				color: /[^]/
+ *			}
+ *		} );
+ */
 export default class DataSchema {
 	constructor( editor ) {
 		this.editor = editor;
 
-		this.allowedContent = {};
+		this._definitions = {};
+
+		this._viewMatchers = {
+			allowedAttributes: {},
+			disallowedAttributes: {}
+		};
 	}
 
-	allow( config ) {
-		if ( !config.name ) {
-			return;
+	/**
+	 * Allow the given element registered by {@link #register} method.
+	 *
+	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all view elements which should be allowed.
+	 */
+	allowElement( config ) {
+		for ( const definition of this._getDefinitions( config.name ) ) {
+			this._defineSchema( definition );
+			this._defineConverters( definition );
+
+			this.allowAttributes( config );
 		}
+	}
 
-		const matchElement = getElementNameMatchingRegExp( config.name );
+	/**
+	 * Allow the given attributes for view element allowed by {@link #allowElement} method.
+	 *
+	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all attributes which should be allowed.
+	 */
+	allowAttributes( config ) {
+		this._addAttributeMatcher( config, this._viewMatchers.allowedAttributes );
+	}
 
-		for ( const viewName in dtd ) {
-			if ( !matchElement.test( viewName ) ) {
-				continue;
-			}
+	/**
+	 * Disallowe the given attributes for view element allowed by {@link #allowElement} method.
+	 *
+	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all attributes which should be disallowed.
+	 */
+	disallowAttributes( config ) {
+		this._addAttributeMatcher( config, this._viewMatchers.disallowedAttributes );
+	}
 
-			this._defineModel( viewName );
+	/**
+	 * Register new data schema definition.
+	 *
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 */
+	register( definition ) {
+		this._definitions[ definition.view ] = definition;
+	}
 
-			const matcher = this._getMatcher( viewName );
-			matcher.add( config );
+	/**
+	 * Adds attribute matcher for every registered data schema definition for the given `config.name`.
+	 *
+	 * @private
+	 * @param {module:engine/view/matcher~MatcherPattern} pattern
+	 * @param {Object} cache Cache object holding matchers.
+	 */
+	_addAttributeMatcher( config, cache ) {
+		const elementName = config.name;
+
+		config = cloneDeep( config );
+		// We don't want match by name when matching attributes.
+		// Matcher will be already attached to specific definition.
+		delete config.name;
+
+		// 1 to 1 relation between matcher and definition. Single matcher
+		// can be extended by adding additional configs.
+		for ( const definition of this._getDefinitions( elementName ) ) {
+			getOrCreateMatcher( definition.view, cache ).add( config );
 		}
 	}
 
-	_getMatcher( elementName ) {
-		if ( !this.allowedContent[ elementName ] ) {
-			this.allowedContent[ elementName ] = new Matcher();
+	/**
+	 * Returns registered data schema definitions for the given view name.
+	 *
+	 * @private
+	 * @param {String|RegExp} name View name registered by {@link #register} method.
+	 * @returns {Iterable.<module:content-compatibility/dataschema~DataSchemaDefinition>}
+	 */
+	* _getDefinitions( name ) {
+		// Match everything if name not given.
+		if ( !name ) {
+			name = /[^]/;
 		}
 
-		return this.allowedContent[ elementName ];
+		if ( !( name instanceof RegExp ) ) {
+			name = new RegExp( escapeRegExp( name ) );
+		}
+
+		for ( const viewName in this._definitions ) {
+			if ( name.test( viewName ) ) {
+				yield this._definitions[ viewName ];
+			}
+		}
 	}
 
-	_defineModel( viewName ) {
+	/**
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition}
+	 */
+	_defineSchema( definition ) {
 		const schema = this.editor.model.schema;
-		const modelName = encodeView( viewName );
 
-		if ( schema.isRegistered( modelName ) ) {
-			return;
+		if ( typeof definition.schema === 'string' ) {
+			schema.register( definition.model, {
+				inheritAllFrom: definition.schema,
+				allowAttributes: DATA_SCHEMA_ATTRIBUTE_KEY
+			} );
+		} else {
+			schema.register( definition.model, definition.schema );
 		}
-
-		schema.register( modelName, dtd[ viewName ] );
-
-		this._defineConverters( viewName, modelName );
 	}
 
-	_defineConverters( viewName, modelName ) {
+	/**
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition}
+	 */
+	_defineConverters( definition ) {
 		const conversion = this.editor.conversion;
+		const viewName = definition.view;
+		const modelName = definition.model;
 
 		conversion.for( 'upcast' ).elementToElement( {
 			view: viewName,
 			model: ( viewElement, conversionApi ) => {
-				const match = this._getMatcher( viewName ).match( viewElement );
-				const attributeMatch = match.match.attributes || [];
+				const viewAttributes = [];
+				const allowedAttributes = this._getAllowedAttributes( viewElement );
 
-				const originalAttributes = attributeMatch.map( attributeName => {
-					return [ attributeName, viewElement.getAttribute( attributeName ) ];
-				} );
+				for ( const key of allowedAttributes.attributes ) {
+					viewAttributes.push( [ key, viewElement.getAttribute( key ) ] );
+				}
+
+				if ( allowedAttributes.classes.length ) {
+					viewAttributes.push( [ 'class', allowedAttributes.classes ] );
+				}
+
+				if ( allowedAttributes.styles.length ) {
+					const stylesObj = {};
+
+					for ( const styleName of allowedAttributes.styles ) {
+						stylesObj[ styleName ] = viewElement.getStyle( styleName );
+					}
+
+					viewAttributes.push( [ 'style', stylesObj ] );
+				}
 
 				let attributesToAdd;
-				if ( originalAttributes.length ) {
-					attributesToAdd = [ [ DATA_SCHEMA_ATTRIBUTE_KEY, originalAttributes ] ];
+				if ( viewAttributes.length ) {
+					attributesToAdd = [ [ DATA_SCHEMA_ATTRIBUTE_KEY, viewAttributes ] ];
 				}
 
 				return conversionApi.writer.createElement( modelName, attributesToAdd );
@@ -125,30 +231,151 @@ export default class DataSchema {
 				const viewWriter = conversionApi.writer;
 				const viewElement = conversionApi.mapper.toViewElement( data.item );
 
+				// Remove old values.
+				if ( data.attributeOldValue !== null ) {
+					data.attributeOldValue.forEach( ( [ key, value ] ) => {
+						if ( key === 'class' ) {
+							const classes = toArray( value );
+
+							for ( const className of classes ) {
+								viewWriter.removeClass( className, viewElement );
+							}
+						} else if ( key === 'style' ) {
+							for ( const key in value ) {
+								viewWriter.removeStyle( key, viewElement );
+							}
+						} else {
+							viewWriter.removeAttribute( key, viewElement );
+						}
+					} );
+				}
+
+				// Apply new values.
 				if ( data.attributeNewValue !== null ) {
 					data.attributeNewValue.forEach( ( [ key, value ] ) => {
-						viewWriter.setAttribute( key, value, viewElement );
+						if ( key === 'class' ) {
+							const classes = toArray( value );
+
+							for ( const className of classes ) {
+								viewWriter.addClass( className, viewElement );
+							}
+						} else if ( key === 'style' ) {
+							for ( const key in value ) {
+								viewWriter.setStyle( key, value[ key ], viewElement );
+							}
+						} else {
+							viewWriter.setAttribute( key, value, viewElement );
+						}
 					} );
 				}
-
-				viewWriter.removeAttribute( DATA_SCHEMA_ATTRIBUTE_KEY, viewElement );
 			} );
 		} );
 	}
+
+	/**
+	 * Returns all allowed view element attributes based on attribute matchers registered via {@link #allowedAttributes}
+	 * and {@link #disallowedAttributes} methods.
+	 *
+	 * @private
+	 * @param {module:engine/view/element~Element} viewElement
+	 * @returns {Object} result
+	 * @returns {Array} result.attributes Array with matched attribute names.
+	 * @returns {Array} result.classes Array with matched class names.
+	 * @returns {Array} result.styles Array with matched style names.
+	 */
+	_getAllowedAttributes( viewElement ) {
+		const allowedAttributes = matchAll( viewElement, this._viewMatchers.allowedAttributes );
+		const disallowedAttributes = matchAll( viewElement, this._viewMatchers.disallowedAttributes );
+
+		// Drop disallowed content.
+		for ( const key in allowedAttributes ) {
+			allowedAttributes[ key ] = removeArray( allowedAttributes[ key ], disallowedAttributes[ key ] );
+		}
+
+		return allowedAttributes;
+	}
 }
 
-function encodeView( name ) {
-	if ( Array.isArray( name ) ) {
-		return name.map( encodeView );
+/**
+ * Helper function restoring matcher for the given key from cache object.
+ *
+ * If matcher for the given key does not exist, this function will create a new one
+ * inside cache object under the given key.
+ *
+ * @private
+ * @param {String} key
+ * @param {Object} cache
+ */
+function getOrCreateMatcher( key, cache ) {
+	if ( !cache[ key ] ) {
+		cache[ key ] = new Matcher();
 	}
 
-	return DATA_SCHEMA_PREFIX + capitalize( name );
+	return cache[ key ];
+}
+
+/**
+ * Helper function matching all attributes for the given element.
+ *
+ * @private
+ * @param {module:engine/view/element~Element} viewElement
+ * @param {Object} cache Cache object holding matchers.
+ * @returns {Object} result
+ * @returns {Array} result.attributes Array with matched attribute names.
+ * @returns {Array} result.classes Array with matched class names.
+ * @returns {Array} result.styles Array with matched style names.
+ */
+function matchAll( viewElement, cache ) {
+	const matcher = getOrCreateMatcher( viewElement.name, cache );
+	const matches = matcher.matchAll( viewElement );
+
+	return mergeMatchAllResult( matches || [] );
 }
 
-function getElementNameMatchingRegExp( value ) {
-	if ( value instanceof RegExp ) {
-		return value;
+/**
+ * Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
+ *
+ * @private
+ * @param {Array} matches
+ * @returns {Object} result
+ * @returns {Array} result.attributes Array with matched attribute names.
+ * @returns {Array} result.classes Array with matched class names.
+ * @returns {Array} result.styles Array with matched style names.
+ */
+function mergeMatchAllResult( matches ) {
+	const matchResult = { attributes: [], classes: [], styles: [] };
+
+	for ( const match of matches ) {
+		for ( const key in matchResult ) {
+			const values = match.match[ key ] || [];
+			matchResult[ key ].push( ...values );
+		}
 	}
 
-	return new RegExp( escapeRegExp( value ) );
+	for ( const key in matchResult ) {
+		matchResult[ key ] = uniq( matchResult[ key ] );
+	}
+
+	return matchResult;
 }
+
+/**
+ * Removes array items included in the second array parameter.
+ *
+ * @param {Array} array
+ * @param {Array} toRemove
+ * @returns {Array} Filtered array items.
+ */
+function removeArray( array, toRemove ) {
+	return array.filter( item => !toRemove.includes( item ) );
+}
+
+/**
+ * A definition of {@link module:content-compatibility/dataschema data schema}.
+ *
+ * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
+ * @property {String} view Name of the view element.
+ * @property {String} model Name of the model element.
+ * @property {String|module:engine/model/schema~SchemaItemDefinition} schema Name of the schema to inherit
+ * or custom schema item definition.
+ */
diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
new file mode 100644
index 00000000000..4cfd3d7b730
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
@@ -0,0 +1,58 @@
+/**
+ * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module content-compatibility/generalhtmlsupport
+ */
+
+import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
+import DataSchema from './dataschema';
+
+/**
+ * @extends module:core/plugin~Plugin
+ */
+export default class GeneralHTMLSupport extends Plugin {
+	constructor( editor ) {
+		super( editor );
+
+		this.dataSchema = new DataSchema( editor );
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	static get pluginName() {
+		return 'GeneralHTMLSupport';
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	init() {
+		const editor = this.editor;
+		const dataSchema = this.dataSchema;
+
+		// Register block elements.
+		editor.model.schema.register( '$ghsBlock', {
+			inheritAllFrom: '$block',
+			allowIn: '$ghsBlock'
+		} );
+
+		dataSchema.register( { view: 'article', model: 'ghsArticle', schema: '$ghsBlock' } );
+		dataSchema.register( { view: 'section', model: 'ghsSection', schema: '$ghsBlock' } );
+		dataSchema.register( { view: 'dl', model: 'ghsDl', schema: '$ghsBlock' } );
+
+		// Register data list elements.
+		editor.model.schema.register( '$ghsDatalist', {
+			allowIn: 'ghsDl',
+			isBlock: true,
+			allowContentOf: '$ghsBlock'
+		} );
+		editor.model.schema.extend( '$text', { allowIn: '$ghsDatalist' } );
+
+		dataSchema.register( { view: 'dt', model: 'ghsDt', schema: '$ghsDatalist' } );
+		dataSchema.register( { view: 'dd', model: 'ghsDd', schema: '$ghsDatalist' } );
+	}
+}
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
new file mode 100644
index 00000000000..e91dfcb1e4f
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -0,0 +1,262 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
+import DataSchema from '../src/dataschema';
+
+import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
+
+describe( 'DataSchema', () => {
+	let editor, model, dataSchema;
+
+	beforeEach( () => {
+		return VirtualTestEditor
+			.create()
+			.then( newEditor => {
+				editor = newEditor;
+				model = editor.model;
+
+				dataSchema = new DataSchema( editor );
+
+				// Define some made up type definitions for testing purposes.
+				dataSchema.register( { view: 'div', model: 'ghsDiv', schema: {
+					inheritAllFrom: '$block',
+					allowIn: 'ghsDiv'
+				} } );
+				dataSchema.register( { view: 'article', model: 'ghsArticle', schema: '$block' } );
+				dataSchema.register( { view: 'section', model: 'ghsSection', schema: {
+					inheritAllFrom: '$block',
+					allowIn: 'ghsArticle'
+				} } );
+			} );
+	} );
+
+	afterEach( () => {
+		return editor.destroy();
+	} );
+
+	it( 'should allow element', () => {
+		dataSchema.allowElement( { name: 'article' } );
+
+		editor.setData( '<article><section>section1</section><section>section2</section></article>' );
+
+		expect( getModelData( model, { withoutSelection: true } ) ).to.eq(
+			'<ghsArticle>section1section2</ghsArticle>'
+		);
+
+		expect( editor.getData() ).to.eq(
+			'<article>section1section2</article>'
+		);
+
+		dataSchema.allowElement( { name: 'section' } );
+
+		editor.setData( '<article><section>section1</section><section>section2</section></article>' );
+
+		expect( getModelData( model, { withoutSelection: true } ) ).to.eq(
+			'<ghsArticle><ghsSection>section1</ghsSection><ghsSection>section2</ghsSection></ghsArticle>'
+		);
+
+		expect( editor.getData() ).to.eq(
+			'<article><section>section1</section><section>section2</section></article>'
+		);
+	} );
+
+	it( 'should allow deeply nested structure', () => {
+		dataSchema.allowElement( { name: 'div' } );
+
+		editor.setData( '<div>1<div>2<div>3</div></div></div>' );
+
+		expect( getModelData( model, { withoutSelection: true } ) ).to.eq(
+			'<ghsDiv>1<ghsDiv>2<ghsDiv>3</ghsDiv></ghsDiv></ghsDiv>'
+		);
+
+		expect( editor.getData() ).to.eq(
+			'<div>1<div>2<div>3</div></div></div>'
+		);
+	} );
+
+	it( 'should allow attributes', () => {
+		dataSchema.allowElement( { name: 'div' } );
+		dataSchema.allowAttributes( { name: 'div', attributes: {
+			'data-foo': 'foobar'
+		} } );
+
+		editor.setData( '<div data-foo="foobar">foobar</div>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
+			data: '<ghsDiv ghsAttributes="(1)">foobar</ghsDiv>',
+			attributes: {
+				1: [ [ 'data-foo', 'foobar' ] ]
+			}
+		} );
+
+		expect( editor.getData() ).to.eq(
+			'<div data-foo="foobar">foobar</div>'
+		);
+	} );
+
+	it( 'should allow attributes (styles)', () => {
+		dataSchema.allowElement( { name: 'div' } );
+		dataSchema.allowAttributes( { name: 'div', styles: {
+			'color': 'red'
+		} } );
+
+		editor.setData( '<div style="color:red;">foobar</div>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
+			data: '<ghsDiv ghsAttributes="(1)">foobar</ghsDiv>',
+			attributes: {
+				1: [ [ 'style', { color: 'red' } ] ]
+			}
+		} );
+
+		expect( editor.getData() ).to.eq(
+			'<div style="color:red;">foobar</div>'
+		);
+	} );
+
+	it( 'should allow attributes (classes)', () => {
+		dataSchema.allowElement( { name: 'div' } );
+		dataSchema.allowAttributes( { name: 'div', classes: [ 'foo', 'bar' ] } );
+
+		editor.setData( '<div class="foo bar">foobar</div>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
+			data: '<ghsDiv ghsAttributes="(1)">foobar</ghsDiv>',
+			attributes: {
+				1: [ [ 'class', [ 'foo', 'bar' ] ] ]
+			}
+		} );
+
+		expect( editor.getData() ).to.eq(
+			'<div class="foo bar">foobar</div>'
+		);
+	} );
+
+	it( 'should allow nested attributes', () => {
+		dataSchema.allowElement( { name: /article|section/ } );
+		dataSchema.allowAttributes( { attributes: { 'data-foo': /foo|bar/ } } );
+
+		editor.setData( '<article data-foo="foo">' +
+				'<section data-foo="bar">section1</secton>' +
+				'<section data-foo="foo">section2</section>' +
+			'</article>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
+			data: '<ghsArticle ghsAttributes="(1)">' +
+				'<ghsSection ghsAttributes="(2)">section1</ghsSection>' +
+				'<ghsSection ghsAttributes="(3)">section2</ghsSection>' +
+			'</ghsArticle>',
+			attributes: {
+				1: [ [ 'data-foo', 'foo' ] ],
+				2: [ [ 'data-foo', 'bar' ] ],
+				3: [ [ 'data-foo', 'foo' ] ]
+			}
+		} );
+	} );
+
+	it( 'should allow attributes for all allowed definitions', () => {
+		dataSchema.allowElement( { name: 'div' } );
+		dataSchema.allowElement( { name: 'article' } );
+		// We skip name purposely to allow attribute on every data schema element.
+		dataSchema.allowAttributes( { attributes: { 'data-foo': 'foo' } } );
+		dataSchema.allowAttributes( { attributes: { 'data-bar': 'bar' } } );
+
+		editor.setData( '<div data-foo="foo">foo</div><article data-bar="bar">bar</article>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
+			data: '<ghsDiv ghsAttributes="(1)">foo</ghsDiv><ghsArticle ghsAttributes="(2)">bar</ghsArticle>',
+			attributes: {
+				1: [ [ 'data-foo', 'foo' ] ],
+				2: [ [ 'data-bar', 'bar' ] ]
+			}
+		} );
+
+		expect( editor.getData() ).to.eq(
+			'<div data-foo="foo">foo</div><article data-bar="bar">bar</article>'
+		);
+	} );
+
+	it( 'should disallow attributes', () => {
+		dataSchema.allowElement( { name: 'div' } );
+		dataSchema.allowAttributes( { name: 'div', attributes: { 'data-foo': /[^]/ } } );
+		dataSchema.disallowAttributes( { name: 'div', attributes: { 'data-foo': 'bar' } } );
+
+		editor.setData( '<div data-foo="foo">foo</div><div data-foo="bar">bar</div>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
+			data: '<ghsDiv ghsAttributes="(1)">foo</ghsDiv><ghsDiv>bar</ghsDiv>',
+			attributes: {
+				1: [ [ 'data-foo', 'foo' ] ]
+			}
+		} );
+
+		expect( editor.getData() ).to.eq(
+			'<div data-foo="foo">foo</div><div>bar</div>'
+		);
+	} );
+
+	it( 'should disallow attributes (styles)', () => {
+		dataSchema.allowElement( { name: 'div' } );
+		dataSchema.allowAttributes( { name: 'div', styles: { color: /[^]/ } } );
+		dataSchema.disallowAttributes( { name: 'div', styles: { color: 'red' } } );
+
+		editor.setData( '<div style="color:blue;">foo</div><div style="color:red">bar</div>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
+			data: '<ghsDiv ghsAttributes="(1)">foo</ghsDiv><ghsDiv>bar</ghsDiv>',
+			attributes: {
+				1: [ [ 'style', { color: 'blue' } ] ]
+			}
+		} );
+
+		expect( editor.getData() ).to.eq(
+			'<div style="color:blue;">foo</div><div>bar</div>'
+		);
+	} );
+
+	it( 'should disallow attributes (classes)', () => {
+		dataSchema.allowElement( { name: 'div' } );
+		dataSchema.allowAttributes( { name: 'div', classes: [ 'foo', 'bar' ] } );
+		dataSchema.disallowAttributes( { name: 'div', classes: [ 'bar' ] } );
+
+		editor.setData( '<div class="foo bar">foo</div><div class="bar">bar</div>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
+			data: '<ghsDiv ghsAttributes="(1)">foo</ghsDiv><ghsDiv>bar</ghsDiv>',
+			attributes: {
+				1: [ [ 'class', [ 'foo' ] ] ]
+			}
+		} );
+
+		expect( editor.getData() ).to.eq(
+			'<div class="foo">foo</div><div>bar</div>'
+		);
+	} );
+} );
+
+function getModelDataWithAttributes( model, options ) {
+	// Simplify GHS attributes as they are not readable at this point due to complex structure.
+	let counter = 1;
+	const data = getModelData( model, options ).replace( /ghsAttributes="(.*?)"/g, () => {
+		return `ghsAttributes="(${ counter++ })"`;
+	} );
+
+	const range = model.createRangeIn( model.document.getRoot() );
+
+	let attributes = [];
+	for ( const item of range.getItems() ) {
+		if ( item.hasAttribute && item.hasAttribute( 'ghsAttributes' ) ) {
+			attributes.push( item.getAttribute( 'ghsAttributes' ) );
+		}
+	}
+
+	attributes = attributes.reduce( ( prev, cur, index ) => {
+		prev[ index + 1 ] = cur;
+		return prev;
+	}, {} );
+
+	return { data, attributes };
+}
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
new file mode 100644
index 00000000000..230a06bc528
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -0,0 +1,11 @@
+<head>
+	<meta http-equiv="Content-Security-Policy" content="script-src 'self' https://ckeditor.com 'unsafe-inline' 'unsafe-eval'">
+</head>
+
+<div id="editor">
+	<article>
+		<section id="section1">Section #1</section>
+		<section id="section2">Section #2</section>
+		<section id="section3" style="color: red" class="special_section">Section #3</section>
+	</article>
+</div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
new file mode 100644
index 00000000000..8987048db4e
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -0,0 +1,46 @@
+/**
+ * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/* globals console:false, window, document */
+
+import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
+import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials';
+import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
+import Bold from '@ckeditor/ckeditor5-basic-styles/src/bold';
+import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
+import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
+import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
+
+import GeneralHTMLSupport from '../../src/generalhtmlsupport';
+
+class ExtendHTMLSupport extends Plugin {
+	static get requires() {
+		return [ GeneralHTMLSupport ];
+	}
+
+	init() {
+		const dataSchema = this.editor.plugins.get( 'GeneralHTMLSupport' ).dataSchema;
+
+		dataSchema.allowElement( { name: 'article' } );
+		dataSchema.allowElement( { name: 'section' } );
+
+		dataSchema.allowAttributes( { name: 'section', attributes: { id: /[^]/ } } );
+		dataSchema.allowAttributes( { name: 'section', classes: /[^]/ } );
+		dataSchema.allowAttributes( { name: 'section', styles: { color: /[^]/ } } );
+	}
+}
+
+ClassicEditor
+	.create( document.querySelector( '#editor' ), {
+		plugins: [ Essentials, Paragraph, Bold, Italic, Strikethrough, GeneralHTMLSupport, ExtendHTMLSupport ],
+		toolbar: [ 'bold', 'italic', 'strikethrough', 'contentTags' ]
+	} )
+	.then( editor => {
+		window.editor = editor;
+		window.dataSchema = editor.plugins.get( 'GeneralHTMLSupport' ).dataSchema;
+	} )
+	.catch( err => {
+		console.error( err.stack );
+	} );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.md b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.md
new file mode 100644
index 00000000000..4f09838d7e4
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.md
@@ -0,0 +1 @@
+# Content compatibility

From 1d74150263b164e85d663c59050986735e7445e7 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 10 Feb 2021 10:20:51 +0100
Subject: [PATCH 007/217] Extended support for details.

---
 .../ckeditor5-content-compatibility/src/dataschema.js    | 7 ++++++-
 .../src/generalhtmlsupport.js                            | 9 +++++++++
 .../tests/manual/generalhtmlsupport.html                 | 4 ++++
 .../tests/manual/generalhtmlsupport.js                   | 5 +++--
 4 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 8082fce08c8..707218ea94c 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -167,7 +167,12 @@ export default class DataSchema {
 				allowAttributes: DATA_SCHEMA_ATTRIBUTE_KEY
 			} );
 		} else {
-			schema.register( definition.model, definition.schema );
+			const schemaDefinition = cloneDeep( definition.schema );
+
+			schemaDefinition.allowAttributes = toArray( schemaDefinition.allowAttributes || [] );
+			schemaDefinition.allowAttributes.push( DATA_SCHEMA_ATTRIBUTE_KEY );
+
+			schema.register( definition.model, schemaDefinition );
 		}
 	}
 
diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
index 4cfd3d7b730..80dcd5091ed 100644
--- a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
@@ -54,5 +54,14 @@ export default class GeneralHTMLSupport extends Plugin {
 
 		dataSchema.register( { view: 'dt', model: 'ghsDt', schema: '$ghsDatalist' } );
 		dataSchema.register( { view: 'dd', model: 'ghsDd', schema: '$ghsDatalist' } );
+
+		// Register details elements.
+		dataSchema.register( { view: 'details', model: 'ghsDetails', schema: '$ghsBlock' } );
+
+		dataSchema.register( { view: 'summary', model: 'ghsSummary', schema: {
+			allowIn: 'ghsDetails'
+		} } );
+
+		editor.model.schema.extend( '$text', { allowIn: 'ghsSummary' } );
 	}
 }
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
index 230a06bc528..e009bc8cc3e 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -8,4 +8,8 @@
 		<section id="section2">Section #2</section>
 		<section id="section3" style="color: red" class="special_section">Section #3</section>
 	</article>
+	<details>
+		<summary>Summary</summary>
+		Hello world
+	</details>
 </div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 8987048db4e..fa0bc6119c8 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -23,12 +23,13 @@ class ExtendHTMLSupport extends Plugin {
 	init() {
 		const dataSchema = this.editor.plugins.get( 'GeneralHTMLSupport' ).dataSchema;
 
-		dataSchema.allowElement( { name: 'article' } );
-		dataSchema.allowElement( { name: 'section' } );
+		dataSchema.allowElement( { name: /article|section/ } );
 
 		dataSchema.allowAttributes( { name: 'section', attributes: { id: /[^]/ } } );
 		dataSchema.allowAttributes( { name: 'section', classes: /[^]/ } );
 		dataSchema.allowAttributes( { name: 'section', styles: { color: /[^]/ } } );
+
+		dataSchema.allowElement( { name: /details|summary/ } );
 	}
 }
 

From 17826af804b544e390e579114ad0bfff06ae9936 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 11 Feb 2021 11:58:47 +0100
Subject: [PATCH 008/217] Fixed dl schema.

---
 .../src/generalhtmlsupport.js                               | 6 +++++-
 .../tests/manual/generalhtmlsupport.html                    | 6 ++++++
 .../tests/manual/generalhtmlsupport.js                      | 2 ++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
index 80dcd5091ed..31ebec34dae 100644
--- a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
@@ -42,9 +42,13 @@ export default class GeneralHTMLSupport extends Plugin {
 
 		dataSchema.register( { view: 'article', model: 'ghsArticle', schema: '$ghsBlock' } );
 		dataSchema.register( { view: 'section', model: 'ghsSection', schema: '$ghsBlock' } );
-		dataSchema.register( { view: 'dl', model: 'ghsDl', schema: '$ghsBlock' } );
 
 		// Register data list elements.
+		dataSchema.register( { view: 'dl', model: 'ghsDl', schema: {
+			allowIn: [ '$ghsBlock', '$root' ],
+			isBlock: true
+		} } );
+
 		editor.model.schema.register( '$ghsDatalist', {
 			allowIn: 'ghsDl',
 			isBlock: true,
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
index e009bc8cc3e..6a0960f8c3e 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -12,4 +12,10 @@
 		<summary>Summary</summary>
 		Hello world
 	</details>
+	<dl>
+		<dt>dt1</dt>
+		<dt>dt2</dt>
+		<dd>dd1</dd>
+		<dd>dd2</dd>
+	</dl>
 </div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index fa0bc6119c8..abf7d1f8e3d 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -30,6 +30,8 @@ class ExtendHTMLSupport extends Plugin {
 		dataSchema.allowAttributes( { name: 'section', styles: { color: /[^]/ } } );
 
 		dataSchema.allowElement( { name: /details|summary/ } );
+
+		dataSchema.allowElement( { name: /dl|dt|dd/ } );
 	}
 }
 

From f54b0706da670d840dea5c16d914a05748685b37 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 16 Feb 2021 10:14:14 +0100
Subject: [PATCH 009/217] Break model into data schema and data filter.

---
 .../src/datafilter.js                         | 325 +++++++++++++++
 .../src/dataschema.js                         | 386 ++++--------------
 .../src/generalhtmlsupport.js                 |  71 ----
 .../tests/{dataschema.js => datafilter.js}    | 117 +++---
 .../tests/manual/generalhtmlsupport.js        |  25 +-
 5 files changed, 461 insertions(+), 463 deletions(-)
 create mode 100644 packages/ckeditor5-content-compatibility/src/datafilter.js
 delete mode 100644 packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
 rename packages/ckeditor5-content-compatibility/tests/{dataschema.js => datafilter.js} (57%)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
new file mode 100644
index 00000000000..ee4711eec10
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -0,0 +1,325 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module content-compatibility/datafilter
+ */
+
+import { escapeRegExp, cloneDeep, uniq } from 'lodash-es';
+import Matcher from '@ckeditor/ckeditor5-engine/src/view/matcher';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
+
+import DataSchema from './dataschema';
+
+const DATA_SCHEMA_ATTRIBUTE_KEY = 'ghsAttributes';
+
+/**
+ * Allows to validate elements and element attributes registered by {@link @module content-compatibility/dataschema~DataSchema}.
+ *
+ * To enable registered element in the editor, use {@link #allowElement} method:
+ *
+ *		dataFilter.allowElement( {
+ *			name: 'section'
+ *		} );
+ *
+ * You can also allow or disallow specific element attributes:
+ *
+ *		// Allow `data-foo` attribute on `section` element.
+ *		dataFilter.allowedAttributes( {
+ *			name: 'section',
+ *			attributes: {
+ *				'data-foo': true
+ *			}
+ *		} );
+ *
+ *		// Disallow `color` style attribute on 'section' element.
+ *		dataFilter.disallowedAttributes( {
+ *			name: 'section',
+ *			styles: {
+ *				color: /[^]/
+ *			}
+ *		} );
+ */
+export default class DataFilter {
+	constructor( editor ) {
+		this.editor = editor;
+
+		this.dataSchema = new DataSchema( editor );
+
+		this._viewMatchers = {
+			allowedAttributes: {},
+			disallowedAttributes: {}
+		};
+	}
+
+	/**
+	 * Allow the given element registered by {@link #register} method.
+	 *
+	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all view elements which should be allowed.
+	 */
+	allowElement( config ) {
+		const nameRegExp = toRegExp( config.name );
+
+		for ( const mapping of this.dataSchema.getModelViewMapping() ) {
+			if ( nameRegExp.test( mapping.view ) ) {
+				this.dataSchema.enable( mapping.model );
+				this._defineConverters( mapping );
+			}
+		}
+
+		this.allowAttributes( config );
+	}
+
+	/**
+	 * Allow the given attributes for view element allowed by {@link #allowElement} method.
+	 *
+	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all attributes which should be allowed.
+	 */
+	allowAttributes( config ) {
+		this._addAttributeMatcher( config, this._viewMatchers.allowedAttributes );
+	}
+
+	/**
+	 * Disallowe the given attributes for view element allowed by {@link #allowElement} method.
+	 *
+	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all attributes which should be disallowed.
+	 */
+	disallowAttributes( config ) {
+		this._addAttributeMatcher( config, this._viewMatchers.disallowedAttributes );
+	}
+
+	/**
+	 * Adds attribute matcher for every registered data schema definition for the given `config.name`.
+	 *
+	 * @private
+	 * @param {module:engine/view/matcher~MatcherPattern} pattern
+	 * @param {Object} cache Cache object holding matchers.
+	 */
+	_addAttributeMatcher( config, cache ) {
+		const nameRegExp = toRegExp( config.name );
+
+		config = cloneDeep( config );
+		// We don't want match by name when matching attributes.
+		// Matcher will be already attached to specific definition.
+		delete config.name;
+
+		for ( const { view } of this.dataSchema.getModelViewMapping() ) {
+			if ( nameRegExp.test( view ) ) {
+				getOrCreateMatcher( view, cache ).add( config );
+			}
+		}
+	}
+
+	/**
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition}
+	 */
+	_defineConverters( definition ) {
+		const conversion = this.editor.conversion;
+		const viewName = definition.view;
+		const modelName = definition.model;
+
+		conversion.for( 'upcast' ).elementToElement( {
+			view: viewName,
+			model: ( viewElement, conversionApi ) => {
+				const viewAttributes = [];
+				const allowedAttributes = this._getAllowedAttributes( viewElement );
+
+				for ( const key of allowedAttributes.attributes ) {
+					viewAttributes.push( [ key, viewElement.getAttribute( key ) ] );
+				}
+
+				if ( allowedAttributes.classes.length ) {
+					viewAttributes.push( [ 'class', allowedAttributes.classes ] );
+				}
+
+				if ( allowedAttributes.styles.length ) {
+					const stylesObj = {};
+
+					for ( const styleName of allowedAttributes.styles ) {
+						stylesObj[ styleName ] = viewElement.getStyle( styleName );
+					}
+
+					viewAttributes.push( [ 'style', stylesObj ] );
+				}
+
+				let attributesToAdd;
+				if ( viewAttributes.length ) {
+					attributesToAdd = [ [ DATA_SCHEMA_ATTRIBUTE_KEY, viewAttributes ] ];
+				}
+
+				return conversionApi.writer.createElement( modelName, attributesToAdd );
+			}
+		} );
+
+		conversion.for( 'downcast' ).elementToElement( {
+			model: modelName,
+			view: viewName
+		} );
+
+		conversion.for( 'downcast' ).add( dispatcher => {
+			dispatcher.on( `attribute:${ DATA_SCHEMA_ATTRIBUTE_KEY }`, ( evt, data, conversionApi ) => {
+				if ( data.item.name != modelName ) {
+					return;
+				}
+
+				if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
+					return;
+				}
+
+				const viewWriter = conversionApi.writer;
+				const viewElement = conversionApi.mapper.toViewElement( data.item );
+
+				// Remove old values.
+				if ( data.attributeOldValue !== null ) {
+					data.attributeOldValue.forEach( ( [ key, value ] ) => {
+						if ( key === 'class' ) {
+							const classes = toArray( value );
+
+							for ( const className of classes ) {
+								viewWriter.removeClass( className, viewElement );
+							}
+						} else if ( key === 'style' ) {
+							for ( const key in value ) {
+								viewWriter.removeStyle( key, viewElement );
+							}
+						} else {
+							viewWriter.removeAttribute( key, viewElement );
+						}
+					} );
+				}
+
+				// Apply new values.
+				if ( data.attributeNewValue !== null ) {
+					data.attributeNewValue.forEach( ( [ key, value ] ) => {
+						if ( key === 'class' ) {
+							const classes = toArray( value );
+
+							for ( const className of classes ) {
+								viewWriter.addClass( className, viewElement );
+							}
+						} else if ( key === 'style' ) {
+							for ( const key in value ) {
+								viewWriter.setStyle( key, value[ key ], viewElement );
+							}
+						} else {
+							viewWriter.setAttribute( key, value, viewElement );
+						}
+					} );
+				}
+			} );
+		} );
+	}
+
+	/**
+	 * Returns all allowed view element attributes based on attribute matchers registered via {@link #allowedAttributes}
+	 * and {@link #disallowedAttributes} methods.
+	 *
+	 * @private
+	 * @param {module:engine/view/element~Element} viewElement
+	 * @returns {Object} result
+	 * @returns {Array} result.attributes Array with matched attribute names.
+	 * @returns {Array} result.classes Array with matched class names.
+	 * @returns {Array} result.styles Array with matched style names.
+	 */
+	_getAllowedAttributes( viewElement ) {
+		const allowedAttributes = matchAll( viewElement, this._viewMatchers.allowedAttributes );
+		const disallowedAttributes = matchAll( viewElement, this._viewMatchers.disallowedAttributes );
+
+		// Drop disallowed content.
+		for ( const key in allowedAttributes ) {
+			allowedAttributes[ key ] = removeArray( allowedAttributes[ key ], disallowedAttributes[ key ] );
+		}
+
+		return allowedAttributes;
+	}
+}
+
+/**
+ * Helper function restoring matcher for the given key from cache object.
+ *
+ * If matcher for the given key does not exist, this function will create a new one
+ * inside cache object under the given key.
+ *
+ * @private
+ * @param {String} key
+ * @param {Object} cache
+ */
+function getOrCreateMatcher( key, cache ) {
+	if ( !cache[ key ] ) {
+		cache[ key ] = new Matcher();
+	}
+
+	return cache[ key ];
+}
+
+/**
+ * Helper function matching all attributes for the given element.
+ *
+ * @private
+ * @param {module:engine/view/element~Element} viewElement
+ * @param {Object} cache Cache object holding matchers.
+ * @returns {Object} result
+ * @returns {Array} result.attributes Array with matched attribute names.
+ * @returns {Array} result.classes Array with matched class names.
+ * @returns {Array} result.styles Array with matched style names.
+ */
+function matchAll( viewElement, cache ) {
+	const matcher = getOrCreateMatcher( viewElement.name, cache );
+	const matches = matcher.matchAll( viewElement );
+
+	return mergeMatchAllResult( matches || [] );
+}
+
+/**
+ * Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
+ *
+ * @private
+ * @param {Array} matches
+ * @returns {Object} result
+ * @returns {Array} result.attributes Array with matched attribute names.
+ * @returns {Array} result.classes Array with matched class names.
+ * @returns {Array} result.styles Array with matched style names.
+ */
+function mergeMatchAllResult( matches ) {
+	const matchResult = { attributes: [], classes: [], styles: [] };
+
+	for ( const match of matches ) {
+		for ( const key in matchResult ) {
+			const values = match.match[ key ] || [];
+			matchResult[ key ].push( ...values );
+		}
+	}
+
+	for ( const key in matchResult ) {
+		matchResult[ key ] = uniq( matchResult[ key ] );
+	}
+
+	return matchResult;
+}
+
+/**
+ * Removes array items included in the second array parameter.
+ *
+ * @param {Array} array
+ * @param {Array} toRemove
+ * @returns {Array} Filtered array items.
+ */
+function removeArray( array, toRemove ) {
+	return array.filter( item => !toRemove.includes( item ) );
+}
+
+function toRegExp( value ) {
+	// Match everything if name not given.
+	if ( !value ) {
+		value = /[^]/;
+	}
+
+	if ( !( value instanceof RegExp ) ) {
+		value = new RegExp( escapeRegExp( value ) );
+	}
+
+	return value;
+}
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 707218ea94c..6cb7e4dd786 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -7,53 +7,22 @@
  * @module content-compatibility/dataschema
  */
 
-import { escapeRegExp, cloneDeep, uniq } from 'lodash-es';
-import Matcher from '@ckeditor/ckeditor5-engine/src/view/matcher';
+import { cloneDeep } from 'lodash-es';
 import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
-const DATA_SCHEMA_ATTRIBUTE_KEY = 'ghsAttributes';
-
 /**
  * Holds representation of the extended HTML document type definitions to be used by the
  * editor in content compatibility support.
  *
- * Allows to validate additional elements and element attributes using declarative data schema API.
- *
- * Data schema is represented by registered definitions. To register new definition, use {@link #register} method:
+ * Data schema is represented by data schema definitions. To add new definition, use {@link #register} method:
  *
- *		dataSchema.register( {
- *			view: 'section',
- *			model: 'my-section',
- *			schema: '$block'
+ *		dataSchema.register( { view: 'section', model: 'my-section' }, {
+ *			inheritAllFrom: '$block'
  *		} );
  *
- * Note that the above code will only register new data schema definition describing document structure
- * for the given element.
+ * Once registered, definition can be enabled in editor's model:
  *
- * To enable registered element in the editor, use {@link #allowElement}
- * method:
- *
- *		dataSchema.allowElement( {
- *			name: 'section'
- *		} );
- *
- * Additionaly, you can allow or disallow specific element attributes:
- *
- *		// Allow `data-foo` attribute on `section` element.
- *		dataSchema.allowedAttributes( {
- *			name: 'section',
- *			attributes: {
- *				'data-foo': true
- *			}
- *		} );
- *
- *		// Disallow `color` style attribute on 'section' element.
- *		dataSchema.disallowedAttributes( {
- *			name: 'section',
- *			styles: {
- *				color: /[^]/
- *			}
- *		} );
+ *		dataSchema.enable( 'my-section' );
  */
 export default class DataSchema {
 	constructor( editor ) {
@@ -61,325 +30,114 @@ export default class DataSchema {
 
 		this._definitions = {};
 
-		this._viewMatchers = {
-			allowedAttributes: {},
-			disallowedAttributes: {}
-		};
-	}
+		// Add block elements.
+		this.register( { model: '$ghsBlock' }, {
+			inheritAllFrom: '$block',
+			allowIn: '$ghsBlock'
+		} );
 
-	/**
-	 * Allow the given element registered by {@link #register} method.
-	 *
-	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all view elements which should be allowed.
-	 */
-	allowElement( config ) {
-		for ( const definition of this._getDefinitions( config.name ) ) {
-			this._defineSchema( definition );
-			this._defineConverters( definition );
+		this.register( { view: 'article', model: 'ghsArticle' }, { inheritAllFrom: '$ghsBlock' } );
+		this.register( { view: 'section', model: 'ghsSection' }, { inheritAllFrom: '$ghsBlock' } );
 
-			this.allowAttributes( config );
-		}
-	}
+		// Add data list elements.
+		this.register( { view: 'dl', model: 'ghsDl' }, {
+			allowIn: [ '$ghsBlock', '$root' ],
+			isBlock: true
+		} );
 
-	/**
-	 * Allow the given attributes for view element allowed by {@link #allowElement} method.
-	 *
-	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all attributes which should be allowed.
-	 */
-	allowAttributes( config ) {
-		this._addAttributeMatcher( config, this._viewMatchers.allowedAttributes );
-	}
+		this.register( { model: '$ghsDatalist' }, {
+			allowIn: 'ghsDl',
+			isBlock: true,
+			allowContentOf: '$ghsBlock',
+			allowText: true
+		} );
 
-	/**
-	 * Disallowe the given attributes for view element allowed by {@link #allowElement} method.
-	 *
-	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all attributes which should be disallowed.
-	 */
-	disallowAttributes( config ) {
-		this._addAttributeMatcher( config, this._viewMatchers.disallowedAttributes );
+		this.register( { view: 'dt', model: 'ghsDt' }, { inheritAllFrom: '$ghsDatalist' } );
+		this.register( { view: 'dd', model: 'ghsDd' }, { inheritAllFrom: '$ghsDatalist' } );
+
+		// Add details elements.
+		this.register( { view: 'details', model: 'ghsDetails' }, { inheritAllFrom: '$ghsBlock' } );
+
+		this.register( { view: 'summary', model: 'ghsSummary' }, {
+			allowIn: 'ghsDetails',
+			allowText: true
+		} );
 	}
 
 	/**
-	 * Register new data schema definition.
+	 * Add new data schema definition.
 	 *
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
-	register( definition ) {
-		this._definitions[ definition.view ] = definition;
+	register( { view, model }, schema ) {
+		this._definitions[ model ] = { view, model, schema };
 	}
 
 	/**
-	 * Adds attribute matcher for every registered data schema definition for the given `config.name`.
+	 * Returns model-view-pairs for the added data schema definitions.
 	 *
-	 * @private
-	 * @param {module:engine/view/matcher~MatcherPattern} pattern
-	 * @param {Object} cache Cache object holding matchers.
-	 */
-	_addAttributeMatcher( config, cache ) {
-		const elementName = config.name;
-
-		config = cloneDeep( config );
-		// We don't want match by name when matching attributes.
-		// Matcher will be already attached to specific definition.
-		delete config.name;
-
-		// 1 to 1 relation between matcher and definition. Single matcher
-		// can be extended by adding additional configs.
-		for ( const definition of this._getDefinitions( elementName ) ) {
-			getOrCreateMatcher( definition.view, cache ).add( config );
-		}
-	}
-
-	/**
-	 * Returns registered data schema definitions for the given view name.
+	 * This method will only return pairs when if
+	 * {@link module:content-compatibility/dataschema~DataSchemaDefinition#view view} has been set.
 	 *
-	 * @private
-	 * @param {String|RegExp} name View name registered by {@link #register} method.
-	 * @returns {Iterable.<module:content-compatibility/dataschema~DataSchemaDefinition>}
+	 * @returns {Object[]} result
 	 */
-	* _getDefinitions( name ) {
-		// Match everything if name not given.
-		if ( !name ) {
-			name = /[^]/;
-		}
-
-		if ( !( name instanceof RegExp ) ) {
-			name = new RegExp( escapeRegExp( name ) );
-		}
-
-		for ( const viewName in this._definitions ) {
-			if ( name.test( viewName ) ) {
-				yield this._definitions[ viewName ];
-			}
-		}
+	getModelViewMapping() {
+		return Object.values( this._definitions )
+			.filter( def => def.view && def.model )
+			.map( def => ( { model: def.model, view: def.view } ) );
 	}
 
 	/**
-	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition}
+	 * Registers model schema item for the given
+	 * {@link module:content-compatibility/dataschema~DataSchemaDefinition data schema definition} name.
+	 *
+	 * @param {String} name
 	 */
-	_defineSchema( definition ) {
+	enable( name ) {
 		const schema = this.editor.model.schema;
 
-		if ( typeof definition.schema === 'string' ) {
-			schema.register( definition.model, {
-				inheritAllFrom: definition.schema,
-				allowAttributes: DATA_SCHEMA_ATTRIBUTE_KEY
-			} );
-		} else {
-			const schemaDefinition = cloneDeep( definition.schema );
-
-			schemaDefinition.allowAttributes = toArray( schemaDefinition.allowAttributes || [] );
-			schemaDefinition.allowAttributes.push( DATA_SCHEMA_ATTRIBUTE_KEY );
-
-			schema.register( definition.model, schemaDefinition );
+		if ( schema.isRegistered( name ) ) {
+			return;
 		}
-	}
-
-	/**
-	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition}
-	 */
-	_defineConverters( definition ) {
-		const conversion = this.editor.conversion;
-		const viewName = definition.view;
-		const modelName = definition.model;
-
-		conversion.for( 'upcast' ).elementToElement( {
-			view: viewName,
-			model: ( viewElement, conversionApi ) => {
-				const viewAttributes = [];
-				const allowedAttributes = this._getAllowedAttributes( viewElement );
-
-				for ( const key of allowedAttributes.attributes ) {
-					viewAttributes.push( [ key, viewElement.getAttribute( key ) ] );
-				}
-
-				if ( allowedAttributes.classes.length ) {
-					viewAttributes.push( [ 'class', allowedAttributes.classes ] );
-				}
-
-				if ( allowedAttributes.styles.length ) {
-					const stylesObj = {};
-
-					for ( const styleName of allowedAttributes.styles ) {
-						stylesObj[ styleName ] = viewElement.getStyle( styleName );
-					}
-
-					viewAttributes.push( [ 'style', stylesObj ] );
-				}
-
-				let attributesToAdd;
-				if ( viewAttributes.length ) {
-					attributesToAdd = [ [ DATA_SCHEMA_ATTRIBUTE_KEY, viewAttributes ] ];
-				}
-
-				return conversionApi.writer.createElement( modelName, attributesToAdd );
-			}
-		} );
-
-		conversion.for( 'downcast' ).elementToElement( {
-			model: modelName,
-			view: viewName
-		} );
 
-		conversion.for( 'downcast' ).add( dispatcher => {
-			dispatcher.on( `attribute:${ DATA_SCHEMA_ATTRIBUTE_KEY }`, ( evt, data, conversionApi ) => {
-				if ( data.item.name != modelName ) {
-					return;
-				}
+		const definition = this._definitions[ name ];
+		const schemaDefinition = cloneDeep( definition.schema );
 
-				if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
-					return;
-				}
-
-				const viewWriter = conversionApi.writer;
-				const viewElement = conversionApi.mapper.toViewElement( data.item );
-
-				// Remove old values.
-				if ( data.attributeOldValue !== null ) {
-					data.attributeOldValue.forEach( ( [ key, value ] ) => {
-						if ( key === 'class' ) {
-							const classes = toArray( value );
-
-							for ( const className of classes ) {
-								viewWriter.removeClass( className, viewElement );
-							}
-						} else if ( key === 'style' ) {
-							for ( const key in value ) {
-								viewWriter.removeStyle( key, viewElement );
-							}
-						} else {
-							viewWriter.removeAttribute( key, viewElement );
-						}
-					} );
-				}
+		for ( const reference of this._getReferences( name ) ) {
+			this.enable( reference );
+		}
 
-				// Apply new values.
-				if ( data.attributeNewValue !== null ) {
-					data.attributeNewValue.forEach( ( [ key, value ] ) => {
-						if ( key === 'class' ) {
-							const classes = toArray( value );
+		schema.register( name, schemaDefinition );
 
-							for ( const className of classes ) {
-								viewWriter.addClass( className, viewElement );
-							}
-						} else if ( key === 'style' ) {
-							for ( const key in value ) {
-								viewWriter.setStyle( key, value[ key ], viewElement );
-							}
-						} else {
-							viewWriter.setAttribute( key, value, viewElement );
-						}
-					} );
-				}
-			} );
-		} );
+		if ( schema.allowText ) {
+			schema.extend( '$text', { allowIn: name } );
+		}
 	}
 
 	/**
-	 * Returns all allowed view element attributes based on attribute matchers registered via {@link #allowedAttributes}
-	 * and {@link #disallowedAttributes} methods.
+	 * Resolves all model references registered for the given data schema definition.
 	 *
 	 * @private
-	 * @param {module:engine/view/element~Element} viewElement
-	 * @returns {Object} result
-	 * @returns {Array} result.attributes Array with matched attribute names.
-	 * @returns {Array} result.classes Array with matched class names.
-	 * @returns {Array} result.styles Array with matched style names.
+	 * @param {String} name Data schema model name.
+	 * @returns {Iterable<String>}
 	 */
-	_getAllowedAttributes( viewElement ) {
-		const allowedAttributes = matchAll( viewElement, this._viewMatchers.allowedAttributes );
-		const disallowedAttributes = matchAll( viewElement, this._viewMatchers.disallowedAttributes );
+	* _getReferences( name ) {
+		// TODO extend with the rest of schema properties based on other model types.
+		const { schema } = this._definitions[ name ];
 
-		// Drop disallowed content.
-		for ( const key in allowedAttributes ) {
-			allowedAttributes[ key ] = removeArray( allowedAttributes[ key ], disallowedAttributes[ key ] );
-		}
-
-		return allowedAttributes;
-	}
-}
-
-/**
- * Helper function restoring matcher for the given key from cache object.
- *
- * If matcher for the given key does not exist, this function will create a new one
- * inside cache object under the given key.
- *
- * @private
- * @param {String} key
- * @param {Object} cache
- */
-function getOrCreateMatcher( key, cache ) {
-	if ( !cache[ key ] ) {
-		cache[ key ] = new Matcher();
-	}
-
-	return cache[ key ];
-}
-
-/**
- * Helper function matching all attributes for the given element.
- *
- * @private
- * @param {module:engine/view/element~Element} viewElement
- * @param {Object} cache Cache object holding matchers.
- * @returns {Object} result
- * @returns {Array} result.attributes Array with matched attribute names.
- * @returns {Array} result.classes Array with matched class names.
- * @returns {Array} result.styles Array with matched style names.
- */
-function matchAll( viewElement, cache ) {
-	const matcher = getOrCreateMatcher( viewElement.name, cache );
-	const matches = matcher.matchAll( viewElement );
-
-	return mergeMatchAllResult( matches || [] );
-}
-
-/**
- * Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
- *
- * @private
- * @param {Array} matches
- * @returns {Object} result
- * @returns {Array} result.attributes Array with matched attribute names.
- * @returns {Array} result.classes Array with matched class names.
- * @returns {Array} result.styles Array with matched style names.
- */
-function mergeMatchAllResult( matches ) {
-	const matchResult = { attributes: [], classes: [], styles: [] };
-
-	for ( const match of matches ) {
-		for ( const key in matchResult ) {
-			const values = match.match[ key ] || [];
-			matchResult[ key ].push( ...values );
+		for ( const model of toArray( schema.inheritAllFrom || [] ) ) {
+			if ( this._definitions[ model ] ) {
+				yield model;
+			}
 		}
 	}
-
-	for ( const key in matchResult ) {
-		matchResult[ key ] = uniq( matchResult[ key ] );
-	}
-
-	return matchResult;
-}
-
-/**
- * Removes array items included in the second array parameter.
- *
- * @param {Array} array
- * @param {Array} toRemove
- * @returns {Array} Filtered array items.
- */
-function removeArray( array, toRemove ) {
-	return array.filter( item => !toRemove.includes( item ) );
 }
 
 /**
  * A definition of {@link module:content-compatibility/dataschema data schema}.
  *
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
- * @property {String} view Name of the view element.
+ * @property {String} [view] Name of the view element.
  * @property {String} model Name of the model element.
  * @property {String|module:engine/model/schema~SchemaItemDefinition} schema Name of the schema to inherit
  * or custom schema item definition.
diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
deleted file mode 100644
index 31ebec34dae..00000000000
--- a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
+++ /dev/null
@@ -1,71 +0,0 @@
-/**
- * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
- * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
- */
-
-/**
- * @module content-compatibility/generalhtmlsupport
- */
-
-import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
-import DataSchema from './dataschema';
-
-/**
- * @extends module:core/plugin~Plugin
- */
-export default class GeneralHTMLSupport extends Plugin {
-	constructor( editor ) {
-		super( editor );
-
-		this.dataSchema = new DataSchema( editor );
-	}
-
-	/**
-	 * @inheritDoc
-	 */
-	static get pluginName() {
-		return 'GeneralHTMLSupport';
-	}
-
-	/**
-	 * @inheritDoc
-	 */
-	init() {
-		const editor = this.editor;
-		const dataSchema = this.dataSchema;
-
-		// Register block elements.
-		editor.model.schema.register( '$ghsBlock', {
-			inheritAllFrom: '$block',
-			allowIn: '$ghsBlock'
-		} );
-
-		dataSchema.register( { view: 'article', model: 'ghsArticle', schema: '$ghsBlock' } );
-		dataSchema.register( { view: 'section', model: 'ghsSection', schema: '$ghsBlock' } );
-
-		// Register data list elements.
-		dataSchema.register( { view: 'dl', model: 'ghsDl', schema: {
-			allowIn: [ '$ghsBlock', '$root' ],
-			isBlock: true
-		} } );
-
-		editor.model.schema.register( '$ghsDatalist', {
-			allowIn: 'ghsDl',
-			isBlock: true,
-			allowContentOf: '$ghsBlock'
-		} );
-		editor.model.schema.extend( '$text', { allowIn: '$ghsDatalist' } );
-
-		dataSchema.register( { view: 'dt', model: 'ghsDt', schema: '$ghsDatalist' } );
-		dataSchema.register( { view: 'dd', model: 'ghsDd', schema: '$ghsDatalist' } );
-
-		// Register details elements.
-		dataSchema.register( { view: 'details', model: 'ghsDetails', schema: '$ghsBlock' } );
-
-		dataSchema.register( { view: 'summary', model: 'ghsSummary', schema: {
-			allowIn: 'ghsDetails'
-		} } );
-
-		editor.model.schema.extend( '$text', { allowIn: 'ghsSummary' } );
-	}
-}
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
similarity index 57%
rename from packages/ckeditor5-content-compatibility/tests/dataschema.js
rename to packages/ckeditor5-content-compatibility/tests/datafilter.js
index e91dfcb1e4f..8a74ffe3b76 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -4,12 +4,12 @@
  */
 
 import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
-import DataSchema from '../src/dataschema';
+import DataFilter from '../src/datafilter';
 
 import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
 
-describe( 'DataSchema', () => {
-	let editor, model, dataSchema;
+describe( 'DataFilter', () => {
+	let editor, model, dataFilter;
 
 	beforeEach( () => {
 		return VirtualTestEditor
@@ -18,18 +18,7 @@ describe( 'DataSchema', () => {
 				editor = newEditor;
 				model = editor.model;
 
-				dataSchema = new DataSchema( editor );
-
-				// Define some made up type definitions for testing purposes.
-				dataSchema.register( { view: 'div', model: 'ghsDiv', schema: {
-					inheritAllFrom: '$block',
-					allowIn: 'ghsDiv'
-				} } );
-				dataSchema.register( { view: 'article', model: 'ghsArticle', schema: '$block' } );
-				dataSchema.register( { view: 'section', model: 'ghsSection', schema: {
-					inheritAllFrom: '$block',
-					allowIn: 'ghsArticle'
-				} } );
+				dataFilter = new DataFilter( editor );
 			} );
 	} );
 
@@ -38,7 +27,7 @@ describe( 'DataSchema', () => {
 	} );
 
 	it( 'should allow element', () => {
-		dataSchema.allowElement( { name: 'article' } );
+		dataFilter.allowElement( { name: 'article' } );
 
 		editor.setData( '<article><section>section1</section><section>section2</section></article>' );
 
@@ -50,7 +39,7 @@ describe( 'DataSchema', () => {
 			'<article>section1section2</article>'
 		);
 
-		dataSchema.allowElement( { name: 'section' } );
+		dataFilter.allowElement( { name: 'section' } );
 
 		editor.setData( '<article><section>section1</section><section>section2</section></article>' );
 
@@ -64,83 +53,83 @@ describe( 'DataSchema', () => {
 	} );
 
 	it( 'should allow deeply nested structure', () => {
-		dataSchema.allowElement( { name: 'div' } );
+		dataFilter.allowElement( { name: 'section' } );
 
-		editor.setData( '<div>1<div>2<div>3</div></div></div>' );
+		editor.setData( '<section>1<section>2<section>3</section></section></section>' );
 
 		expect( getModelData( model, { withoutSelection: true } ) ).to.eq(
-			'<ghsDiv>1<ghsDiv>2<ghsDiv>3</ghsDiv></ghsDiv></ghsDiv>'
+			'<ghsSection>1<ghsSection>2<ghsSection>3</ghsSection></ghsSection></ghsSection>'
 		);
 
 		expect( editor.getData() ).to.eq(
-			'<div>1<div>2<div>3</div></div></div>'
+			'<section>1<section>2<section>3</section></section></section>'
 		);
 	} );
 
 	it( 'should allow attributes', () => {
-		dataSchema.allowElement( { name: 'div' } );
-		dataSchema.allowAttributes( { name: 'div', attributes: {
+		dataFilter.allowElement( { name: 'section' } );
+		dataFilter.allowAttributes( { name: 'section', attributes: {
 			'data-foo': 'foobar'
 		} } );
 
-		editor.setData( '<div data-foo="foobar">foobar</div>' );
+		editor.setData( '<section data-foo="foobar">foobar</section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsDiv ghsAttributes="(1)">foobar</ghsDiv>',
+			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
 			attributes: {
 				1: [ [ 'data-foo', 'foobar' ] ]
 			}
 		} );
 
 		expect( editor.getData() ).to.eq(
-			'<div data-foo="foobar">foobar</div>'
+			'<section data-foo="foobar">foobar</section>'
 		);
 	} );
 
 	it( 'should allow attributes (styles)', () => {
-		dataSchema.allowElement( { name: 'div' } );
-		dataSchema.allowAttributes( { name: 'div', styles: {
+		dataFilter.allowElement( { name: 'section' } );
+		dataFilter.allowAttributes( { name: 'section', styles: {
 			'color': 'red'
 		} } );
 
-		editor.setData( '<div style="color:red;">foobar</div>' );
+		editor.setData( '<section style="color:red;">foobar</section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsDiv ghsAttributes="(1)">foobar</ghsDiv>',
+			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
 			attributes: {
 				1: [ [ 'style', { color: 'red' } ] ]
 			}
 		} );
 
 		expect( editor.getData() ).to.eq(
-			'<div style="color:red;">foobar</div>'
+			'<section style="color:red;">foobar</section>'
 		);
 	} );
 
 	it( 'should allow attributes (classes)', () => {
-		dataSchema.allowElement( { name: 'div' } );
-		dataSchema.allowAttributes( { name: 'div', classes: [ 'foo', 'bar' ] } );
+		dataFilter.allowElement( { name: 'section' } );
+		dataFilter.allowAttributes( { name: 'section', classes: [ 'foo', 'bar' ] } );
 
-		editor.setData( '<div class="foo bar">foobar</div>' );
+		editor.setData( '<section class="foo bar">foobar</section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsDiv ghsAttributes="(1)">foobar</ghsDiv>',
+			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
 			attributes: {
 				1: [ [ 'class', [ 'foo', 'bar' ] ] ]
 			}
 		} );
 
 		expect( editor.getData() ).to.eq(
-			'<div class="foo bar">foobar</div>'
+			'<section class="foo bar">foobar</section>'
 		);
 	} );
 
 	it( 'should allow nested attributes', () => {
-		dataSchema.allowElement( { name: /article|section/ } );
-		dataSchema.allowAttributes( { attributes: { 'data-foo': /foo|bar/ } } );
+		dataFilter.allowElement( { name: /article|section/ } );
+		dataFilter.allowAttributes( { attributes: { 'data-foo': /foo|bar/ } } );
 
 		editor.setData( '<article data-foo="foo">' +
-				'<section data-foo="bar">section1</secton>' +
+				'<section data-foo="bar">section1</section>' +
 				'<section data-foo="foo">section2</section>' +
 			'</article>' );
 
@@ -158,16 +147,16 @@ describe( 'DataSchema', () => {
 	} );
 
 	it( 'should allow attributes for all allowed definitions', () => {
-		dataSchema.allowElement( { name: 'div' } );
-		dataSchema.allowElement( { name: 'article' } );
+		dataFilter.allowElement( { name: 'section' } );
+		dataFilter.allowElement( { name: 'article' } );
 		// We skip name purposely to allow attribute on every data schema element.
-		dataSchema.allowAttributes( { attributes: { 'data-foo': 'foo' } } );
-		dataSchema.allowAttributes( { attributes: { 'data-bar': 'bar' } } );
+		dataFilter.allowAttributes( { attributes: { 'data-foo': 'foo' } } );
+		dataFilter.allowAttributes( { attributes: { 'data-bar': 'bar' } } );
 
-		editor.setData( '<div data-foo="foo">foo</div><article data-bar="bar">bar</article>' );
+		editor.setData( '<section data-foo="foo">foo</section><article data-bar="bar">bar</article>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsDiv ghsAttributes="(1)">foo</ghsDiv><ghsArticle ghsAttributes="(2)">bar</ghsArticle>',
+			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsArticle ghsAttributes="(2)">bar</ghsArticle>',
 			attributes: {
 				1: [ [ 'data-foo', 'foo' ] ],
 				2: [ [ 'data-bar', 'bar' ] ]
@@ -175,64 +164,64 @@ describe( 'DataSchema', () => {
 		} );
 
 		expect( editor.getData() ).to.eq(
-			'<div data-foo="foo">foo</div><article data-bar="bar">bar</article>'
+			'<section data-foo="foo">foo</section><article data-bar="bar">bar</article>'
 		);
 	} );
 
 	it( 'should disallow attributes', () => {
-		dataSchema.allowElement( { name: 'div' } );
-		dataSchema.allowAttributes( { name: 'div', attributes: { 'data-foo': /[^]/ } } );
-		dataSchema.disallowAttributes( { name: 'div', attributes: { 'data-foo': 'bar' } } );
+		dataFilter.allowElement( { name: 'section' } );
+		dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': /[^]/ } } );
+		dataFilter.disallowAttributes( { name: 'section', attributes: { 'data-foo': 'bar' } } );
 
-		editor.setData( '<div data-foo="foo">foo</div><div data-foo="bar">bar</div>' );
+		editor.setData( '<section data-foo="foo">foo</section><section data-foo="bar">bar</section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsDiv ghsAttributes="(1)">foo</ghsDiv><ghsDiv>bar</ghsDiv>',
+			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsSection>bar</ghsSection>',
 			attributes: {
 				1: [ [ 'data-foo', 'foo' ] ]
 			}
 		} );
 
 		expect( editor.getData() ).to.eq(
-			'<div data-foo="foo">foo</div><div>bar</div>'
+			'<section data-foo="foo">foo</section><section>bar</section>'
 		);
 	} );
 
 	it( 'should disallow attributes (styles)', () => {
-		dataSchema.allowElement( { name: 'div' } );
-		dataSchema.allowAttributes( { name: 'div', styles: { color: /[^]/ } } );
-		dataSchema.disallowAttributes( { name: 'div', styles: { color: 'red' } } );
+		dataFilter.allowElement( { name: 'section' } );
+		dataFilter.allowAttributes( { name: 'section', styles: { color: /[^]/ } } );
+		dataFilter.disallowAttributes( { name: 'section', styles: { color: 'red' } } );
 
-		editor.setData( '<div style="color:blue;">foo</div><div style="color:red">bar</div>' );
+		editor.setData( '<section style="color:blue;">foo</section><section style="color:red">bar</section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsDiv ghsAttributes="(1)">foo</ghsDiv><ghsDiv>bar</ghsDiv>',
+			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsSection>bar</ghsSection>',
 			attributes: {
 				1: [ [ 'style', { color: 'blue' } ] ]
 			}
 		} );
 
 		expect( editor.getData() ).to.eq(
-			'<div style="color:blue;">foo</div><div>bar</div>'
+			'<section style="color:blue;">foo</section><section>bar</section>'
 		);
 	} );
 
 	it( 'should disallow attributes (classes)', () => {
-		dataSchema.allowElement( { name: 'div' } );
-		dataSchema.allowAttributes( { name: 'div', classes: [ 'foo', 'bar' ] } );
-		dataSchema.disallowAttributes( { name: 'div', classes: [ 'bar' ] } );
+		dataFilter.allowElement( { name: 'section' } );
+		dataFilter.allowAttributes( { name: 'section', classes: [ 'foo', 'bar' ] } );
+		dataFilter.disallowAttributes( { name: 'section', classes: [ 'bar' ] } );
 
-		editor.setData( '<div class="foo bar">foo</div><div class="bar">bar</div>' );
+		editor.setData( '<section class="foo bar">foo</section><section class="bar">bar</section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsDiv ghsAttributes="(1)">foo</ghsDiv><ghsDiv>bar</ghsDiv>',
+			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsSection>bar</ghsSection>',
 			attributes: {
 				1: [ [ 'class', [ 'foo' ] ] ]
 			}
 		} );
 
 		expect( editor.getData() ).to.eq(
-			'<div class="foo">foo</div><div>bar</div>'
+			'<section class="foo">foo</section><section>bar</section>'
 		);
 	} );
 } );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index abf7d1f8e3d..7fcc915ecc3 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -13,36 +13,33 @@ import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
 import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
 import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
 
-import GeneralHTMLSupport from '../../src/generalhtmlsupport';
+import DataFilter from '../../src/datafilter';
 
 class ExtendHTMLSupport extends Plugin {
-	static get requires() {
-		return [ GeneralHTMLSupport ];
-	}
-
 	init() {
-		const dataSchema = this.editor.plugins.get( 'GeneralHTMLSupport' ).dataSchema;
+		const dataFilter = new DataFilter( this.editor );
+
+		dataFilter.allowElement( { name: /article|section/ } );
 
-		dataSchema.allowElement( { name: /article|section/ } );
+		dataFilter.allowAttributes( { name: 'section', attributes: { id: /[^]/ } } );
+		dataFilter.allowAttributes( { name: 'section', classes: /[^]/ } );
+		dataFilter.allowAttributes( { name: 'section', styles: { color: /[^]/ } } );
 
-		dataSchema.allowAttributes( { name: 'section', attributes: { id: /[^]/ } } );
-		dataSchema.allowAttributes( { name: 'section', classes: /[^]/ } );
-		dataSchema.allowAttributes( { name: 'section', styles: { color: /[^]/ } } );
+		dataFilter.allowElement( { name: /details|summary/ } );
 
-		dataSchema.allowElement( { name: /details|summary/ } );
+		dataFilter.allowElement( { name: /dl|dt|dd/ } );
 
-		dataSchema.allowElement( { name: /dl|dt|dd/ } );
+		window.dataFilter = dataFilter;
 	}
 }
 
 ClassicEditor
 	.create( document.querySelector( '#editor' ), {
-		plugins: [ Essentials, Paragraph, Bold, Italic, Strikethrough, GeneralHTMLSupport, ExtendHTMLSupport ],
+		plugins: [ Essentials, Paragraph, Bold, Italic, Strikethrough, ExtendHTMLSupport ],
 		toolbar: [ 'bold', 'italic', 'strikethrough', 'contentTags' ]
 	} )
 	.then( editor => {
 		window.editor = editor;
-		window.dataSchema = editor.plugins.get( 'GeneralHTMLSupport' ).dataSchema;
 	} )
 	.catch( err => {
 		console.error( err.stack );

From eaa0ec5dcb3dcbc7f28fbc968a066e1f958dd4cc Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 16 Feb 2021 18:34:50 +0100
Subject: [PATCH 010/217] Updated schema inheritance.

---
 .../ckeditor5-content-compatibility/src/dataschema.js  | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 6cb7e4dd786..afdab2b0fff 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -122,12 +122,14 @@ export default class DataSchema {
 	 * @returns {Iterable<String>}
 	 */
 	* _getReferences( name ) {
-		// TODO extend with the rest of schema properties based on other model types.
 		const { schema } = this._definitions[ name ];
+		const inheritProperties = [ 'inheritAllFrom', 'inheritTypesFrom', 'allowWhere', 'allowContentOf', 'allowAttributesOf' ];
 
-		for ( const model of toArray( schema.inheritAllFrom || [] ) ) {
-			if ( this._definitions[ model ] ) {
-				yield model;
+		for ( const property of inheritProperties ) {
+			for ( const model of toArray( schema[ property ] || [] ) ) {
+				if ( model !== name && this._definitions[ model ] ) {
+					yield model;
+				}
 			}
 		}
 	}

From f448f5c5c498082aa27b8bcccea31e979c2f8076 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Feb 2021 08:42:12 +0100
Subject: [PATCH 011/217] Fixed allowText.

---
 packages/ckeditor5-content-compatibility/src/dataschema.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index afdab2b0fff..e77977cc492 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -109,7 +109,7 @@ export default class DataSchema {
 
 		schema.register( name, schemaDefinition );
 
-		if ( schema.allowText ) {
+		if ( schemaDefinition.allowText ) {
 			schema.extend( '$text', { allowIn: name } );
 		}
 	}

From 4e1271dbc547bcd04ea3e1bb7044ea331387fc18 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Feb 2021 08:42:47 +0100
Subject: [PATCH 012/217] Ensure that attribute is not used by other features.

---
 .../src/datafilter.js                         | 26 ++++++++++++++++---
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index ee4711eec10..042d9953338 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -124,27 +124,45 @@ export default class DataFilter {
 		conversion.for( 'upcast' ).elementToElement( {
 			view: viewName,
 			model: ( viewElement, conversionApi ) => {
+				// We will stash only attributes which are not processed by any other features
+				// and should be left unchaged.
+				const viewConsumable = conversionApi.consumable;
+
 				const viewAttributes = [];
 				const allowedAttributes = this._getAllowedAttributes( viewElement );
 
+				// Stash attributes.
 				for ( const key of allowedAttributes.attributes ) {
-					viewAttributes.push( [ key, viewElement.getAttribute( key ) ] );
+					if ( viewConsumable.test( viewElement, { attributes: key } ) ) {
+						viewAttributes.push( [ key, viewElement.getAttribute( key ) ] );
+					}
 				}
 
-				if ( allowedAttributes.classes.length ) {
+				// Stash classes.
+				const classes = allowedAttributes.classes.filter( className => {
+					return viewConsumable.test( viewElement, { classes: className } );
+				} );
+
+				if ( classes.length ) {
 					viewAttributes.push( [ 'class', allowedAttributes.classes ] );
 				}
 
-				if ( allowedAttributes.styles.length ) {
+				// Stash styles.
+				const styles = allowedAttributes.styles.filter( styleName => {
+					return viewConsumable.test( viewElement, { styles: styleName } );
+				} );
+
+				if ( styles.length ) {
 					const stylesObj = {};
 
-					for ( const styleName of allowedAttributes.styles ) {
+					for ( const styleName of styles ) {
 						stylesObj[ styleName ] = viewElement.getStyle( styleName );
 					}
 
 					viewAttributes.push( [ 'style', stylesObj ] );
 				}
 
+				// Keep compatibility attributes inside a single model attribute.
 				let attributesToAdd;
 				if ( viewAttributes.length ) {
 					attributesToAdd = [ [ DATA_SCHEMA_ATTRIBUTE_KEY, viewAttributes ] ];

From bf3d979511816d2cd074a093709308d49d780d25 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 23 Feb 2021 09:47:45 +0100
Subject: [PATCH 013/217] Refactoring.

---
 .../src/datafilter.js                         | 40 +++++++++----------
 1 file changed, 19 insertions(+), 21 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 042d9953338..e76762bb51a 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -48,10 +48,8 @@ export default class DataFilter {
 
 		this.dataSchema = new DataSchema( editor );
 
-		this._viewMatchers = {
-			allowedAttributes: {},
-			disallowedAttributes: {}
-		};
+		this._allowedAttributes = {};
+		this._disallowedAttributes = {};
 	}
 
 	/**
@@ -78,7 +76,7 @@ export default class DataFilter {
 	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all attributes which should be allowed.
 	 */
 	allowAttributes( config ) {
-		this._addAttributeMatcher( config, this._viewMatchers.allowedAttributes );
+		this._addAttributeMatcher( config, this._allowedAttributes );
 	}
 
 	/**
@@ -87,7 +85,7 @@ export default class DataFilter {
 	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all attributes which should be disallowed.
 	 */
 	disallowAttributes( config ) {
-		this._addAttributeMatcher( config, this._viewMatchers.disallowedAttributes );
+		this._addAttributeMatcher( config, this._disallowedAttributes );
 	}
 
 	/**
@@ -95,9 +93,9 @@ export default class DataFilter {
 	 *
 	 * @private
 	 * @param {module:engine/view/matcher~MatcherPattern} pattern
-	 * @param {Object} cache Cache object holding matchers.
+	 * @param {Object} rules Rules object holding matchers.
 	 */
-	_addAttributeMatcher( config, cache ) {
+	_addAttributeMatcher( config, rules ) {
 		const nameRegExp = toRegExp( config.name );
 
 		config = cloneDeep( config );
@@ -107,7 +105,7 @@ export default class DataFilter {
 
 		for ( const { view } of this.dataSchema.getModelViewMapping() ) {
 			if ( nameRegExp.test( view ) ) {
-				getOrCreateMatcher( view, cache ).add( config );
+				getOrCreateMatcher( view, rules ).add( config );
 			}
 		}
 	}
@@ -243,8 +241,8 @@ export default class DataFilter {
 	 * @returns {Array} result.styles Array with matched style names.
 	 */
 	_getAllowedAttributes( viewElement ) {
-		const allowedAttributes = matchAll( viewElement, this._viewMatchers.allowedAttributes );
-		const disallowedAttributes = matchAll( viewElement, this._viewMatchers.disallowedAttributes );
+		const allowedAttributes = matchAll( viewElement, this._allowedAttributes );
+		const disallowedAttributes = matchAll( viewElement, this._disallowedAttributes );
 
 		// Drop disallowed content.
 		for ( const key in allowedAttributes ) {
@@ -256,21 +254,21 @@ export default class DataFilter {
 }
 
 /**
- * Helper function restoring matcher for the given key from cache object.
+ * Helper function restoring matcher for the given key from `rules` object.
  *
  * If matcher for the given key does not exist, this function will create a new one
- * inside cache object under the given key.
+ * inside `rules` object under the given key.
  *
  * @private
  * @param {String} key
- * @param {Object} cache
+ * @param {Object} rules
  */
-function getOrCreateMatcher( key, cache ) {
-	if ( !cache[ key ] ) {
-		cache[ key ] = new Matcher();
+function getOrCreateMatcher( key, rules ) {
+	if ( !rules[ key ] ) {
+		rules[ key ] = new Matcher();
 	}
 
-	return cache[ key ];
+	return rules[ key ];
 }
 
 /**
@@ -278,14 +276,14 @@ function getOrCreateMatcher( key, cache ) {
  *
  * @private
  * @param {module:engine/view/element~Element} viewElement
- * @param {Object} cache Cache object holding matchers.
+ * @param {Object} rules Rules object holding matchers.
  * @returns {Object} result
  * @returns {Array} result.attributes Array with matched attribute names.
  * @returns {Array} result.classes Array with matched class names.
  * @returns {Array} result.styles Array with matched style names.
  */
-function matchAll( viewElement, cache ) {
-	const matcher = getOrCreateMatcher( viewElement.name, cache );
+function matchAll( viewElement, rules ) {
+	const matcher = getOrCreateMatcher( viewElement.name, rules );
 	const matches = matcher.matchAll( viewElement );
 
 	return mergeMatchAllResult( matches || [] );

From 067ac0348f38538a22a47d6c32b008b6c78c8336 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 23 Feb 2021 09:48:36 +0100
Subject: [PATCH 014/217] Removed unnecessary code.

---
 .../src/datafilter.js                         | 19 -------------------
 1 file changed, 19 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index e76762bb51a..a1f25a5de11 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -188,25 +188,6 @@ export default class DataFilter {
 				const viewWriter = conversionApi.writer;
 				const viewElement = conversionApi.mapper.toViewElement( data.item );
 
-				// Remove old values.
-				if ( data.attributeOldValue !== null ) {
-					data.attributeOldValue.forEach( ( [ key, value ] ) => {
-						if ( key === 'class' ) {
-							const classes = toArray( value );
-
-							for ( const className of classes ) {
-								viewWriter.removeClass( className, viewElement );
-							}
-						} else if ( key === 'style' ) {
-							for ( const key in value ) {
-								viewWriter.removeStyle( key, viewElement );
-							}
-						} else {
-							viewWriter.removeAttribute( key, viewElement );
-						}
-					} );
-				}
-
 				// Apply new values.
 				if ( data.attributeNewValue !== null ) {
 					data.attributeNewValue.forEach( ( [ key, value ] ) => {

From 1dea09f321693efad51a7246f81b6bba46f2db15 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 23 Feb 2021 12:54:22 +0100
Subject: [PATCH 015/217] Use additional upcast converter to disallow
 attributes.

---
 .../src/datafilter.js                         | 88 ++++++-------------
 .../tests/datafilter.js                       |  8 +-
 2 files changed, 31 insertions(+), 65 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index a1f25a5de11..bd92c7eda52 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -119,54 +119,57 @@ export default class DataFilter {
 		const viewName = definition.view;
 		const modelName = definition.model;
 
+		// Consumes disallowed element attributes to prevent them of being processed by other converters.
+		conversion.for( 'upcast' ).add( dispatcher => {
+			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
+				for ( const match of matchAll( data.viewItem, this._disallowedAttributes ) ) {
+					conversionApi.consumable.consume( data.viewItem, match.match );
+				}
+			}, { priority: 'high' } );
+		} );
+
+		// Stash unused, allowed element attributes, so they can be reapplied later in data conversion.
 		conversion.for( 'upcast' ).elementToElement( {
 			view: viewName,
 			model: ( viewElement, conversionApi ) => {
-				// We will stash only attributes which are not processed by any other features
-				// and should be left unchaged.
-				const viewConsumable = conversionApi.consumable;
+				const matches = [];
+				for ( const match of matchAll( viewElement, this._allowedAttributes ) ) {
+					if ( conversionApi.consumable.consume( viewElement, match.match ) ) {
+						matches.push( match );
+					}
+				}
 
+				const allowedAttributes = mergeMatchResults( matches );
 				const viewAttributes = [];
-				const allowedAttributes = this._getAllowedAttributes( viewElement );
 
 				// Stash attributes.
 				for ( const key of allowedAttributes.attributes ) {
-					if ( viewConsumable.test( viewElement, { attributes: key } ) ) {
-						viewAttributes.push( [ key, viewElement.getAttribute( key ) ] );
-					}
+					viewAttributes.push( [ key, viewElement.getAttribute( key ) ] );
 				}
 
 				// Stash classes.
-				const classes = allowedAttributes.classes.filter( className => {
-					return viewConsumable.test( viewElement, { classes: className } );
-				} );
-
-				if ( classes.length ) {
+				if ( allowedAttributes.classes.length ) {
 					viewAttributes.push( [ 'class', allowedAttributes.classes ] );
 				}
 
 				// Stash styles.
-				const styles = allowedAttributes.styles.filter( styleName => {
-					return viewConsumable.test( viewElement, { styles: styleName } );
-				} );
-
-				if ( styles.length ) {
+				if ( allowedAttributes.styles.length ) {
 					const stylesObj = {};
 
-					for ( const styleName of styles ) {
+					for ( const styleName of allowedAttributes.styles ) {
 						stylesObj[ styleName ] = viewElement.getStyle( styleName );
 					}
 
 					viewAttributes.push( [ 'style', stylesObj ] );
 				}
 
-				// Keep compatibility attributes inside a single model attribute.
-				let attributesToAdd;
+				const element = conversionApi.writer.createElement( modelName );
+
 				if ( viewAttributes.length ) {
-					attributesToAdd = [ [ DATA_SCHEMA_ATTRIBUTE_KEY, viewAttributes ] ];
+					conversionApi.writer.setAttribute( DATA_SCHEMA_ATTRIBUTE_KEY, viewAttributes, element );
 				}
 
-				return conversionApi.writer.createElement( modelName, attributesToAdd );
+				return element;
 			}
 		} );
 
@@ -209,29 +212,6 @@ export default class DataFilter {
 			} );
 		} );
 	}
-
-	/**
-	 * Returns all allowed view element attributes based on attribute matchers registered via {@link #allowedAttributes}
-	 * and {@link #disallowedAttributes} methods.
-	 *
-	 * @private
-	 * @param {module:engine/view/element~Element} viewElement
-	 * @returns {Object} result
-	 * @returns {Array} result.attributes Array with matched attribute names.
-	 * @returns {Array} result.classes Array with matched class names.
-	 * @returns {Array} result.styles Array with matched style names.
-	 */
-	_getAllowedAttributes( viewElement ) {
-		const allowedAttributes = matchAll( viewElement, this._allowedAttributes );
-		const disallowedAttributes = matchAll( viewElement, this._disallowedAttributes );
-
-		// Drop disallowed content.
-		for ( const key in allowedAttributes ) {
-			allowedAttributes[ key ] = removeArray( allowedAttributes[ key ], disallowedAttributes[ key ] );
-		}
-
-		return allowedAttributes;
-	}
 }
 
 /**
@@ -253,7 +233,7 @@ function getOrCreateMatcher( key, rules ) {
 }
 
 /**
- * Helper function matching all attributes for the given element.
+ * Alias for {@link module:engine/view/matcher~Matcher#matchAll matchAll}.
  *
  * @private
  * @param {module:engine/view/element~Element} viewElement
@@ -265,9 +245,8 @@ function getOrCreateMatcher( key, rules ) {
  */
 function matchAll( viewElement, rules ) {
 	const matcher = getOrCreateMatcher( viewElement.name, rules );
-	const matches = matcher.matchAll( viewElement );
 
-	return mergeMatchAllResult( matches || [] );
+	return matcher.matchAll( viewElement ) || [];
 }
 
 /**
@@ -280,7 +259,7 @@ function matchAll( viewElement, rules ) {
  * @returns {Array} result.classes Array with matched class names.
  * @returns {Array} result.styles Array with matched style names.
  */
-function mergeMatchAllResult( matches ) {
+function mergeMatchResults( matches ) {
 	const matchResult = { attributes: [], classes: [], styles: [] };
 
 	for ( const match of matches ) {
@@ -297,17 +276,6 @@ function mergeMatchAllResult( matches ) {
 	return matchResult;
 }
 
-/**
- * Removes array items included in the second array parameter.
- *
- * @param {Array} array
- * @param {Array} toRemove
- * @returns {Array} Filtered array items.
- */
-function removeArray( array, toRemove ) {
-	return array.filter( item => !toRemove.includes( item ) );
-}
-
 function toRegExp( value ) {
 	// Match everything if name not given.
 	if ( !value ) {
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 8a74ffe3b76..134042bdd03 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -214,14 +214,12 @@ describe( 'DataFilter', () => {
 		editor.setData( '<section class="foo bar">foo</section><section class="bar">bar</section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsSection>bar</ghsSection>',
-			attributes: {
-				1: [ [ 'class', [ 'foo' ] ] ]
-			}
+			data: '<ghsSection>foo</ghsSection><ghsSection>bar</ghsSection>',
+			attributes: {}
 		} );
 
 		expect( editor.getData() ).to.eq(
-			'<section class="foo">foo</section><section>bar</section>'
+			'<section>foo</section><section>bar</section>'
 		);
 	} );
 } );

From db8df3fb9646419c003c3d195b33265ad97363e3 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 23 Feb 2021 13:21:14 +0100
Subject: [PATCH 016/217] Changed conversion priority.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index bd92c7eda52..440ed2d1505 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -170,7 +170,8 @@ export default class DataFilter {
 				}
 
 				return element;
-			}
+			},
+			converterPriority: 'low'
 		} );
 
 		conversion.for( 'downcast' ).elementToElement( {

From e84a96f575ccd41bf66370780aba986e6a85fae9 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 23 Feb 2021 13:29:33 +0100
Subject: [PATCH 017/217] Fixed autoparagraphing for some elements.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 440ed2d1505..d002797b721 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -11,6 +11,8 @@ import { escapeRegExp, cloneDeep, uniq } from 'lodash-es';
 import Matcher from '@ckeditor/ckeditor5-engine/src/view/matcher';
 import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
+import { priorities } from 'ckeditor5/src/utils';
+
 import DataSchema from './dataschema';
 
 const DATA_SCHEMA_ATTRIBUTE_KEY = 'ghsAttributes';
@@ -171,7 +173,9 @@ export default class DataFilter {
 
 				return element;
 			},
-			converterPriority: 'low'
+			// With a `low` priority, `paragraph` plugin autoparagraphing mechanism is executed. Make sure
+			// this listener is called before it. If not, some elements will be transformed into a paragraph.
+			converterPriority: priorities.get( 'low' ) + 1
 		} );
 
 		conversion.for( 'downcast' ).elementToElement( {

From 665b13cdf88590db0164e4a0f10d5b69a807fd5e Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 23 Feb 2021 13:33:57 +0100
Subject: [PATCH 018/217] Fixed dependencies.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 5 ++---
 packages/ckeditor5-content-compatibility/src/dataschema.js | 2 +-
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index d002797b721..cc9ee394469 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -8,10 +8,9 @@
  */
 
 import { escapeRegExp, cloneDeep, uniq } from 'lodash-es';
-import Matcher from '@ckeditor/ckeditor5-engine/src/view/matcher';
-import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
-import { priorities } from 'ckeditor5/src/utils';
+import { Matcher } from 'ckeditor5/src/engine';
+import { priorities, toArray } from 'ckeditor5/src/utils';
 
 import DataSchema from './dataschema';
 
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index e77977cc492..ded87e0f825 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -8,7 +8,7 @@
  */
 
 import { cloneDeep } from 'lodash-es';
-import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
+import { toArray } from 'ckeditor5/src/utils';
 
 /**
  * Holds representation of the extended HTML document type definitions to be used by the

From 3628142493489076a12a6a921f3af29fa8574c2f Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 23 Feb 2021 14:08:22 +0100
Subject: [PATCH 019/217] Refactored element name matching.

---
 .../src/datafilter.js                         | 21 ++++++++-----------
 .../tests/datafilter.js                       | 11 +++++-----
 2 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index cc9ee394469..7e3618eecc7 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -59,10 +59,8 @@ export default class DataFilter {
 	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all view elements which should be allowed.
 	 */
 	allowElement( config ) {
-		const nameRegExp = toRegExp( config.name );
-
 		for ( const mapping of this.dataSchema.getModelViewMapping() ) {
-			if ( nameRegExp.test( mapping.view ) ) {
+			if ( matchViewName( config.name, mapping.view ) ) {
 				this.dataSchema.enable( mapping.model );
 				this._defineConverters( mapping );
 			}
@@ -97,7 +95,7 @@ export default class DataFilter {
 	 * @param {Object} rules Rules object holding matchers.
 	 */
 	_addAttributeMatcher( config, rules ) {
-		const nameRegExp = toRegExp( config.name );
+		const name = config.name;
 
 		config = cloneDeep( config );
 		// We don't want match by name when matching attributes.
@@ -105,7 +103,7 @@ export default class DataFilter {
 		delete config.name;
 
 		for ( const { view } of this.dataSchema.getModelViewMapping() ) {
-			if ( nameRegExp.test( view ) ) {
+			if ( matchViewName( name, view ) ) {
 				getOrCreateMatcher( view, rules ).add( config );
 			}
 		}
@@ -280,15 +278,14 @@ function mergeMatchResults( matches ) {
 	return matchResult;
 }
 
-function toRegExp( value ) {
-	// Match everything if name not given.
-	if ( !value ) {
-		value = /[^]/;
+function matchViewName( pattern, viewName ) {
+	if ( typeof pattern === 'string' ) {
+		return pattern === viewName;
 	}
 
-	if ( !( value instanceof RegExp ) ) {
-		value = new RegExp( escapeRegExp( value ) );
+	if ( pattern instanceof RegExp ) {
+		return pattern.test( viewName );
 	}
 
-	return value;
+	return false;
 }
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 134042bdd03..8e98e6c20db 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -126,7 +126,7 @@ describe( 'DataFilter', () => {
 
 	it( 'should allow nested attributes', () => {
 		dataFilter.allowElement( { name: /article|section/ } );
-		dataFilter.allowAttributes( { attributes: { 'data-foo': /foo|bar/ } } );
+		dataFilter.allowAttributes( { name: /[^]/, attributes: { 'data-foo': /foo|bar/ } } );
 
 		editor.setData( '<article data-foo="foo">' +
 				'<section data-foo="bar">section1</section>' +
@@ -147,11 +147,10 @@ describe( 'DataFilter', () => {
 	} );
 
 	it( 'should allow attributes for all allowed definitions', () => {
-		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowElement( { name: 'article' } );
-		// We skip name purposely to allow attribute on every data schema element.
-		dataFilter.allowAttributes( { attributes: { 'data-foo': 'foo' } } );
-		dataFilter.allowAttributes( { attributes: { 'data-bar': 'bar' } } );
+		dataFilter.allowElement( { name: /section|article/ } );
+
+		dataFilter.allowAttributes( { name: /section|article/, attributes: { 'data-foo': 'foo' } } );
+		dataFilter.allowAttributes( { name: /section|article/, attributes: { 'data-bar': 'bar' } } );
 
 		editor.setData( '<section data-foo="foo">foo</section><article data-bar="bar">bar</article>' );
 

From 2b110eb0a03828e2062464f3c24d79d3f36a605d Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 23 Feb 2021 15:44:31 +0100
Subject: [PATCH 020/217] Better dataSchema and dataFilter separation.

---
 .../src/datafilter.js                         | 64 +++++++++------
 .../src/dataschema.js                         | 77 ++++++++++++++-----
 2 files changed, 99 insertions(+), 42 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 7e3618eecc7..a9bee7bfdec 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -7,7 +7,7 @@
  * @module content-compatibility/datafilter
  */
 
-import { escapeRegExp, cloneDeep, uniq } from 'lodash-es';
+import { cloneDeep, uniq } from 'lodash-es';
 
 import { Matcher } from 'ckeditor5/src/engine';
 import { priorities, toArray } from 'ckeditor5/src/utils';
@@ -59,11 +59,12 @@ export default class DataFilter {
 	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all view elements which should be allowed.
 	 */
 	allowElement( config ) {
-		for ( const mapping of this.dataSchema.getModelViewMapping() ) {
-			if ( matchViewName( config.name, mapping.view ) ) {
-				this.dataSchema.enable( mapping.model );
-				this._defineConverters( mapping );
+		for ( const definition of this.dataSchema.getDefinitionsForView( config.name ) ) {
+			for ( const reference of definition.references ) {
+				this._registerElement( reference );
 			}
+
+			this._registerElement( definition );
 		}
 
 		this.allowAttributes( config );
@@ -95,17 +96,44 @@ export default class DataFilter {
 	 * @param {Object} rules Rules object holding matchers.
 	 */
 	_addAttributeMatcher( config, rules ) {
-		const name = config.name;
+		const viewName = config.name;
 
 		config = cloneDeep( config );
-		// We don't want match by name when matching attributes.
-		// Matcher will be already attached to specific definition.
+		// We don't want match by name when matching attributes. Matcher will be already attached to specific definition.
 		delete config.name;
 
-		for ( const { view } of this.dataSchema.getModelViewMapping() ) {
-			if ( matchViewName( name, view ) ) {
-				getOrCreateMatcher( view, rules ).add( config );
-			}
+		for ( const definition of this.dataSchema.getDefinitionsForView( viewName ) ) {
+			getOrCreateMatcher( definition.view, rules ).add( config );
+		}
+	}
+
+	/**
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 */
+	_registerElement( definition ) {
+		if ( this.editor.model.schema.isRegistered( definition.model ) ) {
+			return;
+		}
+
+		this._defineSchema( definition );
+
+		if ( definition.view ) {
+			this._defineConverters( definition );
+		}
+	}
+
+	/**
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 */
+	_defineSchema( definition ) {
+		const schema = this.editor.model.schema;
+
+		schema.register( definition.model, definition.schema );
+
+		if ( definition.schema.allowText ) {
+			schema.extend( '$text', { allowIn: definition.model } );
 		}
 	}
 
@@ -277,15 +305,3 @@ function mergeMatchResults( matches ) {
 
 	return matchResult;
 }
-
-function matchViewName( pattern, viewName ) {
-	if ( typeof pattern === 'string' ) {
-		return pattern === viewName;
-	}
-
-	if ( pattern instanceof RegExp ) {
-		return pattern.test( viewName );
-	}
-
-	return false;
-}
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index ded87e0f825..5610e88ac56 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -73,20 +73,6 @@ export default class DataSchema {
 		this._definitions[ model ] = { view, model, schema };
 	}
 
-	/**
-	 * Returns model-view-pairs for the added data schema definitions.
-	 *
-	 * This method will only return pairs when if
-	 * {@link module:content-compatibility/dataschema~DataSchemaDefinition#view view} has been set.
-	 *
-	 * @returns {Object[]} result
-	 */
-	getModelViewMapping() {
-		return Object.values( this._definitions )
-			.filter( def => def.view && def.model )
-			.map( def => ( { model: def.model, view: def.view } ) );
-	}
-
 	/**
 	 * Registers model schema item for the given
 	 * {@link module:content-compatibility/dataschema~DataSchemaDefinition data schema definition} name.
@@ -115,7 +101,39 @@ export default class DataSchema {
 	}
 
 	/**
-	 * Resolves all model references registered for the given data schema definition.
+	 * Returns all definitions matching the given view name.
+	 *
+	 * @param {String} viewName
+	 * @returns {Iterable<*>}
+	 */
+	* getDefinitionsForView( viewName ) {
+		const definitions = Object.values( this._definitions )
+			.filter( def => def.view && testViewName( viewName, def.view ) );
+
+		for ( const definition of definitions ) {
+			yield this.getDefinition( definition.model );
+		}
+	}
+
+	/**
+	 * Returns definition for the given model name.
+	 *
+	 * Definition will also include `references` property including all definitions
+	 * referenced by this definition.
+	 *
+	 * @param {String} modelName
+	 * @returns {module:content-compatibility/dataschema~DataSchemaDefinition}
+	 */
+	getDefinition( modelName ) {
+		const definition = cloneDeep( this._definitions[ modelName ] );
+
+		definition.references = this._getReferences( modelName );
+
+		return definition;
+	}
+
+	/**
+	 * Resolves all definition references registered for the given data schema definition.
 	 *
 	 * @private
 	 * @param {String} name Data schema model name.
@@ -126,15 +144,38 @@ export default class DataSchema {
 		const inheritProperties = [ 'inheritAllFrom', 'inheritTypesFrom', 'allowWhere', 'allowContentOf', 'allowAttributesOf' ];
 
 		for ( const property of inheritProperties ) {
-			for ( const model of toArray( schema[ property ] || [] ) ) {
-				if ( model !== name && this._definitions[ model ] ) {
-					yield model;
+			for ( const modelName of toArray( schema[ property ] || [] ) ) {
+				const definition = this._definitions[ modelName ];
+
+				if ( modelName !== name && definition ) {
+					yield* this._getReferences( definition.model );
+					yield definition;
 				}
 			}
 		}
 	}
 }
 
+/**
+ * Test view name against the given pattern.
+ *
+ * @private
+ * @param {String|RegExp} pattern
+ * @param {String} viewName
+ * @returns {Boolean}
+ */
+function testViewName( pattern, viewName ) {
+	if ( typeof pattern === 'string' ) {
+		return pattern === viewName;
+	}
+
+	if ( pattern instanceof RegExp ) {
+		return pattern.test( viewName );
+	}
+
+	return false;
+}
+
 /**
  * A definition of {@link module:content-compatibility/dataschema data schema}.
  *

From 2f5f5a0d6fc6af4ed1aefb36f2849e804576e610 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 24 Feb 2021 09:33:06 +0100
Subject: [PATCH 021/217] Flatten styles and classes structure to simplify
 code.

---
 .../src/datafilter.js                         | 44 ++++++++++---------
 .../tests/datafilter.js                       | 13 +++---
 2 files changed, 31 insertions(+), 26 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index a9bee7bfdec..b262834810b 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -10,7 +10,9 @@
 import { cloneDeep, uniq } from 'lodash-es';
 
 import { Matcher } from 'ckeditor5/src/engine';
-import { priorities, toArray } from 'ckeditor5/src/utils';
+import { priorities } from 'ckeditor5/src/utils';
+
+import StylesMap, { StylesProcessor } from '@ckeditor/ckeditor5-engine/src/view/stylesmap';
 
 import DataSchema from './dataschema';
 
@@ -176,7 +178,7 @@ export default class DataFilter {
 
 				// Stash classes.
 				if ( allowedAttributes.classes.length ) {
-					viewAttributes.push( [ 'class', allowedAttributes.classes ] );
+					viewAttributes.push( [ 'class', allowedAttributes.classes.join( ' ' ) ] );
 				}
 
 				// Stash styles.
@@ -187,7 +189,7 @@ export default class DataFilter {
 						stylesObj[ styleName ] = viewElement.getStyle( styleName );
 					}
 
-					viewAttributes.push( [ 'style', stylesObj ] );
+					viewAttributes.push( [ 'style', inlineStyles( stylesObj ) ] );
 				}
 
 				const element = conversionApi.writer.createElement( modelName );
@@ -214,6 +216,10 @@ export default class DataFilter {
 					return;
 				}
 
+				if ( data.attributeNewValue === null ) {
+					return;
+				}
+
 				if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
 					return;
 				}
@@ -222,23 +228,9 @@ export default class DataFilter {
 				const viewElement = conversionApi.mapper.toViewElement( data.item );
 
 				// Apply new values.
-				if ( data.attributeNewValue !== null ) {
-					data.attributeNewValue.forEach( ( [ key, value ] ) => {
-						if ( key === 'class' ) {
-							const classes = toArray( value );
-
-							for ( const className of classes ) {
-								viewWriter.addClass( className, viewElement );
-							}
-						} else if ( key === 'style' ) {
-							for ( const key in value ) {
-								viewWriter.setStyle( key, value[ key ], viewElement );
-							}
-						} else {
-							viewWriter.setAttribute( key, value, viewElement );
-						}
-					} );
-				}
+				data.attributeNewValue.forEach( ( [ key, value ] ) => {
+					viewWriter.setAttribute( key, value, viewElement );
+				} );
 			} );
 		} );
 	}
@@ -305,3 +297,15 @@ function mergeMatchResults( matches ) {
 
 	return matchResult;
 }
+
+/**
+ * Inlines styles object into normalized style string.
+ *
+ * @param {Object} stylesObject
+ * @returns {String}
+ */
+function inlineStyles( stylesObj ) {
+	const stylesMap = new StylesMap( new StylesProcessor() );
+	stylesMap.set( stylesObj );
+	return stylesMap.toString();
+}
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 8e98e6c20db..3295698e7b3 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -89,20 +89,21 @@ describe( 'DataFilter', () => {
 	it( 'should allow attributes (styles)', () => {
 		dataFilter.allowElement( { name: 'section' } );
 		dataFilter.allowAttributes( { name: 'section', styles: {
-			'color': 'red'
+			'color': 'red',
+			'background-color': 'blue'
 		} } );
 
-		editor.setData( '<section style="color:red;">foobar</section>' );
+		editor.setData( '<section style="background-color:blue;color:red;">foobar</section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
 			attributes: {
-				1: [ [ 'style', { color: 'red' } ] ]
+				1: [ [ 'style', 'background-color:blue;color:red;' ] ]
 			}
 		} );
 
 		expect( editor.getData() ).to.eq(
-			'<section style="color:red;">foobar</section>'
+			'<section style="background-color:blue;color:red;">foobar</section>'
 		);
 	} );
 
@@ -115,7 +116,7 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
 			attributes: {
-				1: [ [ 'class', [ 'foo', 'bar' ] ] ]
+				1: [ [ 'class', 'foo bar' ] ]
 			}
 		} );
 
@@ -196,7 +197,7 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsSection>bar</ghsSection>',
 			attributes: {
-				1: [ [ 'style', { color: 'blue' } ] ]
+				1: [ [ 'style', 'color:blue;' ] ]
 			}
 		} );
 

From af048b7be274bc4cc6d94b9442651ac43605759d Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 24 Feb 2021 10:12:15 +0100
Subject: [PATCH 022/217] Refactoring, removed unused code.

---
 .../src/datafilter.js                         | 16 +++----
 .../src/dataschema.js                         | 47 ++++---------------
 2 files changed, 18 insertions(+), 45 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index b262834810b..d09bad1874a 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -51,8 +51,8 @@ export default class DataFilter {
 
 		this.dataSchema = new DataSchema( editor );
 
-		this._allowedAttributes = {};
-		this._disallowedAttributes = {};
+		this._allowedAttributes = new Map();
+		this._disallowedAttributes = new Map();
 	}
 
 	/**
@@ -95,7 +95,7 @@ export default class DataFilter {
 	 *
 	 * @private
 	 * @param {module:engine/view/matcher~MatcherPattern} pattern
-	 * @param {Object} rules Rules object holding matchers.
+	 * @param {Map} rules Rules map holding matchers.
 	 */
 	_addAttributeMatcher( config, rules ) {
 		const viewName = config.name;
@@ -244,14 +244,14 @@ export default class DataFilter {
  *
  * @private
  * @param {String} key
- * @param {Object} rules
+ * @param {Map} rules
  */
 function getOrCreateMatcher( key, rules ) {
-	if ( !rules[ key ] ) {
-		rules[ key ] = new Matcher();
+	if ( !rules.has( key ) ) {
+		rules.set( key, new Matcher() );
 	}
 
-	return rules[ key ];
+	return rules.get( key );
 }
 
 /**
@@ -259,7 +259,7 @@ function getOrCreateMatcher( key, rules ) {
  *
  * @private
  * @param {module:engine/view/element~Element} viewElement
- * @param {Object} rules Rules object holding matchers.
+ * @param {Map} rules Rules map holding matchers.
  * @returns {Object} result
  * @returns {Array} result.attributes Array with matched attribute names.
  * @returns {Array} result.classes Array with matched class names.
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 5610e88ac56..5ec7f1fd547 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -28,7 +28,7 @@ export default class DataSchema {
 	constructor( editor ) {
 		this.editor = editor;
 
-		this._definitions = {};
+		this._definitions = new Map();
 
 		// Add block elements.
 		this.register( { model: '$ghsBlock' }, {
@@ -70,34 +70,7 @@ export default class DataSchema {
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
 	register( { view, model }, schema ) {
-		this._definitions[ model ] = { view, model, schema };
-	}
-
-	/**
-	 * Registers model schema item for the given
-	 * {@link module:content-compatibility/dataschema~DataSchemaDefinition data schema definition} name.
-	 *
-	 * @param {String} name
-	 */
-	enable( name ) {
-		const schema = this.editor.model.schema;
-
-		if ( schema.isRegistered( name ) ) {
-			return;
-		}
-
-		const definition = this._definitions[ name ];
-		const schemaDefinition = cloneDeep( definition.schema );
-
-		for ( const reference of this._getReferences( name ) ) {
-			this.enable( reference );
-		}
-
-		schema.register( name, schemaDefinition );
-
-		if ( schemaDefinition.allowText ) {
-			schema.extend( '$text', { allowIn: name } );
-		}
+		this._definitions.set( model, { view, model, schema } );
 	}
 
 	/**
@@ -107,7 +80,7 @@ export default class DataSchema {
 	 * @returns {Iterable<*>}
 	 */
 	* getDefinitionsForView( viewName ) {
-		const definitions = Object.values( this._definitions )
+		const definitions = Array.from( this._definitions.values() )
 			.filter( def => def.view && testViewName( viewName, def.view ) );
 
 		for ( const definition of definitions ) {
@@ -125,7 +98,7 @@ export default class DataSchema {
 	 * @returns {module:content-compatibility/dataschema~DataSchemaDefinition}
 	 */
 	getDefinition( modelName ) {
-		const definition = cloneDeep( this._definitions[ modelName ] );
+		const definition = cloneDeep( this._definitions.get( modelName ) );
 
 		definition.references = this._getReferences( modelName );
 
@@ -136,18 +109,18 @@ export default class DataSchema {
 	 * Resolves all definition references registered for the given data schema definition.
 	 *
 	 * @private
-	 * @param {String} name Data schema model name.
+	 * @param {String} modelName Data schema model name.
 	 * @returns {Iterable<String>}
 	 */
-	* _getReferences( name ) {
-		const { schema } = this._definitions[ name ];
+	* _getReferences( modelName ) {
+		const { schema } = this._definitions.get( modelName );
 		const inheritProperties = [ 'inheritAllFrom', 'inheritTypesFrom', 'allowWhere', 'allowContentOf', 'allowAttributesOf' ];
 
 		for ( const property of inheritProperties ) {
-			for ( const modelName of toArray( schema[ property ] || [] ) ) {
-				const definition = this._definitions[ modelName ];
+			for ( const referenceName of toArray( schema[ property ] || [] ) ) {
+				const definition = this._definitions.get( referenceName );
 
-				if ( modelName !== name && definition ) {
+				if ( referenceName !== modelName && definition ) {
 					yield* this._getReferences( definition.model );
 					yield definition;
 				}

From 79fd7da4a91ba954d99f7a8556421f4155465af7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jacek=20Bogda=C5=84ski?= <jacekbogd@gmail.com>
Date: Fri, 26 Feb 2021 09:19:33 +0100
Subject: [PATCH 023/217] Docs update.

Co-authored-by: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index d09bad1874a..b4911f56c1b 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -19,7 +19,7 @@ import DataSchema from './dataschema';
 const DATA_SCHEMA_ATTRIBUTE_KEY = 'ghsAttributes';
 
 /**
- * Allows to validate elements and element attributes registered by {@link @module content-compatibility/dataschema~DataSchema}.
+ * Allows to validate elements and element attributes registered by {@link module:content-compatibility/dataschema~DataSchema}.
  *
  * To enable registered element in the editor, use {@link #allowElement} method:
  *

From ef5e974baa7a315e38a8c512ca46b20d77bd2470 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jacek=20Bogda=C5=84ski?= <jacekbogd@gmail.com>
Date: Fri, 26 Feb 2021 09:19:56 +0100
Subject: [PATCH 024/217] Simplified downcast converter.

Co-authored-by: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index b4911f56c1b..4e9f7696208 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -211,10 +211,7 @@ export default class DataFilter {
 		} );
 
 		conversion.for( 'downcast' ).add( dispatcher => {
-			dispatcher.on( `attribute:${ DATA_SCHEMA_ATTRIBUTE_KEY }`, ( evt, data, conversionApi ) => {
-				if ( data.item.name != modelName ) {
-					return;
-				}
+			dispatcher.on( `attribute:${ DATA_SCHEMA_ATTRIBUTE_KEY }:${ modelName }`, ( evt, data, conversionApi ) => {
 
 				if ( data.attributeNewValue === null ) {
 					return;

From 36ab682d2db78b23f2a9dce4e7d55ced5937c551 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 26 Feb 2021 09:36:29 +0100
Subject: [PATCH 025/217] Used view document styles processor.

---
 .../src/datafilter.js                         | 32 ++++++++++---------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 4e9f7696208..704dcc29f34 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -12,7 +12,7 @@ import { cloneDeep, uniq } from 'lodash-es';
 import { Matcher } from 'ckeditor5/src/engine';
 import { priorities } from 'ckeditor5/src/utils';
 
-import StylesMap, { StylesProcessor } from '@ckeditor/ckeditor5-engine/src/view/stylesmap';
+import StylesMap from '@ckeditor/ckeditor5-engine/src/view/stylesmap';
 
 import DataSchema from './dataschema';
 
@@ -189,7 +189,7 @@ export default class DataFilter {
 						stylesObj[ styleName ] = viewElement.getStyle( styleName );
 					}
 
-					viewAttributes.push( [ 'style', inlineStyles( stylesObj ) ] );
+					viewAttributes.push( [ 'style', this.inlineStyles( stylesObj ) ] );
 				}
 
 				const element = conversionApi.writer.createElement( modelName );
@@ -212,7 +212,6 @@ export default class DataFilter {
 
 		conversion.for( 'downcast' ).add( dispatcher => {
 			dispatcher.on( `attribute:${ DATA_SCHEMA_ATTRIBUTE_KEY }:${ modelName }`, ( evt, data, conversionApi ) => {
-
 				if ( data.attributeNewValue === null ) {
 					return;
 				}
@@ -231,6 +230,21 @@ export default class DataFilter {
 			} );
 		} );
 	}
+
+	/**
+	 * Inlines styles object into normalized style string.
+	 *
+	 * @param {Object} stylesObject
+	 * @returns {String}
+	 */
+	inlineStyles( stylesObj ) {
+		const stylesProcessor = this.editor.editing.view.document.stylesProcessor;
+		const stylesMap = new StylesMap( stylesProcessor );
+
+		stylesMap.set( stylesObj );
+
+		return stylesMap.toString();
+	}
 }
 
 /**
@@ -294,15 +308,3 @@ function mergeMatchResults( matches ) {
 
 	return matchResult;
 }
-
-/**
- * Inlines styles object into normalized style string.
- *
- * @param {Object} stylesObject
- * @returns {String}
- */
-function inlineStyles( stylesObj ) {
-	const stylesMap = new StylesMap( new StylesProcessor() );
-	stylesMap.set( stylesObj );
-	return stylesMap.toString();
-}

From 47bd784bb51d693bb783513f010b4b438f3a125c Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 26 Feb 2021 10:11:47 +0100
Subject: [PATCH 026/217] Changed ghs attributes format to object.

---
 .../src/datafilter.js                         | 20 +++++++++-------
 .../tests/datafilter.js                       | 24 +++++++++----------
 2 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 704dcc29f34..4dc65e7ebdb 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -169,16 +169,16 @@ export default class DataFilter {
 				}
 
 				const allowedAttributes = mergeMatchResults( matches );
-				const viewAttributes = [];
+				const viewAttributes = {};
 
 				// Stash attributes.
 				for ( const key of allowedAttributes.attributes ) {
-					viewAttributes.push( [ key, viewElement.getAttribute( key ) ] );
+					viewAttributes[ key ] = viewElement.getAttribute( key );
 				}
 
 				// Stash classes.
 				if ( allowedAttributes.classes.length ) {
-					viewAttributes.push( [ 'class', allowedAttributes.classes.join( ' ' ) ] );
+					viewAttributes.class = allowedAttributes.classes.join( ' ' );
 				}
 
 				// Stash styles.
@@ -189,12 +189,12 @@ export default class DataFilter {
 						stylesObj[ styleName ] = viewElement.getStyle( styleName );
 					}
 
-					viewAttributes.push( [ 'style', this.inlineStyles( stylesObj ) ] );
+					viewAttributes.style = this.inlineStyles( stylesObj );
 				}
 
 				const element = conversionApi.writer.createElement( modelName );
 
-				if ( viewAttributes.length ) {
+				if ( Object.keys( viewAttributes ).length ) {
 					conversionApi.writer.setAttribute( DATA_SCHEMA_ATTRIBUTE_KEY, viewAttributes, element );
 				}
 
@@ -212,7 +212,9 @@ export default class DataFilter {
 
 		conversion.for( 'downcast' ).add( dispatcher => {
 			dispatcher.on( `attribute:${ DATA_SCHEMA_ATTRIBUTE_KEY }:${ modelName }`, ( evt, data, conversionApi ) => {
-				if ( data.attributeNewValue === null ) {
+				const viewAttributes = data.attributeNewValue;
+
+				if ( viewAttributes === null ) {
 					return;
 				}
 
@@ -224,9 +226,9 @@ export default class DataFilter {
 				const viewElement = conversionApi.mapper.toViewElement( data.item );
 
 				// Apply new values.
-				data.attributeNewValue.forEach( ( [ key, value ] ) => {
-					viewWriter.setAttribute( key, value, viewElement );
-				} );
+				for ( const key in viewAttributes ) {
+					viewWriter.setAttribute( key, viewAttributes[ key ], viewElement );
+				}
 			} );
 		} );
 	}
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 3295698e7b3..ec78b8ec49b 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -77,7 +77,7 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
 			attributes: {
-				1: [ [ 'data-foo', 'foobar' ] ]
+				1: { 'data-foo': 'foobar' }
 			}
 		} );
 
@@ -98,7 +98,7 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
 			attributes: {
-				1: [ [ 'style', 'background-color:blue;color:red;' ] ]
+				1: { 'style': 'background-color:blue;color:red;' }
 			}
 		} );
 
@@ -116,7 +116,7 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
 			attributes: {
-				1: [ [ 'class', 'foo bar' ] ]
+				1: { 'class': 'foo bar' }
 			}
 		} );
 
@@ -140,9 +140,9 @@ describe( 'DataFilter', () => {
 				'<ghsSection ghsAttributes="(3)">section2</ghsSection>' +
 			'</ghsArticle>',
 			attributes: {
-				1: [ [ 'data-foo', 'foo' ] ],
-				2: [ [ 'data-foo', 'bar' ] ],
-				3: [ [ 'data-foo', 'foo' ] ]
+				1: { 'data-foo': 'foo' },
+				2: { 'data-foo': 'bar' },
+				3: { 'data-foo': 'foo' }
 			}
 		} );
 	} );
@@ -158,8 +158,8 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsArticle ghsAttributes="(2)">bar</ghsArticle>',
 			attributes: {
-				1: [ [ 'data-foo', 'foo' ] ],
-				2: [ [ 'data-bar', 'bar' ] ]
+				1: { 'data-foo': 'foo' },
+				2: { 'data-bar': 'bar' }
 			}
 		} );
 
@@ -178,7 +178,7 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsSection>bar</ghsSection>',
 			attributes: {
-				1: [ [ 'data-foo', 'foo' ] ]
+				1: { 'data-foo': 'foo' }
 			}
 		} );
 
@@ -197,7 +197,7 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsSection>bar</ghsSection>',
 			attributes: {
-				1: [ [ 'style', 'color:blue;' ] ]
+				1: { 'style': 'color:blue;' }
 			}
 		} );
 
@@ -225,9 +225,9 @@ describe( 'DataFilter', () => {
 } );
 
 function getModelDataWithAttributes( model, options ) {
-	// Simplify GHS attributes as they are not readable at this point due to complex structure.
+	// Simplify GHS attributes as they are not very readable at this point due to object structure.
 	let counter = 1;
-	const data = getModelData( model, options ).replace( /ghsAttributes="(.*?)"/g, () => {
+	const data = getModelData( model, options ).replace( /ghsAttributes="{(.*?)}"/g, () => {
 		return `ghsAttributes="(${ counter++ })"`;
 	} );
 

From 08cdbcf9c0a3f772b141bd1e7a8f8f3f8554e100 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 26 Feb 2021 10:33:06 +0100
Subject: [PATCH 027/217] Replaced uniq with Set.

---
 .../src/datafilter.js                         | 22 ++++++++-----------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 4dc65e7ebdb..72b6ca4d874 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -7,7 +7,7 @@
  * @module content-compatibility/datafilter
  */
 
-import { cloneDeep, uniq } from 'lodash-es';
+import { cloneDeep } from 'lodash-es';
 
 import { Matcher } from 'ckeditor5/src/engine';
 import { priorities } from 'ckeditor5/src/utils';
@@ -168,24 +168,24 @@ export default class DataFilter {
 					}
 				}
 
-				const allowedAttributes = mergeMatchResults( matches );
+				const { attributes, classes, styles } = mergeMatchResults( matches );
 				const viewAttributes = {};
 
 				// Stash attributes.
-				for ( const key of allowedAttributes.attributes ) {
+				for ( const key of attributes.values() ) {
 					viewAttributes[ key ] = viewElement.getAttribute( key );
 				}
 
 				// Stash classes.
-				if ( allowedAttributes.classes.length ) {
-					viewAttributes.class = allowedAttributes.classes.join( ' ' );
+				if ( classes.size ) {
+					viewAttributes.class = [ ...classes.values() ].join( ' ' );
 				}
 
 				// Stash styles.
-				if ( allowedAttributes.styles.length ) {
+				if ( styles.size ) {
 					const stylesObj = {};
 
-					for ( const styleName of allowedAttributes.styles ) {
+					for ( const styleName of styles.values() ) {
 						stylesObj[ styleName ] = viewElement.getStyle( styleName );
 					}
 
@@ -295,18 +295,14 @@ function matchAll( viewElement, rules ) {
  * @returns {Array} result.styles Array with matched style names.
  */
 function mergeMatchResults( matches ) {
-	const matchResult = { attributes: [], classes: [], styles: [] };
+	const matchResult = { attributes: new Set(), classes: new Set(), styles: new Set() };
 
 	for ( const match of matches ) {
 		for ( const key in matchResult ) {
 			const values = match.match[ key ] || [];
-			matchResult[ key ].push( ...values );
+			values.forEach( value => matchResult[ key ].add( value ) );
 		}
 	}
 
-	for ( const key in matchResult ) {
-		matchResult[ key ] = uniq( matchResult[ key ] );
-	}
-
 	return matchResult;
 }

From 0c15a7a14d4aec6d91edee90ef10bbecbd9efa6f Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 26 Feb 2021 11:08:21 +0100
Subject: [PATCH 028/217] Docs update.

---
 .../ckeditor5-content-compatibility/src/datafilter.js     | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 72b6ca4d874..703b00da596 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -58,7 +58,7 @@ export default class DataFilter {
 	/**
 	 * Allow the given element registered by {@link #register} method.
 	 *
-	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all view elements which should be allowed.
+	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all view elements which should be allowed.
 	 */
 	allowElement( config ) {
 		for ( const definition of this.dataSchema.getDefinitionsForView( config.name ) ) {
@@ -75,7 +75,7 @@ export default class DataFilter {
 	/**
 	 * Allow the given attributes for view element allowed by {@link #allowElement} method.
 	 *
-	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all attributes which should be allowed.
+	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all attributes which should be allowed.
 	 */
 	allowAttributes( config ) {
 		this._addAttributeMatcher( config, this._allowedAttributes );
@@ -84,7 +84,7 @@ export default class DataFilter {
 	/**
 	 * Disallowe the given attributes for view element allowed by {@link #allowElement} method.
 	 *
-	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching all attributes which should be disallowed.
+	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all attributes which should be disallowed.
 	 */
 	disallowAttributes( config ) {
 		this._addAttributeMatcher( config, this._disallowedAttributes );
@@ -94,7 +94,7 @@ export default class DataFilter {
 	 * Adds attribute matcher for every registered data schema definition for the given `config.name`.
 	 *
 	 * @private
-	 * @param {module:engine/view/matcher~MatcherPattern} pattern
+	 * @param {module:engine/view/matcher~MatcherPattern} config
 	 * @param {Map} rules Rules map holding matchers.
 	 */
 	_addAttributeMatcher( config, rules ) {

From 38d3f8ae14fea1aca7fe547cb6b319e5cb476a71 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 26 Feb 2021 11:16:29 +0100
Subject: [PATCH 029/217] Removed hard dependency on data schema.

---
 .../ckeditor5-content-compatibility/src/datafilter.js  | 10 ++++------
 .../ckeditor5-content-compatibility/src/dataschema.js  |  4 +---
 .../tests/datafilter.js                                |  3 ++-
 .../tests/manual/generalhtmlsupport.js                 |  6 +++---
 4 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 703b00da596..3868ceed31a 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -14,8 +14,6 @@ import { priorities } from 'ckeditor5/src/utils';
 
 import StylesMap from '@ckeditor/ckeditor5-engine/src/view/stylesmap';
 
-import DataSchema from './dataschema';
-
 const DATA_SCHEMA_ATTRIBUTE_KEY = 'ghsAttributes';
 
 /**
@@ -46,10 +44,10 @@ const DATA_SCHEMA_ATTRIBUTE_KEY = 'ghsAttributes';
  *		} );
  */
 export default class DataFilter {
-	constructor( editor ) {
+	constructor( editor, dataSchema ) {
 		this.editor = editor;
 
-		this.dataSchema = new DataSchema( editor );
+		this._dataSchema = dataSchema;
 
 		this._allowedAttributes = new Map();
 		this._disallowedAttributes = new Map();
@@ -61,7 +59,7 @@ export default class DataFilter {
 	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all view elements which should be allowed.
 	 */
 	allowElement( config ) {
-		for ( const definition of this.dataSchema.getDefinitionsForView( config.name ) ) {
+		for ( const definition of this._dataSchema.getDefinitionsForView( config.name ) ) {
 			for ( const reference of definition.references ) {
 				this._registerElement( reference );
 			}
@@ -104,7 +102,7 @@ export default class DataFilter {
 		// We don't want match by name when matching attributes. Matcher will be already attached to specific definition.
 		delete config.name;
 
-		for ( const definition of this.dataSchema.getDefinitionsForView( viewName ) ) {
+		for ( const definition of this._dataSchema.getDefinitionsForView( viewName ) ) {
 			getOrCreateMatcher( definition.view, rules ).add( config );
 		}
 	}
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 5ec7f1fd547..04f250250af 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -25,9 +25,7 @@ import { toArray } from 'ckeditor5/src/utils';
  *		dataSchema.enable( 'my-section' );
  */
 export default class DataSchema {
-	constructor( editor ) {
-		this.editor = editor;
-
+	constructor() {
 		this._definitions = new Map();
 
 		// Add block elements.
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index ec78b8ec49b..5c010fb191e 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -4,6 +4,7 @@
  */
 
 import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
+import DataSchema from '../src/dataschema';
 import DataFilter from '../src/datafilter';
 
 import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
@@ -18,7 +19,7 @@ describe( 'DataFilter', () => {
 				editor = newEditor;
 				model = editor.model;
 
-				dataFilter = new DataFilter( editor );
+				dataFilter = new DataFilter( editor, new DataSchema() );
 			} );
 	} );
 
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 7fcc915ecc3..468b38483e1 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -13,11 +13,13 @@ import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
 import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
 import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
 
+import DataSchema from '../../src/dataschema';
 import DataFilter from '../../src/datafilter';
 
 class ExtendHTMLSupport extends Plugin {
 	init() {
-		const dataFilter = new DataFilter( this.editor );
+		const dataSchema = new DataSchema();
+		const dataFilter = new DataFilter( this.editor, dataSchema );
 
 		dataFilter.allowElement( { name: /article|section/ } );
 
@@ -28,8 +30,6 @@ class ExtendHTMLSupport extends Plugin {
 		dataFilter.allowElement( { name: /details|summary/ } );
 
 		dataFilter.allowElement( { name: /dl|dt|dd/ } );
-
-		window.dataFilter = dataFilter;
 	}
 }
 

From 7d231ca101867d6d1f9121c61485e1229d19f3df Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 26 Feb 2021 14:08:13 +0100
Subject: [PATCH 030/217] Improved manual test with some additional comments.

---
 .../tests/manual/generalhtmlsupport.html      |  3 +-
 .../tests/manual/generalhtmlsupport.js        | 36 +++++++++++++++----
 2 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
index 6a0960f8c3e..140129ab86e 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -5,7 +5,7 @@
 <div id="editor">
 	<article>
 		<section id="section1">Section #1</section>
-		<section id="section2">Section #2</section>
+		<section id="_section2">Section #2</section>
 		<section id="section3" style="color: red" class="special_section">Section #3</section>
 	</article>
 	<details>
@@ -18,4 +18,5 @@
 		<dd>dd1</dd>
 		<dd>dd2</dd>
 	</dl>
+	<xyz>XYZ</xyz>
 </div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 468b38483e1..0176e4efc3a 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -16,20 +16,44 @@ import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
 import DataSchema from '../../src/dataschema';
 import DataFilter from '../../src/datafilter';
 
+/**
+ * Client custom plugin extending HTML support for compatibility.
+ */
 class ExtendHTMLSupport extends Plugin {
 	init() {
+		// Create data schema object including default configuration based on CKE4
+		// DTD elements, missing dedicated feature in CKEditor 5.
+		// Data schema only behaves as container for DTD definitions, it doesn't change
+		// anything inside the editor itself. Registered elements are not extending editor
+		// model schema at this point.
 		const dataSchema = new DataSchema();
+
+		// Extend schema with custom `xyz` element.
+		dataSchema.register( { view: 'xyz', model: 'ghsXyz' }, {
+			inheritAllFrom: '$ghsBlock',
+			allowText: true
+		} );
+
+		// Create data filter which will register editor model schema and converters required
+		// to allow elements and filter attributes.
 		const dataFilter = new DataFilter( this.editor, dataSchema );
 
-		dataFilter.allowElement( { name: /article|section/ } );
+		// Allow some elements, at this point model schema will include information about view-model mapping
+		// e.g. article -> ghsArticle
+		dataFilter.allowElement( { name: 'article' } );
+		dataFilter.allowElement( { name: 'section' } );
+		dataFilter.allowElement( { name: /^details|summary$/ } );
+		dataFilter.allowElement( { name: /^dl|dd|dt$/ } );
+		dataFilter.allowElement( { name: 'xyz' } );
 
-		dataFilter.allowAttributes( { name: 'section', attributes: { id: /[^]/ } } );
+		// Let's extend 'section' with some attributes. Data filter will take care of
+		// creating proper converters and attribute matchers:
+		dataFilter.allowAttributes( { name: 'section', attributes: { id: /[^]/, 'data-foo': /[^]/ } } );
 		dataFilter.allowAttributes( { name: 'section', classes: /[^]/ } );
-		dataFilter.allowAttributes( { name: 'section', styles: { color: /[^]/ } } );
-
-		dataFilter.allowElement( { name: /details|summary/ } );
+		dataFilter.allowAttributes( { name: 'section', styles: { color: 'red' } } );
 
-		dataFilter.allowElement( { name: /dl|dt|dd/ } );
+		// but disallow setting id attribute if it start with `_` prefix:
+		dataFilter.disallowAttributes( { name: 'section', attributes: { id: /^_.*/ } } );
 	}
 }
 

From 19eece0133791931db5fdf44e4537b00684185cf Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 26 Feb 2021 14:24:36 +0100
Subject: [PATCH 031/217] Removed unused attribute group.

---
 .../tests/manual/generalhtmlsupport.js                          | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 0176e4efc3a..818eec2dbf3 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -48,7 +48,7 @@ class ExtendHTMLSupport extends Plugin {
 
 		// Let's extend 'section' with some attributes. Data filter will take care of
 		// creating proper converters and attribute matchers:
-		dataFilter.allowAttributes( { name: 'section', attributes: { id: /[^]/, 'data-foo': /[^]/ } } );
+		dataFilter.allowAttributes( { name: 'section', attributes: { id: /[^]/ } } );
 		dataFilter.allowAttributes( { name: 'section', classes: /[^]/ } );
 		dataFilter.allowAttributes( { name: 'section', styles: { color: 'red' } } );
 

From 30b0c0b09c2dd078323c7f274bfde39a576c5bae Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 1 Mar 2021 09:20:57 +0100
Subject: [PATCH 032/217] Extended definition with allowChildren.

---
 .../src/datafilter.js                         | 12 ++-
 .../src/dataschema.js                         | 90 ++++++++++++++-----
 .../tests/manual/generalhtmlsupport.js        | 34 +++++--
 3 files changed, 107 insertions(+), 29 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 3868ceed31a..e89445c88c2 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -10,7 +10,7 @@
 import { cloneDeep } from 'lodash-es';
 
 import { Matcher } from 'ckeditor5/src/engine';
-import { priorities } from 'ckeditor5/src/utils';
+import { priorities, toArray } from 'ckeditor5/src/utils';
 
 import StylesMap from '@ckeditor/ckeditor5-engine/src/view/stylesmap';
 
@@ -132,8 +132,14 @@ export default class DataFilter {
 
 		schema.register( definition.model, definition.schema );
 
-		if ( definition.schema.allowText ) {
-			schema.extend( '$text', { allowIn: definition.model } );
+		const allowedChildren = toArray( definition.allowChildren || [] );
+
+		for ( const child of allowedChildren ) {
+			if ( schema.isRegistered( child ) ) {
+				schema.extend( child, {
+					allowIn: definition.model
+				} );
+			}
 		}
 	}
 
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 04f250250af..9766ccb2c9f 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -29,36 +29,83 @@ export default class DataSchema {
 		this._definitions = new Map();
 
 		// Add block elements.
-		this.register( { model: '$ghsBlock' }, {
-			inheritAllFrom: '$block',
-			allowIn: '$ghsBlock'
+		this.register( {
+			model: '$ghsBlock',
+			allowChildren: '$block',
+			schema: {
+				inheritAllFrom: '$block',
+				allowIn: '$ghsBlock'
+			}
+		} );
+
+		this.register( {
+			view: 'article',
+			model: 'ghsArticle',
+			schema: {
+				inheritAllFrom: '$ghsBlock'
+			}
 		} );
 
-		this.register( { view: 'article', model: 'ghsArticle' }, { inheritAllFrom: '$ghsBlock' } );
-		this.register( { view: 'section', model: 'ghsSection' }, { inheritAllFrom: '$ghsBlock' } );
+		this.register( {
+			view: 'section',
+			model: 'ghsSection',
+			schema: {
+				inheritAllFrom: '$ghsBlock'
+			}
+		} );
 
 		// Add data list elements.
-		this.register( { view: 'dl', model: 'ghsDl' }, {
-			allowIn: [ '$ghsBlock', '$root' ],
-			isBlock: true
+		this.register( {
+			view: 'dl',
+			model: 'ghsDl',
+			schema: {
+				allowIn: [ '$ghsBlock', '$root' ],
+				isBlock: true
+			}
+		} );
+
+		this.register( {
+			model: '$ghsDatalist',
+			allowChildren: '$text',
+			schema: {
+				allowIn: 'ghsDl',
+				isBlock: true,
+				allowContentOf: '$ghsBlock'
+			}
 		} );
 
-		this.register( { model: '$ghsDatalist' }, {
-			allowIn: 'ghsDl',
-			isBlock: true,
-			allowContentOf: '$ghsBlock',
-			allowText: true
+		this.register( {
+			view: 'dt',
+			model: 'ghsDt',
+			schema: {
+				inheritAllFrom: '$ghsDatalist'
+			}
 		} );
 
-		this.register( { view: 'dt', model: 'ghsDt' }, { inheritAllFrom: '$ghsDatalist' } );
-		this.register( { view: 'dd', model: 'ghsDd' }, { inheritAllFrom: '$ghsDatalist' } );
+		this.register( {
+			view: 'dd',
+			model: 'ghsDd',
+			schema: {
+				inheritAllFrom: '$ghsDatalist'
+			}
+		} );
 
 		// Add details elements.
-		this.register( { view: 'details', model: 'ghsDetails' }, { inheritAllFrom: '$ghsBlock' } );
+		this.register( {
+			view: 'details',
+			model: 'ghsDetails',
+			schema: {
+				inheritAllFrom: '$ghsBlock'
+			}
+		} );
 
-		this.register( { view: 'summary', model: 'ghsSummary' }, {
-			allowIn: 'ghsDetails',
-			allowText: true
+		this.register( {
+			view: 'summary',
+			model: 'ghsSummary',
+			allowChildren: '$text',
+			schema: {
+				allowIn: 'ghsDetails'
+			}
 		} );
 	}
 
@@ -67,8 +114,8 @@ export default class DataSchema {
 	 *
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
-	register( { view, model }, schema ) {
-		this._definitions.set( model, { view, model, schema } );
+	register( definition ) {
+		this._definitions.set( definition.model, definition );
 	}
 
 	/**
@@ -154,5 +201,6 @@ function testViewName( pattern, viewName ) {
  * @property {String} [view] Name of the view element.
  * @property {String} model Name of the model element.
  * @property {String|module:engine/model/schema~SchemaItemDefinition} schema Name of the schema to inherit
+ * @property {String|Array} allowChildren Extends the given children list to allow definition model.
  * or custom schema item definition.
  */
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 818eec2dbf3..0bd8fb2d7b2 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -12,6 +12,8 @@ import Bold from '@ckeditor/ckeditor5-basic-styles/src/bold';
 import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
 import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
 import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
+import BlockQuote from '@ckeditor/ckeditor5-block-quote/src/blockquote';
+import List from '@ckeditor/ckeditor5-list/src/list';
 
 import DataSchema from '../../src/dataschema';
 import DataFilter from '../../src/datafilter';
@@ -29,9 +31,13 @@ class ExtendHTMLSupport extends Plugin {
 		const dataSchema = new DataSchema();
 
 		// Extend schema with custom `xyz` element.
-		dataSchema.register( { view: 'xyz', model: 'ghsXyz' }, {
-			inheritAllFrom: '$ghsBlock',
-			allowText: true
+		dataSchema.register( {
+			view: 'xyz',
+			model: 'ghsXyz',
+			schema: {
+				inheritAllFrom: '$ghsBlock',
+				allowText: true
+			}
 		} );
 
 		// Create data filter which will register editor model schema and converters required
@@ -59,8 +65,26 @@ class ExtendHTMLSupport extends Plugin {
 
 ClassicEditor
 	.create( document.querySelector( '#editor' ), {
-		plugins: [ Essentials, Paragraph, Bold, Italic, Strikethrough, ExtendHTMLSupport ],
-		toolbar: [ 'bold', 'italic', 'strikethrough', 'contentTags' ]
+		plugins: [
+			BlockQuote,
+			Bold,
+			Essentials,
+			ExtendHTMLSupport,
+			Italic,
+			List,
+			Paragraph,
+			Strikethrough
+		],
+		toolbar: [
+			'bold',
+			'italic',
+			'strikethrough',
+			'|',
+			'numberedList',
+			'bulletedList',
+			'|',
+			'blockquote'
+		]
 	} )
 	.then( editor => {
 		window.editor = editor;

From 161fe88abfce4db23c0426a65e33bacc6d615a77 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 1 Mar 2021 10:00:53 +0100
Subject: [PATCH 033/217] Changed attributes structure.

---
 .../src/datafilter.js                         | 48 ++++++++--------
 .../tests/datafilter.js                       | 57 +++++++++++++++----
 2 files changed, 70 insertions(+), 35 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index e89445c88c2..2a7557df0af 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -12,8 +12,6 @@ import { cloneDeep } from 'lodash-es';
 import { Matcher } from 'ckeditor5/src/engine';
 import { priorities, toArray } from 'ckeditor5/src/utils';
 
-import StylesMap from '@ckeditor/ckeditor5-engine/src/view/stylesmap';
-
 const DATA_SCHEMA_ATTRIBUTE_KEY = 'ghsAttributes';
 
 /**
@@ -176,24 +174,30 @@ export default class DataFilter {
 				const viewAttributes = {};
 
 				// Stash attributes.
-				for ( const key of attributes.values() ) {
-					viewAttributes[ key ] = viewElement.getAttribute( key );
+				if ( attributes.size ) {
+					const attributesObject = {};
+
+					for ( const attributeName of attributes ) {
+						attributesObject[ attributeName ] = viewElement.getAttribute( attributeName );
+					}
+
+					viewAttributes.attributes = attributesObject;
 				}
 
 				// Stash classes.
 				if ( classes.size ) {
-					viewAttributes.class = [ ...classes.values() ].join( ' ' );
+					viewAttributes.classes = Array.from( classes );
 				}
 
 				// Stash styles.
 				if ( styles.size ) {
 					const stylesObj = {};
 
-					for ( const styleName of styles.values() ) {
+					for ( const styleName of styles ) {
 						stylesObj[ styleName ] = viewElement.getStyle( styleName );
 					}
 
-					viewAttributes.style = this.inlineStyles( stylesObj );
+					viewAttributes.styles = stylesObj;
 				}
 
 				const element = conversionApi.writer.createElement( modelName );
@@ -229,27 +233,21 @@ export default class DataFilter {
 				const viewWriter = conversionApi.writer;
 				const viewElement = conversionApi.mapper.toViewElement( data.item );
 
-				// Apply new values.
-				for ( const key in viewAttributes ) {
-					viewWriter.setAttribute( key, viewAttributes[ key ], viewElement );
+				if ( viewAttributes.attributes ) {
+					for ( const [ key, value ] of Object.entries( viewAttributes.attributes ) ) {
+						viewWriter.setAttribute( key, value, viewElement );
+					}
 				}
-			} );
-		} );
-	}
 
-	/**
-	 * Inlines styles object into normalized style string.
-	 *
-	 * @param {Object} stylesObject
-	 * @returns {String}
-	 */
-	inlineStyles( stylesObj ) {
-		const stylesProcessor = this.editor.editing.view.document.stylesProcessor;
-		const stylesMap = new StylesMap( stylesProcessor );
-
-		stylesMap.set( stylesObj );
+				if ( viewAttributes.styles ) {
+					viewWriter.setStyle( viewAttributes.styles, viewElement );
+				}
 
-		return stylesMap.toString();
+				if ( viewAttributes.classes ) {
+					viewWriter.addClass( viewAttributes.classes, viewElement );
+				}
+			} );
+		} );
 	}
 }
 
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 5c010fb191e..71abda893c6 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -78,7 +78,11 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
 			attributes: {
-				1: { 'data-foo': 'foobar' }
+				1: {
+					attributes: {
+						'data-foo': 'foobar'
+					}
+				}
 			}
 		} );
 
@@ -99,7 +103,12 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
 			attributes: {
-				1: { 'style': 'background-color:blue;color:red;' }
+				1: {
+					styles: {
+						'background-color': 'blue',
+						color: 'red'
+					}
+				}
 			}
 		} );
 
@@ -117,7 +126,7 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
 			attributes: {
-				1: { 'class': 'foo bar' }
+				1: { classes: [ 'foo', 'bar' ] }
 			}
 		} );
 
@@ -141,9 +150,21 @@ describe( 'DataFilter', () => {
 				'<ghsSection ghsAttributes="(3)">section2</ghsSection>' +
 			'</ghsArticle>',
 			attributes: {
-				1: { 'data-foo': 'foo' },
-				2: { 'data-foo': 'bar' },
-				3: { 'data-foo': 'foo' }
+				1: {
+					attributes: {
+						'data-foo': 'foo'
+					}
+				},
+				2: {
+					attributes: {
+						'data-foo': 'bar'
+					}
+				},
+				3: {
+					attributes: {
+						'data-foo': 'foo'
+					}
+				}
 			}
 		} );
 	} );
@@ -159,8 +180,16 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsArticle ghsAttributes="(2)">bar</ghsArticle>',
 			attributes: {
-				1: { 'data-foo': 'foo' },
-				2: { 'data-bar': 'bar' }
+				1: {
+					attributes: {
+						'data-foo': 'foo'
+					}
+				},
+				2: {
+					attributes: {
+						'data-bar': 'bar'
+					}
+				}
 			}
 		} );
 
@@ -179,7 +208,11 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsSection>bar</ghsSection>',
 			attributes: {
-				1: { 'data-foo': 'foo' }
+				1: {
+					attributes: {
+						'data-foo': 'foo'
+					}
+				}
 			}
 		} );
 
@@ -198,7 +231,11 @@ describe( 'DataFilter', () => {
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
 			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsSection>bar</ghsSection>',
 			attributes: {
-				1: { 'style': 'color:blue;' }
+				1: {
+					styles: {
+						color: 'blue'
+					}
+				}
 			}
 		} );
 

From ca56a068f5ad2cce260e132ae04c8483e3f9461f Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 1 Mar 2021 10:09:28 +0100
Subject: [PATCH 034/217] Minor refactoring.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 2a7557df0af..112b0fd8f41 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -297,7 +297,11 @@ function matchAll( viewElement, rules ) {
  * @returns {Array} result.styles Array with matched style names.
  */
 function mergeMatchResults( matches ) {
-	const matchResult = { attributes: new Set(), classes: new Set(), styles: new Set() };
+	const matchResult = {
+		attributes: new Set(),
+		classes: new Set(),
+		styles: new Set()
+	};
 
 	for ( const match of matches ) {
 		for ( const key in matchResult ) {

From 8143ac355062e9ba431fe1349202ae3d0e84e13f Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 1 Mar 2021 11:10:50 +0100
Subject: [PATCH 035/217] Flatten definitions for getDefinitionsForView method.

---
 .../src/datafilter.js                         |  6 +--
 .../src/dataschema.js                         | 40 ++++++++++---------
 2 files changed, 22 insertions(+), 24 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 112b0fd8f41..2e9fa13036c 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -57,11 +57,7 @@ export default class DataFilter {
 	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all view elements which should be allowed.
 	 */
 	allowElement( config ) {
-		for ( const definition of this._dataSchema.getDefinitionsForView( config.name ) ) {
-			for ( const reference of definition.references ) {
-				this._registerElement( reference );
-			}
-
+		for ( const definition of this._dataSchema.getDefinitionsForView( config.name, true ) ) {
 			this._registerElement( definition );
 		}
 
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 9766ccb2c9f..c402bac0534 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -7,7 +7,6 @@
  * @module content-compatibility/dataschema
  */
 
-import { cloneDeep } from 'lodash-es';
 import { toArray } from 'ckeditor5/src/utils';
 
 /**
@@ -122,32 +121,35 @@ export default class DataSchema {
 	 * Returns all definitions matching the given view name.
 	 *
 	 * @param {String} viewName
-	 * @returns {Iterable<*>}
+	 * @param {Boolean} [includeReferences] Indicates if this method should also include definitions of referenced models.
+	 * @returns {Set<*>}
 	 */
-	* getDefinitionsForView( viewName ) {
-		const definitions = Array.from( this._definitions.values() )
-			.filter( def => def.view && testViewName( viewName, def.view ) );
+	getDefinitionsForView( viewName, includeReferences ) {
+		const definitions = new Set();
+
+		for ( const definition of this._filterViewDefinitions( viewName ) ) {
+			if ( includeReferences ) {
+				for ( const reference of this._getReferences( definition.model ) ) {
+					definitions.add( reference );
+				}
+			}
 
-		for ( const definition of definitions ) {
-			yield this.getDefinition( definition.model );
+			definitions.add( definition );
 		}
+
+		return definitions;
 	}
 
 	/**
-	 * Returns definition for the given model name.
-	 *
-	 * Definition will also include `references` property including all definitions
-	 * referenced by this definition.
+	 * Filters definitions matching the given view name.
 	 *
-	 * @param {String} modelName
-	 * @returns {module:content-compatibility/dataschema~DataSchemaDefinition}
+	 * @private
+	 * @param {String} viewName
+	 * @returns {Array}
 	 */
-	getDefinition( modelName ) {
-		const definition = cloneDeep( this._definitions.get( modelName ) );
-
-		definition.references = this._getReferences( modelName );
-
-		return definition;
+	_filterViewDefinitions( viewName ) {
+		return Array.from( this._definitions.values() )
+			.filter( def => def.view && testViewName( viewName, def.view ) );
 	}
 
 	/**

From e3f4b61099d46f5710aaeab5cddea70539cabbff Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 1 Mar 2021 11:22:21 +0100
Subject: [PATCH 036/217] Refactoring.

---
 .../src/datafilter.js                         | 42 +++++++++++--------
 1 file changed, 24 insertions(+), 18 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 2e9fa13036c..2ba7074f19d 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -166,18 +166,17 @@ export default class DataFilter {
 					}
 				}
 
-				const { attributes, classes, styles } = mergeMatchResults( matches );
+				const { attributes, styles, classes } = mergeMatchResults( matches );
 				const viewAttributes = {};
 
 				// Stash attributes.
 				if ( attributes.size ) {
-					const attributesObject = {};
-
-					for ( const attributeName of attributes ) {
-						attributesObject[ attributeName ] = viewElement.getAttribute( attributeName );
-					}
+					viewAttributes.attributes = iterableToObject( attributes, key => viewElement.getAttribute( key ) );
+				}
 
-					viewAttributes.attributes = attributesObject;
+				// Stash styles.
+				if ( styles.size ) {
+					viewAttributes.styles = iterableToObject( styles, key => viewElement.getStyle( key ) );
 				}
 
 				// Stash classes.
@@ -185,17 +184,6 @@ export default class DataFilter {
 					viewAttributes.classes = Array.from( classes );
 				}
 
-				// Stash styles.
-				if ( styles.size ) {
-					const stylesObj = {};
-
-					for ( const styleName of styles ) {
-						stylesObj[ styleName ] = viewElement.getStyle( styleName );
-					}
-
-					viewAttributes.styles = stylesObj;
-				}
-
 				const element = conversionApi.writer.createElement( modelName );
 
 				if ( Object.keys( viewAttributes ).length ) {
@@ -308,3 +296,21 @@ function mergeMatchResults( matches ) {
 
 	return matchResult;
 }
+
+/**
+ * Convertes the given iterable object into an object.
+ *
+ * @private
+ * @param {Iterable<String>} iterable
+ * @param {Function} getValue Shoud result with value for the given object key.
+ * @returns {Object}
+ */
+function iterableToObject( iterable, getValue ) {
+	const attributesObject = {};
+
+	for ( const prop of iterable ) {
+		attributesObject[ prop ] = getValue( prop );
+	}
+
+	return attributesObject;
+}

From a0749849a34e67f23c564c4b8cbbdffadaed857c Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 1 Mar 2021 12:24:56 +0100
Subject: [PATCH 037/217] Removed leftover.

---
 .../tests/manual/generalhtmlsupport.js                         | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 0bd8fb2d7b2..8e1bba81c11 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -35,8 +35,7 @@ class ExtendHTMLSupport extends Plugin {
 			view: 'xyz',
 			model: 'ghsXyz',
 			schema: {
-				inheritAllFrom: '$ghsBlock',
-				allowText: true
+				inheritAllFrom: '$ghsBlock'
 			}
 		} );
 

From ebf1f94c7471cd6384cce8a3d736e68c01e99a64 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 2 Mar 2021 16:25:05 +0100
Subject: [PATCH 038/217] Docs.

---
 .../src/datafilter.js                         | 29 ++++++++++++++-
 .../src/dataschema.js                         | 36 +++++++++++--------
 2 files changed, 50 insertions(+), 15 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 2ba7074f19d..325e7a5b6f7 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -45,9 +45,36 @@ export default class DataFilter {
 	constructor( editor, dataSchema ) {
 		this.editor = editor;
 
+		/**
+		 * An instance of the {@link module:content-compatibility/dataschema~DataSchema}.
+		 *
+		 * @readonly
+		 * @private
+		 * @member {module:content-compatibility/dataschema~DataSchema} module:content-compatibility/datafilter~DataFilter#_dataSchema
+		 */
 		this._dataSchema = dataSchema;
 
+		/**
+		 * A map of registered {@link module:engine/view/matcher~Matcher Matcher} instances.
+		 *
+		 * Describes rules upon which content attributes should be allowed.
+		 *
+		 * @readonly
+		 * @private
+		 * @member {Map<string, module:engine/view/matcher~Matcher>} module:content-compatibility/datafilter~DataFilter#_allowedAttributes
+		 */
 		this._allowedAttributes = new Map();
+
+		/**
+		 * A map of registered {@link module:engine/view/matcher~Matcher Matcher} instances.
+		 *
+		 * Describes rules upon which content attributes should be disallowed.
+		 *
+		 * @readonly
+		 * @private
+		 * @member {Map<string, module:engine/view/matcher~Matcher>}
+		 * module:content-compatibility/datafilter~DataFilter#_disallowedAttributes
+		 */
 		this._disallowedAttributes = new Map();
 	}
 
@@ -87,7 +114,7 @@ export default class DataFilter {
 	 *
 	 * @private
 	 * @param {module:engine/view/matcher~MatcherPattern} config
-	 * @param {Map} rules Rules map holding matchers.
+	 * @param {Map<string, module:engine/view/matcher~Matcher>} rules Rules map holding matchers.
 	 */
 	_addAttributeMatcher( config, rules ) {
 		const viewName = config.name;
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index c402bac0534..919fcfd21a3 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -15,16 +15,24 @@ import { toArray } from 'ckeditor5/src/utils';
  *
  * Data schema is represented by data schema definitions. To add new definition, use {@link #register} method:
  *
- *		dataSchema.register( { view: 'section', model: 'my-section' }, {
- *			inheritAllFrom: '$block'
+ *		dataSchema.register( {
+ *			view: 'section',
+ *			model: 'my-section',
+ *			schema: {
+ *				inheritAllFrom: '$block'
+ *			}
  *		} );
- *
- * Once registered, definition can be enabled in editor's model:
- *
- *		dataSchema.enable( 'my-section' );
  */
 export default class DataSchema {
 	constructor() {
+		/**
+		 * A map of registered data schema definitions via {@link #register} method.
+		 *
+		 * @readonly
+		 * @private
+		 * @member {Map<string, module:content-compatibility/dataschema~DataSchemaDefinition>}
+		 * module:content-compatibility/dataschema~DataSchema#_definitions
+		 */
 		this._definitions = new Map();
 
 		// Add block elements.
@@ -120,14 +128,14 @@ export default class DataSchema {
 	/**
 	 * Returns all definitions matching the given view name.
 	 *
-	 * @param {String} viewName
+	 * @param {String|RegExp} viewName
 	 * @param {Boolean} [includeReferences] Indicates if this method should also include definitions of referenced models.
-	 * @returns {Set<*>}
+	 * @returns {Set<module:content-compatibility/dataschema~DataSchemaDefinition>}
 	 */
 	getDefinitionsForView( viewName, includeReferences ) {
 		const definitions = new Set();
 
-		for ( const definition of this._filterViewDefinitions( viewName ) ) {
+		for ( const definition of this._getMatchingViewDefinitions( viewName ) ) {
 			if ( includeReferences ) {
 				for ( const reference of this._getReferences( definition.model ) ) {
 					definitions.add( reference );
@@ -141,13 +149,13 @@ export default class DataSchema {
 	}
 
 	/**
-	 * Filters definitions matching the given view name.
+	 * Returns definitions matching the given view name.
 	 *
 	 * @private
-	 * @param {String} viewName
+	 * @param {String|RegExp} viewName
 	 * @returns {Array}
 	 */
-	_filterViewDefinitions( viewName ) {
+	_getMatchingViewDefinitions( viewName ) {
 		return Array.from( this._definitions.values() )
 			.filter( def => def.view && testViewName( viewName, def.view ) );
 	}
@@ -157,7 +165,7 @@ export default class DataSchema {
 	 *
 	 * @private
 	 * @param {String} modelName Data schema model name.
-	 * @returns {Iterable<String>}
+	 * @returns {Iterable<module:content-compatibility/dataschema~DataSchemaDefinition>}
 	 */
 	* _getReferences( modelName ) {
 		const { schema } = this._definitions.get( modelName );
@@ -202,7 +210,7 @@ function testViewName( pattern, viewName ) {
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
  * @property {String} [view] Name of the view element.
  * @property {String} model Name of the model element.
- * @property {String|module:engine/model/schema~SchemaItemDefinition} schema Name of the schema to inherit
+ * @property {module:engine/model/schema~SchemaItemDefinition} Model schema item definition describing registered model.
  * @property {String|Array} allowChildren Extends the given children list to allow definition model.
  * or custom schema item definition.
  */

From baea36afc39bfd59043eb0f6fa59c915ece8d431 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 3 Mar 2021 09:52:28 +0100
Subject: [PATCH 039/217] Updated block elements to allow only flow content.

---
 .../src/dataschema.js                         |   9 +-
 .../tests/datafilter.js                       | 161 +++++++++++-------
 .../tests/manual/generalhtmlsupport.html      |  16 +-
 3 files changed, 115 insertions(+), 71 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 919fcfd21a3..19ad2ed308b 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -40,8 +40,8 @@ export default class DataSchema {
 			model: '$ghsBlock',
 			allowChildren: '$block',
 			schema: {
-				inheritAllFrom: '$block',
-				allowIn: '$ghsBlock'
+				allowIn: [ '$root', '$ghsBlock' ],
+				isBlock: true
 			}
 		} );
 
@@ -73,11 +73,10 @@ export default class DataSchema {
 
 		this.register( {
 			model: '$ghsDatalist',
-			allowChildren: '$text',
+			allowChildren: '$block',
 			schema: {
 				allowIn: 'ghsDl',
-				isBlock: true,
-				allowContentOf: '$ghsBlock'
+				isBlock: true
 			}
 		} );
 
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 71abda893c6..49215bea8cb 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -4,6 +4,7 @@
  */
 
 import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
+import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
 import DataSchema from '../src/dataschema';
 import DataFilter from '../src/datafilter';
 
@@ -14,7 +15,9 @@ describe( 'DataFilter', () => {
 
 	beforeEach( () => {
 		return VirtualTestEditor
-			.create()
+			.create( {
+				plugins: [ Paragraph ]
+			} )
 			.then( newEditor => {
 				editor = newEditor;
 				model = editor.model;
@@ -30,40 +33,61 @@ describe( 'DataFilter', () => {
 	it( 'should allow element', () => {
 		dataFilter.allowElement( { name: 'article' } );
 
-		editor.setData( '<article><section>section1</section><section>section2</section></article>' );
+		editor.setData( '<article>' +
+			'<section><paragraph>section1</paragraph></section>' +
+			'<section><paragraph>section2</paragraph></section></article>'
+		);
 
-		expect( getModelData( model, { withoutSelection: true } ) ).to.eq(
-			'<ghsArticle>section1section2</ghsArticle>'
+		expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
+			'<ghsArticle><paragraph>section1section2</paragraph></ghsArticle>'
 		);
 
-		expect( editor.getData() ).to.eq(
-			'<article>section1section2</article>'
+		expect( editor.getData() ).to.equal(
+			'<article><p>section1section2</p></article>'
 		);
 
 		dataFilter.allowElement( { name: 'section' } );
 
-		editor.setData( '<article><section>section1</section><section>section2</section></article>' );
+		editor.setData( '<article>' +
+			'<section><paragraph>section1</paragraph></section>' +
+			'<section><paragraph>section2</paragraph></section></article>'
+		);
 
-		expect( getModelData( model, { withoutSelection: true } ) ).to.eq(
-			'<ghsArticle><ghsSection>section1</ghsSection><ghsSection>section2</ghsSection></ghsArticle>'
+		expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
+			'<ghsArticle>' +
+			'<ghsSection><paragraph>section1</paragraph></ghsSection>' +
+			'<ghsSection><paragraph>section2</paragraph></ghsSection></ghsArticle>'
 		);
 
-		expect( editor.getData() ).to.eq(
-			'<article><section>section1</section><section>section2</section></article>'
+		expect( editor.getData() ).to.equal(
+			'<article>' +
+			'<section><p>section1</p></section>' +
+			'<section><p>section2</p></section></article>'
 		);
 	} );
 
 	it( 'should allow deeply nested structure', () => {
 		dataFilter.allowElement( { name: 'section' } );
 
-		editor.setData( '<section>1<section>2<section>3</section></section></section>' );
+		editor.setData(
+			'<section><p>1</p>' +
+			'<section><p>2</p>' +
+			'<section><p>3</p>' +
+			'</section></section></section>'
+		);
 
-		expect( getModelData( model, { withoutSelection: true } ) ).to.eq(
-			'<ghsSection>1<ghsSection>2<ghsSection>3</ghsSection></ghsSection></ghsSection>'
+		expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
+			'<ghsSection><paragraph>1</paragraph>' +
+			'<ghsSection><paragraph>2</paragraph>' +
+			'<ghsSection><paragraph>3</paragraph>' +
+			'</ghsSection></ghsSection></ghsSection>'
 		);
 
-		expect( editor.getData() ).to.eq(
-			'<section>1<section>2<section>3</section></section></section>'
+		expect( editor.getData() ).to.equal(
+			'<section><p>1</p>' +
+			'<section><p>2</p>' +
+			'<section><p>3</p>' +
+			'</section></section></section>'
 		);
 	} );
 
@@ -73,10 +97,10 @@ describe( 'DataFilter', () => {
 			'data-foo': 'foobar'
 		} } );
 
-		editor.setData( '<section data-foo="foobar">foobar</section>' );
+		editor.setData( '<section data-foo="foobar"><p>foobar</p></section>' );
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<ghsSection ghsAttributes="(1)"><paragraph>foobar</paragraph></ghsSection>',
 			attributes: {
 				1: {
 					attributes: {
@@ -86,8 +110,8 @@ describe( 'DataFilter', () => {
 			}
 		} );
 
-		expect( editor.getData() ).to.eq(
-			'<section data-foo="foobar">foobar</section>'
+		expect( editor.getData() ).to.equal(
+			'<section data-foo="foobar"><p>foobar</p></section>'
 		);
 	} );
 
@@ -98,10 +122,10 @@ describe( 'DataFilter', () => {
 			'background-color': 'blue'
 		} } );
 
-		editor.setData( '<section style="background-color:blue;color:red;">foobar</section>' );
+		editor.setData( '<section style="background-color:blue;color:red;"><p>foobar</p></section>' );
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<ghsSection ghsAttributes="(1)"><paragraph>foobar</paragraph></ghsSection>',
 			attributes: {
 				1: {
 					styles: {
@@ -112,8 +136,8 @@ describe( 'DataFilter', () => {
 			}
 		} );
 
-		expect( editor.getData() ).to.eq(
-			'<section style="background-color:blue;color:red;">foobar</section>'
+		expect( editor.getData() ).to.equal(
+			'<section style="background-color:blue;color:red;"><p>foobar</p></section>'
 		);
 	} );
 
@@ -121,17 +145,17 @@ describe( 'DataFilter', () => {
 		dataFilter.allowElement( { name: 'section' } );
 		dataFilter.allowAttributes( { name: 'section', classes: [ 'foo', 'bar' ] } );
 
-		editor.setData( '<section class="foo bar">foobar</section>' );
+		editor.setData( '<section class="foo bar"><p>foobar</p></section>' );
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsSection ghsAttributes="(1)">foobar</ghsSection>',
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<ghsSection ghsAttributes="(1)"><paragraph>foobar</paragraph></ghsSection>',
 			attributes: {
 				1: { classes: [ 'foo', 'bar' ] }
 			}
 		} );
 
-		expect( editor.getData() ).to.eq(
-			'<section class="foo bar">foobar</section>'
+		expect( editor.getData() ).to.equal(
+			'<section class="foo bar"><p>foobar</p></section>'
 		);
 	} );
 
@@ -140,15 +164,16 @@ describe( 'DataFilter', () => {
 		dataFilter.allowAttributes( { name: /[^]/, attributes: { 'data-foo': /foo|bar/ } } );
 
 		editor.setData( '<article data-foo="foo">' +
-				'<section data-foo="bar">section1</section>' +
-				'<section data-foo="foo">section2</section>' +
-			'</article>' );
+			'<section data-foo="bar"><p>section1</p></section>' +
+			'<section data-foo="foo"><p>section2</p></section>' +
+			'</article>'
+		);
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 			data: '<ghsArticle ghsAttributes="(1)">' +
-				'<ghsSection ghsAttributes="(2)">section1</ghsSection>' +
-				'<ghsSection ghsAttributes="(3)">section2</ghsSection>' +
-			'</ghsArticle>',
+				'<ghsSection ghsAttributes="(2)"><paragraph>section1</paragraph></ghsSection>' +
+				'<ghsSection ghsAttributes="(3)"><paragraph>section2</paragraph></ghsSection>' +
+				'</ghsArticle>',
 			attributes: {
 				1: {
 					attributes: {
@@ -175,10 +200,14 @@ describe( 'DataFilter', () => {
 		dataFilter.allowAttributes( { name: /section|article/, attributes: { 'data-foo': 'foo' } } );
 		dataFilter.allowAttributes( { name: /section|article/, attributes: { 'data-bar': 'bar' } } );
 
-		editor.setData( '<section data-foo="foo">foo</section><article data-bar="bar">bar</article>' );
+		editor.setData(
+			'<section data-foo="foo"><p>foo</p></section>' +
+			'<article data-bar="bar"><p>bar</p></article>'
+		);
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsArticle ghsAttributes="(2)">bar</ghsArticle>',
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<ghsSection ghsAttributes="(1)"><paragraph>foo</paragraph></ghsSection>' +
+				'<ghsArticle ghsAttributes="(2)"><paragraph>bar</paragraph></ghsArticle>',
 			attributes: {
 				1: {
 					attributes: {
@@ -193,8 +222,9 @@ describe( 'DataFilter', () => {
 			}
 		} );
 
-		expect( editor.getData() ).to.eq(
-			'<section data-foo="foo">foo</section><article data-bar="bar">bar</article>'
+		expect( editor.getData() ).to.equal(
+			'<section data-foo="foo"><p>foo</p></section>' +
+			'<article data-bar="bar"><p>bar</p></article>'
 		);
 	} );
 
@@ -203,10 +233,14 @@ describe( 'DataFilter', () => {
 		dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': /[^]/ } } );
 		dataFilter.disallowAttributes( { name: 'section', attributes: { 'data-foo': 'bar' } } );
 
-		editor.setData( '<section data-foo="foo">foo</section><section data-foo="bar">bar</section>' );
+		editor.setData(
+			'<section data-foo="foo"><p>foo</p></section>' +
+			'<section data-foo="bar"><p>bar</p></section>'
+		);
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsSection>bar</ghsSection>',
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<ghsSection ghsAttributes="(1)"><paragraph>foo</paragraph></ghsSection>' +
+				'<ghsSection><paragraph>bar</paragraph></ghsSection>',
 			attributes: {
 				1: {
 					attributes: {
@@ -216,8 +250,9 @@ describe( 'DataFilter', () => {
 			}
 		} );
 
-		expect( editor.getData() ).to.eq(
-			'<section data-foo="foo">foo</section><section>bar</section>'
+		expect( editor.getData() ).to.equal(
+			'<section data-foo="foo"><p>foo</p></section>' +
+			'<section><p>bar</p></section>'
 		);
 	} );
 
@@ -226,10 +261,14 @@ describe( 'DataFilter', () => {
 		dataFilter.allowAttributes( { name: 'section', styles: { color: /[^]/ } } );
 		dataFilter.disallowAttributes( { name: 'section', styles: { color: 'red' } } );
 
-		editor.setData( '<section style="color:blue;">foo</section><section style="color:red">bar</section>' );
+		editor.setData(
+			'<section style="color:blue;"><p>foo</p></section>' +
+			'<section style="color:red"><p>bar</p></section>'
+		);
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsSection ghsAttributes="(1)">foo</ghsSection><ghsSection>bar</ghsSection>',
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<ghsSection ghsAttributes="(1)"><paragraph>foo</paragraph></ghsSection>' +
+				'<ghsSection><paragraph>bar</paragraph></ghsSection>',
 			attributes: {
 				1: {
 					styles: {
@@ -239,8 +278,9 @@ describe( 'DataFilter', () => {
 			}
 		} );
 
-		expect( editor.getData() ).to.eq(
-			'<section style="color:blue;">foo</section><section>bar</section>'
+		expect( editor.getData() ).to.equal(
+			'<section style="color:blue;"><p>foo</p></section>' +
+			'<section><p>bar</p></section>'
 		);
 	} );
 
@@ -249,15 +289,20 @@ describe( 'DataFilter', () => {
 		dataFilter.allowAttributes( { name: 'section', classes: [ 'foo', 'bar' ] } );
 		dataFilter.disallowAttributes( { name: 'section', classes: [ 'bar' ] } );
 
-		editor.setData( '<section class="foo bar">foo</section><section class="bar">bar</section>' );
+		editor.setData(
+			'<section class="foo bar"><p>foo</p></section>' +
+			'<section class="bar"><p>bar</p></section>'
+		);
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.eq( {
-			data: '<ghsSection>foo</ghsSection><ghsSection>bar</ghsSection>',
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<ghsSection><paragraph>foo</paragraph></ghsSection>' +
+				'<ghsSection><paragraph>bar</paragraph></ghsSection>',
 			attributes: {}
 		} );
 
-		expect( editor.getData() ).to.eq(
-			'<section>foo</section><section>bar</section>'
+		expect( editor.getData() ).to.equal(
+			'<section><p>foo</p></section>' +
+			'<section><p>bar</p></section>'
 		);
 	} );
 } );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
index 140129ab86e..3d5c4a5ccb3 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -4,19 +4,19 @@
 
 <div id="editor">
 	<article>
-		<section id="section1">Section #1</section>
-		<section id="_section2">Section #2</section>
-		<section id="section3" style="color: red" class="special_section">Section #3</section>
+		<section id="section1"><p>Section #1</p></section>
+		<section id="_section2"><p>Section #2</p></section>
+		<section id="section3" style="color: red" class="special_section"><p>Section #3</p></section>
 	</article>
 	<details>
 		<summary>Summary</summary>
 		Hello world
 	</details>
 	<dl>
-		<dt>dt1</dt>
-		<dt>dt2</dt>
-		<dd>dd1</dd>
-		<dd>dd2</dd>
+		<dt><p>dt1</p></dt>
+		<dt><p>dt2</p></dt>
+		<dd><p>dd1</p></dd>
+		<dd><p>dd2</p></dd>
 	</dl>
-	<xyz>XYZ</xyz>
+	<xyz><p>XYZ</p></xyz>
 </div>

From 78b30d0a83fdfd7b8f11626d69785cc8967344ec Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 3 Mar 2021 12:14:55 +0100
Subject: [PATCH 040/217] Added test coverage for DataSchema.

---
 .../tests/dataschema.js                       | 153 ++++++++++++++++++
 1 file changed, 153 insertions(+)
 create mode 100644 packages/ckeditor5-content-compatibility/tests/dataschema.js

diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
new file mode 100644
index 00000000000..ace286e6117
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -0,0 +1,153 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
+import DataSchema from '../src/dataschema';
+
+const fakeDefinitions = [
+	{
+		view: 'def1',
+		model: 'ghsDef1',
+		allowChildren: [ 'ghsDef2', 'ghsDef3' ],
+		schema: {
+			inheritAllFrom: '$block'
+		}
+	},
+	{
+		view: 'def2',
+		model: 'ghsDef2',
+		schema: {
+			inheritAllFrom: 'ghsDef1'
+		}
+	},
+	{
+		view: 'def3',
+		model: 'ghsDef3',
+		schema: {
+			inheritTypesFrom: 'ghsDef2'
+		}
+	},
+	{
+		view: 'def4',
+		model: 'ghsDef4',
+		schema: {
+			allowWhere: 'ghsDef3'
+		}
+	},
+	{
+		view: 'def5',
+		model: 'ghsDef5',
+		schema: {
+			allowContentOf: 'ghsDef4'
+		}
+	},
+	{
+		view: 'def6',
+		model: 'ghsDef6',
+		schema: {
+			allowAttributesOf: 'ghsDef5'
+		}
+	}
+];
+
+describe( 'DataSchema', () => {
+	let editor, dataSchema;
+
+	beforeEach( () => {
+		return VirtualTestEditor
+			.create()
+			.then( newEditor => {
+				editor = newEditor;
+
+				dataSchema = new DataSchema();
+			} );
+	} );
+
+	afterEach( () => {
+		return editor.destroy();
+	} );
+
+	it( 'should allow registering schema with proper definition', () => {
+		const definitions = getFakeDefinitions( 'def1' );
+
+		dataSchema.register( definitions[ 0 ] );
+
+		const result = dataSchema.getDefinitionsForView( 'def1' );
+
+		expect( Array.from( result ) ).to.deep.equal( definitions );
+	} );
+
+	it( 'should allow resolving definitions by view name (string)', () => {
+		registerMany( dataSchema, fakeDefinitions );
+
+		const result = dataSchema.getDefinitionsForView( 'def2' );
+
+		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def2' ) );
+	} );
+
+	it( 'should allow resolving definitions by view name (RegExp)', () => {
+		registerMany( dataSchema, fakeDefinitions );
+
+		const result = dataSchema.getDefinitionsForView( /^def1|def2$/ );
+
+		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def1', 'def2' ) );
+	} );
+
+	it( 'should allow resolving definitions by view name including references (inheritAllFrom)', () => {
+		registerMany( dataSchema, fakeDefinitions );
+
+		const result = dataSchema.getDefinitionsForView( 'def2', true );
+
+		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def1', 'def2' ) );
+	} );
+
+	it( 'should allow resolving definitions by view name including references (inheritTypes)', () => {
+		registerMany( dataSchema, fakeDefinitions );
+
+		const result = dataSchema.getDefinitionsForView( 'def3', true );
+
+		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def1', 'def2', 'def3' ) );
+	} );
+
+	it( 'should allow resolving definitions by view name including references (allowWhere)', () => {
+		registerMany( dataSchema, fakeDefinitions );
+
+		const result = dataSchema.getDefinitionsForView( 'def4', true );
+
+		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def1', 'def2', 'def3', 'def4' ) );
+	} );
+
+	it( 'should allow resolving definitions by view name including references (allowContentOf)', () => {
+		registerMany( dataSchema, fakeDefinitions );
+
+		const result = dataSchema.getDefinitionsForView( 'def5', true );
+
+		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def1', 'def2', 'def3', 'def4', 'def5' ) );
+	} );
+
+	it( 'should allow resolving definitions by view name including references (allowAttributesOf)', () => {
+		registerMany( dataSchema, fakeDefinitions );
+
+		const result = dataSchema.getDefinitionsForView( 'def6', true );
+
+		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def1', 'def2', 'def3', 'def4', 'def5', 'def6' ) );
+	} );
+
+	it( 'should return nothing for invalid view name', () => {
+		registerMany( dataSchema, fakeDefinitions );
+
+		const result = dataSchema.getDefinitionsForView( null );
+
+		expect( result.size ).to.equal( 0 );
+	} );
+} );
+
+function registerMany( dataSchema, definitions ) {
+	definitions.forEach( def => dataSchema.register( def ) );
+}
+
+function getFakeDefinitions( ...viewNames ) {
+	return fakeDefinitions.filter( def => viewNames.includes( def.view ) );
+}

From 878d544154cfda6eda08af527fce557706a39ef4 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 3 Mar 2021 16:11:25 +0100
Subject: [PATCH 041/217] Removed unreachable code.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 325e7a5b6f7..e1423ae5a17 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -233,10 +233,6 @@ export default class DataFilter {
 			dispatcher.on( `attribute:${ DATA_SCHEMA_ATTRIBUTE_KEY }:${ modelName }`, ( evt, data, conversionApi ) => {
 				const viewAttributes = data.attributeNewValue;
 
-				if ( viewAttributes === null ) {
-					return;
-				}
-
 				if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
 					return;
 				}

From 274500b55308b84f8dc9d3ad520aa3c7b7df28a0 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 3 Mar 2021 16:13:24 +0100
Subject: [PATCH 042/217] Added test coverage for DataFilter.

---
 .../tests/datafilter.js                       | 67 ++++++++++++++++++-
 1 file changed, 65 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 49215bea8cb..c800b0e11c1 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -11,7 +11,7 @@ import DataFilter from '../src/datafilter';
 import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
 
 describe( 'DataFilter', () => {
-	let editor, model, dataFilter;
+	let editor, model, dataFilter, dataSchema;
 
 	beforeEach( () => {
 		return VirtualTestEditor
@@ -22,7 +22,8 @@ describe( 'DataFilter', () => {
 				editor = newEditor;
 				model = editor.model;
 
-				dataFilter = new DataFilter( editor, new DataSchema() );
+				dataSchema = new DataSchema();
+				dataFilter = new DataFilter( editor, dataSchema );
 			} );
 	} );
 
@@ -305,6 +306,68 @@ describe( 'DataFilter', () => {
 			'<section><p>bar</p></section>'
 		);
 	} );
+
+	it( 'should extend allowed children only if specified model schema exists', () => {
+		dataSchema.register( {
+			view: 'xyz',
+			model: 'ghsXyz',
+			allowChildren: 'not-exists',
+			schema: {
+				inheritAllFrom: '$ghsBlock'
+			}
+		} );
+
+		expect( () => {
+			dataFilter.allowElement( { name: 'xyz' } );
+		} ).to.not.throw();
+	} );
+
+	it( 'should not consume attribute already consumed (upcast)', () => {
+		editor.conversion.for( 'upcast' ).add( dispatcher => {
+			dispatcher.on( 'element:section', ( evt, data, conversionApi ) => {
+				conversionApi.consumable.consume( data.viewItem, { attributes: [ 'data-foo' ] } );
+			} );
+		} );
+
+		dataFilter.allowElement( { name: 'section' } );
+		dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': true } } );
+
+		editor.setData( '<section data-foo><p>foo</p></section>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<ghsSection><paragraph>foo</paragraph></ghsSection>',
+			attributes: {}
+		} );
+
+		expect( editor.getData() ).to.equal( '<section><p>foo</p></section>' );
+	} );
+
+	it( 'should not consume attribute already consumed (downcast)', () => {
+		editor.conversion.for( 'downcast' ).add( dispatcher => {
+			dispatcher.on( 'attribute:ghsAttributes:ghsSection', ( evt, data, conversionApi ) => {
+				conversionApi.consumable.consume( data.item, evt.name );
+			}, { priority: 'high' } );
+		} );
+
+		dataFilter.allowElement( { name: 'section' } );
+		dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': true } } );
+
+		editor.setData( '<section data-foo><p>foo</p></section>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<ghsSection ghsAttributes="(1)"><paragraph>foo</paragraph></ghsSection>',
+			// At this point, attribute should still be in the model, as we are testing downcast conversion.
+			attributes: {
+				1: {
+					attributes: {
+						'data-foo': ''
+					}
+				}
+			}
+		} );
+
+		expect( editor.getData() ).to.equal( '<section><p>foo</p></section>' );
+	} );
 } );
 
 function getModelDataWithAttributes( model, options ) {

From 9fffed12e8a2d9d5f43918f77380433091e36e3a Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 3 Mar 2021 17:07:01 +0100
Subject: [PATCH 043/217] Added package.json file.

---
 .../package.json                              | 50 +++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 packages/ckeditor5-content-compatibility/package.json

diff --git a/packages/ckeditor5-content-compatibility/package.json b/packages/ckeditor5-content-compatibility/package.json
new file mode 100644
index 00000000000..89bb1f11e13
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/package.json
@@ -0,0 +1,50 @@
+{
+  "name": "@ckeditor/ckeditor5-content-compatibility",
+  "version": "25.0.0",
+  "description": "Content compatibility feature",
+  "private": true,
+  "keywords": [
+    "ckeditor",
+    "ckeditor4",
+    "ckeditor 4",
+    "ckeditor5",
+    "ckeditor 5",
+    "ckeditor5-feature",
+    "ckeditor5-plugin",
+    "WYSIWYG",
+    "WYSIWYM",
+    "text",
+    "rich-text",
+    "richtext",
+    "ckeditor",
+    "editor",
+    "editing",
+    "html",
+    "contentEditable",
+    "compatibility",
+    "content compatibility"
+  ],
+  "dependencies": {
+    "ckeditor5": "^25.0.0",
+    "lodash-es": "^4.17.15"
+  },
+  "devDependencies": {
+    "@ckeditor/ckeditor5-basic-styles": "^25.0.0",
+    "@ckeditor/ckeditor5-block-quote": "^25.0.0",
+    "@ckeditor/ckeditor5-core": ">=19.0.0",
+    "@ckeditor/ckeditor5-list": "^25.0.0",
+    "@ckeditor/ckeditor5-paragraph": "^25.0.0",
+    "@ckeditor/ckeditor5-utils": "^25.0.0"
+  },
+  "engines": {
+    "node": ">=12.0.0",
+    "npm": ">=5.7.1"
+  },
+  "license": "SEE LICENSE IN LICENSE.md",
+  "author": "CKSource (http://cksource.com/)",
+  "homepage": "https://ckeditor.com",
+  "bugs": "https://github.com/ckeditor/ckeditor5/issues",
+  "files": [
+    "src"
+  ]
+}

From 88f0659c1ff1f1815287f0db166c0c69c70838d9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jacek=20Bogda=C5=84ski?= <jacekbogd@gmail.com>
Date: Fri, 5 Mar 2021 09:02:16 +0100
Subject: [PATCH 044/217] Corrected docs.

Co-authored-by: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
---
 .../src/datafilter.js                               | 11 +++++------
 .../src/dataschema.js                               | 13 ++++++-------
 2 files changed, 11 insertions(+), 13 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index e1423ae5a17..e0d1682e30d 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -50,7 +50,7 @@ export default class DataFilter {
 		 *
 		 * @readonly
 		 * @private
-		 * @member {module:content-compatibility/dataschema~DataSchema} module:content-compatibility/datafilter~DataFilter#_dataSchema
+		 * @member {module:content-compatibility/dataschema~DataSchema} #_dataSchema
 		 */
 		this._dataSchema = dataSchema;
 
@@ -61,7 +61,7 @@ export default class DataFilter {
 		 *
 		 * @readonly
 		 * @private
-		 * @member {Map<string, module:engine/view/matcher~Matcher>} module:content-compatibility/datafilter~DataFilter#_allowedAttributes
+		 * @member {Map.<String, module:engine/view/matcher~Matcher>} #_allowedAttributes
 		 */
 		this._allowedAttributes = new Map();
 
@@ -72,8 +72,7 @@ export default class DataFilter {
 		 *
 		 * @readonly
 		 * @private
-		 * @member {Map<string, module:engine/view/matcher~Matcher>}
-		 * module:content-compatibility/datafilter~DataFilter#_disallowedAttributes
+		 * @member {Map.<String, module:engine/view/matcher~Matcher>} #_disallowedAttributes
 		 */
 		this._disallowedAttributes = new Map();
 	}
@@ -114,7 +113,7 @@ export default class DataFilter {
 	 *
 	 * @private
 	 * @param {module:engine/view/matcher~MatcherPattern} config
-	 * @param {Map<string, module:engine/view/matcher~Matcher>} rules Rules map holding matchers.
+	 * @param {Map.<String, module:engine/view/matcher~Matcher>} rules Rules map holding matchers.
 	 */
 	_addAttributeMatcher( config, rules ) {
 		const viewName = config.name;
@@ -324,7 +323,7 @@ function mergeMatchResults( matches ) {
  * Convertes the given iterable object into an object.
  *
  * @private
- * @param {Iterable<String>} iterable
+ * @param {Iterable.<String>} iterable
  * @param {Function} getValue Shoud result with value for the given object key.
  * @returns {Object}
  */
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 19ad2ed308b..344c4f3bce0 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -30,8 +30,7 @@ export default class DataSchema {
 		 *
 		 * @readonly
 		 * @private
-		 * @member {Map<string, module:content-compatibility/dataschema~DataSchemaDefinition>}
-		 * module:content-compatibility/dataschema~DataSchema#_definitions
+         * @member {Map.<String, module:content-compatibility/dataschema~DataSchemaDefinition>} #_definitions
 		 */
 		this._definitions = new Map();
 
@@ -129,7 +128,7 @@ export default class DataSchema {
 	 *
 	 * @param {String|RegExp} viewName
 	 * @param {Boolean} [includeReferences] Indicates if this method should also include definitions of referenced models.
-	 * @returns {Set<module:content-compatibility/dataschema~DataSchemaDefinition>}
+	 * @returns {Set.<module:content-compatibility/dataschema~DataSchemaDefinition>}
 	 */
 	getDefinitionsForView( viewName, includeReferences ) {
 		const definitions = new Set();
@@ -152,7 +151,7 @@ export default class DataSchema {
 	 *
 	 * @private
 	 * @param {String|RegExp} viewName
-	 * @returns {Array}
+	 * @returns {Array.<module:content-compatibility/dataschema~DataSchemaDefinition>}
 	 */
 	_getMatchingViewDefinitions( viewName ) {
 		return Array.from( this._definitions.values() )
@@ -164,7 +163,7 @@ export default class DataSchema {
 	 *
 	 * @private
 	 * @param {String} modelName Data schema model name.
-	 * @returns {Iterable<module:content-compatibility/dataschema~DataSchemaDefinition>}
+	 * @returns {Iterable.<module:content-compatibility/dataschema~DataSchemaDefinition>}
 	 */
 	* _getReferences( modelName ) {
 		const { schema } = this._definitions.get( modelName );
@@ -209,7 +208,7 @@ function testViewName( pattern, viewName ) {
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
  * @property {String} [view] Name of the view element.
  * @property {String} model Name of the model element.
- * @property {module:engine/model/schema~SchemaItemDefinition} Model schema item definition describing registered model.
- * @property {String|Array} allowChildren Extends the given children list to allow definition model.
+ * @property {module:engine/model/schema~SchemaItemDefinition} schema The model schema item definition describing registered model.
+ * @property {String|Array.<String>} allowChildren Extends the given children list to allow definition model.
  * or custom schema item definition.
  */

From 5b7e58aa1d1b36c761b977fb2c39a4f91ee441ae Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 5 Mar 2021 09:20:23 +0100
Subject: [PATCH 045/217] Updated package.json.

---
 .../package.json                              | 32 +++++++------------
 1 file changed, 11 insertions(+), 21 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/package.json b/packages/ckeditor5-content-compatibility/package.json
index 89bb1f11e13..ef59dc79cd2 100644
--- a/packages/ckeditor5-content-compatibility/package.json
+++ b/packages/ckeditor5-content-compatibility/package.json
@@ -1,40 +1,30 @@
 {
   "name": "@ckeditor/ckeditor5-content-compatibility",
-  "version": "25.0.0",
+  "version": "26.0.0",
   "description": "Content compatibility feature",
   "private": true,
   "keywords": [
     "ckeditor",
-    "ckeditor4",
-    "ckeditor 4",
     "ckeditor5",
     "ckeditor 5",
     "ckeditor5-feature",
     "ckeditor5-plugin",
-    "WYSIWYG",
-    "WYSIWYM",
-    "text",
-    "rich-text",
-    "richtext",
-    "ckeditor",
-    "editor",
-    "editing",
-    "html",
-    "contentEditable",
     "compatibility",
-    "content compatibility"
+    "content compatibility",
+    "generic html support"
   ],
+  "main": "src/index.js",
   "dependencies": {
-    "ckeditor5": "^25.0.0",
+    "ckeditor5": "^26.0.0",
     "lodash-es": "^4.17.15"
   },
   "devDependencies": {
-    "@ckeditor/ckeditor5-basic-styles": "^25.0.0",
-    "@ckeditor/ckeditor5-block-quote": "^25.0.0",
-    "@ckeditor/ckeditor5-core": ">=19.0.0",
-    "@ckeditor/ckeditor5-list": "^25.0.0",
-    "@ckeditor/ckeditor5-paragraph": "^25.0.0",
-    "@ckeditor/ckeditor5-utils": "^25.0.0"
+    "@ckeditor/ckeditor5-basic-styles": "^26.0.0",
+    "@ckeditor/ckeditor5-block-quote": "^26.0.0",
+    "@ckeditor/ckeditor5-core": "^26.0.0",
+    "@ckeditor/ckeditor5-list": "^26.0.0",
+    "@ckeditor/ckeditor5-paragraph": "^26.0.0",
+    "@ckeditor/ckeditor5-utils": "^26.0.0"
   },
   "engines": {
     "node": ">=12.0.0",

From f88cdf5f64f9bcd6ffd166d75f5524ef4809440d Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 5 Mar 2021 10:04:21 +0100
Subject: [PATCH 046/217] Refactoring.

---
 .../src/datafilter.js                         | 74 +++++++++----------
 .../src/dataschema.js                         | 14 ++--
 2 files changed, 39 insertions(+), 49 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index e0d1682e30d..0faa030223c 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -7,11 +7,11 @@
  * @module content-compatibility/datafilter
  */
 
-import { cloneDeep } from 'lodash-es';
-
 import { Matcher } from 'ckeditor5/src/engine';
 import { priorities, toArray } from 'ckeditor5/src/utils';
 
+import { cloneDeep } from 'lodash-es';
+
 const DATA_SCHEMA_ATTRIBUTE_KEY = 'ghsAttributes';
 
 /**
@@ -257,16 +257,14 @@ export default class DataFilter {
 	}
 }
 
-/**
- * Helper function restoring matcher for the given key from `rules` object.
- *
- * If matcher for the given key does not exist, this function will create a new one
- * inside `rules` object under the given key.
- *
- * @private
- * @param {String} key
- * @param {Map} rules
- */
+// Helper function restoring matcher for the given key from `rules` object.
+
+// If matcher for the given key does not exist, this function will create a new one
+// inside `rules` object under the given key.
+
+// @private
+// @param {String} key
+// @param {Map.<String, module:engine/view/matcher~Matcher>} rules
 function getOrCreateMatcher( key, rules ) {
 	if ( !rules.has( key ) ) {
 		rules.set( key, new Matcher() );
@@ -275,33 +273,29 @@ function getOrCreateMatcher( key, rules ) {
 	return rules.get( key );
 }
 
-/**
- * Alias for {@link module:engine/view/matcher~Matcher#matchAll matchAll}.
- *
- * @private
- * @param {module:engine/view/element~Element} viewElement
- * @param {Map} rules Rules map holding matchers.
- * @returns {Object} result
- * @returns {Array} result.attributes Array with matched attribute names.
- * @returns {Array} result.classes Array with matched class names.
- * @returns {Array} result.styles Array with matched style names.
- */
+// Alias for {@link module:engine/view/matcher~Matcher#matchAll matchAll}.
+
+// @private
+// @param {module:engine/view/element~Element} viewElement
+// @param {Map} rules Rules map holding matchers.
+// @returns {Object} result
+// @returns {Array.<String>} result.attributes Array with matched attribute names.
+// @returns {Array.<String>} result.classes Array with matched class names.
+// @returns {Array.<String>} result.styles Array with matched style names.
 function matchAll( viewElement, rules ) {
 	const matcher = getOrCreateMatcher( viewElement.name, rules );
 
 	return matcher.matchAll( viewElement ) || [];
 }
 
-/**
- * Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
- *
- * @private
- * @param {Array} matches
- * @returns {Object} result
- * @returns {Array} result.attributes Array with matched attribute names.
- * @returns {Array} result.classes Array with matched class names.
- * @returns {Array} result.styles Array with matched style names.
- */
+// Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
+
+// @private
+// @param {Array} matches
+// @returns {Object} result
+// @returns {Array.<String>} result.attributes Array with matched attribute names.
+// @returns {Array.<String>} result.classes Array with matched class names.
+// @returns {Array.<String>} result.styles Array with matched style names.
 function mergeMatchResults( matches ) {
 	const matchResult = {
 		attributes: new Set(),
@@ -319,14 +313,12 @@ function mergeMatchResults( matches ) {
 	return matchResult;
 }
 
-/**
- * Convertes the given iterable object into an object.
- *
- * @private
- * @param {Iterable.<String>} iterable
- * @param {Function} getValue Shoud result with value for the given object key.
- * @returns {Object}
- */
+// Convertes the given iterable object into an object.
+
+// @private
+// @param {Iterable.<String>} iterable
+// @param {Function} getValue Shoud result with value for the given object key.
+// @returns {Object}
 function iterableToObject( iterable, getValue ) {
 	const attributesObject = {};
 
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 344c4f3bce0..9c3a813acb9 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -182,14 +182,12 @@ export default class DataSchema {
 	}
 }
 
-/**
- * Test view name against the given pattern.
- *
- * @private
- * @param {String|RegExp} pattern
- * @param {String} viewName
- * @returns {Boolean}
- */
+// Test view name against the given pattern.
+
+// @private
+// @param {String|RegExp} pattern
+// @param {String} viewName
+// @returns {Boolean}
 function testViewName( pattern, viewName ) {
 	if ( typeof pattern === 'string' ) {
 		return pattern === viewName;

From 89d8e4b90fd2b822dac72e925fee36740443e4df Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 5 Mar 2021 10:11:59 +0100
Subject: [PATCH 047/217] Corrected docs indentation.

---
 packages/ckeditor5-content-compatibility/src/dataschema.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 9c3a813acb9..35e1a30d88b 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -30,7 +30,7 @@ export default class DataSchema {
 		 *
 		 * @readonly
 		 * @private
-         * @member {Map.<String, module:content-compatibility/dataschema~DataSchemaDefinition>} #_definitions
+		 * @member {Map.<String, module:content-compatibility/dataschema~DataSchemaDefinition>} #_definitions
 		 */
 		this._definitions = new Map();
 

From af7781dfa1fd31d9858aca5d9d14b67cb9b78a9f Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 10 Mar 2021 10:29:13 +0100
Subject: [PATCH 048/217] Renaming from ghs to html.

---
 .../src/datafilter.js                         |  2 +-
 .../src/dataschema.js                         | 36 +++++------
 .../tests/datafilter.js                       | 64 +++++++++----------
 3 files changed, 51 insertions(+), 51 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 0faa030223c..435c4828181 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -12,7 +12,7 @@ import { priorities, toArray } from 'ckeditor5/src/utils';
 
 import { cloneDeep } from 'lodash-es';
 
-const DATA_SCHEMA_ATTRIBUTE_KEY = 'ghsAttributes';
+const DATA_SCHEMA_ATTRIBUTE_KEY = 'htmlAttributes';
 
 /**
  * Allows to validate elements and element attributes registered by {@link module:content-compatibility/dataschema~DataSchema}.
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 35e1a30d88b..5252b00d8e0 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -36,80 +36,80 @@ export default class DataSchema {
 
 		// Add block elements.
 		this.register( {
-			model: '$ghsBlock',
+			model: '$htmlBlock',
 			allowChildren: '$block',
 			schema: {
-				allowIn: [ '$root', '$ghsBlock' ],
+				allowIn: [ '$root', '$htmlBlock' ],
 				isBlock: true
 			}
 		} );
 
 		this.register( {
 			view: 'article',
-			model: 'ghsArticle',
+			model: 'htmlArticle',
 			schema: {
-				inheritAllFrom: '$ghsBlock'
+				inheritAllFrom: '$htmlBlock'
 			}
 		} );
 
 		this.register( {
 			view: 'section',
-			model: 'ghsSection',
+			model: 'htmlSection',
 			schema: {
-				inheritAllFrom: '$ghsBlock'
+				inheritAllFrom: '$htmlBlock'
 			}
 		} );
 
 		// Add data list elements.
 		this.register( {
 			view: 'dl',
-			model: 'ghsDl',
+			model: 'htmlDl',
 			schema: {
-				allowIn: [ '$ghsBlock', '$root' ],
+				allowIn: [ '$htmlBlock', '$root' ],
 				isBlock: true
 			}
 		} );
 
 		this.register( {
-			model: '$ghsDatalist',
+			model: '$htmlDatalist',
 			allowChildren: '$block',
 			schema: {
-				allowIn: 'ghsDl',
+				allowIn: 'htmlDl',
 				isBlock: true
 			}
 		} );
 
 		this.register( {
 			view: 'dt',
-			model: 'ghsDt',
+			model: 'htmlDt',
 			schema: {
-				inheritAllFrom: '$ghsDatalist'
+				inheritAllFrom: '$htmlDatalist'
 			}
 		} );
 
 		this.register( {
 			view: 'dd',
-			model: 'ghsDd',
+			model: 'htmlDd',
 			schema: {
-				inheritAllFrom: '$ghsDatalist'
+				inheritAllFrom: '$htmlDatalist'
 			}
 		} );
 
 		// Add details elements.
 		this.register( {
 			view: 'details',
-			model: 'ghsDetails',
+			model: 'htmlDetails',
 			schema: {
-				inheritAllFrom: '$ghsBlock'
+				inheritAllFrom: '$htmlBlock'
 			}
 		} );
 
 		this.register( {
 			view: 'summary',
-			model: 'ghsSummary',
+			model: 'htmlSummary',
 			allowChildren: '$text',
 			schema: {
-				allowIn: 'ghsDetails'
+				allowIn: 'htmlDetails'
 			}
 		} );
 	}
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index c800b0e11c1..1caccd91d84 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -40,7 +40,7 @@ describe( 'DataFilter', () => {
 		);
 
 		expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
-			'<ghsArticle><paragraph>section1section2</paragraph></ghsArticle>'
+			'<htmlArticle><paragraph>section1section2</paragraph></htmlArticle>'
 		);
 
 		expect( editor.getData() ).to.equal(
@@ -55,9 +55,9 @@ describe( 'DataFilter', () => {
 		);
 
 		expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
-			'<ghsArticle>' +
-			'<ghsSection><paragraph>section1</paragraph></ghsSection>' +
-			'<ghsSection><paragraph>section2</paragraph></ghsSection></ghsArticle>'
+			'<htmlArticle>' +
+			'<htmlSection><paragraph>section1</paragraph></htmlSection>' +
+			'<htmlSection><paragraph>section2</paragraph></htmlSection></htmlArticle>'
 		);
 
 		expect( editor.getData() ).to.equal(
@@ -78,10 +78,10 @@ describe( 'DataFilter', () => {
 		);
 
 		expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
-			'<ghsSection><paragraph>1</paragraph>' +
-			'<ghsSection><paragraph>2</paragraph>' +
-			'<ghsSection><paragraph>3</paragraph>' +
-			'</ghsSection></ghsSection></ghsSection>'
+			'<htmlSection><paragraph>1</paragraph>' +
+			'<htmlSection><paragraph>2</paragraph>' +
+			'<htmlSection><paragraph>3</paragraph>' +
+			'</htmlSection></htmlSection></htmlSection>'
 		);
 
 		expect( editor.getData() ).to.equal(
@@ -101,7 +101,7 @@ describe( 'DataFilter', () => {
 		editor.setData( '<section data-foo="foobar"><p>foobar</p></section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<ghsSection ghsAttributes="(1)"><paragraph>foobar</paragraph></ghsSection>',
+			data: '<htmlSection htmlAttributes="(1)"><paragraph>foobar</paragraph></htmlSection>',
 			attributes: {
 				1: {
 					attributes: {
@@ -126,7 +126,7 @@ describe( 'DataFilter', () => {
 		editor.setData( '<section style="background-color:blue;color:red;"><p>foobar</p></section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<ghsSection ghsAttributes="(1)"><paragraph>foobar</paragraph></ghsSection>',
+			data: '<htmlSection htmlAttributes="(1)"><paragraph>foobar</paragraph></htmlSection>',
 			attributes: {
 				1: {
 					styles: {
@@ -149,7 +149,7 @@ describe( 'DataFilter', () => {
 		editor.setData( '<section class="foo bar"><p>foobar</p></section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<ghsSection ghsAttributes="(1)"><paragraph>foobar</paragraph></ghsSection>',
+			data: '<htmlSection htmlAttributes="(1)"><paragraph>foobar</paragraph></htmlSection>',
 			attributes: {
 				1: { classes: [ 'foo', 'bar' ] }
 			}
@@ -171,10 +171,10 @@ describe( 'DataFilter', () => {
 		);
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<ghsArticle ghsAttributes="(1)">' +
-				'<ghsSection ghsAttributes="(2)"><paragraph>section1</paragraph></ghsSection>' +
-				'<ghsSection ghsAttributes="(3)"><paragraph>section2</paragraph></ghsSection>' +
-				'</ghsArticle>',
+			data: '<htmlArticle htmlAttributes="(1)">' +
+				'<htmlSection htmlAttributes="(2)"><paragraph>section1</paragraph></htmlSection>' +
+				'<htmlSection htmlAttributes="(3)"><paragraph>section2</paragraph></htmlSection>' +
+				'</htmlArticle>',
 			attributes: {
 				1: {
 					attributes: {
@@ -207,8 +207,8 @@ describe( 'DataFilter', () => {
 		);
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<ghsSection ghsAttributes="(1)"><paragraph>foo</paragraph></ghsSection>' +
-				'<ghsArticle ghsAttributes="(2)"><paragraph>bar</paragraph></ghsArticle>',
+			data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>' +
+				'<htmlArticle htmlAttributes="(2)"><paragraph>bar</paragraph></htmlArticle>',
 			attributes: {
 				1: {
 					attributes: {
@@ -240,8 +240,8 @@ describe( 'DataFilter', () => {
 		);
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<ghsSection ghsAttributes="(1)"><paragraph>foo</paragraph></ghsSection>' +
-				'<ghsSection><paragraph>bar</paragraph></ghsSection>',
+			data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>' +
+				'<htmlSection><paragraph>bar</paragraph></htmlSection>',
 			attributes: {
 				1: {
 					attributes: {
@@ -268,8 +268,8 @@ describe( 'DataFilter', () => {
 		);
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<ghsSection ghsAttributes="(1)"><paragraph>foo</paragraph></ghsSection>' +
-				'<ghsSection><paragraph>bar</paragraph></ghsSection>',
+			data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>' +
+				'<htmlSection><paragraph>bar</paragraph></htmlSection>',
 			attributes: {
 				1: {
 					styles: {
@@ -296,8 +296,8 @@ describe( 'DataFilter', () => {
 		);
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<ghsSection><paragraph>foo</paragraph></ghsSection>' +
-				'<ghsSection><paragraph>bar</paragraph></ghsSection>',
+			data: '<htmlSection><paragraph>foo</paragraph></htmlSection>' +
+				'<htmlSection><paragraph>bar</paragraph></htmlSection>',
 			attributes: {}
 		} );
 
@@ -310,10 +310,10 @@ describe( 'DataFilter', () => {
 	it( 'should extend allowed children only if specified model schema exists', () => {
 		dataSchema.register( {
 			view: 'xyz',
-			model: 'ghsXyz',
+			model: 'htmlXyz',
 			allowChildren: 'not-exists',
 			schema: {
-				inheritAllFrom: '$ghsBlock'
+				inheritAllFrom: '$htmlBlock'
 			}
 		} );
 
@@ -335,7 +335,7 @@ describe( 'DataFilter', () => {
 		editor.setData( '<section data-foo><p>foo</p></section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<ghsSection><paragraph>foo</paragraph></ghsSection>',
+			data: '<htmlSection><paragraph>foo</paragraph></htmlSection>',
 			attributes: {}
 		} );
 
@@ -344,7 +344,7 @@ describe( 'DataFilter', () => {
 
 	it( 'should not consume attribute already consumed (downcast)', () => {
 		editor.conversion.for( 'downcast' ).add( dispatcher => {
-			dispatcher.on( 'attribute:ghsAttributes:ghsSection', ( evt, data, conversionApi ) => {
+			dispatcher.on( 'attribute:htmlAttributes:htmlSection', ( evt, data, conversionApi ) => {
 				conversionApi.consumable.consume( data.item, evt.name );
 			}, { priority: 'high' } );
 		} );
@@ -355,7 +355,7 @@ describe( 'DataFilter', () => {
 		editor.setData( '<section data-foo><p>foo</p></section>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<ghsSection ghsAttributes="(1)"><paragraph>foo</paragraph></ghsSection>',
+			data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>',
 			// At this point, attribute should still be in the model, as we are testing downcast conversion.
 			attributes: {
 				1: {
@@ -373,16 +373,16 @@ describe( 'DataFilter', () => {
 function getModelDataWithAttributes( model, options ) {
 	// Simplify GHS attributes as they are not very readable at this point due to object structure.
 	let counter = 1;
-	const data = getModelData( model, options ).replace( /ghsAttributes="{(.*?)}"/g, () => {
-		return `ghsAttributes="(${ counter++ })"`;
+	const data = getModelData( model, options ).replace( /htmlAttributes="{(.*?)}"/g, () => {
+		return `htmlAttributes="(${ counter++ })"`;
 	} );
 
 	const range = model.createRangeIn( model.document.getRoot() );
 
 	let attributes = [];
 	for ( const item of range.getItems() ) {
-		if ( item.hasAttribute && item.hasAttribute( 'ghsAttributes' ) ) {
-			attributes.push( item.getAttribute( 'ghsAttributes' ) );
+		if ( item.hasAttribute && item.hasAttribute( 'htmlAttributes' ) ) {
+			attributes.push( item.getAttribute( 'htmlAttributes' ) );
 		}
 	}
 

From c90ebf07643b78c7a1eb2dabb0f1bc6759aabfb4 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 10 Mar 2021 10:31:57 +0100
Subject: [PATCH 049/217] Renaming from ghs to html (part2).

---
 .../tests/dataschema.js                       | 24 +++++++++----------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index ace286e6117..84fe698780d 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -9,45 +9,45 @@ import DataSchema from '../src/dataschema';
 const fakeDefinitions = [
 	{
 		view: 'def1',
-		model: 'ghsDef1',
-		allowChildren: [ 'ghsDef2', 'ghsDef3' ],
+		model: 'htmlDef1',
+		allowChildren: [ 'htmlDef2', 'htmlDef3' ],
 		schema: {
 			inheritAllFrom: '$block'
 		}
 	},
 	{
 		view: 'def2',
-		model: 'ghsDef2',
+		model: 'htmlDef2',
 		schema: {
-			inheritAllFrom: 'ghsDef1'
+			inheritAllFrom: 'htmlDef1'
 		}
 	},
 	{
 		view: 'def3',
-		model: 'ghsDef3',
+		model: 'htmlDef3',
 		schema: {
-			inheritTypesFrom: 'ghsDef2'
+			inheritTypesFrom: 'htmlDef2'
 		}
 	},
 	{
 		view: 'def4',
-		model: 'ghsDef4',
+		model: 'htmlDef4',
 		schema: {
-			allowWhere: 'ghsDef3'
+			allowWhere: 'htmlDef3'
 		}
 	},
 	{
 		view: 'def5',
-		model: 'ghsDef5',
+		model: 'htmlDef5',
 		schema: {
-			allowContentOf: 'ghsDef4'
+			allowContentOf: 'htmlDef4'
 		}
 	},
 	{
 		view: 'def6',
-		model: 'ghsDef6',
+		model: 'htmlDef6',
 		schema: {
-			allowAttributesOf: 'ghsDef5'
+			allowAttributesOf: 'htmlDef5'
 		}
 	}
 ];

From 97c4ccb7dfe7f170b05ce6fdd870081ce03e56a2 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 11 Mar 2021 13:53:25 +0100
Subject: [PATCH 050/217] Minor docs correction.

---
 packages/ckeditor5-content-compatibility/src/dataschema.js | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 5252b00d8e0..a2ca75b3745 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -207,6 +207,5 @@ function testViewName( pattern, viewName ) {
  * @property {String} [view] Name of the view element.
  * @property {String} model Name of the model element.
  * @property {module:engine/model/schema~SchemaItemDefinition} schema The model schema item definition describing registered model.
- * @property {String|Array.<String>} allowChildren Extends the given children list to allow definition model.
- * or custom schema item definition.
+ * @property {String|Array.<String>} [allowChildren] Extends the given children list to allow definition model.
  */

From fdb4d6c59a9e3e268bc20671dc83e14d988dd4f6 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
Date: Thu, 11 Mar 2021 18:11:51 +0100
Subject: [PATCH 051/217] Typo fix.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 435c4828181..080df5782c9 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -100,7 +100,7 @@ export default class DataFilter {
 	}
 
 	/**
-	 * Disallowe the given attributes for view element allowed by {@link #allowElement} method.
+	 * Disallow the given attributes for view element allowed by {@link #allowElement} method.
 	 *
 	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all attributes which should be disallowed.
 	 */

From eb4bd1a5e5d290abdbf15b6b28f4808cb756687c Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
Date: Thu, 11 Mar 2021 18:13:54 +0100
Subject: [PATCH 052/217] Added missing empty line.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 1 +
 1 file changed, 1 insertion(+)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 080df5782c9..079752c97ec 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -119,6 +119,7 @@ export default class DataFilter {
 		const viewName = config.name;
 
 		config = cloneDeep( config );
+
 		// We don't want match by name when matching attributes. Matcher will be already attached to specific definition.
 		delete config.name;
 

From bd1920f598fd4c3511cd16cef6d6067964075b7a Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
Date: Thu, 11 Mar 2021 18:20:25 +0100
Subject: [PATCH 053/217] Added missing empty line.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 1 +
 1 file changed, 1 insertion(+)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 079752c97ec..df8e462be9d 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -187,6 +187,7 @@ export default class DataFilter {
 			view: viewName,
 			model: ( viewElement, conversionApi ) => {
 				const matches = [];
+
 				for ( const match of matchAll( viewElement, this._allowedAttributes ) ) {
 					if ( conversionApi.consumable.consume( viewElement, match.match ) ) {
 						matches.push( match );

From c4c2f6821426c2d825adb7e4c5029d48774bb581 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
Date: Thu, 11 Mar 2021 18:38:56 +0100
Subject: [PATCH 054/217] Apply suggestions from code review

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index df8e462be9d..bb12c1d3212 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -260,10 +260,10 @@ export default class DataFilter {
 }
 
 // Helper function restoring matcher for the given key from `rules` object.
-
+//
 // If matcher for the given key does not exist, this function will create a new one
 // inside `rules` object under the given key.
-
+//
 // @private
 // @param {String} key
 // @param {Map.<String, module:engine/view/matcher~Matcher>} rules

From 681fead7cbbfdedce66662e8c424ddc576538a62 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
Date: Thu, 11 Mar 2021 18:41:47 +0100
Subject: [PATCH 055/217] Apply suggestions from code review

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index bb12c1d3212..a9ee0cbe81d 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -267,6 +267,7 @@ export default class DataFilter {
 // @private
 // @param {String} key
 // @param {Map.<String, module:engine/view/matcher~Matcher>} rules
+// @returns {module:engine/view/matcher~Matcher}
 function getOrCreateMatcher( key, rules ) {
 	if ( !rules.has( key ) ) {
 		rules.set( key, new Matcher() );
@@ -276,10 +277,10 @@ function getOrCreateMatcher( key, rules ) {
 }
 
 // Alias for {@link module:engine/view/matcher~Matcher#matchAll matchAll}.
-
+//
 // @private
 // @param {module:engine/view/element~Element} viewElement
-// @param {Map} rules Rules map holding matchers.
+// @param {Map.<String, module:engine/view/matcher~Matcher>} rules Rules map holding matchers.
 // @returns {Object} result
 // @returns {Array.<String>} result.attributes Array with matched attribute names.
 // @returns {Array.<String>} result.classes Array with matched class names.

From 819ccfc90faf8e02f80b31852d0147013f8f51ee Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
Date: Thu, 11 Mar 2021 18:44:29 +0100
Subject: [PATCH 056/217] Apply suggestions from code review

---
 .../ckeditor5-content-compatibility/src/datafilter.js | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index a9ee0cbe81d..912f7bfa4b1 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -292,13 +292,13 @@ function matchAll( viewElement, rules ) {
 }
 
 // Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
-
+//
 // @private
 // @param {Array} matches
 // @returns {Object} result
-// @returns {Array.<String>} result.attributes Array with matched attribute names.
-// @returns {Array.<String>} result.classes Array with matched class names.
-// @returns {Array.<String>} result.styles Array with matched style names.
+// @returns {Set.<String>} result.attributes Set with matched attribute names.
+// @returns {Set.<String>} result.classes Set with matched class names.
+// @returns {Set.<String>} result.styles Set with matched style names.
 function mergeMatchResults( matches ) {
 	const matchResult = {
 		attributes: new Set(),
@@ -309,6 +309,7 @@ function mergeMatchResults( matches ) {
 	for ( const match of matches ) {
 		for ( const key in matchResult ) {
 			const values = match.match[ key ] || [];
+
 			values.forEach( value => matchResult[ key ].add( value ) );
 		}
 	}
@@ -317,7 +318,7 @@ function mergeMatchResults( matches ) {
 }
 
 // Convertes the given iterable object into an object.
-
+//
 // @private
 // @param {Iterable.<String>} iterable
 // @param {Function} getValue Shoud result with value for the given object key.

From 838b68e4f6053af17cdbddb82a2c8f2a68953adb Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
Date: Thu, 11 Mar 2021 18:47:26 +0100
Subject: [PATCH 057/217] Apply suggestions from code review

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 912f7bfa4b1..b80583faea2 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -281,10 +281,7 @@ function getOrCreateMatcher( key, rules ) {
 // @private
 // @param {module:engine/view/element~Element} viewElement
 // @param {Map.<String, module:engine/view/matcher~Matcher>} rules Rules map holding matchers.
-// @returns {Object} result
-// @returns {Array.<String>} result.attributes Array with matched attribute names.
-// @returns {Array.<String>} result.classes Array with matched class names.
-// @returns {Array.<String>} result.styles Array with matched style names.
+// @returns {Array.<Object>} Array with match information about found elements.
 function matchAll( viewElement, rules ) {
 	const matcher = getOrCreateMatcher( viewElement.name, rules );
 

From 9b447fb3b69c5767c49cac67924d83a98fe3603c Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
Date: Thu, 11 Mar 2021 18:49:26 +0100
Subject: [PATCH 058/217] Apply suggestions from code review

---
 packages/ckeditor5-content-compatibility/src/dataschema.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index a2ca75b3745..320d7ebdc35 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -183,7 +183,7 @@ export default class DataSchema {
 }
 
 // Test view name against the given pattern.
-
+//
 // @private
 // @param {String|RegExp} pattern
 // @param {String} viewName
@@ -201,7 +201,7 @@ function testViewName( pattern, viewName ) {
 }
 
 /**
- * A definition of {@link module:content-compatibility/dataschema data schema}.
+ * A definition of {@link module:content-compatibility/dataschema~DataSchema data schema}.
  *
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
  * @property {String} [view] Name of the view element.

From 84a7492c9f63a3455ee7cd86221f51a3f584aa12 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
Date: Thu, 11 Mar 2021 18:52:50 +0100
Subject: [PATCH 059/217] Apply suggestions from code review

---
 packages/ckeditor5-content-compatibility/tests/datafilter.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 1caccd91d84..27215a2590a 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -5,11 +5,11 @@
 
 import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
 import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
+import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
+
 import DataSchema from '../src/dataschema';
 import DataFilter from '../src/datafilter';
 
-import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
-
 describe( 'DataFilter', () => {
 	let editor, model, dataFilter, dataSchema;
 

From fa1c77c4c39701226eac7eea5d819a0148d6fc06 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <j.niegowski@cksource.com>
Date: Thu, 11 Mar 2021 18:58:39 +0100
Subject: [PATCH 060/217] Code review fixes.

---
 .../src/datafilter.js                         |   8 +-
 .../tests/datafilter.js                       |  56 ++++-----
 .../tests/dataschema.js                       | 106 +++++++++---------
 3 files changed, 87 insertions(+), 83 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index b80583faea2..980329d29b2 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -166,7 +166,7 @@ export default class DataFilter {
 
 	/**
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition}
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
 	_defineConverters( definition ) {
 		const conversion = this.editor.conversion;
@@ -220,7 +220,7 @@ export default class DataFilter {
 
 				return element;
 			},
-			// With a `low` priority, `paragraph` plugin autoparagraphing mechanism is executed. Make sure
+			// With a `low` priority, `paragraph` plugin auto-paragraphing mechanism is executed. Make sure
 			// this listener is called before it. If not, some elements will be transformed into a paragraph.
 			converterPriority: priorities.get( 'low' ) + 1
 		} );
@@ -314,11 +314,11 @@ function mergeMatchResults( matches ) {
 	return matchResult;
 }
 
-// Convertes the given iterable object into an object.
+// Converts the given iterable object into an object.
 //
 // @private
 // @param {Iterable.<String>} iterable
-// @param {Function} getValue Shoud result with value for the given object key.
+// @param {Function} getValue Should result with value for the given object key.
 // @returns {Object}
 function iterableToObject( iterable, getValue ) {
 	const attributesObject = {};
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 27215a2590a..0f7ba803014 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -94,9 +94,11 @@ describe( 'DataFilter', () => {
 
 	it( 'should allow attributes', () => {
 		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowAttributes( { name: 'section', attributes: {
-			'data-foo': 'foobar'
-		} } );
+		dataFilter.allowAttributes( {
+			name: 'section', attributes: {
+				'data-foo': 'foobar'
+			}
+		} );
 
 		editor.setData( '<section data-foo="foobar"><p>foobar</p></section>' );
 
@@ -118,10 +120,12 @@ describe( 'DataFilter', () => {
 
 	it( 'should allow attributes (styles)', () => {
 		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowAttributes( { name: 'section', styles: {
-			'color': 'red',
-			'background-color': 'blue'
-		} } );
+		dataFilter.allowAttributes( {
+			name: 'section', styles: {
+				'color': 'red',
+				'background-color': 'blue'
+			}
+		} );
 
 		editor.setData( '<section style="background-color:blue;color:red;"><p>foobar</p></section>' );
 
@@ -368,28 +372,28 @@ describe( 'DataFilter', () => {
 
 		expect( editor.getData() ).to.equal( '<section><p>foo</p></section>' );
 	} );
-} );
 
-function getModelDataWithAttributes( model, options ) {
-	// Simplify GHS attributes as they are not very readable at this point due to object structure.
-	let counter = 1;
-	const data = getModelData( model, options ).replace( /htmlAttributes="{(.*?)}"/g, () => {
-		return `htmlAttributes="(${ counter++ })"`;
-	} );
+	function getModelDataWithAttributes( model, options ) {
+		// Simplify GHS attributes as they are not very readable at this point due to object structure.
+		let counter = 1;
+		const data = getModelData( model, options ).replace( /htmlAttributes="{(.*?)}"/g, () => {
+			return `htmlAttributes="(${ counter++ })"`;
+		} );
 
-	const range = model.createRangeIn( model.document.getRoot() );
+		const range = model.createRangeIn( model.document.getRoot() );
 
-	let attributes = [];
-	for ( const item of range.getItems() ) {
-		if ( item.hasAttribute && item.hasAttribute( 'htmlAttributes' ) ) {
-			attributes.push( item.getAttribute( 'htmlAttributes' ) );
+		let attributes = [];
+		for ( const item of range.getItems() ) {
+			if ( item.hasAttribute && item.hasAttribute( 'htmlAttributes' ) ) {
+				attributes.push( item.getAttribute( 'htmlAttributes' ) );
+			}
 		}
-	}
 
-	attributes = attributes.reduce( ( prev, cur, index ) => {
-		prev[ index + 1 ] = cur;
-		return prev;
-	}, {} );
+		attributes = attributes.reduce( ( prev, cur, index ) => {
+			prev[ index + 1 ] = cur;
+			return prev;
+		}, {} );
 
-	return { data, attributes };
-}
+		return { data, attributes };
+	}
+} );
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index 84fe698780d..60ce0843d24 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -6,55 +6,55 @@
 import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
 import DataSchema from '../src/dataschema';
 
-const fakeDefinitions = [
-	{
-		view: 'def1',
-		model: 'htmlDef1',
-		allowChildren: [ 'htmlDef2', 'htmlDef3' ],
-		schema: {
-			inheritAllFrom: '$block'
-		}
-	},
-	{
-		view: 'def2',
-		model: 'htmlDef2',
-		schema: {
-			inheritAllFrom: 'htmlDef1'
-		}
-	},
-	{
-		view: 'def3',
-		model: 'htmlDef3',
-		schema: {
-			inheritTypesFrom: 'htmlDef2'
-		}
-	},
-	{
-		view: 'def4',
-		model: 'htmlDef4',
-		schema: {
-			allowWhere: 'htmlDef3'
-		}
-	},
-	{
-		view: 'def5',
-		model: 'htmlDef5',
-		schema: {
-			allowContentOf: 'htmlDef4'
-		}
-	},
-	{
-		view: 'def6',
-		model: 'htmlDef6',
-		schema: {
-			allowAttributesOf: 'htmlDef5'
-		}
-	}
-];
-
 describe( 'DataSchema', () => {
 	let editor, dataSchema;
 
+	const fakeDefinitions = [
+		{
+			view: 'def1',
+			model: 'htmlDef1',
+			allowChildren: [ 'htmlDef2', 'htmlDef3' ],
+			schema: {
+				inheritAllFrom: '$block'
+			}
+		},
+		{
+			view: 'def2',
+			model: 'htmlDef2',
+			schema: {
+				inheritAllFrom: 'htmlDef1'
+			}
+		},
+		{
+			view: 'def3',
+			model: 'htmlDef3',
+			schema: {
+				inheritTypesFrom: 'htmlDef2'
+			}
+		},
+		{
+			view: 'def4',
+			model: 'htmlDef4',
+			schema: {
+				allowWhere: 'htmlDef3'
+			}
+		},
+		{
+			view: 'def5',
+			model: 'htmlDef5',
+			schema: {
+				allowContentOf: 'htmlDef4'
+			}
+		},
+		{
+			view: 'def6',
+			model: 'htmlDef6',
+			schema: {
+				allowAttributesOf: 'htmlDef5'
+			}
+		}
+	];
+
 	beforeEach( () => {
 		return VirtualTestEditor
 			.create()
@@ -142,12 +142,12 @@ describe( 'DataSchema', () => {
 
 		expect( result.size ).to.equal( 0 );
 	} );
-} );
 
-function registerMany( dataSchema, definitions ) {
-	definitions.forEach( def => dataSchema.register( def ) );
-}
+	function registerMany( dataSchema, definitions ) {
+		definitions.forEach( def => dataSchema.register( def ) );
+	}
 
-function getFakeDefinitions( ...viewNames ) {
-	return fakeDefinitions.filter( def => viewNames.includes( def.view ) );
-}
+	function getFakeDefinitions( ...viewNames ) {
+		return fakeDefinitions.filter( def => viewNames.includes( def.view ) );
+	}
+} );

From 9fc6ab1e66e52574cad3a8403085a1e063f48632 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <j.niegowski@cksource.com>
Date: Thu, 11 Mar 2021 19:02:58 +0100
Subject: [PATCH 061/217] Code review fixes.

---
 .../ckeditor5-content-compatibility/tests/datafilter.js     | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 0f7ba803014..bd192f1d088 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -95,7 +95,8 @@ describe( 'DataFilter', () => {
 	it( 'should allow attributes', () => {
 		dataFilter.allowElement( { name: 'section' } );
 		dataFilter.allowAttributes( {
-			name: 'section', attributes: {
+			name: 'section',
+			attributes: {
 				'data-foo': 'foobar'
 			}
 		} );
@@ -121,7 +122,8 @@ describe( 'DataFilter', () => {
 	it( 'should allow attributes (styles)', () => {
 		dataFilter.allowElement( { name: 'section' } );
 		dataFilter.allowAttributes( {
-			name: 'section', styles: {
+			name: 'section',
+			styles: {
 				'color': 'red',
 				'background-color': 'blue'
 			}

From 840a9245e8273c28258ebffd8354075083e57300 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 29 Mar 2021 12:50:11 +0200
Subject: [PATCH 062/217] Updated package.json to match the latest release.

---
 .../package.json                              | 20 +++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/package.json b/packages/ckeditor5-content-compatibility/package.json
index ef59dc79cd2..b175869e6b6 100644
--- a/packages/ckeditor5-content-compatibility/package.json
+++ b/packages/ckeditor5-content-compatibility/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@ckeditor/ckeditor5-content-compatibility",
-  "version": "26.0.0",
+  "version": "27.0.0",
   "description": "Content compatibility feature",
   "private": true,
   "keywords": [
@@ -15,16 +15,20 @@
   ],
   "main": "src/index.js",
   "dependencies": {
-    "ckeditor5": "^26.0.0",
+    "ckeditor5": "^27.0.0",
     "lodash-es": "^4.17.15"
   },
   "devDependencies": {
-    "@ckeditor/ckeditor5-basic-styles": "^26.0.0",
-    "@ckeditor/ckeditor5-block-quote": "^26.0.0",
-    "@ckeditor/ckeditor5-core": "^26.0.0",
-    "@ckeditor/ckeditor5-list": "^26.0.0",
-    "@ckeditor/ckeditor5-paragraph": "^26.0.0",
-    "@ckeditor/ckeditor5-utils": "^26.0.0"
+    "@ckeditor/ckeditor5-basic-styles": "^27.0.0",
+    "@ckeditor/ckeditor5-block-quote": "^27.0.0",
+    "@ckeditor/ckeditor5-core": "^27.0.0",
+    "@ckeditor/ckeditor5-editor-classic": "^27.0.0",
+    "@ckeditor/ckeditor5-engine": "^27.0.0",
+    "@ckeditor/ckeditor5-essentials": "^27.0.0",
+    "@ckeditor/ckeditor5-list": "^27.0.0",
+    "@ckeditor/ckeditor5-paragraph": "^27.0.0",
+    "webpack": "^4.43.0",
+    "webpack-cli": "^3.3.11"
   },
   "engines": {
     "node": ">=12.0.0",

From beecd7ab1920480a2ccd7b2b0c85146969937d7c Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 10 Mar 2021 13:30:12 +0100
Subject: [PATCH 063/217] Added initial support for inline elements.

---
 .../src/datafilter.js                         | 200 ++++++++++++++----
 .../src/dataschema.js                         |  12 ++
 .../tests/datafilter.js                       |   6 +-
 .../tests/manual/generalhtmlsupport.html      |  10 +
 .../tests/manual/generalhtmlsupport.js        |  10 +-
 5 files changed, 187 insertions(+), 51 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 980329d29b2..25f6f408cea 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -37,7 +37,7 @@ const DATA_SCHEMA_ATTRIBUTE_KEY = 'htmlAttributes';
  *		dataFilter.disallowedAttributes( {
  *			name: 'section',
  *			styles: {
- *				color: /[^]/
+ *				color: /[\s\S]+/
  *			}
  *		} );
  */
@@ -133,15 +133,47 @@ export default class DataFilter {
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
 	_registerElement( definition ) {
+		if ( definition.isInline ) {
+			this._defineInlineElement( definition );
+		} else {
+			this._defineBlockElement( definition );
+		}
+	}
+
+	/**
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 */
+	_defineBlockElement( definition ) {
 		if ( this.editor.model.schema.isRegistered( definition.model ) ) {
 			return;
 		}
 
 		this._defineSchema( definition );
 
-		if ( definition.view ) {
-			this._defineConverters( definition );
+		if ( !definition.view ) {
+			return;
 		}
+
+		this._defineBlockElementConverters( definition );
+	}
+
+	/**
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 */
+	_defineInlineElement( definition ) {
+		const schema = this.editor.model.schema;
+
+		schema.extend( '$text', {
+			allowAttributes: definition.model
+		} );
+
+		schema.setAttributeProperties( definition.model, {
+			copyOnEnter: true
+		} );
+
+		this._defineInlineElementConverters( definition );
 	}
 
 	/**
@@ -168,53 +200,58 @@ export default class DataFilter {
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
-	_defineConverters( definition ) {
+	_defineInlineElementConverters( definition ) {
 		const conversion = this.editor.conversion;
 		const viewName = definition.view;
 		const modelName = definition.model;
 
-		// Consumes disallowed element attributes to prevent them of being processed by other converters.
-		conversion.for( 'upcast' ).add( dispatcher => {
-			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
-				for ( const match of matchAll( data.viewItem, this._disallowedAttributes ) ) {
-					conversionApi.consumable.consume( data.viewItem, match.match );
-				}
-			}, { priority: 'high' } );
-		} );
+		this._addDisallowedAttributesConverter( viewName );
 
-		// Stash unused, allowed element attributes, so they can be reapplied later in data conversion.
-		conversion.for( 'upcast' ).elementToElement( {
+		conversion.for( 'upcast' ).elementToAttribute( {
 			view: viewName,
-			model: ( viewElement, conversionApi ) => {
-				const matches = [];
+			model: {
+				key: modelName,
+				value: this._matchAndConsumeAttributes.bind( this )
+			},
+			converterPriority: 'low'
+		} );
 
-				for ( const match of matchAll( viewElement, this._allowedAttributes ) ) {
-					if ( conversionApi.consumable.consume( viewElement, match.match ) ) {
-						matches.push( match );
-					}
+		conversion.for( 'downcast' ).attributeToElement( {
+			model: modelName,
+			view: ( attributeValue, conversionApi ) => {
+				if ( !attributeValue ) {
+					return;
 				}
 
-				const { attributes, styles, classes } = mergeMatchResults( matches );
-				const viewAttributes = {};
+				const { writer } = conversionApi;
+				const viewElement = writer.createAttributeElement( viewName );
 
-				// Stash attributes.
-				if ( attributes.size ) {
-					viewAttributes.attributes = iterableToObject( attributes, key => viewElement.getAttribute( key ) );
-				}
+				setAttributesOn( writer, attributeValue, viewElement );
 
-				// Stash styles.
-				if ( styles.size ) {
-					viewAttributes.styles = iterableToObject( styles, key => viewElement.getStyle( key ) );
-				}
+				return viewElement;
+			}
+		} )
+	}
 
-				// Stash classes.
-				if ( classes.size ) {
-					viewAttributes.classes = Array.from( classes );
-				}
+	/**
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition}
+	 */
+	_defineBlockElementConverters( definition ) {
+		const conversion = this.editor.conversion;
+		const viewName = definition.view;
+		const modelName = definition.model;
+
+		this._addDisallowedAttributesConverter( viewName );
 
+		// Stash unused, allowed element attributes, so they can be reapplied later in data conversion.
+		conversion.for( 'upcast' ).elementToElement( {
+			view: viewName,
+			model: ( viewElement, conversionApi ) => {
 				const element = conversionApi.writer.createElement( modelName );
+				const viewAttributes = this._matchAndConsumeAttributes( viewElement, conversionApi );
 
-				if ( Object.keys( viewAttributes ).length ) {
+				if ( viewAttributes ) {
 					conversionApi.writer.setAttribute( DATA_SCHEMA_ATTRIBUTE_KEY, viewAttributes, element );
 				}
 
@@ -241,22 +278,93 @@ export default class DataFilter {
 				const viewWriter = conversionApi.writer;
 				const viewElement = conversionApi.mapper.toViewElement( data.item );
 
-				if ( viewAttributes.attributes ) {
-					for ( const [ key, value ] of Object.entries( viewAttributes.attributes ) ) {
-						viewWriter.setAttribute( key, value, viewElement );
-					}
-				}
+				setAttributesOn( viewWriter, viewAttributes, viewElement );
+			} );
+		} );
+	}
 
-				if ( viewAttributes.styles ) {
-					viewWriter.setStyle( viewAttributes.styles, viewElement );
-				}
+	/**
+	 * Adds converter responsible for consuming disallowed view attributes.
+	 *
+	 * @private
+	 * @param {String} viewName
+	 */
+	_addDisallowedAttributesConverter( viewName ) {
+		const conversion = this.editor.conversion;
 
-				if ( viewAttributes.classes ) {
-					viewWriter.addClass( viewAttributes.classes, viewElement );
+		// Consumes disallowed element attributes to prevent them of being processed by other converters.
+		conversion.for( 'upcast' ).add( dispatcher => {
+			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
+				for ( const match of matchAll( data.viewItem, this._disallowedAttributes ) ) {
+					conversionApi.consumable.consume( data.viewItem, match.match );
 				}
-			} );
+			}, { priority: 'high' } );
 		} );
 	}
+
+	/**
+	 * Matches and consumes allowed view attributes.
+	 *
+	 * @private
+	 * @param {module:engine/view/element~Element} viewElement
+	 * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
+	 * @returns {Object} [result]
+	 * @returns {Array.<String>} result.attributes Array with matched attribute names.
+	 * @returns {Array.<String>} result.classes Array with matched class names.
+	 * @returns {Array.<String>} result.styles Array with matched style names.
+	 */
+	_matchAndConsumeAttributes( viewElement, { consumable } ) {
+		const matches = [];
+		for ( const match of matchAll( viewElement, this._allowedAttributes ) ) {
+			if ( consumable.consume( viewElement, match.match ) ) {
+				matches.push( match );
+			}
+		}
+
+		const { attributes, styles, classes } = mergeMatchResults( matches );
+		const viewAttributes = {};
+
+		if ( attributes.size ) {
+			viewAttributes.attributes = iterableToObject( attributes, key => viewElement.getAttribute( key ) );
+		}
+
+		if ( styles.size ) {
+			viewAttributes.styles = iterableToObject( styles, key => viewElement.getStyle( key ) );
+		}
+
+		if ( classes.size ) {
+			viewAttributes.classes = Array.from( classes );
+		}
+
+		if ( !Object.keys( viewAttributes ).length ) {
+			return null;
+		}
+
+		return viewAttributes;
+	}
+}
+
+// Helper function for downcast converter. Sets attributes on the given view element.
+//
+// @private
+// @param {module:engine/view/downcastwriter~DowncastWriter} writer
+// @param {Object} viewAttributes
+// @param {module:engine/view/element~Element} viewElement
+// on all elements in the range.
+function setAttributesOn( writer, viewAttributes, viewElement ) {
+	if ( viewAttributes.attributes ) {
+		for ( const [ key, value ] of Object.entries( viewAttributes.attributes ) ) {
+			writer.setAttribute( key, value, viewElement );
+		}
+	}
+
+	if ( viewAttributes.styles ) {
+		writer.setStyle( viewAttributes.styles, viewElement );
+	}
+
+	if ( viewAttributes.classes ) {
+		writer.addClass( viewAttributes.classes, viewElement );
+	}
 }
 
 // Helper function restoring matcher for the given key from `rules` object.
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 320d7ebdc35..df519a0290c 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -112,6 +112,13 @@ export default class DataSchema {
 				allowIn: 'htmlDetails'
 			}
 		} );
+
+		// Inline elements.
+		this.register( {
+			view: 'span',
+			model: 'htmlSpan',
+			isInline: true
+		} );
 	}
 
 	/**
@@ -167,6 +174,11 @@ export default class DataSchema {
 	 */
 	* _getReferences( modelName ) {
 		const { schema } = this._definitions.get( modelName );
+
+		if ( !schema ) {
+			return;
+		}
+
 		const inheritProperties = [ 'inheritAllFrom', 'inheritTypesFrom', 'allowWhere', 'allowContentOf', 'allowAttributesOf' ];
 
 		for ( const property of inheritProperties ) {
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index bd192f1d088..243cb96ff40 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -168,7 +168,7 @@ describe( 'DataFilter', () => {
 
 	it( 'should allow nested attributes', () => {
 		dataFilter.allowElement( { name: /article|section/ } );
-		dataFilter.allowAttributes( { name: /[^]/, attributes: { 'data-foo': /foo|bar/ } } );
+		dataFilter.allowAttributes( { name: /[\s\S]+/, attributes: { 'data-foo': /foo|bar/ } } );
 
 		editor.setData( '<article data-foo="foo">' +
 			'<section data-foo="bar"><p>section1</p></section>' +
@@ -237,7 +237,7 @@ describe( 'DataFilter', () => {
 
 	it( 'should disallow attributes', () => {
 		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': /[^]/ } } );
+		dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': /[\s\S]+/ } } );
 		dataFilter.disallowAttributes( { name: 'section', attributes: { 'data-foo': 'bar' } } );
 
 		editor.setData(
@@ -265,7 +265,7 @@ describe( 'DataFilter', () => {
 
 	it( 'should disallow attributes (styles)', () => {
 		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowAttributes( { name: 'section', styles: { color: /[^]/ } } );
+		dataFilter.allowAttributes( { name: 'section', styles: { color: /[\s\S]+/ } } );
 		dataFilter.disallowAttributes( { name: 'section', styles: { color: 'red' } } );
 
 		editor.setData(
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
index 3d5c4a5ccb3..bf9924f6fd3 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -8,15 +8,25 @@
 		<section id="_section2"><p>Section #2</p></section>
 		<section id="section3" style="color: red" class="special_section"><p>Section #3</p></section>
 	</article>
+
 	<details>
 		<summary>Summary</summary>
 		Hello world
 	</details>
+
 	<dl>
 		<dt><p>dt1</p></dt>
 		<dt><p>dt2</p></dt>
 		<dd><p>dd1</p></dd>
 		<dd><p>dd2</p></dd>
 	</dl>
+
 	<xyz><p>XYZ</p></xyz>
+
+	<p>
+		<span data-foo="foo" style="color:blue">Some span element with allowed attributes!</span>
+	</p>
+	<p>
+		<span style="color:red">Some span element with disallowed attributes!</span>
+	</p>
 </div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 8e1bba81c11..9a8e1e7f118 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -53,12 +53,18 @@ class ExtendHTMLSupport extends Plugin {
 
 		// Let's extend 'section' with some attributes. Data filter will take care of
 		// creating proper converters and attribute matchers:
-		dataFilter.allowAttributes( { name: 'section', attributes: { id: /[^]/ } } );
-		dataFilter.allowAttributes( { name: 'section', classes: /[^]/ } );
+		dataFilter.allowAttributes( { name: 'section', attributes: { id: /[\s\S]+/ } } );
+		dataFilter.allowAttributes( { name: 'section', classes: /[\s\S]+/ } );
 		dataFilter.allowAttributes( { name: 'section', styles: { color: 'red' } } );
 
 		// but disallow setting id attribute if it start with `_` prefix:
 		dataFilter.disallowAttributes( { name: 'section', attributes: { id: /^_.*/ } } );
+
+		// Let's also add some inline elements support:
+		dataFilter.allowElement( { name: 'span' } );
+		dataFilter.allowAttributes( { name: 'span', attributes: { 'data-foo': /[\s\S]+/ } } );
+		dataFilter.allowAttributes( { name: 'span', styles: { color: /[\s\S]+/ } } );
+		dataFilter.disallowAttributes( { name: 'span', styles: { color: 'red' } } );
 	}
 }
 

From 31accfe4818b435c739ddedc8556f1bbe8d10a71 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 11 Mar 2021 14:21:53 +0100
Subject: [PATCH 064/217] Nested inline elements support.

---
 .../src/datafilter.js                         | 54 +++++++++++++++----
 .../src/dataschema.js                         |  9 +++-
 .../tests/manual/generalhtmlsupport.html      |  4 +-
 .../tests/manual/generalhtmlsupport.js        |  8 +--
 4 files changed, 57 insertions(+), 18 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 25f6f408cea..507f4c58cc5 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -10,7 +10,7 @@
 import { Matcher } from 'ckeditor5/src/engine';
 import { priorities, toArray } from 'ckeditor5/src/utils';
 
-import { cloneDeep } from 'lodash-es';
+import { cloneDeep, uniq } from 'lodash-es';
 
 const DATA_SCHEMA_ATTRIBUTE_KEY = 'htmlAttributes';
 
@@ -203,21 +203,33 @@ export default class DataFilter {
 	_defineInlineElementConverters( definition ) {
 		const conversion = this.editor.conversion;
 		const viewName = definition.view;
-		const modelName = definition.model;
+		const attributeKey = definition.model;
 
 		this._addDisallowedAttributesConverter( viewName );
 
-		conversion.for( 'upcast' ).elementToAttribute( {
-			view: viewName,
-			model: {
-				key: modelName,
-				value: this._matchAndConsumeAttributes.bind( this )
-			},
-			converterPriority: 'low'
+		conversion.for( 'upcast' ).add( dispatcher => {
+			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
+				const viewAttributes = this._matchAndConsumeAttributes( data.viewItem, conversionApi );
+
+				// Convert children and set conversion result as a current data.
+				data = Object.assign( data, conversionApi.convertChildren( data.viewItem, data.modelCursor ) );
+
+				// Set attribute on each item in range according to Schema.
+				for ( const node of data.modelRange.getItems() ) {
+					if ( conversionApi.schema.checkAttribute( node, attributeKey ) ) {
+						// Node's children are converter recursively, so node can already include model attribute.
+						// We want to extend it, not replace.
+						const attributesToAdd = mergeAttributes( node.getAttribute( attributeKey ), viewAttributes );
+						conversionApi.writer.setAttribute( attributeKey, attributesToAdd, node );
+					}
+				}
+			}, {
+				priority: 'low'
+			} );
 		} );
 
 		conversion.for( 'downcast' ).attributeToElement( {
-			model: modelName,
+			model: attributeKey,
 			view: ( attributeValue, conversionApi ) => {
 				if ( !attributeValue ) {
 					return;
@@ -230,7 +242,7 @@ export default class DataFilter {
 
 				return viewElement;
 			}
-		} )
+		} );
 	}
 
 	/**
@@ -437,3 +449,23 @@ function iterableToObject( iterable, getValue ) {
 
 	return attributesObject;
 }
+
+// Merges attribute objects.
+//
+// @private
+// @param {Object} oldValue
+// @param {Object} newValue
+// @returns {Object}
+function mergeAttributes( oldValue, newValue ) {
+	const result = cloneDeep( newValue );
+
+	for ( const key in oldValue ) {
+		if ( Array.isArray( oldValue[ key ] ) ) {
+			result[ key ] = uniq( [ ...oldValue[ key ], ...newValue[ key ] ] );
+		} else {
+			result[ key ] = Object.assign( {}, oldValue[ key ], newValue[ key ] );
+		}
+	}
+
+	return result;
+}
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index df519a0290c..969bd7936eb 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -113,12 +113,18 @@ export default class DataSchema {
 			}
 		} );
 
-		// Inline elements.
+		// Add inline elements.
 		this.register( {
 			view: 'span',
 			model: 'htmlSpan',
 			isInline: true
 		} );
+
+		this.register( {
+			view: 'cite',
+			model: 'htmlCite',
+			isInline: true
+		} );
 	}
 
 	/**
@@ -220,4 +226,5 @@ function testViewName( pattern, viewName ) {
  * @property {String} model Name of the model element.
  * @property {module:engine/model/schema~SchemaItemDefinition} schema The model schema item definition describing registered model.
  * @property {String|Array.<String>} [allowChildren] Extends the given children list to allow definition model.
+ * @property {Boolean} [isInline] Indicates if the element decribed by data schema definition is inline.
  */
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
index bf9924f6fd3..53c0ddafed3 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -24,9 +24,9 @@
 	<xyz><p>XYZ</p></xyz>
 
 	<p>
-		<span data-foo="foo" style="color:blue">Some span element with allowed attributes!</span>
+		<span data-foo="foo">Nested cite: <cite style="color:blue;">I'm blue!</cite></span>
 	</p>
 	<p>
-		<span style="color:red">Some span element with disallowed attributes!</span>
+		<span data-foo="foo">Nested span: <span style="color:blue;">I'm blue!</span></span>
 	</p>
 </div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 9a8e1e7f118..3a1f9987860 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -61,10 +61,10 @@ class ExtendHTMLSupport extends Plugin {
 		dataFilter.disallowAttributes( { name: 'section', attributes: { id: /^_.*/ } } );
 
 		// Let's also add some inline elements support:
-		dataFilter.allowElement( { name: 'span' } );
-		dataFilter.allowAttributes( { name: 'span', attributes: { 'data-foo': /[\s\S]+/ } } );
-		dataFilter.allowAttributes( { name: 'span', styles: { color: /[\s\S]+/ } } );
-		dataFilter.disallowAttributes( { name: 'span', styles: { color: 'red' } } );
+		dataFilter.allowElement( { name: /^span|cite$/ } );
+		dataFilter.allowAttributes( { name: /^span|cite$/, attributes: { 'data-foo': /[\s\S]+/ } } );
+		dataFilter.allowAttributes( { name: /^span|cite$/, styles: { color: /[\s\S]+/ } } );
+		dataFilter.disallowAttributes( { name: /^span|cite$/, styles: { color: 'red' } } );
 	}
 }
 

From c1c6c6226cbefd57d0e9e7b93ba4940d8a48e3af Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 12 Mar 2021 08:55:21 +0100
Subject: [PATCH 065/217] Added initial test for inline elements.

---
 .../tests/datafilter.js                       | 598 +++++++++---------
 1 file changed, 308 insertions(+), 290 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 243cb96ff40..b73188a74cd 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -31,363 +31,381 @@ describe( 'DataFilter', () => {
 		return editor.destroy();
 	} );
 
-	it( 'should allow element', () => {
-		dataFilter.allowElement( { name: 'article' } );
-
-		editor.setData( '<article>' +
-			'<section><paragraph>section1</paragraph></section>' +
-			'<section><paragraph>section2</paragraph></section></article>'
-		);
-
-		expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
-			'<htmlArticle><paragraph>section1section2</paragraph></htmlArticle>'
-		);
-
-		expect( editor.getData() ).to.equal(
-			'<article><p>section1section2</p></article>'
-		);
-
-		dataFilter.allowElement( { name: 'section' } );
-
-		editor.setData( '<article>' +
-			'<section><paragraph>section1</paragraph></section>' +
-			'<section><paragraph>section2</paragraph></section></article>'
-		);
-
-		expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
-			'<htmlArticle>' +
-			'<htmlSection><paragraph>section1</paragraph></htmlSection>' +
-			'<htmlSection><paragraph>section2</paragraph></htmlSection></htmlArticle>'
-		);
-
-		expect( editor.getData() ).to.equal(
-			'<article>' +
-			'<section><p>section1</p></section>' +
-			'<section><p>section2</p></section></article>'
-		);
-	} );
-
-	it( 'should allow deeply nested structure', () => {
-		dataFilter.allowElement( { name: 'section' } );
-
-		editor.setData(
-			'<section><p>1</p>' +
-			'<section><p>2</p>' +
-			'<section><p>3</p>' +
-			'</section></section></section>'
-		);
-
-		expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
-			'<htmlSection><paragraph>1</paragraph>' +
-			'<htmlSection><paragraph>2</paragraph>' +
-			'<htmlSection><paragraph>3</paragraph>' +
-			'</htmlSection></htmlSection></htmlSection>'
-		);
-
-		expect( editor.getData() ).to.equal(
-			'<section><p>1</p>' +
-			'<section><p>2</p>' +
-			'<section><p>3</p>' +
-			'</section></section></section>'
-		);
-	} );
+	describe( 'block', () => {
+		it( 'should allow element', () => {
+			dataFilter.allowElement( { name: 'article' } );
+
+			editor.setData( '<article>' +
+				'<section><paragraph>section1</paragraph></section>' +
+				'<section><paragraph>section2</paragraph></section></article>'
+			);
+
+			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
+				'<htmlArticle><paragraph>section1section2</paragraph></htmlArticle>'
+			);
+
+			expect( editor.getData() ).to.equal(
+				'<article><p>section1section2</p></article>'
+			);
+
+			dataFilter.allowElement( { name: 'section' } );
+
+			editor.setData( '<article>' +
+				'<section><paragraph>section1</paragraph></section>' +
+				'<section><paragraph>section2</paragraph></section></article>'
+			);
+
+			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
+				'<htmlArticle>' +
+				'<htmlSection><paragraph>section1</paragraph></htmlSection>' +
+				'<htmlSection><paragraph>section2</paragraph></htmlSection></htmlArticle>'
+			);
+
+			expect( editor.getData() ).to.equal(
+				'<article>' +
+				'<section><p>section1</p></section>' +
+				'<section><p>section2</p></section></article>'
+			);
+		} );
 
-	it( 'should allow attributes', () => {
-		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowAttributes( {
-			name: 'section',
-			attributes: {
-				'data-foo': 'foobar'
-			}
+		it( 'should allow deeply nested structure', () => {
+			dataFilter.allowElement( { name: 'section' } );
+
+			editor.setData(
+				'<section><p>1</p>' +
+				'<section><p>2</p>' +
+				'<section><p>3</p>' +
+				'</section></section></section>'
+			);
+
+			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
+				'<htmlSection><paragraph>1</paragraph>' +
+				'<htmlSection><paragraph>2</paragraph>' +
+				'<htmlSection><paragraph>3</paragraph>' +
+				'</htmlSection></htmlSection></htmlSection>'
+			);
+
+			expect( editor.getData() ).to.equal(
+				'<section><p>1</p>' +
+				'<section><p>2</p>' +
+				'<section><p>3</p>' +
+				'</section></section></section>'
+			);
 		} );
 
-		editor.setData( '<section data-foo="foobar"><p>foobar</p></section>' );
+		it( 'should allow attributes', () => {
+			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowAttributes( {
+				name: 'section',
+				attributes: {
+					'data-foo': 'foobar'
+				}
+			} );
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<htmlSection htmlAttributes="(1)"><paragraph>foobar</paragraph></htmlSection>',
-			attributes: {
-				1: {
-					attributes: {
-						'data-foo': 'foobar'
+			editor.setData( '<section data-foo="foobar"><p>foobar</p></section>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<htmlSection htmlAttributes="(1)"><paragraph>foobar</paragraph></htmlSection>',
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': 'foobar'
+						}
 					}
 				}
-			}
-		} );
-
-		expect( editor.getData() ).to.equal(
-			'<section data-foo="foobar"><p>foobar</p></section>'
-		);
-	} );
+			} );
 
-	it( 'should allow attributes (styles)', () => {
-		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowAttributes( {
-			name: 'section',
-			styles: {
-				'color': 'red',
-				'background-color': 'blue'
-			}
+			expect( editor.getData() ).to.equal(
+				'<section data-foo="foobar"><p>foobar</p></section>'
+			);
 		} );
 
-		editor.setData( '<section style="background-color:blue;color:red;"><p>foobar</p></section>' );
+		it( 'should allow attributes (styles)', () => {
+			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowAttributes( {
+				name: 'section',
+				styles: {
+					'color': 'red',
+					'background-color': 'blue'
+				}
+			} );
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<htmlSection htmlAttributes="(1)"><paragraph>foobar</paragraph></htmlSection>',
-			attributes: {
-				1: {
-					styles: {
-						'background-color': 'blue',
-						color: 'red'
+			editor.setData( '<section style="background-color:blue;color:red;"><p>foobar</p></section>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<htmlSection htmlAttributes="(1)"><paragraph>foobar</paragraph></htmlSection>',
+				attributes: {
+					1: {
+						styles: {
+							'background-color': 'blue',
+							color: 'red'
+						}
 					}
 				}
-			}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<section style="background-color:blue;color:red;"><p>foobar</p></section>'
+			);
 		} );
 
-		expect( editor.getData() ).to.equal(
-			'<section style="background-color:blue;color:red;"><p>foobar</p></section>'
-		);
-	} );
+		it( 'should allow attributes (classes)', () => {
+			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowAttributes( { name: 'section', classes: [ 'foo', 'bar' ] } );
 
-	it( 'should allow attributes (classes)', () => {
-		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowAttributes( { name: 'section', classes: [ 'foo', 'bar' ] } );
+			editor.setData( '<section class="foo bar"><p>foobar</p></section>' );
 
-		editor.setData( '<section class="foo bar"><p>foobar</p></section>' );
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<htmlSection htmlAttributes="(1)"><paragraph>foobar</paragraph></htmlSection>',
+				attributes: {
+					1: { classes: [ 'foo', 'bar' ] }
+				}
+			} );
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<htmlSection htmlAttributes="(1)"><paragraph>foobar</paragraph></htmlSection>',
-			attributes: {
-				1: { classes: [ 'foo', 'bar' ] }
-			}
+			expect( editor.getData() ).to.equal(
+				'<section class="foo bar"><p>foobar</p></section>'
+			);
 		} );
 
-		expect( editor.getData() ).to.equal(
-			'<section class="foo bar"><p>foobar</p></section>'
-		);
-	} );
-
-	it( 'should allow nested attributes', () => {
-		dataFilter.allowElement( { name: /article|section/ } );
-		dataFilter.allowAttributes( { name: /[\s\S]+/, attributes: { 'data-foo': /foo|bar/ } } );
-
-		editor.setData( '<article data-foo="foo">' +
-			'<section data-foo="bar"><p>section1</p></section>' +
-			'<section data-foo="foo"><p>section2</p></section>' +
-			'</article>'
-		);
-
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<htmlArticle htmlAttributes="(1)">' +
-				'<htmlSection htmlAttributes="(2)"><paragraph>section1</paragraph></htmlSection>' +
-				'<htmlSection htmlAttributes="(3)"><paragraph>section2</paragraph></htmlSection>' +
-				'</htmlArticle>',
-			attributes: {
-				1: {
-					attributes: {
-						'data-foo': 'foo'
-					}
-				},
-				2: {
-					attributes: {
-						'data-foo': 'bar'
-					}
-				},
-				3: {
-					attributes: {
-						'data-foo': 'foo'
+		it( 'should allow nested attributes', () => {
+			dataFilter.allowElement( { name: /article|section/ } );
+			dataFilter.allowAttributes( { name: /[\s\S]+/, attributes: { 'data-foo': /foo|bar/ } } );
+
+			editor.setData( '<article data-foo="foo">' +
+				'<section data-foo="bar"><p>section1</p></section>' +
+				'<section data-foo="foo"><p>section2</p></section>' +
+				'</article>'
+			);
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<htmlArticle htmlAttributes="(1)">' +
+					'<htmlSection htmlAttributes="(2)"><paragraph>section1</paragraph></htmlSection>' +
+					'<htmlSection htmlAttributes="(3)"><paragraph>section2</paragraph></htmlSection>' +
+					'</htmlArticle>',
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': 'foo'
+						}
+					},
+					2: {
+						attributes: {
+							'data-foo': 'bar'
+						}
+					},
+					3: {
+						attributes: {
+							'data-foo': 'foo'
+						}
 					}
 				}
-			}
+			} );
 		} );
-	} );
-
-	it( 'should allow attributes for all allowed definitions', () => {
-		dataFilter.allowElement( { name: /section|article/ } );
 
-		dataFilter.allowAttributes( { name: /section|article/, attributes: { 'data-foo': 'foo' } } );
-		dataFilter.allowAttributes( { name: /section|article/, attributes: { 'data-bar': 'bar' } } );
-
-		editor.setData(
-			'<section data-foo="foo"><p>foo</p></section>' +
-			'<article data-bar="bar"><p>bar</p></article>'
-		);
-
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>' +
-				'<htmlArticle htmlAttributes="(2)"><paragraph>bar</paragraph></htmlArticle>',
-			attributes: {
-				1: {
-					attributes: {
-						'data-foo': 'foo'
-					}
-				},
-				2: {
-					attributes: {
-						'data-bar': 'bar'
+		it( 'should allow attributes for all allowed definitions', () => {
+			dataFilter.allowElement( { name: /section|article/ } );
+
+			dataFilter.allowAttributes( { name: /section|article/, attributes: { 'data-foo': 'foo' } } );
+			dataFilter.allowAttributes( { name: /section|article/, attributes: { 'data-bar': 'bar' } } );
+
+			editor.setData(
+				'<section data-foo="foo"><p>foo</p></section>' +
+				'<article data-bar="bar"><p>bar</p></article>'
+			);
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>' +
+					'<htmlArticle htmlAttributes="(2)"><paragraph>bar</paragraph></htmlArticle>',
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': 'foo'
+						}
+					},
+					2: {
+						attributes: {
+							'data-bar': 'bar'
+						}
 					}
 				}
-			}
-		} );
+			} );
 
-		expect( editor.getData() ).to.equal(
-			'<section data-foo="foo"><p>foo</p></section>' +
-			'<article data-bar="bar"><p>bar</p></article>'
-		);
-	} );
+			expect( editor.getData() ).to.equal(
+				'<section data-foo="foo"><p>foo</p></section>' +
+				'<article data-bar="bar"><p>bar</p></article>'
+			);
+		} );
 
-	it( 'should disallow attributes', () => {
-		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': /[\s\S]+/ } } );
-		dataFilter.disallowAttributes( { name: 'section', attributes: { 'data-foo': 'bar' } } );
-
-		editor.setData(
-			'<section data-foo="foo"><p>foo</p></section>' +
-			'<section data-foo="bar"><p>bar</p></section>'
-		);
-
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>' +
-				'<htmlSection><paragraph>bar</paragraph></htmlSection>',
-			attributes: {
-				1: {
-					attributes: {
-						'data-foo': 'foo'
+		it( 'should disallow attributes', () => {
+			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': /[\s\S]+/ } } );
+			dataFilter.disallowAttributes( { name: 'section', attributes: { 'data-foo': 'bar' } } );
+
+			editor.setData(
+				'<section data-foo="foo"><p>foo</p></section>' +
+				'<section data-foo="bar"><p>bar</p></section>'
+			);
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>' +
+					'<htmlSection><paragraph>bar</paragraph></htmlSection>',
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': 'foo'
+						}
 					}
 				}
-			}
-		} );
+			} );
 
-		expect( editor.getData() ).to.equal(
-			'<section data-foo="foo"><p>foo</p></section>' +
-			'<section><p>bar</p></section>'
-		);
-	} );
+			expect( editor.getData() ).to.equal(
+				'<section data-foo="foo"><p>foo</p></section>' +
+				'<section><p>bar</p></section>'
+			);
+		} );
 
-	it( 'should disallow attributes (styles)', () => {
-		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowAttributes( { name: 'section', styles: { color: /[\s\S]+/ } } );
-		dataFilter.disallowAttributes( { name: 'section', styles: { color: 'red' } } );
-
-		editor.setData(
-			'<section style="color:blue;"><p>foo</p></section>' +
-			'<section style="color:red"><p>bar</p></section>'
-		);
-
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>' +
-				'<htmlSection><paragraph>bar</paragraph></htmlSection>',
-			attributes: {
-				1: {
-					styles: {
-						color: 'blue'
+		it( 'should disallow attributes (styles)', () => {
+			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowAttributes( { name: 'section', styles: { color: /[\s\S]+/ } } );
+			dataFilter.disallowAttributes( { name: 'section', styles: { color: 'red' } } );
+
+			editor.setData(
+				'<section style="color:blue;"><p>foo</p></section>' +
+				'<section style="color:red"><p>bar</p></section>'
+			);
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>' +
+					'<htmlSection><paragraph>bar</paragraph></htmlSection>',
+				attributes: {
+					1: {
+						styles: {
+							color: 'blue'
+						}
 					}
 				}
-			}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<section style="color:blue;"><p>foo</p></section>' +
+				'<section><p>bar</p></section>'
+			);
 		} );
 
-		expect( editor.getData() ).to.equal(
-			'<section style="color:blue;"><p>foo</p></section>' +
-			'<section><p>bar</p></section>'
-		);
-	} );
+		it( 'should disallow attributes (classes)', () => {
+			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowAttributes( { name: 'section', classes: [ 'foo', 'bar' ] } );
+			dataFilter.disallowAttributes( { name: 'section', classes: [ 'bar' ] } );
 
-	it( 'should disallow attributes (classes)', () => {
-		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowAttributes( { name: 'section', classes: [ 'foo', 'bar' ] } );
-		dataFilter.disallowAttributes( { name: 'section', classes: [ 'bar' ] } );
+			editor.setData(
+				'<section class="foo bar"><p>foo</p></section>' +
+				'<section class="bar"><p>bar</p></section>'
+			);
 
-		editor.setData(
-			'<section class="foo bar"><p>foo</p></section>' +
-			'<section class="bar"><p>bar</p></section>'
-		);
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<htmlSection><paragraph>foo</paragraph></htmlSection>' +
+					'<htmlSection><paragraph>bar</paragraph></htmlSection>',
+				attributes: {}
+			} );
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<htmlSection><paragraph>foo</paragraph></htmlSection>' +
-				'<htmlSection><paragraph>bar</paragraph></htmlSection>',
-			attributes: {}
+			expect( editor.getData() ).to.equal(
+				'<section><p>foo</p></section>' +
+				'<section><p>bar</p></section>'
+			);
 		} );
 
-		expect( editor.getData() ).to.equal(
-			'<section><p>foo</p></section>' +
-			'<section><p>bar</p></section>'
-		);
-	} );
+		it( 'should extend allowed children only if specified model schema exists', () => {
+			dataSchema.register( {
+				view: 'xyz',
+				model: 'htmlXyz',
+				allowChildren: 'not-exists',
+				schema: {
+					inheritAllFrom: '$htmlBlock'
+				}
+			} );
 
-	it( 'should extend allowed children only if specified model schema exists', () => {
-		dataSchema.register( {
-			view: 'xyz',
-			model: 'htmlXyz',
-			allowChildren: 'not-exists',
-			schema: {
-				inheritAllFrom: '$htmlBlock'
-			}
+			expect( () => {
+				dataFilter.allowElement( { name: 'xyz' } );
+			} ).to.not.throw();
 		} );
 
-		expect( () => {
-			dataFilter.allowElement( { name: 'xyz' } );
-		} ).to.not.throw();
-	} );
-
-	it( 'should not consume attribute already consumed (upcast)', () => {
-		editor.conversion.for( 'upcast' ).add( dispatcher => {
-			dispatcher.on( 'element:section', ( evt, data, conversionApi ) => {
-				conversionApi.consumable.consume( data.viewItem, { attributes: [ 'data-foo' ] } );
+		it( 'should not consume attribute already consumed (upcast)', () => {
+			editor.conversion.for( 'upcast' ).add( dispatcher => {
+				dispatcher.on( 'element:section', ( evt, data, conversionApi ) => {
+					conversionApi.consumable.consume( data.viewItem, { attributes: [ 'data-foo' ] } );
+				} );
 			} );
-		} );
 
-		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': true } } );
+			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': true } } );
 
-		editor.setData( '<section data-foo><p>foo</p></section>' );
-
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<htmlSection><paragraph>foo</paragraph></htmlSection>',
-			attributes: {}
-		} );
+			editor.setData( '<section data-foo><p>foo</p></section>' );
 
-		expect( editor.getData() ).to.equal( '<section><p>foo</p></section>' );
-	} );
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<htmlSection><paragraph>foo</paragraph></htmlSection>',
+				attributes: {}
+			} );
 
-	it( 'should not consume attribute already consumed (downcast)', () => {
-		editor.conversion.for( 'downcast' ).add( dispatcher => {
-			dispatcher.on( 'attribute:htmlAttributes:htmlSection', ( evt, data, conversionApi ) => {
-				conversionApi.consumable.consume( data.item, evt.name );
-			}, { priority: 'high' } );
+			expect( editor.getData() ).to.equal( '<section><p>foo</p></section>' );
 		} );
 
-		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': true } } );
+		it( 'should not consume attribute already consumed (downcast)', () => {
+			editor.conversion.for( 'downcast' ).add( dispatcher => {
+				dispatcher.on( 'attribute:htmlAttributes:htmlSection', ( evt, data, conversionApi ) => {
+					conversionApi.consumable.consume( data.item, evt.name );
+				}, { priority: 'high' } );
+			} );
+
+			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': true } } );
 
-		editor.setData( '<section data-foo><p>foo</p></section>' );
+			editor.setData( '<section data-foo><p>foo</p></section>' );
 
-		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-			data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>',
-			// At this point, attribute should still be in the model, as we are testing downcast conversion.
-			attributes: {
-				1: {
-					attributes: {
-						'data-foo': ''
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>',
+				// At this point, attribute should still be in the model, as we are testing downcast conversion.
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': ''
+						}
 					}
 				}
-			}
+			} );
+
+			expect( editor.getData() ).to.equal( '<section><p>foo</p></section>' );
 		} );
+	} );
+
+	describe( 'inline', () => {
+		it( 'should allow element', () => {
+			dataFilter.allowElement( { name: 'cite' } );
 
-		expect( editor.getData() ).to.equal( '<section><p>foo</p></section>' );
+			editor.setData( '<p><cite>foobar</cite></p>' );
+
+			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
+				'<paragraph><$text htmlCite="(1)">foobar</$text></paragraph>'
+			);
+
+			expect( editor.getData() ).to.equal( '<p><cite>foobar</cite></p>' );
+		} );
 	} );
 
 	function getModelDataWithAttributes( model, options ) {
 		// Simplify GHS attributes as they are not very readable at this point due to object structure.
 		let counter = 1;
-		const data = getModelData( model, options ).replace( /htmlAttributes="{(.*?)}"/g, () => {
-			return `htmlAttributes="(${ counter++ })"`;
+		const data = getModelData( model, options ).replace( /(html.*?)="{.*?}"/g, ( fullMatch, attributeName ) => {
+			return `${ attributeName }="(${ counter++ })"`;
 		} );
 
 		const range = model.createRangeIn( model.document.getRoot() );
 
 		let attributes = [];
 		for ( const item of range.getItems() ) {
-			if ( item.hasAttribute && item.hasAttribute( 'htmlAttributes' ) ) {
-				attributes.push( item.getAttribute( 'htmlAttributes' ) );
+			for ( const [ key, value ] of item.getAttributes() ) {
+				if ( key.startsWith( 'html' ) ) {
+					attributes.push( value );
+				}
 			}
 		}
 

From a7f17a8af595ea967a74b66c00540358a2b2123a Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 15 Mar 2021 13:06:53 +0100
Subject: [PATCH 066/217] Added tests, improved element nesting.

---
 .../src/datafilter.js                         |  18 +-
 .../tests/datafilter.js                       | 280 +++++++++++++++++-
 .../tests/manual/generalhtmlsupport.html      |   4 +
 3 files changed, 298 insertions(+), 4 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 507f4c58cc5..3fc885377f3 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -75,6 +75,15 @@ export default class DataFilter {
 		 * @member {Map.<String, module:engine/view/matcher~Matcher>} #_disallowedAttributes
 		 */
 		this._disallowedAttributes = new Map();
+
+		/**
+		 * A set of inline elements which should not be preserved during conversion if
+		 * they are missing attributes.
+		 *
+		 * @readonly
+		 * @member {Set.<String>} #transparentElements
+		 */
+		this.transparentElements = new Set( [ 'span' ] );
 	}
 
 	/**
@@ -211,6 +220,11 @@ export default class DataFilter {
 			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
 				const viewAttributes = this._matchAndConsumeAttributes( data.viewItem, conversionApi );
 
+				// Skip information about transparent element type if there is no attribute to convert.
+				if ( !viewAttributes && this.transparentElements.has( viewName ) ) {
+					return;
+				}
+
 				// Convert children and set conversion result as a current data.
 				data = Object.assign( data, conversionApi.convertChildren( data.viewItem, data.modelCursor ) );
 
@@ -219,7 +233,9 @@ export default class DataFilter {
 					if ( conversionApi.schema.checkAttribute( node, attributeKey ) ) {
 						// Node's children are converter recursively, so node can already include model attribute.
 						// We want to extend it, not replace.
-						const attributesToAdd = mergeAttributes( node.getAttribute( attributeKey ), viewAttributes );
+						const nodeAttributes = node.getAttribute( attributeKey );
+						const attributesToAdd = mergeAttributes( nodeAttributes, viewAttributes || {} );
+
 						conversionApi.writer.setAttribute( attributeKey, attributesToAdd, node );
 					}
 				}
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index b73188a74cd..476cbe8e50c 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -383,12 +383,267 @@ describe( 'DataFilter', () => {
 
 			editor.setData( '<p><cite>foobar</cite></p>' );
 
-			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
-				'<paragraph><$text htmlCite="(1)">foobar</$text></paragraph>'
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlCite="(1)">foobar</$text></paragraph>',
+				attributes: {
+					1: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><cite>foobar</cite></p>' );
+		} );
+
+		it( 'should allow deeply nested structure', () => {
+			dataFilter.allowElement( { name: 'cite' } );
+
+			editor.setData( '<p><cite>foo<cite>bar<cite>baz</cite></cite></cite>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlCite="(1)">foobarbaz</$text></paragraph>',
+				attributes: {
+					1: {},
+					2: {},
+					3: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><cite>foobarbaz</cite></p>' );
+		} );
+
+		it( 'should allow attributes', () => {
+			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowAttributes( {
+				name: 'cite',
+				attributes: {
+					'data-foo': 'foobar'
+				}
+			} );
+
+			editor.setData( '<p><cite data-foo="foobar">foobar</cite></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlCite="(1)">foobar</$text></paragraph>',
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': 'foobar'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><cite data-foo="foobar">foobar</cite></p>' );
+		} );
+
+		it( 'should allow attributes (styles)', () => {
+			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowAttributes( {
+				name: 'cite',
+				styles: {
+					'color': 'red',
+					'background-color': 'blue'
+				}
+			} );
+
+			editor.setData( '<p><cite style="background-color:blue;color:red;">foobar</cite></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlCite="(1)">foobar</$text></paragraph>',
+				attributes: {
+					1: {
+						styles: {
+							'background-color': 'blue',
+							color: 'red'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p><cite style="background-color:blue;color:red;">foobar</cite></p>'
 			);
+		} );
+
+		it( 'should allow attributes (classes)', () => {
+			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowAttributes( { name: 'cite', classes: [ 'foo', 'bar' ] } );
+
+			editor.setData( '<p><cite class="foo bar">foobar</cite></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlCite="(1)">foobar</$text></paragraph>',
+				attributes: {
+					1: { classes: [ 'foo', 'bar' ] }
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><cite class="foo bar">foobar</cite></p>' );
+		} );
+
+		it( 'should allow nested attributes', () => {
+			dataFilter.allowElement( { name: /span|cite/ } );
+			dataFilter.allowAttributes( { name: /span|cite/, attributes: { 'data-foo': 'foo' } } );
+			dataFilter.allowAttributes( { name: /span|cite/, attributes: { 'data-bar': 'bar' } } );
+
+			editor.setData( '<p><cite data-foo="foo">' +
+					'<cite data-bar="bar">cite</cite>' +
+					'<span data-bar="bar">span</span>' +
+				'</cite></p>'
+			);
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+					'<$text htmlCite="(1)">cite</$text>' +
+					'<$text htmlCite="(2)" htmlSpan="(3)">span</$text>' +
+				'</paragraph>',
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': 'foo',
+							'data-bar': 'bar'
+						}
+					},
+					2: {
+						attributes: {
+							'data-foo': 'foo'
+						}
+					},
+					3: {
+						attributes: {
+							'data-bar': 'bar'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p>' +
+				'<cite data-bar="bar" data-foo="foo">cite</cite>' +
+				'<cite data-foo="foo"><span data-bar="bar">span</span></cite>' +
+				'</p>' );
+		} );
+
+		it( 'should disallow attributes', () => {
+			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowAttributes( { name: 'cite', attributes: { 'data-foo': /[\s\S]+/ } } );
+			dataFilter.disallowAttributes( { name: 'cite', attributes: { 'data-foo': 'bar' } } );
+
+			editor.setData( '<p><cite data-foo="foo">foo</cite><cite data-bar="bar">bar</cite></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlCite="(1)">foo</$text><$text htmlCite="(2)">bar</$text></paragraph>',
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': 'foo'
+						}
+					},
+					2: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><cite data-foo="foo">foo</cite><cite>bar</cite></p>' );
+		} );
+
+		it( 'should disallow attributes (styles)', () => {
+			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowAttributes( { name: 'cite', styles: { color: /[\s\S]+/ } } );
+			dataFilter.disallowAttributes( { name: 'cite', styles: { color: 'red' } } );
+
+			editor.setData(
+				'<p>' +
+				'<cite style="color:blue;">foo</cite>' +
+				'<cite style="color:red;">bar</cite>' +
+				'</p>'
+			);
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlCite="(1)">foo</$text><$text htmlCite="(2)">bar</$text></paragraph>',
+				attributes: {
+					1: {
+						styles: {
+							color: 'blue'
+						}
+					},
+					2: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p><cite style="color:blue;">foo</cite><cite>bar</cite></p>'
+			);
+		} );
+
+		it( 'should disallow attributes (classes)', () => {
+			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowAttributes( { name: 'cite', classes: [ 'foo', 'bar' ] } );
+			dataFilter.disallowAttributes( { name: 'cite', classes: [ 'bar' ] } );
+
+			editor.setData(
+				'<p>' +
+				'<cite class="foo bar">foo</cite>' +
+				'<cite class="bar">bar</cite>' +
+				'</p>'
+			);
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlCite="(1)">foobar</$text></paragraph>',
+				attributes: {
+					1: {},
+					2: {}
+				}
+			} );
 
 			expect( editor.getData() ).to.equal( '<p><cite>foobar</cite></p>' );
 		} );
+
+		it( 'should not consume attribute already consumed (upcast)', () => {
+			editor.conversion.for( 'upcast' ).add( dispatcher => {
+				dispatcher.on( 'element:cite', ( evt, data, conversionApi ) => {
+					conversionApi.consumable.consume( data.viewItem, { attributes: [ 'data-foo' ] } );
+				} );
+			} );
+
+			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowAttributes( { name: 'cite', attributes: { 'data-foo': true } } );
+
+			editor.setData( '<p><cite data-foo>foo</cite></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlCite="(1)">foo</$text></paragraph>',
+				attributes: {
+					1: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><cite>foo</cite></p>' );
+		} );
+
+		it( 'should not consume attribute already consumed (downcast)', () => {
+			editor.conversion.for( 'downcast' ).add( dispatcher => {
+				dispatcher.on( 'attribute:htmlCite:$text', ( evt, data, conversionApi ) => {
+					conversionApi.consumable.consume( data.item, evt.name );
+				}, { priority: 'high' } );
+			} );
+
+			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowAttributes( { name: 'cite', attributes: { 'data-foo': true } } );
+
+			editor.setData( '<p><cite data-foo>foo</cite></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlCite="(1)">foo</$text></paragraph>',
+				// At this point, attribute should still be in the model, as we are testing downcast conversion.
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': ''
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p>foo</p>' );
+		} );
 	} );
 
 	function getModelDataWithAttributes( model, options ) {
@@ -402,7 +657,7 @@ describe( 'DataFilter', () => {
 
 		let attributes = [];
 		for ( const item of range.getItems() ) {
-			for ( const [ key, value ] of item.getAttributes() ) {
+			for ( const [ key, value ] of sortAttributes( item.getAttributes() ) ) {
 				if ( key.startsWith( 'html' ) ) {
 					attributes.push( value );
 				}
@@ -416,4 +671,23 @@ describe( 'DataFilter', () => {
 
 		return { data, attributes };
 	}
+
+	function sortAttributes( attributes ) {
+		attributes = Array.from( attributes );
+
+		return attributes.sort( ( attr1, attr2 ) => {
+			const key1 = attr1[ 0 ];
+			const key2 = attr2[ 0 ];
+
+			if ( key1 > key2 ) {
+				return 1;
+			}
+
+			if ( key1 < key2 ) {
+				return -1;
+			}
+
+			return 0;
+		} );
+	}
 } );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
index 53c0ddafed3..a0ef6682e19 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -29,4 +29,8 @@
 	<p>
 		<span data-foo="foo">Nested span: <span style="color:blue;">I'm blue!</span></span>
 	</p>
+
+	<p><cite>Deeply<cite> nested<cite> cite<span style="color:blue;"> with span!</span></cite></cite></cite></p>
+
+	<p><span>Span with no attributes!</span></p>
 </div>

From 3d014e984af54e5dd17aeee4fe3dd862ac8c13be Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 15 Mar 2021 13:58:51 +0100
Subject: [PATCH 067/217] Added missing unit tests.

---
 .../tests/datafilter.js                       | 39 +++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 476cbe8e50c..bf7a69ba14c 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -644,6 +644,45 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal( '<p>foo</p>' );
 		} );
+
+		it( 'should not preserve span with no attributes', () => {
+			dataFilter.allowElement( { name: 'span' } );
+
+			editor.setData( '<p><span>foo</span></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>foo</paragraph>',
+				attributes: {}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p>foo</p>' );
+		} );
+
+		it( 'should correctly merge class names', () => {
+			dataFilter.allowElement( { name: 'span' } );
+			dataFilter.allowAttributes( { name: 'span', classes: /[\s\S]+/ } );
+
+			editor.setData( '<p><span class="foo">foo<span class="bar">bar<span class="baz">baz</span></span></span></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+						'<$text htmlSpan="(1)">foo</$text>' +
+						'<$text htmlSpan="(2)">bar</$text>' +
+						'<$text htmlSpan="(3)">baz</$text>' +
+					'</paragraph>',
+				attributes: {
+					1: {
+						classes: [ 'foo' ]
+					},
+					2: {
+						classes: [ 'bar', 'foo' ]
+					},
+					3: {
+						classes: [ 'baz', 'bar', 'foo' ]
+					}
+				}
+			} );
+		} );
 	} );
 
 	function getModelDataWithAttributes( model, options ) {

From d4ba2d0a0b8cc90b0e86dfa012c6319952bea814 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 15 Mar 2021 14:05:32 +0100
Subject: [PATCH 068/217] Docs corrections.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 3fc885377f3..12a1c4bf7d0 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -378,7 +378,6 @@ export default class DataFilter {
 // @param {module:engine/view/downcastwriter~DowncastWriter} writer
 // @param {Object} viewAttributes
 // @param {module:engine/view/element~Element} viewElement
-// on all elements in the range.
 function setAttributesOn( writer, viewAttributes, viewElement ) {
 	if ( viewAttributes.attributes ) {
 		for ( const [ key, value ] of Object.entries( viewAttributes.attributes ) ) {
@@ -476,8 +475,10 @@ function mergeAttributes( oldValue, newValue ) {
 	const result = cloneDeep( newValue );
 
 	for ( const key in oldValue ) {
+		// Merge classes.
 		if ( Array.isArray( oldValue[ key ] ) ) {
 			result[ key ] = uniq( [ ...oldValue[ key ], ...newValue[ key ] ] );
+		// Merge attributes or styles.
 		} else {
 			result[ key ] = Object.assign( {}, oldValue[ key ], newValue[ key ] );
 		}

From 142d013bb00292eee8354571eca0d4b7c4e388d6 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 15 Mar 2021 15:07:21 +0100
Subject: [PATCH 069/217] Corrected attributes merging order.

---
 .../src/datafilter.js                         |  8 +++----
 .../tests/datafilter.js                       | 24 ++++++++++++++++---
 .../tests/manual/generalhtmlsupport.js        |  2 +-
 3 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 12a1c4bf7d0..52d05adf166 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -234,7 +234,7 @@ export default class DataFilter {
 						// Node's children are converter recursively, so node can already include model attribute.
 						// We want to extend it, not replace.
 						const nodeAttributes = node.getAttribute( attributeKey );
-						const attributesToAdd = mergeAttributes( nodeAttributes, viewAttributes || {} );
+						const attributesToAdd = mergeAttributes( viewAttributes || {}, nodeAttributes || {} );
 
 						conversionApi.writer.setAttribute( attributeKey, attributesToAdd, node );
 					}
@@ -472,11 +472,11 @@ function iterableToObject( iterable, getValue ) {
 // @param {Object} newValue
 // @returns {Object}
 function mergeAttributes( oldValue, newValue ) {
-	const result = cloneDeep( newValue );
+	const result = cloneDeep( oldValue );
 
-	for ( const key in oldValue ) {
+	for ( const key in newValue ) {
 		// Merge classes.
-		if ( Array.isArray( oldValue[ key ] ) ) {
+		if ( Array.isArray( newValue[ key ] ) ) {
 			result[ key ] = uniq( [ ...oldValue[ key ], ...newValue[ key ] ] );
 		// Merge attributes or styles.
 		} else {
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index bf7a69ba14c..5435403008a 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -517,7 +517,7 @@ describe( 'DataFilter', () => {
 			} );
 
 			expect( editor.getData() ).to.equal( '<p>' +
-				'<cite data-bar="bar" data-foo="foo">cite</cite>' +
+				'<cite data-foo="foo" data-bar="bar">cite</cite>' +
 				'<cite data-foo="foo"><span data-bar="bar">span</span></cite>' +
 				'</p>' );
 		} );
@@ -675,16 +675,34 @@ describe( 'DataFilter', () => {
 						classes: [ 'foo' ]
 					},
 					2: {
-						classes: [ 'bar', 'foo' ]
+						classes: [ 'foo', 'bar' ]
 					},
 					3: {
-						classes: [ 'baz', 'bar', 'foo' ]
+						classes: [ 'foo', 'bar', 'baz' ]
 					}
 				}
 			} );
 		} );
 	} );
 
+	it( 'should correctly resolve attributes nesting order', () => {
+		dataFilter.allowElement( { name: 'span' } );
+		dataFilter.allowAttributes( { name: 'span', styles: { color: /[\s\S]+/ } } );
+
+		editor.setData( '<p><span style="color:red;"><span style="color:blue;">foobar</span></span>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<paragraph><$text htmlSpan="(1)">foobar</$text></paragraph>',
+			attributes: {
+				1: {
+					styles: { color: 'blue' }
+				}
+			}
+		} );
+
+		expect( editor.getData() ).to.equal( '<p><span style="color:blue;">foobar</span></p>' );
+	} );
+
 	function getModelDataWithAttributes( model, options ) {
 		// Simplify GHS attributes as they are not very readable at this point due to object structure.
 		let counter = 1;
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 3a1f9987860..97b637efad3 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -64,7 +64,7 @@ class ExtendHTMLSupport extends Plugin {
 		dataFilter.allowElement( { name: /^span|cite$/ } );
 		dataFilter.allowAttributes( { name: /^span|cite$/, attributes: { 'data-foo': /[\s\S]+/ } } );
 		dataFilter.allowAttributes( { name: /^span|cite$/, styles: { color: /[\s\S]+/ } } );
-		dataFilter.disallowAttributes( { name: /^span|cite$/, styles: { color: 'red' } } );
+		// dataFilter.disallowAttributes( { name: /^span|cite$/, styles: { color: 'red' } } );
 	}
 }
 

From 91fc98c2aab5fb0c2f6e19b49336283edc941a68 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 15 Mar 2021 15:12:04 +0100
Subject: [PATCH 070/217] Manual test fixes.

---
 .../tests/manual/generalhtmlsupport.html                        | 2 ++
 .../tests/manual/generalhtmlsupport.js                          | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
index a0ef6682e19..e64de28457f 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -33,4 +33,6 @@
 	<p><cite>Deeply<cite> nested<cite> cite<span style="color:blue;"> with span!</span></cite></cite></cite></p>
 
 	<p><span>Span with no attributes!</span></p>
+
+	<p><span style="color:blue;"><span style="color:green;">Span with nested styles!</span></span></p>
 </div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 97b637efad3..3a1f9987860 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -64,7 +64,7 @@ class ExtendHTMLSupport extends Plugin {
 		dataFilter.allowElement( { name: /^span|cite$/ } );
 		dataFilter.allowAttributes( { name: /^span|cite$/, attributes: { 'data-foo': /[\s\S]+/ } } );
 		dataFilter.allowAttributes( { name: /^span|cite$/, styles: { color: /[\s\S]+/ } } );
-		// dataFilter.disallowAttributes( { name: /^span|cite$/, styles: { color: 'red' } } );
+		dataFilter.disallowAttributes( { name: /^span|cite$/, styles: { color: 'red' } } );
 	}
 }
 

From 7e2ed81f4b083618cfee77770e6b6de155fb32a3 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 15 Mar 2021 15:17:54 +0100
Subject: [PATCH 071/217] Favor Set over uniq.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 52d05adf166..0ce68e4fd3c 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -10,7 +10,7 @@
 import { Matcher } from 'ckeditor5/src/engine';
 import { priorities, toArray } from 'ckeditor5/src/utils';
 
-import { cloneDeep, uniq } from 'lodash-es';
+import { cloneDeep } from 'lodash-es';
 
 const DATA_SCHEMA_ATTRIBUTE_KEY = 'htmlAttributes';
 
@@ -477,7 +477,7 @@ function mergeAttributes( oldValue, newValue ) {
 	for ( const key in newValue ) {
 		// Merge classes.
 		if ( Array.isArray( newValue[ key ] ) ) {
-			result[ key ] = uniq( [ ...oldValue[ key ], ...newValue[ key ] ] );
+			result[ key ] = Array.from( new Set( [ ...oldValue[ key ], ...newValue[ key ] ] ) );
 		// Merge attributes or styles.
 		} else {
 			result[ key ] = Object.assign( {}, oldValue[ key ], newValue[ key ] );

From 0a7fe46ab305d52f8b3b4e845324fb6bd3b49716 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 16 Mar 2021 13:30:49 +0100
Subject: [PATCH 072/217] Removed 'transparent' elements.

---
 .../src/datafilter.js                              | 14 --------------
 .../tests/datafilter.js                            | 13 -------------
 2 files changed, 27 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 0ce68e4fd3c..10aaf72be43 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -75,15 +75,6 @@ export default class DataFilter {
 		 * @member {Map.<String, module:engine/view/matcher~Matcher>} #_disallowedAttributes
 		 */
 		this._disallowedAttributes = new Map();
-
-		/**
-		 * A set of inline elements which should not be preserved during conversion if
-		 * they are missing attributes.
-		 *
-		 * @readonly
-		 * @member {Set.<String>} #transparentElements
-		 */
-		this.transparentElements = new Set( [ 'span' ] );
 	}
 
 	/**
@@ -220,11 +211,6 @@ export default class DataFilter {
 			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
 				const viewAttributes = this._matchAndConsumeAttributes( data.viewItem, conversionApi );
 
-				// Skip information about transparent element type if there is no attribute to convert.
-				if ( !viewAttributes && this.transparentElements.has( viewName ) ) {
-					return;
-				}
-
 				// Convert children and set conversion result as a current data.
 				data = Object.assign( data, conversionApi.convertChildren( data.viewItem, data.modelCursor ) );
 
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 5435403008a..6a02616b2fb 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -645,19 +645,6 @@ describe( 'DataFilter', () => {
 			expect( editor.getData() ).to.equal( '<p>foo</p>' );
 		} );
 
-		it( 'should not preserve span with no attributes', () => {
-			dataFilter.allowElement( { name: 'span' } );
-
-			editor.setData( '<p><span>foo</span></p>' );
-
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph>foo</paragraph>',
-				attributes: {}
-			} );
-
-			expect( editor.getData() ).to.equal( '<p>foo</p>' );
-		} );
-
 		it( 'should correctly merge class names', () => {
 			dataFilter.allowElement( { name: 'span' } );
 			dataFilter.allowAttributes( { name: 'span', classes: /[\s\S]+/ } );

From 87bea0954be466bffbbe8feb32ef3d1d96ba9d0f Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 16 Mar 2021 14:02:52 +0100
Subject: [PATCH 073/217] Corrected regexpes.

---
 .../tests/datafilter.js                            | 14 +++++++-------
 .../tests/manual/generalhtmlsupport.js             | 12 ++++++------
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 6a02616b2fb..13e958098d5 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -168,7 +168,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow nested attributes', () => {
-			dataFilter.allowElement( { name: /article|section/ } );
+			dataFilter.allowElement( { name: /^(article|section)$/ } );
 			dataFilter.allowAttributes( { name: /[\s\S]+/, attributes: { 'data-foo': /foo|bar/ } } );
 
 			editor.setData( '<article data-foo="foo">' +
@@ -203,10 +203,10 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow attributes for all allowed definitions', () => {
-			dataFilter.allowElement( { name: /section|article/ } );
+			dataFilter.allowElement( { name: /^(section|article)$/ } );
 
-			dataFilter.allowAttributes( { name: /section|article/, attributes: { 'data-foo': 'foo' } } );
-			dataFilter.allowAttributes( { name: /section|article/, attributes: { 'data-bar': 'bar' } } );
+			dataFilter.allowAttributes( { name: /^(section|article)$/, attributes: { 'data-foo': 'foo' } } );
+			dataFilter.allowAttributes( { name: /^(section|article)$/, attributes: { 'data-bar': 'bar' } } );
 
 			editor.setData(
 				'<section data-foo="foo"><p>foo</p></section>' +
@@ -481,9 +481,9 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow nested attributes', () => {
-			dataFilter.allowElement( { name: /span|cite/ } );
-			dataFilter.allowAttributes( { name: /span|cite/, attributes: { 'data-foo': 'foo' } } );
-			dataFilter.allowAttributes( { name: /span|cite/, attributes: { 'data-bar': 'bar' } } );
+			dataFilter.allowElement( { name: /^(span|cite)$/ } );
+			dataFilter.allowAttributes( { name: /^(span|cite)$/, attributes: { 'data-foo': 'foo' } } );
+			dataFilter.allowAttributes( { name: /^(span|cite)$/, attributes: { 'data-bar': 'bar' } } );
 
 			editor.setData( '<p><cite data-foo="foo">' +
 					'<cite data-bar="bar">cite</cite>' +
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 3a1f9987860..2a97c2ddb78 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -47,8 +47,8 @@ class ExtendHTMLSupport extends Plugin {
 		// e.g. article -> ghsArticle
 		dataFilter.allowElement( { name: 'article' } );
 		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowElement( { name: /^details|summary$/ } );
-		dataFilter.allowElement( { name: /^dl|dd|dt$/ } );
+		dataFilter.allowElement( { name: /^(details|summary)$/ } );
+		dataFilter.allowElement( { name: /^(dl|dd|dt)$/ } );
 		dataFilter.allowElement( { name: 'xyz' } );
 
 		// Let's extend 'section' with some attributes. Data filter will take care of
@@ -61,10 +61,10 @@ class ExtendHTMLSupport extends Plugin {
 		dataFilter.disallowAttributes( { name: 'section', attributes: { id: /^_.*/ } } );
 
 		// Let's also add some inline elements support:
-		dataFilter.allowElement( { name: /^span|cite$/ } );
-		dataFilter.allowAttributes( { name: /^span|cite$/, attributes: { 'data-foo': /[\s\S]+/ } } );
-		dataFilter.allowAttributes( { name: /^span|cite$/, styles: { color: /[\s\S]+/ } } );
-		dataFilter.disallowAttributes( { name: /^span|cite$/, styles: { color: 'red' } } );
+		dataFilter.allowElement( { name: /^(span|cite)$/ } );
+		dataFilter.allowAttributes( { name: /^(span|cite)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
+		dataFilter.allowAttributes( { name: /^(span|cite)$/, styles: { color: /[\s\S]+/ } } );
+		dataFilter.disallowAttributes( { name: /^(span|cite)$/, styles: { color: 'red' } } );
 	}
 }
 

From 7f1d7d8c79b2322eff6c087d3629d6cfb03bd172 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 16 Mar 2021 15:12:46 +0100
Subject: [PATCH 074/217] Fixed converter to include passed model range.

---
 .../package.json                              |  1 +
 .../src/datafilter.js                         |  7 ++-
 .../tests/datafilter.js                       | 63 ++++++++++++++++---
 3 files changed, 60 insertions(+), 11 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/package.json b/packages/ckeditor5-content-compatibility/package.json
index b175869e6b6..05c00a34771 100644
--- a/packages/ckeditor5-content-compatibility/package.json
+++ b/packages/ckeditor5-content-compatibility/package.json
@@ -25,6 +25,7 @@
     "@ckeditor/ckeditor5-editor-classic": "^27.0.0",
     "@ckeditor/ckeditor5-engine": "^27.0.0",
     "@ckeditor/ckeditor5-essentials": "^27.0.0",
+    "@ckeditor/ckeditor5-font": "^27.0.0",
     "@ckeditor/ckeditor5-list": "^27.0.0",
     "@ckeditor/ckeditor5-paragraph": "^27.0.0",
     "webpack": "^4.43.0",
diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 10aaf72be43..9ee2997ff15 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -211,8 +211,11 @@ export default class DataFilter {
 			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
 				const viewAttributes = this._matchAndConsumeAttributes( data.viewItem, conversionApi );
 
-				// Convert children and set conversion result as a current data.
-				data = Object.assign( data, conversionApi.convertChildren( data.viewItem, data.modelCursor ) );
+				// Since we are converting to attribute we need an range on which we will set the attribute.
+				// If the range is not created yet, we will create it.
+				if ( !data.modelRange ) {
+					data = Object.assign( data, conversionApi.convertChildren( data.viewItem, data.modelCursor ) );
+				}
 
 				// Set attribute on each item in range according to Schema.
 				for ( const node of data.modelRange.getItems() ) {
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 13e958098d5..95449d2a45c 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -3,20 +3,26 @@
  * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
  */
 
-import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
+/* global document */
+
+import ClassicTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/classictesteditor';
 import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
+import Font from '@ckeditor/ckeditor5-font/src/font';
 import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
 
 import DataSchema from '../src/dataschema';
 import DataFilter from '../src/datafilter';
 
 describe( 'DataFilter', () => {
-	let editor, model, dataFilter, dataSchema;
+	let editor, model, dataFilter, dataSchema, element;
 
 	beforeEach( () => {
-		return VirtualTestEditor
-			.create( {
-				plugins: [ Paragraph ]
+		element = document.createElement( 'div' );
+		document.body.appendChild( element );
+
+		return ClassicTestEditor
+			.create( element, {
+				plugins: [ Paragraph, Font ]
 			} )
 			.then( newEditor => {
 				editor = newEditor;
@@ -28,6 +34,8 @@ describe( 'DataFilter', () => {
 	} );
 
 	afterEach( () => {
+		element.remove();
+
 		return editor.destroy();
 	} );
 
@@ -674,20 +682,57 @@ describe( 'DataFilter', () => {
 
 	it( 'should correctly resolve attributes nesting order', () => {
 		dataFilter.allowElement( { name: 'span' } );
-		dataFilter.allowAttributes( { name: 'span', styles: { color: /[\s\S]+/ } } );
+		dataFilter.allowAttributes( { name: 'span', styles: { 'font-weight': /[\s\S]+/ } } );
 
-		editor.setData( '<p><span style="color:red;"><span style="color:blue;">foobar</span></span>' );
+		editor.setData( '<p><span style="font-weight:700;"><span style="font-weight:400;">foobar</span></span>' );
 
 		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 			data: '<paragraph><$text htmlSpan="(1)">foobar</$text></paragraph>',
 			attributes: {
 				1: {
-					styles: { color: 'blue' }
+					styles: { 'font-weight': '400' }
+				}
+			}
+		} );
+
+		expect( editor.getData() ).to.equal( '<p><span style="font-weight:400;">foobar</span></p>' );
+	} );
+
+	it( 'should allow using attributes by other features', () => {
+		dataFilter.allowElement( { name: 'span' } );
+		dataFilter.allowAttributes( { name: 'span', styles: { 'color': /[\s\S]+/ } } );
+
+		editor.setData( '<p><span style="color:blue;">foobar</span></p>' );
+
+		// Font feature should take over color CSS property.
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<paragraph><$text fontColor="blue" htmlSpan="(1)">foobar</$text></paragraph>',
+			attributes: {
+				1: {}
+			}
+		} );
+
+		expect( editor.getData() ).to.equal( '<p><span style="color:blue;"><span>foobar</span></span></p>' );
+	} );
+
+	it( 'should preserve attributes not used by other features', () => {
+		dataFilter.allowElement( { name: 'span' } );
+		dataFilter.allowAttributes( { name: 'span', styles: { 'color': /[\s\S]+/ } } );
+		dataFilter.allowAttributes( { name: 'span', classes: [ 'foo', 'bar' ] } );
+
+		editor.setData( '<p><span style="color:blue;" class="foo bar">foobar</span></p>' );
+
+		// Font feature should take over color CSS property.
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<paragraph><$text fontColor="blue" htmlSpan="(1)">foobar</$text></paragraph>',
+			attributes: {
+				1: {
+					classes: [ 'foo', 'bar' ]
 				}
 			}
 		} );
 
-		expect( editor.getData() ).to.equal( '<p><span style="color:blue;">foobar</span></p>' );
+		expect( editor.getData() ).to.equal( '<p><span style="color:blue;"><span class="foo bar">foobar</span></span></p>' );
 	} );
 
 	function getModelDataWithAttributes( model, options ) {

From 11e15e16bd1c614b81e3572a140c20dcd0640ef8 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 16 Mar 2021 15:52:53 +0100
Subject: [PATCH 075/217] Splitted schema register method into inline and block
 elements.

---
 .../src/datafilter.js                         |  33 ++-
 .../src/dataschema.js                         |  72 +++---
 .../tests/datafilter.js                       |   2 +-
 .../tests/dataschema.js                       | 215 ++++++++++--------
 4 files changed, 187 insertions(+), 135 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 9ee2997ff15..c8ee6e726d6 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -8,7 +8,7 @@
  */
 
 import { Matcher } from 'ckeditor5/src/engine';
-import { priorities, toArray } from 'ckeditor5/src/utils';
+import { priorities, toArray, CKEditorError } from 'ckeditor5/src/utils';
 
 import { cloneDeep } from 'lodash-es';
 
@@ -130,19 +130,32 @@ export default class DataFilter {
 
 	/**
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
+	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
 	_registerElement( definition ) {
 		if ( definition.isInline ) {
 			this._defineInlineElement( definition );
-		} else {
+		} else if ( definition.isBlock ) {
 			this._defineBlockElement( definition );
+		} else {
+			/**
+			 * Only a definition marked as inline or block can be allowed.
+			 *
+			 * @error data-filter-invalid-definition-type
+			 */
+			throw new CKEditorError(
+				'data-filter-invalid-definition-type',
+				null,
+				{ definition }
+			);
 		}
 	}
 
 	/**
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
+	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
 	_defineBlockElement( definition ) {
 		if ( this.editor.model.schema.isRegistered( definition.model ) ) {
@@ -160,7 +173,8 @@ export default class DataFilter {
 
 	/**
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
+	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
 	_defineInlineElement( definition ) {
 		const schema = this.editor.model.schema;
@@ -178,7 +192,8 @@ export default class DataFilter {
 
 	/**
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
+	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
 	_defineSchema( definition ) {
 		const schema = this.editor.model.schema;
@@ -198,7 +213,8 @@ export default class DataFilter {
 
 	/**
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
+	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
 	_defineInlineElementConverters( definition ) {
 		const conversion = this.editor.conversion;
@@ -252,7 +268,8 @@ export default class DataFilter {
 
 	/**
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition}
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
+	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
 	_defineBlockElementConverters( definition ) {
 		const conversion = this.editor.conversion;
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 969bd7936eb..d50bab59809 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -30,12 +30,12 @@ export default class DataSchema {
 		 *
 		 * @readonly
 		 * @private
-		 * @member {Map.<String, module:content-compatibility/dataschema~DataSchemaDefinition>} #_definitions
+		 * @member {Map.<String, module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
+		 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition>} #_definitions
 		 */
 		this._definitions = new Map();
 
-		// Add block elements.
-		this.register( {
+		this.registerBlockElement( {
 			model: '$htmlBlock',
 			allowChildren: '$block',
 			schema: {
@@ -44,7 +44,7 @@ export default class DataSchema {
 			}
 		} );
 
-		this.register( {
+		this.registerBlockElement( {
 			view: 'article',
 			model: 'htmlArticle',
 			schema: {
@@ -52,7 +52,7 @@ export default class DataSchema {
 			}
 		} );
 
-		this.register( {
+		this.registerBlockElement( {
 			view: 'section',
 			model: 'htmlSection',
 			schema: {
@@ -61,7 +61,7 @@ export default class DataSchema {
 		} );
 
 		// Add data list elements.
-		this.register( {
+		this.registerBlockElement( {
 			view: 'dl',
 			model: 'htmlDl',
 			schema: {
@@ -70,7 +70,7 @@ export default class DataSchema {
 			}
 		} );
 
-		this.register( {
+		this.registerBlockElement( {
 			model: '$htmlDatalist',
 			allowChildren: '$block',
 			schema: {
@@ -79,7 +79,7 @@ export default class DataSchema {
 			}
 		} );
 
-		this.register( {
+		this.registerBlockElement( {
 			view: 'dt',
 			model: 'htmlDt',
 			schema: {
@@ -87,7 +87,7 @@ export default class DataSchema {
 			}
 		} );
 
-		this.register( {
+		this.registerBlockElement( {
 			view: 'dd',
 			model: 'htmlDd',
 			schema: {
@@ -96,7 +96,7 @@ export default class DataSchema {
 		} );
 
 		// Add details elements.
-		this.register( {
+		this.registerBlockElement( {
 			view: 'details',
 			model: 'htmlDetails',
 			schema: {
@@ -104,7 +104,7 @@ export default class DataSchema {
 			}
 		} );
 
-		this.register( {
+		this.registerBlockElement( {
 			view: 'summary',
 			model: 'htmlSummary',
 			allowChildren: '$text',
@@ -113,27 +113,33 @@ export default class DataSchema {
 			}
 		} );
 
-		// Add inline elements.
-		this.register( {
+		this.registerInlineElement( {
 			view: 'span',
-			model: 'htmlSpan',
-			isInline: true
+			model: 'htmlSpan'
 		} );
 
-		this.register( {
+		this.registerInlineElement( {
 			view: 'cite',
-			model: 'htmlCite',
-			isInline: true
+			model: 'htmlCite'
 		} );
 	}
 
 	/**
-	 * Add new data schema definition.
+	 * Add new data schema definition for block element.
 	 *
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
-	register( definition ) {
-		this._definitions.set( definition.model, definition );
+	registerBlockElement( definition ) {
+		this._definitions.set( definition.model, { ...definition, isBlock: true } );
+	}
+
+	/**
+	 * Add new data schema definition for inline element.
+	 *
+	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 */
+	registerInlineElement( definition ) {
+		this._definitions.set( definition.model, { ...definition, isInline: true } );
 	}
 
 	/**
@@ -141,7 +147,8 @@ export default class DataSchema {
 	 *
 	 * @param {String|RegExp} viewName
 	 * @param {Boolean} [includeReferences] Indicates if this method should also include definitions of referenced models.
-	 * @returns {Set.<module:content-compatibility/dataschema~DataSchemaDefinition>}
+	 * @returns {Set.<module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
+	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition>}
 	 */
 	getDefinitionsForView( viewName, includeReferences ) {
 		const definitions = new Set();
@@ -164,7 +171,8 @@ export default class DataSchema {
 	 *
 	 * @private
 	 * @param {String|RegExp} viewName
-	 * @returns {Array.<module:content-compatibility/dataschema~DataSchemaDefinition>}
+	 * @returns {Array.<module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
+	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition>}
 	 */
 	_getMatchingViewDefinitions( viewName ) {
 		return Array.from( this._definitions.values() )
@@ -176,7 +184,8 @@ export default class DataSchema {
 	 *
 	 * @private
 	 * @param {String} modelName Data schema model name.
-	 * @returns {Iterable.<module:content-compatibility/dataschema~DataSchemaDefinition>}
+	 * @returns {Iterable.<module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
+	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition>}
 	 */
 	* _getReferences( modelName ) {
 		const { schema } = this._definitions.get( modelName );
@@ -219,12 +228,19 @@ function testViewName( pattern, viewName ) {
 }
 
 /**
- * A definition of {@link module:content-compatibility/dataschema~DataSchema data schema}.
+ * A definition of {@link module:content-compatibility/dataschema~DataSchema data schema} for block elements.
  *
- * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
+ * @typedef {Object} module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
  * @property {String} [view] Name of the view element.
  * @property {String} model Name of the model element.
  * @property {module:engine/model/schema~SchemaItemDefinition} schema The model schema item definition describing registered model.
  * @property {String|Array.<String>} [allowChildren] Extends the given children list to allow definition model.
- * @property {Boolean} [isInline] Indicates if the element decribed by data schema definition is inline.
+ */
+
+/**
+ * A definition of {@link module:content-compatibility/dataschema~DataSchema data schema} for inline elements.
+ *
+ * @typedef {Object} module:content-compatibility/dataschema~DataSchemaInlineElementDefinition
+ * @property {String} view Name of the view element.
+ * @property {String} model Name of the model attribute key.
  */
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 95449d2a45c..7e65ff45baf 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -323,7 +323,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should extend allowed children only if specified model schema exists', () => {
-			dataSchema.register( {
+			dataSchema.registerBlockElement( {
 				view: 'xyz',
 				model: 'htmlXyz',
 				allowChildren: 'not-exists',
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index 60ce0843d24..adc0623ad57 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -9,52 +9,6 @@ import DataSchema from '../src/dataschema';
 describe( 'DataSchema', () => {
 	let editor, dataSchema;
 
-	const fakeDefinitions = [
-		{
-			view: 'def1',
-			model: 'htmlDef1',
-			allowChildren: [ 'htmlDef2', 'htmlDef3' ],
-			schema: {
-				inheritAllFrom: '$block'
-			}
-		},
-		{
-			view: 'def2',
-			model: 'htmlDef2',
-			schema: {
-				inheritAllFrom: 'htmlDef1'
-			}
-		},
-		{
-			view: 'def3',
-			model: 'htmlDef3',
-			schema: {
-				inheritTypesFrom: 'htmlDef2'
-			}
-		},
-		{
-			view: 'def4',
-			model: 'htmlDef4',
-			schema: {
-				allowWhere: 'htmlDef3'
-			}
-		},
-		{
-			view: 'def5',
-			model: 'htmlDef5',
-			schema: {
-				allowContentOf: 'htmlDef4'
-			}
-		},
-		{
-			view: 'def6',
-			model: 'htmlDef6',
-			schema: {
-				allowAttributesOf: 'htmlDef5'
-			}
-		}
-	];
-
 	beforeEach( () => {
 		return VirtualTestEditor
 			.create()
@@ -69,85 +23,150 @@ describe( 'DataSchema', () => {
 		return editor.destroy();
 	} );
 
-	it( 'should allow registering schema with proper definition', () => {
-		const definitions = getFakeDefinitions( 'def1' );
-
-		dataSchema.register( definitions[ 0 ] );
+	describe( 'registerInlineElement', () => {
+		it( 'should register proper definition', () => {
+			dataSchema.registerInlineElement( { model: 'htmlDef', view: 'def' } );
 
-		const result = dataSchema.getDefinitionsForView( 'def1' );
+			const result = dataSchema.getDefinitionsForView( 'def' );
 
-		expect( Array.from( result ) ).to.deep.equal( definitions );
+			expect( Array.from( result ) ).to.deep.equal( [ {
+				model: 'htmlDef',
+				view: 'def',
+				isInline: true
+			} ] );
+		} );
 	} );
 
-	it( 'should allow resolving definitions by view name (string)', () => {
-		registerMany( dataSchema, fakeDefinitions );
+	describe( 'registerBlockElement', () => {
+		const fakeDefinitions = [
+			{
+				view: 'def1',
+				model: 'htmlDef1',
+				allowChildren: [ 'htmlDef2', 'htmlDef3' ],
+				schema: {
+					inheritAllFrom: '$block'
+				}
+			},
+			{
+				view: 'def2',
+				model: 'htmlDef2',
+				schema: {
+					inheritAllFrom: 'htmlDef1'
+				}
+			},
+			{
+				view: 'def3',
+				model: 'htmlDef3',
+				schema: {
+					inheritTypesFrom: 'htmlDef2'
+				}
+			},
+			{
+				view: 'def4',
+				model: 'htmlDef4',
+				schema: {
+					allowWhere: 'htmlDef3'
+				}
+			},
+			{
+				view: 'def5',
+				model: 'htmlDef5',
+				schema: {
+					allowContentOf: 'htmlDef4'
+				}
+			},
+			{
+				view: 'def6',
+				model: 'htmlDef6',
+				schema: {
+					allowAttributesOf: 'htmlDef5'
+				}
+			}
+		];
 
-		const result = dataSchema.getDefinitionsForView( 'def2' );
+		it( 'should allow registering schema with proper definition', () => {
+			dataSchema.registerBlockElement( getFakeDefinitions( 'def1' )[ 0 ] );
 
-		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def2' ) );
-	} );
+			const result = dataSchema.getDefinitionsForView( 'def1' );
 
-	it( 'should allow resolving definitions by view name (RegExp)', () => {
-		registerMany( dataSchema, fakeDefinitions );
+			expect( Array.from( result ) ).to.deep.equal( getExpectedFakeDefinitions( 'def1' ) );
+		} );
 
-		const result = dataSchema.getDefinitionsForView( /^def1|def2$/ );
+		it( 'should allow resolving definitions by view name (string)', () => {
+			registerMany( dataSchema, fakeDefinitions );
 
-		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def1', 'def2' ) );
-	} );
+			const result = dataSchema.getDefinitionsForView( 'def2' );
 
-	it( 'should allow resolving definitions by view name including references (inheritAllFrom)', () => {
-		registerMany( dataSchema, fakeDefinitions );
+			expect( Array.from( result ) ).to.deep.equal( getExpectedFakeDefinitions( 'def2' ) );
+		} );
 
-		const result = dataSchema.getDefinitionsForView( 'def2', true );
+		it( 'should allow resolving definitions by view name (RegExp)', () => {
+			registerMany( dataSchema, fakeDefinitions );
 
-		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def1', 'def2' ) );
-	} );
+			const result = dataSchema.getDefinitionsForView( /^(def1|def2)$/ );
 
-	it( 'should allow resolving definitions by view name including references (inheritTypes)', () => {
-		registerMany( dataSchema, fakeDefinitions );
+			expect( Array.from( result ) ).to.deep.equal( getExpectedFakeDefinitions( 'def1', 'def2' ) );
+		} );
 
-		const result = dataSchema.getDefinitionsForView( 'def3', true );
+		it( 'should allow resolving definitions by view name including references (inheritAllFrom)', () => {
+			registerMany( dataSchema, fakeDefinitions );
 
-		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def1', 'def2', 'def3' ) );
-	} );
+			const result = dataSchema.getDefinitionsForView( 'def2', true );
 
-	it( 'should allow resolving definitions by view name including references (allowWhere)', () => {
-		registerMany( dataSchema, fakeDefinitions );
+			expect( Array.from( result ) ).to.deep.equal( getExpectedFakeDefinitions( 'def1', 'def2' ) );
+		} );
 
-		const result = dataSchema.getDefinitionsForView( 'def4', true );
+		it( 'should allow resolving definitions by view name including references (inheritTypes)', () => {
+			registerMany( dataSchema, fakeDefinitions );
 
-		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def1', 'def2', 'def3', 'def4' ) );
-	} );
+			const result = dataSchema.getDefinitionsForView( 'def3', true );
 
-	it( 'should allow resolving definitions by view name including references (allowContentOf)', () => {
-		registerMany( dataSchema, fakeDefinitions );
+			expect( Array.from( result ) ).to.deep.equal( getExpectedFakeDefinitions( 'def1', 'def2', 'def3' ) );
+		} );
 
-		const result = dataSchema.getDefinitionsForView( 'def5', true );
+		it( 'should allow resolving definitions by view name including references (allowWhere)', () => {
+			registerMany( dataSchema, fakeDefinitions );
 
-		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def1', 'def2', 'def3', 'def4', 'def5' ) );
-	} );
+			const result = dataSchema.getDefinitionsForView( 'def4', true );
 
-	it( 'should allow resolving definitions by view name including references (allowAttributesOf)', () => {
-		registerMany( dataSchema, fakeDefinitions );
+			expect( Array.from( result ) ).to.deep.equal( getExpectedFakeDefinitions( 'def1', 'def2', 'def3', 'def4' ) );
+		} );
 
-		const result = dataSchema.getDefinitionsForView( 'def6', true );
+		it( 'should allow resolving definitions by view name including references (allowContentOf)', () => {
+			registerMany( dataSchema, fakeDefinitions );
 
-		expect( Array.from( result ) ).to.deep.equal( getFakeDefinitions( 'def1', 'def2', 'def3', 'def4', 'def5', 'def6' ) );
-	} );
+			const result = dataSchema.getDefinitionsForView( 'def5', true );
 
-	it( 'should return nothing for invalid view name', () => {
-		registerMany( dataSchema, fakeDefinitions );
+			expect( Array.from( result ) ).to.deep.equal( getExpectedFakeDefinitions( 'def1', 'def2', 'def3', 'def4', 'def5' ) );
+		} );
 
-		const result = dataSchema.getDefinitionsForView( null );
+		it( 'should allow resolving definitions by view name including references (allowAttributesOf)', () => {
+			registerMany( dataSchema, fakeDefinitions );
 
-		expect( result.size ).to.equal( 0 );
-	} );
+			const result = dataSchema.getDefinitionsForView( 'def6', true );
+
+			expect( Array.from( result ) ).to.deep.equal( getExpectedFakeDefinitions( 'def1', 'def2', 'def3', 'def4', 'def5', 'def6' ) );
+		} );
+
+		it( 'should return nothing for invalid view name', () => {
+			registerMany( dataSchema, fakeDefinitions );
+
+			const result = dataSchema.getDefinitionsForView( null );
 
-	function registerMany( dataSchema, definitions ) {
-		definitions.forEach( def => dataSchema.register( def ) );
-	}
+			expect( result.size ).to.equal( 0 );
+		} );
 
-	function getFakeDefinitions( ...viewNames ) {
-		return fakeDefinitions.filter( def => viewNames.includes( def.view ) );
-	}
+		function registerMany( dataSchema, definitions ) {
+			definitions.forEach( def => dataSchema.registerBlockElement( def ) );
+		}
+
+		function getFakeDefinitions( ...viewNames ) {
+			return fakeDefinitions.filter( def => viewNames.includes( def.view ) );
+		}
+
+		function getExpectedFakeDefinitions( ...viewNames ) {
+			// It's expected that definition will include `isBlock` property.
+			return getFakeDefinitions( ...viewNames ).map( def => ( { ...def, isBlock: true } ) );
+		}
+	} );
 } );

From 2f2a32055b2de6c86e894d6b3f035d4bcf155dc0 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 16 Mar 2021 15:56:59 +0100
Subject: [PATCH 076/217] Renaming schema to modelSchema.

---
 .../src/datafilter.js                         |  2 +-
 .../src/dataschema.js                         | 28 +++++++++----------
 .../tests/dataschema.js                       | 12 ++++----
 3 files changed, 21 insertions(+), 21 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index c8ee6e726d6..f96b68e6b2f 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -198,7 +198,7 @@ export default class DataFilter {
 	_defineSchema( definition ) {
 		const schema = this.editor.model.schema;
 
-		schema.register( definition.model, definition.schema );
+		schema.register( definition.model, definition.modelSchema );
 
 		const allowedChildren = toArray( definition.allowChildren || [] );
 
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index d50bab59809..c55a13ea4b7 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -18,7 +18,7 @@ import { toArray } from 'ckeditor5/src/utils';
  *		dataSchema.register( {
  *			view: 'section',
  *			model: 'my-section',
- *			schema: {
+ *			modelSchema: {
  *				inheritAllFrom: '$block'
  *			}
  *		} );
@@ -38,7 +38,7 @@ export default class DataSchema {
 		this.registerBlockElement( {
 			model: '$htmlBlock',
 			allowChildren: '$block',
-			schema: {
+			modelSchema: {
 				allowIn: [ '$root', '$htmlBlock' ],
 				isBlock: true
 			}
@@ -47,7 +47,7 @@ export default class DataSchema {
 		this.registerBlockElement( {
 			view: 'article',
 			model: 'htmlArticle',
-			schema: {
+			modelSchema: {
 				inheritAllFrom: '$htmlBlock'
 			}
 		} );
@@ -55,7 +55,7 @@ export default class DataSchema {
 		this.registerBlockElement( {
 			view: 'section',
 			model: 'htmlSection',
-			schema: {
+			modelSchema: {
 				inheritAllFrom: '$htmlBlock'
 			}
 		} );
@@ -64,7 +64,7 @@ export default class DataSchema {
 		this.registerBlockElement( {
 			view: 'dl',
 			model: 'htmlDl',
-			schema: {
+			modelSchema: {
 				allowIn: [ '$htmlBlock', '$root' ],
 				isBlock: true
 			}
@@ -73,7 +73,7 @@ export default class DataSchema {
 		this.registerBlockElement( {
 			model: '$htmlDatalist',
 			allowChildren: '$block',
-			schema: {
+			modelSchema: {
 				allowIn: 'htmlDl',
 				isBlock: true
 			}
@@ -82,7 +82,7 @@ export default class DataSchema {
 		this.registerBlockElement( {
 			view: 'dt',
 			model: 'htmlDt',
-			schema: {
+			modelSchema: {
 				inheritAllFrom: '$htmlDatalist'
 			}
 		} );
@@ -90,7 +90,7 @@ export default class DataSchema {
 		this.registerBlockElement( {
 			view: 'dd',
 			model: 'htmlDd',
-			schema: {
+			modelSchema: {
 				inheritAllFrom: '$htmlDatalist'
 			}
 		} );
@@ -99,7 +99,7 @@ export default class DataSchema {
 		this.registerBlockElement( {
 			view: 'details',
 			model: 'htmlDetails',
-			schema: {
+			modelSchema: {
 				inheritAllFrom: '$htmlBlock'
 			}
 		} );
@@ -108,7 +108,7 @@ export default class DataSchema {
 			view: 'summary',
 			model: 'htmlSummary',
 			allowChildren: '$text',
-			schema: {
+			modelSchema: {
 				allowIn: 'htmlDetails'
 			}
 		} );
@@ -188,16 +188,16 @@ export default class DataSchema {
 	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition>}
 	 */
 	* _getReferences( modelName ) {
-		const { schema } = this._definitions.get( modelName );
+		const { modelSchema } = this._definitions.get( modelName );
 
-		if ( !schema ) {
+		if ( !modelSchema ) {
 			return;
 		}
 
 		const inheritProperties = [ 'inheritAllFrom', 'inheritTypesFrom', 'allowWhere', 'allowContentOf', 'allowAttributesOf' ];
 
 		for ( const property of inheritProperties ) {
-			for ( const referenceName of toArray( schema[ property ] || [] ) ) {
+			for ( const referenceName of toArray( modelSchema[ property ] || [] ) ) {
 				const definition = this._definitions.get( referenceName );
 
 				if ( referenceName !== modelName && definition ) {
@@ -233,7 +233,7 @@ function testViewName( pattern, viewName ) {
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
  * @property {String} [view] Name of the view element.
  * @property {String} model Name of the model element.
- * @property {module:engine/model/schema~SchemaItemDefinition} schema The model schema item definition describing registered model.
+ * @property {module:engine/model/schema~SchemaItemDefinition} modelSchema The model schema item definition describing registered model.
  * @property {String|Array.<String>} [allowChildren] Extends the given children list to allow definition model.
  */
 
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index adc0623ad57..a23d7eb2d0f 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -43,42 +43,42 @@ describe( 'DataSchema', () => {
 				view: 'def1',
 				model: 'htmlDef1',
 				allowChildren: [ 'htmlDef2', 'htmlDef3' ],
-				schema: {
+				modelSchema: {
 					inheritAllFrom: '$block'
 				}
 			},
 			{
 				view: 'def2',
 				model: 'htmlDef2',
-				schema: {
+				modelSchema: {
 					inheritAllFrom: 'htmlDef1'
 				}
 			},
 			{
 				view: 'def3',
 				model: 'htmlDef3',
-				schema: {
+				modelSchema: {
 					inheritTypesFrom: 'htmlDef2'
 				}
 			},
 			{
 				view: 'def4',
 				model: 'htmlDef4',
-				schema: {
+				modelSchema: {
 					allowWhere: 'htmlDef3'
 				}
 			},
 			{
 				view: 'def5',
 				model: 'htmlDef5',
-				schema: {
+				modelSchema: {
 					allowContentOf: 'htmlDef4'
 				}
 			},
 			{
 				view: 'def6',
 				model: 'htmlDef6',
-				schema: {
+				modelSchema: {
 					allowAttributesOf: 'htmlDef5'
 				}
 			}

From 65966543a86414c26d574611f23c258c432e0eb7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jacek=20Bogda=C5=84ski?= <jacekbogd@gmail.com>
Date: Wed, 17 Mar 2021 09:43:17 +0100
Subject: [PATCH 077/217] Apply suggestions from code review

Co-authored-by: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
---
 .../src/datafilter.js                            | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index f96b68e6b2f..81c2068a9f3 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -227,16 +227,16 @@ export default class DataFilter {
 			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
 				const viewAttributes = this._matchAndConsumeAttributes( data.viewItem, conversionApi );
 
-				// Since we are converting to attribute we need an range on which we will set the attribute.
+				// Since we are converting to attribute we need a range on which we will set the attribute.
 				// If the range is not created yet, we will create it.
 				if ( !data.modelRange ) {
 					data = Object.assign( data, conversionApi.convertChildren( data.viewItem, data.modelCursor ) );
 				}
 
-				// Set attribute on each item in range according to Schema.
+				// Set attribute on each item in range according to the schema.
 				for ( const node of data.modelRange.getItems() ) {
 					if ( conversionApi.schema.checkAttribute( node, attributeKey ) ) {
-						// Node's children are converter recursively, so node can already include model attribute.
+						// Node's children are converted recursively, so node can already include model attribute.
 						// We want to extend it, not replace.
 						const nodeAttributes = node.getAttribute( attributeKey );
 						const attributesToAdd = mergeAttributes( viewAttributes || {}, nodeAttributes || {} );
@@ -244,9 +244,7 @@ export default class DataFilter {
 						conversionApi.writer.setAttribute( attributeKey, attributesToAdd, node );
 					}
 				}
-			}, {
-				priority: 'low'
-			} );
+			}, { priority: 'low' } );
 		} );
 
 		conversion.for( 'downcast' ).attributeToElement( {
@@ -484,9 +482,11 @@ function mergeAttributes( oldValue, newValue ) {
 		// Merge classes.
 		if ( Array.isArray( newValue[ key ] ) ) {
 			result[ key ] = Array.from( new Set( [ ...oldValue[ key ], ...newValue[ key ] ] ) );
+		} 
+		
 		// Merge attributes or styles.
-		} else {
-			result[ key ] = Object.assign( {}, oldValue[ key ], newValue[ key ] );
+		else {
+			result[ key ] = { ...oldValue[ key ], ...newValue[ key ] };
 		}
 	}
 

From b2ca37193c05857e44c4413fbead710668c31ba6 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Mar 2021 08:51:56 +0100
Subject: [PATCH 078/217] Fixed manual test.

---
 .../tests/manual/generalhtmlsupport.js                      | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 2a97c2ddb78..54d8c2849b1 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -31,11 +31,11 @@ class ExtendHTMLSupport extends Plugin {
 		const dataSchema = new DataSchema();
 
 		// Extend schema with custom `xyz` element.
-		dataSchema.register( {
+		dataSchema.registerBlockElement( {
 			view: 'xyz',
 			model: 'ghsXyz',
-			schema: {
-				inheritAllFrom: '$ghsBlock'
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
 			}
 		} );
 

From 2f3626b806c0fa9cd23bea5067fd58420a8f7e3c Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Mar 2021 08:53:54 +0100
Subject: [PATCH 079/217] Renaming general to generic.

---
 .../manual/{generalhtmlsupport.html => generichtmlsupport.html} | 0
 .../manual/{generalhtmlsupport.js => generichtmlsupport.js}     | 2 +-
 .../manual/{generalhtmlsupport.md => generichtmlsupport.md}     | 0
 3 files changed, 1 insertion(+), 1 deletion(-)
 rename packages/ckeditor5-content-compatibility/tests/manual/{generalhtmlsupport.html => generichtmlsupport.html} (100%)
 rename packages/ckeditor5-content-compatibility/tests/manual/{generalhtmlsupport.js => generichtmlsupport.js} (99%)
 rename packages/ckeditor5-content-compatibility/tests/manual/{generalhtmlsupport.md => generichtmlsupport.md} (100%)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.html
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
rename to packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.html
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
similarity index 99%
rename from packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
rename to packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
index 54d8c2849b1..dd3604a16a6 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
@@ -33,7 +33,7 @@ class ExtendHTMLSupport extends Plugin {
 		// Extend schema with custom `xyz` element.
 		dataSchema.registerBlockElement( {
 			view: 'xyz',
-			model: 'ghsXyz',
+			model: 'htmlXyz',
 			modelSchema: {
 				inheritAllFrom: '$htmlBlock'
 			}
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.md b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.md
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.md
rename to packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.md

From 834b4d6a6d1060f509a3c8237be5120fdbe5ab53 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Mar 2021 09:40:18 +0100
Subject: [PATCH 080/217] Refactoring.

---
 .../src/datafilter.js                         | 62 +++++++++++--------
 .../src/dataschema.js                         | 11 +++-
 2 files changed, 45 insertions(+), 28 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 81c2068a9f3..35e9e5b69bb 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -164,11 +164,9 @@ export default class DataFilter {
 
 		this._defineSchema( definition );
 
-		if ( !definition.view ) {
-			return;
+		if ( definition.view ) {
+			this._defineBlockElementConverters( definition );
 		}
-
-		this._defineBlockElementConverters( definition );
 	}
 
 	/**
@@ -183,9 +181,9 @@ export default class DataFilter {
 			allowAttributes: definition.model
 		} );
 
-		schema.setAttributeProperties( definition.model, {
-			copyOnEnter: true
-		} );
+		if ( definition.attributeProperties ) {
+			schema.setAttributeProperties( definition.model, definition.attributeProperties );
+		}
 
 		this._defineInlineElementConverters( definition );
 	}
@@ -225,7 +223,7 @@ export default class DataFilter {
 
 		conversion.for( 'upcast' ).add( dispatcher => {
 			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
-				const viewAttributes = this._matchAndConsumeAttributes( data.viewItem, conversionApi );
+				const viewAttributes = this._matchAndConsumeAllowedAttributes( data.viewItem, conversionApi );
 
 				// Since we are converting to attribute we need a range on which we will set the attribute.
 				// If the range is not created yet, we will create it.
@@ -281,7 +279,7 @@ export default class DataFilter {
 			view: viewName,
 			model: ( viewElement, conversionApi ) => {
 				const element = conversionApi.writer.createElement( modelName );
-				const viewAttributes = this._matchAndConsumeAttributes( viewElement, conversionApi );
+				const viewAttributes = this._matchAndConsumeAllowedAttributes( viewElement, conversionApi );
 
 				if ( viewAttributes ) {
 					conversionApi.writer.setAttribute( DATA_SCHEMA_ATTRIBUTE_KEY, viewAttributes, element );
@@ -327,9 +325,7 @@ export default class DataFilter {
 		// Consumes disallowed element attributes to prevent them of being processed by other converters.
 		conversion.for( 'upcast' ).add( dispatcher => {
 			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
-				for ( const match of matchAll( data.viewItem, this._disallowedAttributes ) ) {
-					conversionApi.consumable.consume( data.viewItem, match.match );
-				}
+				consumeAttributeMatches( data.viewItem, conversionApi, this._disallowedAttributes );
 			}, { priority: 'high' } );
 		} );
 	}
@@ -341,18 +337,12 @@ export default class DataFilter {
 	 * @param {module:engine/view/element~Element} viewElement
 	 * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
 	 * @returns {Object} [result]
-	 * @returns {Array.<String>} result.attributes Array with matched attribute names.
-	 * @returns {Array.<String>} result.classes Array with matched class names.
-	 * @returns {Array.<String>} result.styles Array with matched style names.
+	 * @returns {Set.<Object>} result.attributes Set with matched attribute names.
+	 * @returns {Set.<Object>} result.styles Set with matched style names.
+	 * @returns {Set.<String>} result.classes Set with matched class names.
 	 */
-	_matchAndConsumeAttributes( viewElement, { consumable } ) {
-		const matches = [];
-		for ( const match of matchAll( viewElement, this._allowedAttributes ) ) {
-			if ( consumable.consume( viewElement, match.match ) ) {
-				matches.push( match );
-			}
-		}
-
+	_matchAndConsumeAllowedAttributes( viewElement, conversionApi ) {
+		const matches = consumeAttributeMatches( viewElement, conversionApi, this._allowedAttributes );
 		const { attributes, styles, classes } = mergeMatchResults( matches );
 		const viewAttributes = {};
 
@@ -376,6 +366,26 @@ export default class DataFilter {
 	}
 }
 
+// Consumes attributes matched for the given `rules`.
+//
+// Returns sucessfully consumed attribute matches.
+//
+// @private
+// @param {module:engine/view/element~Element} viewElement
+// @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
+// @param {Map.<String, module:engine/view/matcher~Matcher>} rules
+// @returns {Array.<Object>} Array with match information about found attributes.
+function consumeAttributeMatches( viewElement, { consumable }, rules ) {
+	const matches = [];
+	for ( const match of matchAll( viewElement, rules ) ) {
+		if ( consumable.consume( viewElement, match.match ) ) {
+			matches.push( match );
+		}
+	}
+
+	return matches;
+}
+
 // Helper function for downcast converter. Sets attributes on the given view element.
 //
 // @private
@@ -430,11 +440,11 @@ function matchAll( viewElement, rules ) {
 // Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
 //
 // @private
-// @param {Array} matches
+// @param {Array.<Object>} matches
 // @returns {Object} result
-// @returns {Set.<String>} result.attributes Set with matched attribute names.
+// @returns {Set.<Object>} result.attributes Set with matched attribute names.
+// @returns {Set.<Object>} result.styles Set with matched style names.
 // @returns {Set.<String>} result.classes Set with matched class names.
-// @returns {Set.<String>} result.styles Set with matched style names.
 function mergeMatchResults( matches ) {
 	const matchResult = {
 		attributes: new Set(),
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index c55a13ea4b7..ea94c3a8245 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -115,12 +115,18 @@ export default class DataSchema {
 
 		this.registerInlineElement( {
 			view: 'span',
-			model: 'htmlSpan'
+			model: 'htmlSpan',
+			attributeProperties: {
+				copyOnEnter: true
+			}
 		} );
 
 		this.registerInlineElement( {
 			view: 'cite',
-			model: 'htmlCite'
+			model: 'htmlCite',
+			attributeProperties: {
+				copyOnEnter: true
+			}
 		} );
 	}
 
@@ -243,4 +249,5 @@ function testViewName( pattern, viewName ) {
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaInlineElementDefinition
  * @property {String} view Name of the view element.
  * @property {String} model Name of the model attribute key.
+ * @property {module:engine/model/schema~AttributeProperties} [attributeProperties] Additional metadata describing the model attribute.
  */

From baa3f8b595a75593fabe2a5cf2248de184163db1 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Mar 2021 09:50:54 +0100
Subject: [PATCH 081/217] Renaming.

---
 .../src/datafilter.js                             | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 35e9e5b69bb..803466e6dbf 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -237,7 +237,7 @@ export default class DataFilter {
 						// Node's children are converted recursively, so node can already include model attribute.
 						// We want to extend it, not replace.
 						const nodeAttributes = node.getAttribute( attributeKey );
-						const attributesToAdd = mergeAttributes( viewAttributes || {}, nodeAttributes || {} );
+						const attributesToAdd = mergeViewElementAttributes( viewAttributes || {}, nodeAttributes || {} );
 
 						conversionApi.writer.setAttribute( attributeKey, attributesToAdd, node );
 					}
@@ -255,7 +255,7 @@ export default class DataFilter {
 				const { writer } = conversionApi;
 				const viewElement = writer.createAttributeElement( viewName );
 
-				setAttributesOn( writer, attributeValue, viewElement );
+				setViewElementAttributes( writer, attributeValue, viewElement );
 
 				return viewElement;
 			}
@@ -308,7 +308,7 @@ export default class DataFilter {
 				const viewWriter = conversionApi.writer;
 				const viewElement = conversionApi.mapper.toViewElement( data.item );
 
-				setAttributesOn( viewWriter, viewAttributes, viewElement );
+				setViewElementAttributes( viewWriter, viewAttributes, viewElement );
 			} );
 		} );
 	}
@@ -377,6 +377,7 @@ export default class DataFilter {
 // @returns {Array.<Object>} Array with match information about found attributes.
 function consumeAttributeMatches( viewElement, { consumable }, rules ) {
 	const matches = [];
+
 	for ( const match of matchAll( viewElement, rules ) ) {
 		if ( consumable.consume( viewElement, match.match ) ) {
 			matches.push( match );
@@ -392,7 +393,7 @@ function consumeAttributeMatches( viewElement, { consumable }, rules ) {
 // @param {module:engine/view/downcastwriter~DowncastWriter} writer
 // @param {Object} viewAttributes
 // @param {module:engine/view/element~Element} viewElement
-function setAttributesOn( writer, viewAttributes, viewElement ) {
+function setViewElementAttributes( writer, viewAttributes, viewElement ) {
 	if ( viewAttributes.attributes ) {
 		for ( const [ key, value ] of Object.entries( viewAttributes.attributes ) ) {
 			writer.setAttribute( key, value, viewElement );
@@ -485,15 +486,15 @@ function iterableToObject( iterable, getValue ) {
 // @param {Object} oldValue
 // @param {Object} newValue
 // @returns {Object}
-function mergeAttributes( oldValue, newValue ) {
+function mergeViewElementAttributes( oldValue, newValue ) {
 	const result = cloneDeep( oldValue );
 
 	for ( const key in newValue ) {
 		// Merge classes.
 		if ( Array.isArray( newValue[ key ] ) ) {
 			result[ key ] = Array.from( new Set( [ ...oldValue[ key ], ...newValue[ key ] ] ) );
-		} 
-		
+		}
+
 		// Merge attributes or styles.
 		else {
 			result[ key ] = { ...oldValue[ key ], ...newValue[ key ] };

From b73e6c85babb681fb3e74d29415c7f3135635dc8 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Mar 2021 10:22:31 +0100
Subject: [PATCH 082/217] Docs.

---
 .../src/datafilter.js                         | 20 +++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 803466e6dbf..a1fd77e2af1 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -129,6 +129,8 @@ export default class DataFilter {
 	}
 
 	/**
+	 * Registers element and attribute converters for the given data schema definition.
+	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
 	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
@@ -153,6 +155,10 @@ export default class DataFilter {
 	}
 
 	/**
+	 * Registers block element and attribute converters for the given data schema definition.
+	 *
+	 * If the element model schema is already registered, this method will do nothing.
+	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
 	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
@@ -162,7 +168,7 @@ export default class DataFilter {
 			return;
 		}
 
-		this._defineSchema( definition );
+		this._defineBlockElementSchema( definition );
 
 		if ( definition.view ) {
 			this._defineBlockElementConverters( definition );
@@ -170,6 +176,10 @@ export default class DataFilter {
 	}
 
 	/**
+	 * Registers inline element and attribute converters for the given data schema definition.
+	 *
+	 * Extends `$text` model schema to allow the given definition model attribute and its properties.
+	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
 	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
@@ -189,11 +199,13 @@ export default class DataFilter {
 	}
 
 	/**
+	 * Registers model schema definition for the given block element definition.
+	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
 	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
-	_defineSchema( definition ) {
+	_defineBlockElementSchema( definition ) {
 		const schema = this.editor.model.schema;
 
 		schema.register( definition.model, definition.modelSchema );
@@ -210,6 +222,8 @@ export default class DataFilter {
 	}
 
 	/**
+	 * Registers attribute converters for the given inline element definition.
+	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
 	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
@@ -263,6 +277,8 @@ export default class DataFilter {
 	}
 
 	/**
+	 * Registers attribute converters for the given block element definition.
+	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
 	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition

From 16e22f1817ebc6682d010679bf40bfd767736ec0 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Mar 2021 12:35:53 +0100
Subject: [PATCH 083/217] Added test coverage, updated error message.

---
 .../src/datafilter.js                         |  2 +-
 .../tests/datafilter.js                       | 68 +++++++++++++++++++
 2 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index a1fd77e2af1..9c75872c2d0 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -149,7 +149,7 @@ export default class DataFilter {
 			throw new CKEditorError(
 				'data-filter-invalid-definition-type',
 				null,
-				{ definition }
+				definition
 			);
 		}
 	}
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 7e65ff45baf..b1543879d39 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -8,6 +8,8 @@
 import ClassicTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/classictesteditor';
 import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
 import Font from '@ckeditor/ckeditor5-font/src/font';
+import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
+import { expectToThrowCKEditorError } from '@ckeditor/ckeditor5-utils/tests/_utils/utils';
 import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
 
 import DataSchema from '../src/dataschema';
@@ -16,6 +18,8 @@ import DataFilter from '../src/datafilter';
 describe( 'DataFilter', () => {
 	let editor, model, dataFilter, dataSchema, element;
 
+	testUtils.createSinonSandbox();
+
 	beforeEach( () => {
 		element = document.createElement( 'div' );
 		document.body.appendChild( element );
@@ -678,6 +682,57 @@ describe( 'DataFilter', () => {
 				}
 			} );
 		} );
+
+		describe( 'attribute properties', () => {
+			it( 'should set if given', () => {
+				dataSchema.registerInlineElement( {
+					view: 'xyz',
+					model: 'htmlXyz',
+					attributeProperties: {
+						copyOnEnter: true
+					}
+				} );
+
+				dataFilter.allowElement( { name: 'xyz' } );
+
+				expect( editor.model.schema.getAttributeProperties( 'htmlXyz' ) ).to.deep.equal( { copyOnEnter: true } );
+			} );
+
+			it( 'should not set if missing', () => {
+				dataSchema.registerInlineElement( {
+					view: 'xyz',
+					model: 'htmlXyz'
+				} );
+
+				dataFilter.allowElement( { name: 'xyz' } );
+
+				expect( editor.model.schema.getAttributeProperties( 'htmlXyz' ) ).to.deep.equal( {} );
+			} );
+		} );
+
+		it( 'should not set attribute if disallowed by schema', () => {
+			editor.model.schema.addAttributeCheck( ( context, attributeName ) => {
+				if ( context.endsWith( '$text' ) && attributeName === 'htmlXyz' ) {
+					return false;
+				}
+			} );
+
+			dataSchema.registerInlineElement( {
+				view: 'xyz',
+				model: 'htmlXyz',
+				attributeProperties: {
+					copyOnEnter: true
+				}
+			} );
+
+			dataFilter.allowElement( { name: 'xyz' } );
+
+			editor.setData( '<p><xyz>foobar</xyz></p>' );
+
+			expect( getModelData( model, { withoutSelection: true } ) ).to.equal( '<paragraph>foobar</paragraph>' );
+
+			editor.getData( '<p>foobar</p>' );
+		} );
 	} );
 
 	it( 'should correctly resolve attributes nesting order', () => {
@@ -735,6 +790,19 @@ describe( 'DataFilter', () => {
 		expect( editor.getData() ).to.equal( '<p><span style="color:blue;"><span class="foo bar">foobar</span></span></p>' );
 	} );
 
+	it( 'should throw error if definition has no specified element type', () => {
+		const definition = {
+			view: 'xyz',
+			model: 'htmlXyz'
+		};
+
+		sinon.stub( dataSchema, 'getDefinitionsForView' ).returns( new Set( [ definition ] ) );
+
+		expectToThrowCKEditorError( () => {
+			dataFilter.allowElement( { name: 'xyz' } );
+		}, /data-filter-invalid-definition-type/, null, definition );
+	} );
+
 	function getModelDataWithAttributes( model, options ) {
 		// Simplify GHS attributes as they are not very readable at this point due to object structure.
 		let counter = 1;

From 6a9e3c89fb92878e907bbd9ae8693039e6521192 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Mar 2021 12:45:27 +0100
Subject: [PATCH 084/217] Updated data schema docs to new API.

---
 .../src/dataschema.js                          | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index ea94c3a8245..9d609906f84 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -13,15 +13,27 @@ import { toArray } from 'ckeditor5/src/utils';
  * Holds representation of the extended HTML document type definitions to be used by the
  * editor in content compatibility support.
  *
- * Data schema is represented by data schema definitions. To add new definition, use {@link #register} method:
+ * Data schema is represented by data schema definitions.
  *
- *		dataSchema.register( {
+ * To add new definition for block element, use {@link #registerBlockElement} method:
+ *
+ *		dataSchema.registerBlockElement( {
  *			view: 'section',
  *			model: 'my-section',
  *			modelSchema: {
  *				inheritAllFrom: '$block'
  *			}
  *		} );
+ *
+ * To add new definition for inline element, use {@link #registerInlineElement} method:
+ *
+ *		dataSchema.registerInlineElement( {
+ *			view: 'span',
+ *			model: 'my-span',
+ *			attributeProperties: {
+ *				copyOnEnter: true
+ *			}
+ *		} );
  */
 export default class DataSchema {
 	constructor() {
@@ -35,6 +47,7 @@ export default class DataSchema {
 		 */
 		this._definitions = new Map();
 
+		// Block elements.
 		this.registerBlockElement( {
 			model: '$htmlBlock',
 			allowChildren: '$block',
@@ -113,6 +126,7 @@ export default class DataSchema {
 			}
 		} );
 
+		// Inline elements.
 		this.registerInlineElement( {
 			view: 'span',
 			model: 'htmlSpan',

From 15a5be3fb796521f02ec1074a0e6acc7449fde76 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Mar 2021 12:58:23 +0100
Subject: [PATCH 085/217] Extracted base data schema definition type.

---
 .../src/datafilter.js                         | 18 +++++----------
 .../src/dataschema.js                         | 23 +++++++++++--------
 2 files changed, 19 insertions(+), 22 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 9c75872c2d0..bdddaca19ff 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -132,8 +132,7 @@ export default class DataFilter {
 	 * Registers element and attribute converters for the given data schema definition.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
-	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
 	_registerElement( definition ) {
 		if ( definition.isInline ) {
@@ -160,8 +159,7 @@ export default class DataFilter {
 	 * If the element model schema is already registered, this method will do nothing.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
-	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
 	_defineBlockElement( definition ) {
 		if ( this.editor.model.schema.isRegistered( definition.model ) ) {
@@ -181,8 +179,7 @@ export default class DataFilter {
 	 * Extends `$text` model schema to allow the given definition model attribute and its properties.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
-	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
 	_defineInlineElement( definition ) {
 		const schema = this.editor.model.schema;
@@ -202,8 +199,7 @@ export default class DataFilter {
 	 * Registers model schema definition for the given block element definition.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
-	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
 	_defineBlockElementSchema( definition ) {
 		const schema = this.editor.model.schema;
@@ -225,8 +221,7 @@ export default class DataFilter {
 	 * Registers attribute converters for the given inline element definition.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
-	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
 	_defineInlineElementConverters( definition ) {
 		const conversion = this.editor.conversion;
@@ -280,8 +275,7 @@ export default class DataFilter {
 	 * Registers attribute converters for the given block element definition.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
-	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
 	_defineBlockElementConverters( definition ) {
 		const conversion = this.editor.conversion;
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 9d609906f84..62dcd9e5414 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -42,8 +42,7 @@ export default class DataSchema {
 		 *
 		 * @readonly
 		 * @private
-		 * @member {Map.<String, module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
-		 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition>} #_definitions
+		 * @member {Map.<String, module:content-compatibility/dataschema~DataSchemaDefinition>} #_definitions
 		 */
 		this._definitions = new Map();
 
@@ -167,8 +166,7 @@ export default class DataSchema {
 	 *
 	 * @param {String|RegExp} viewName
 	 * @param {Boolean} [includeReferences] Indicates if this method should also include definitions of referenced models.
-	 * @returns {Set.<module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
-	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition>}
+	 * @returns {Set.<module:content-compatibility/dataschema~DataSchemaDefinition>}
 	 */
 	getDefinitionsForView( viewName, includeReferences ) {
 		const definitions = new Set();
@@ -191,8 +189,7 @@ export default class DataSchema {
 	 *
 	 * @private
 	 * @param {String|RegExp} viewName
-	 * @returns {Array.<module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
-	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition>}
+	 * @returns {Array.<module:content-compatibility/dataschema~DataSchemaDefinition>}
 	 */
 	_getMatchingViewDefinitions( viewName ) {
 		return Array.from( this._definitions.values() )
@@ -204,8 +201,7 @@ export default class DataSchema {
 	 *
 	 * @private
 	 * @param {String} modelName Data schema model name.
-	 * @returns {Iterable.<module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
-	 * |module:content-compatibility/dataschema~DataSchemaInlineElementDefinition>}
+	 * @returns {Iterable.<module:content-compatibility/dataschema~DataSchemaDefinition>}
 	 */
 	* _getReferences( modelName ) {
 		const { modelSchema } = this._definitions.get( modelName );
@@ -247,14 +243,21 @@ function testViewName( pattern, viewName ) {
 	return false;
 }
 
+/**
+ * A base definition of {@link module:content-compatibility/dataschema~DataSchema data schema}.
+ *
+ * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
+ * @property {String} model Name of the model.
+ */
+
 /**
  * A definition of {@link module:content-compatibility/dataschema~DataSchema data schema} for block elements.
  *
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
  * @property {String} [view] Name of the view element.
- * @property {String} model Name of the model element.
  * @property {module:engine/model/schema~SchemaItemDefinition} modelSchema The model schema item definition describing registered model.
  * @property {String|Array.<String>} [allowChildren] Extends the given children list to allow definition model.
+ * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */
 
 /**
@@ -262,6 +265,6 @@ function testViewName( pattern, viewName ) {
  *
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaInlineElementDefinition
  * @property {String} view Name of the view element.
- * @property {String} model Name of the model attribute key.
  * @property {module:engine/model/schema~AttributeProperties} [attributeProperties] Additional metadata describing the model attribute.
+ * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */

From fd542acc7167928a607b35328c403d441d5bfbae Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Mar 2021 13:01:44 +0100
Subject: [PATCH 086/217] Minor docs update.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index bdddaca19ff..4f133e46f94 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -490,7 +490,7 @@ function iterableToObject( iterable, getValue ) {
 	return attributesObject;
 }
 
-// Merges attribute objects.
+// Merges view element attribute objects.
 //
 // @private
 // @param {Object} oldValue

From c8b0e5cb37f806de0da13c504ac31596d808a1d7 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Mar 2021 13:03:47 +0100
Subject: [PATCH 087/217] Added additional test for attribute properties.

---
 .../tests/dataschema.js                       | 21 +++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index a23d7eb2d0f..273f9e1d25d 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -35,6 +35,27 @@ describe( 'DataSchema', () => {
 				isInline: true
 			} ] );
 		} );
+
+		it( 'should include attribute properties', () => {
+			dataSchema.registerInlineElement( {
+				model: 'htmlDef',
+				view: 'def',
+				attributeProperties: {
+					copyOnEnter: true
+				}
+			} );
+
+			const result = dataSchema.getDefinitionsForView( 'def' );
+
+			expect( Array.from( result ) ).to.deep.equal( [ {
+				model: 'htmlDef',
+				view: 'def',
+				attributeProperties: {
+					copyOnEnter: true
+				},
+				isInline: true
+			} ] );
+		} );
 	} );
 
 	describe( 'registerBlockElement', () => {

From 16d00e37853fae4338bd7b8ffcea558f4c873274 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 17 Mar 2021 13:11:02 +0100
Subject: [PATCH 088/217] Added information about definition specific
 properties.

---
 packages/ckeditor5-content-compatibility/src/dataschema.js | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 62dcd9e5414..c2bf8fd6c42 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -255,8 +255,10 @@ function testViewName( pattern, viewName ) {
  *
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
  * @property {String} [view] Name of the view element.
- * @property {module:engine/model/schema~SchemaItemDefinition} modelSchema The model schema item definition describing registered model.
+ * @property {module:engine/model/schema~SchemaItemDefinition} [modelSchema] The model schema item definition describing registered model.
  * @property {String|Array.<String>} [allowChildren] Extends the given children list to allow definition model.
+ * @property {Boolean} isBlock Indicates that the definition describes block element.
+ * Set by {@link @link module:content-compatibility/dataschema~DataSchema#registerBlockElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */
 
@@ -266,5 +268,7 @@ function testViewName( pattern, viewName ) {
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaInlineElementDefinition
  * @property {String} view Name of the view element.
  * @property {module:engine/model/schema~AttributeProperties} [attributeProperties] Additional metadata describing the model attribute.
+ * @property {Boolean} isInline Indicates that the definition descibes inline element.
+ * Set by {@link @link module:content-compatibility/dataschema~DataSchema#registerInlineElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */

From 8382a8dccb0a8c38d66851d4c7a4850868239a5b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jacek=20Bogda=C5=84ski?= <jacekbogd@gmail.com>
Date: Mon, 29 Mar 2021 11:13:17 +0200
Subject: [PATCH 089/217] Update
 packages/ckeditor5-content-compatibility/src/datafilter.js

Co-authored-by: Kuba Niegowski <1232187+niegowski@users.noreply.github.com>
---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 4f133e46f94..1db78b8eeb3 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -347,9 +347,9 @@ export default class DataFilter {
 	 * @param {module:engine/view/element~Element} viewElement
 	 * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
 	 * @returns {Object} [result]
-	 * @returns {Set.<Object>} result.attributes Set with matched attribute names.
-	 * @returns {Set.<Object>} result.styles Set with matched style names.
-	 * @returns {Set.<String>} result.classes Set with matched class names.
+	 * @returns {Object} result.attributes Set with matched attribute names.
+	 * @returns {Object} result.styles Set with matched style names.
+	 * @returns {Array.<String>} result.classes Set with matched class names.
 	 */
 	_matchAndConsumeAllowedAttributes( viewElement, conversionApi ) {
 		const matches = consumeAttributeMatches( viewElement, conversionApi, this._allowedAttributes );

From f40afe00323c5bbd5e00f6842688c309cfa72498 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 29 Mar 2021 11:17:53 +0200
Subject: [PATCH 090/217] Docs update.

---
 packages/ckeditor5-content-compatibility/src/dataschema.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index c2bf8fd6c42..9df5bc1b817 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -246,7 +246,7 @@ function testViewName( pattern, viewName ) {
 /**
  * A base definition of {@link module:content-compatibility/dataschema~DataSchema data schema}.
  *
- * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
+ * @interface module:content-compatibility/dataschema~DataSchemaDefinition
  * @property {String} model Name of the model.
  */
 

From 88b9fdb80b77fa374b6443d81f6a826808d3c099 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 30 Mar 2021 08:51:30 +0200
Subject: [PATCH 091/217] Updated tests to use VirtualEditor.

---
 .../package.json                              |  1 +
 .../tests/datafilter.js                       | 19 ++++++-------------
 2 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/package.json b/packages/ckeditor5-content-compatibility/package.json
index 05c00a34771..67b600df95c 100644
--- a/packages/ckeditor5-content-compatibility/package.json
+++ b/packages/ckeditor5-content-compatibility/package.json
@@ -28,6 +28,7 @@
     "@ckeditor/ckeditor5-font": "^27.0.0",
     "@ckeditor/ckeditor5-list": "^27.0.0",
     "@ckeditor/ckeditor5-paragraph": "^27.0.0",
+    "@ckeditor/ckeditor5-utils": "^27.0.0",
     "webpack": "^4.43.0",
     "webpack-cli": "^3.3.11"
   },
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index b1543879d39..f5c020507bf 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -3,11 +3,9 @@
  * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
  */
 
-/* global document */
-
-import ClassicTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/classictesteditor';
+import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
 import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
-import Font from '@ckeditor/ckeditor5-font/src/font';
+import FontColorEditing from '@ckeditor/ckeditor5-font/src/fontcolor/fontcolorediting';
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import { expectToThrowCKEditorError } from '@ckeditor/ckeditor5-utils/tests/_utils/utils';
 import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
@@ -16,17 +14,14 @@ import DataSchema from '../src/dataschema';
 import DataFilter from '../src/datafilter';
 
 describe( 'DataFilter', () => {
-	let editor, model, dataFilter, dataSchema, element;
+	let editor, model, dataFilter, dataSchema;
 
 	testUtils.createSinonSandbox();
 
 	beforeEach( () => {
-		element = document.createElement( 'div' );
-		document.body.appendChild( element );
-
-		return ClassicTestEditor
-			.create( element, {
-				plugins: [ Paragraph, Font ]
+		return VirtualTestEditor
+			.create( {
+				plugins: [ Paragraph, FontColorEditing ]
 			} )
 			.then( newEditor => {
 				editor = newEditor;
@@ -38,8 +33,6 @@ describe( 'DataFilter', () => {
 	} );
 
 	afterEach( () => {
-		element.remove();
-
 		return editor.destroy();
 	} );
 

From 0a10e2d4cea12c270397653c7f1ab812470855da Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 30 Mar 2021 09:22:06 +0200
Subject: [PATCH 092/217] Corrected docs based on build verification.

---
 .../src/datafilter.js                               |  8 ++++++--
 .../src/dataschema.js                               | 13 ++++++++-----
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 1db78b8eeb3..dcf9f5d75fc 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -5,6 +5,7 @@
 
 /**
  * @module content-compatibility/datafilter
+ * @publicApi
  */
 
 import { Matcher } from 'ckeditor5/src/engine';
@@ -17,7 +18,7 @@ const DATA_SCHEMA_ATTRIBUTE_KEY = 'htmlAttributes';
 /**
  * Allows to validate elements and element attributes registered by {@link module:content-compatibility/dataschema~DataSchema}.
  *
- * To enable registered element in the editor, use {@link #allowElement} method:
+ * To enable registered element in the editor, use {@link module:content-compatibility/datafilter~DataFilter#allowElement} method:
  *
  *		dataFilter.allowElement( {
  *			name: 'section'
@@ -78,7 +79,10 @@ export default class DataFilter {
 	}
 
 	/**
-	 * Allow the given element registered by {@link #register} method.
+	 * Allow the given element in the editor context.
+	 *
+	 * This method will only allow elements described by the {@link module:content-compatibility/dataschema~DataSchema} used
+	 * to create data filter.
 	 *
 	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all view elements which should be allowed.
 	 */
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 9df5bc1b817..b3103838277 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -5,6 +5,7 @@
 
 /**
  * @module content-compatibility/dataschema
+ * @publicApi
  */
 
 import { toArray } from 'ckeditor5/src/utils';
@@ -15,7 +16,8 @@ import { toArray } from 'ckeditor5/src/utils';
  *
  * Data schema is represented by data schema definitions.
  *
- * To add new definition for block element, use {@link #registerBlockElement} method:
+ * To add new definition for block element,
+ * use {@link module:content-compatibility/dataschema~DataSchema#registerBlockElement} method:
  *
  *		dataSchema.registerBlockElement( {
  *			view: 'section',
@@ -25,7 +27,8 @@ import { toArray } from 'ckeditor5/src/utils';
  *			}
  *		} );
  *
- * To add new definition for inline element, use {@link #registerInlineElement} method:
+ * To add new definition for inline element,
+ * use {@link module:content-compatibility/dataschema~DataSchema#registerInlineElement} method:
  *
  *		dataSchema.registerInlineElement( {
  *			view: 'span',
@@ -246,7 +249,7 @@ function testViewName( pattern, viewName ) {
 /**
  * A base definition of {@link module:content-compatibility/dataschema~DataSchema data schema}.
  *
- * @interface module:content-compatibility/dataschema~DataSchemaDefinition
+ * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
  * @property {String} model Name of the model.
  */
 
@@ -258,7 +261,7 @@ function testViewName( pattern, viewName ) {
  * @property {module:engine/model/schema~SchemaItemDefinition} [modelSchema] The model schema item definition describing registered model.
  * @property {String|Array.<String>} [allowChildren] Extends the given children list to allow definition model.
  * @property {Boolean} isBlock Indicates that the definition describes block element.
- * Set by {@link @link module:content-compatibility/dataschema~DataSchema#registerBlockElement} method.
+ * Set by {@link module:content-compatibility/dataschema~DataSchema#registerBlockElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */
 
@@ -269,6 +272,6 @@ function testViewName( pattern, viewName ) {
  * @property {String} view Name of the view element.
  * @property {module:engine/model/schema~AttributeProperties} [attributeProperties] Additional metadata describing the model attribute.
  * @property {Boolean} isInline Indicates that the definition descibes inline element.
- * Set by {@link @link module:content-compatibility/dataschema~DataSchema#registerInlineElement} method.
+ * Set by {@link module:content-compatibility/dataschema~DataSchema#registerInlineElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */

From 6bdeed158f11b2c1f756d8f1ae48201cd686ae40 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <j.niegowski@cksource.com>
Date: Tue, 30 Mar 2021 10:11:42 +0200
Subject: [PATCH 093/217] Removed @publicApi tags.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 1 -
 packages/ckeditor5-content-compatibility/src/dataschema.js | 1 -
 2 files changed, 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index dcf9f5d75fc..07ea67c04f5 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -5,7 +5,6 @@
 
 /**
  * @module content-compatibility/datafilter
- * @publicApi
  */
 
 import { Matcher } from 'ckeditor5/src/engine';
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index b3103838277..ebdd61537e1 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -5,7 +5,6 @@
 
 /**
  * @module content-compatibility/dataschema
- * @publicApi
  */
 
 import { toArray } from 'ckeditor5/src/utils';

From 3f51d92020bfc396f7453d724339d745b1a9a691 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 31 Mar 2021 11:39:59 +0200
Subject: [PATCH 094/217] Simplified data filter attribute matchers.

---
 .../src/datafilter.js                         | 89 +++++--------------
 1 file changed, 21 insertions(+), 68 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 07ea67c04f5..e8385203948 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -55,26 +55,24 @@ export default class DataFilter {
 		this._dataSchema = dataSchema;
 
 		/**
-		 * A map of registered {@link module:engine/view/matcher~Matcher Matcher} instances.
-		 *
-		 * Describes rules upon which content attributes should be allowed.
+		 * {@link module:engine/view/matcher~Matcher Matcher} instance describing rules upon which
+		 * content attributes should be allowed.
 		 *
 		 * @readonly
 		 * @private
-		 * @member {Map.<String, module:engine/view/matcher~Matcher>} #_allowedAttributes
+		 * @member {module:engine/view/matcher~Matcher} #_allowedAttributes
 		 */
-		this._allowedAttributes = new Map();
+		this._allowedAttributes = new Matcher();
 
 		/**
-		 * A map of registered {@link module:engine/view/matcher~Matcher Matcher} instances.
-		 *
-		 * Describes rules upon which content attributes should be disallowed.
+		 * {@link module:engine/view/matcher~Matcher Matcher} instance describing rules upon which
+		 * content attributes should be disallowed.
 		 *
 		 * @readonly
 		 * @private
-		 * @member {Map.<String, module:engine/view/matcher~Matcher>} #_disallowedAttributes
+		 * @member {module:engine/view/matcher~Matcher} #_disallowedAttributes
 		 */
-		this._disallowedAttributes = new Map();
+		this._disallowedAttributes = new Matcher();
 	}
 
 	/**
@@ -99,7 +97,7 @@ export default class DataFilter {
 	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all attributes which should be allowed.
 	 */
 	allowAttributes( config ) {
-		this._addAttributeMatcher( config, this._allowedAttributes );
+		this._allowedAttributes.add( config );
 	}
 
 	/**
@@ -108,27 +106,7 @@ export default class DataFilter {
 	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all attributes which should be disallowed.
 	 */
 	disallowAttributes( config ) {
-		this._addAttributeMatcher( config, this._disallowedAttributes );
-	}
-
-	/**
-	 * Adds attribute matcher for every registered data schema definition for the given `config.name`.
-	 *
-	 * @private
-	 * @param {module:engine/view/matcher~MatcherPattern} config
-	 * @param {Map.<String, module:engine/view/matcher~Matcher>} rules Rules map holding matchers.
-	 */
-	_addAttributeMatcher( config, rules ) {
-		const viewName = config.name;
-
-		config = cloneDeep( config );
-
-		// We don't want match by name when matching attributes. Matcher will be already attached to specific definition.
-		delete config.name;
-
-		for ( const definition of this._dataSchema.getDefinitionsForView( viewName ) ) {
-			getOrCreateMatcher( definition.view, rules ).add( config );
-		}
+		this._disallowedAttributes.add( config );
 	}
 
 	/**
@@ -379,25 +357,29 @@ export default class DataFilter {
 	}
 }
 
-// Consumes attributes matched for the given `rules`.
+// Consumes matched attributes.
 //
 // Returns sucessfully consumed attribute matches.
 //
 // @private
 // @param {module:engine/view/element~Element} viewElement
 // @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
-// @param {Map.<String, module:engine/view/matcher~Matcher>} rules
+// @param {module:engine/view/matcher~Matcher Matcher} matcher
 // @returns {Array.<Object>} Array with match information about found attributes.
-function consumeAttributeMatches( viewElement, { consumable }, rules ) {
-	const matches = [];
+function consumeAttributeMatches( viewElement, { consumable }, matcher ) {
+	const matches = matcher.matchAll( viewElement ) || [];
+	const consumedMatches = [];
+
+	for ( const match of matches ) {
+		// We only want to consume attributes, so element can be still processed by other converters.
+		delete match.match.name;
 
-	for ( const match of matchAll( viewElement, rules ) ) {
 		if ( consumable.consume( viewElement, match.match ) ) {
-			matches.push( match );
+			consumedMatches.push( match );
 		}
 	}
 
-	return matches;
+	return consumedMatches;
 }
 
 // Helper function for downcast converter. Sets attributes on the given view element.
@@ -422,35 +404,6 @@ function setViewElementAttributes( writer, viewAttributes, viewElement ) {
 	}
 }
 
-// Helper function restoring matcher for the given key from `rules` object.
-//
-// If matcher for the given key does not exist, this function will create a new one
-// inside `rules` object under the given key.
-//
-// @private
-// @param {String} key
-// @param {Map.<String, module:engine/view/matcher~Matcher>} rules
-// @returns {module:engine/view/matcher~Matcher}
-function getOrCreateMatcher( key, rules ) {
-	if ( !rules.has( key ) ) {
-		rules.set( key, new Matcher() );
-	}
-
-	return rules.get( key );
-}
-
-// Alias for {@link module:engine/view/matcher~Matcher#matchAll matchAll}.
-//
-// @private
-// @param {module:engine/view/element~Element} viewElement
-// @param {Map.<String, module:engine/view/matcher~Matcher>} rules Rules map holding matchers.
-// @returns {Array.<Object>} Array with match information about found elements.
-function matchAll( viewElement, rules ) {
-	const matcher = getOrCreateMatcher( viewElement.name, rules );
-
-	return matcher.matchAll( viewElement ) || [];
-}
-
 // Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
 //
 // @private

From ebe79c3f3705d4cbe894f2155014254f86a79a72 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 6 Apr 2021 09:40:45 +0200
Subject: [PATCH 095/217] Added support to allow attributes on existing
 features.

---
 .../src/datafilter.js                         | 155 ++++++++++--------
 .../src/dataschema.js                         |  29 +++-
 .../tests/datafilter.js                       | 134 +++++++++++++++
 .../tests/dataschema.js                       |  30 +++-
 .../tests/manual/generichtmlsupport.html      |  21 ++-
 .../tests/manual/generichtmlsupport.js        |  11 ++
 6 files changed, 305 insertions(+), 75 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index e8385203948..8cba235cd0a 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -143,15 +143,13 @@ export default class DataFilter {
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
 	_defineBlockElement( definition ) {
-		if ( this.editor.model.schema.isRegistered( definition.model ) ) {
-			return;
+		if ( !definition.extend ) {
+			this._defineBlockElementSchema( definition );
+			this._addBlockElementToElementConversion( definition );
 		}
 
-		this._defineBlockElementSchema( definition );
-
-		if ( definition.view ) {
-			this._defineBlockElementConverters( definition );
-		}
+		this._addDisallowedAttributeConversion( definition );
+		this._addBlockElementAttributeConversion( definition );
 	}
 
 	/**
@@ -173,7 +171,8 @@ export default class DataFilter {
 			schema.setAttributeProperties( definition.model, definition.attributeProperties );
 		}
 
-		this._defineInlineElementConverters( definition );
+		this._addDisallowedAttributeConversion( definition );
+		this._addInlineElementConversion( definition );
 	}
 
 	/**
@@ -185,6 +184,10 @@ export default class DataFilter {
 	_defineBlockElementSchema( definition ) {
 		const schema = this.editor.model.schema;
 
+		if ( schema.isRegistered( definition.model ) ) {
+			return;
+		}
+
 		schema.register( definition.model, definition.modelSchema );
 
 		const allowedChildren = toArray( definition.allowChildren || [] );
@@ -199,18 +202,86 @@ export default class DataFilter {
 	}
 
 	/**
-	 * Registers attribute converters for the given inline element definition.
+	 * Registers element to element converters for the given block element definition.
+	 *
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+	 */
+	_addBlockElementToElementConversion( { model: modelName, view: viewName } ) {
+		const conversion = this.editor.conversion;
+
+		if ( !viewName ) {
+			return;
+		}
+
+		conversion.for( 'upcast' ).elementToElement( {
+			model: modelName,
+			view: viewName,
+			// With a `low` priority, `paragraph` plugin auto-paragraphing mechanism is executed. Make sure
+			// this listener is called before it. If not, some elements will be transformed into a paragraph.
+			converterPriority: priorities.get( 'low' ) + 1
+		} );
+
+		conversion.for( 'downcast' ).elementToElement( {
+			model: modelName,
+			view: viewName
+		} );
+	}
+
+	/**
+	 * Registers attribute converters for the given block element definition.
+	 *
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+	 */
+	_addBlockElementAttributeConversion( { model: modelName, view: viewName } ) {
+		const conversion = this.editor.conversion;
+
+		if ( !viewName ) {
+			return;
+		}
+
+		conversion.for( 'upcast' ).add( dispatcher => {
+			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
+				if ( !data.modelRange ) {
+					return;
+				}
+
+				const viewAttributes = this._matchAndConsumeAllowedAttributes( data.viewItem, conversionApi );
+
+				if ( viewAttributes ) {
+					conversionApi.writer.setAttribute( DATA_SCHEMA_ATTRIBUTE_KEY, viewAttributes, data.modelRange );
+				}
+			}, { priority: 'low' } );
+		} );
+
+		conversion.for( 'downcast' ).add( dispatcher => {
+			dispatcher.on( `attribute:${ DATA_SCHEMA_ATTRIBUTE_KEY }:${ modelName }`, ( evt, data, conversionApi ) => {
+				const viewAttributes = data.attributeNewValue;
+
+				if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
+					return;
+				}
+
+				const viewWriter = conversionApi.writer;
+				const viewElement = conversionApi.mapper.toViewElement( data.item );
+
+				setViewElementAttributes( viewWriter, viewAttributes, viewElement );
+			} );
+		} );
+	}
+
+	/**
+	 * Registers converters for the given inline element definition.
 	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
-	_defineInlineElementConverters( definition ) {
+	_addInlineElementConversion( definition ) {
 		const conversion = this.editor.conversion;
 		const viewName = definition.view;
 		const attributeKey = definition.model;
 
-		this._addDisallowedAttributesConverter( viewName );
-
 		conversion.for( 'upcast' ).add( dispatcher => {
 			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
 				const viewAttributes = this._matchAndConsumeAllowedAttributes( data.viewItem, conversionApi );
@@ -253,65 +324,17 @@ export default class DataFilter {
 	}
 
 	/**
-	 * Registers attribute converters for the given block element definition.
+	 * Registers converters responsible for consuming disallowed view attributes.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
-	_defineBlockElementConverters( definition ) {
+	_addDisallowedAttributeConversion( { view: viewName } ) {
 		const conversion = this.editor.conversion;
-		const viewName = definition.view;
-		const modelName = definition.model;
-
-		this._addDisallowedAttributesConverter( viewName );
-
-		// Stash unused, allowed element attributes, so they can be reapplied later in data conversion.
-		conversion.for( 'upcast' ).elementToElement( {
-			view: viewName,
-			model: ( viewElement, conversionApi ) => {
-				const element = conversionApi.writer.createElement( modelName );
-				const viewAttributes = this._matchAndConsumeAllowedAttributes( viewElement, conversionApi );
-
-				if ( viewAttributes ) {
-					conversionApi.writer.setAttribute( DATA_SCHEMA_ATTRIBUTE_KEY, viewAttributes, element );
-				}
-
-				return element;
-			},
-			// With a `low` priority, `paragraph` plugin auto-paragraphing mechanism is executed. Make sure
-			// this listener is called before it. If not, some elements will be transformed into a paragraph.
-			converterPriority: priorities.get( 'low' ) + 1
-		} );
 
-		conversion.for( 'downcast' ).elementToElement( {
-			model: modelName,
-			view: viewName
-		} );
-
-		conversion.for( 'downcast' ).add( dispatcher => {
-			dispatcher.on( `attribute:${ DATA_SCHEMA_ATTRIBUTE_KEY }:${ modelName }`, ( evt, data, conversionApi ) => {
-				const viewAttributes = data.attributeNewValue;
-
-				if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
-					return;
-				}
-
-				const viewWriter = conversionApi.writer;
-				const viewElement = conversionApi.mapper.toViewElement( data.item );
-
-				setViewElementAttributes( viewWriter, viewAttributes, viewElement );
-			} );
-		} );
-	}
-
-	/**
-	 * Adds converter responsible for consuming disallowed view attributes.
-	 *
-	 * @private
-	 * @param {String} viewName
-	 */
-	_addDisallowedAttributesConverter( viewName ) {
-		const conversion = this.editor.conversion;
+		if ( !viewName ) {
+			return;
+		}
 
 		// Consumes disallowed element attributes to prevent them of being processed by other converters.
 		conversion.for( 'upcast' ).add( dispatcher => {
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index ebdd61537e1..3d119f33578 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -49,6 +49,21 @@ export default class DataSchema {
 		this._definitions = new Map();
 
 		// Block elements.
+		this.extendBlockElement( {
+			model: 'paragraph',
+			view: 'p'
+		} );
+
+		this.extendBlockElement( {
+			model: 'blockQuote',
+			view: 'blockquote'
+		} );
+
+		this.extendBlockElement( {
+			model: 'listItem',
+			view: 'li'
+		} );
+
 		this.registerBlockElement( {
 			model: '$htmlBlock',
 			allowChildren: '$block',
@@ -146,7 +161,7 @@ export default class DataSchema {
 	}
 
 	/**
-	 * Add new data schema definition for block element.
+	 * Add new data schema definition describing block element.
 	 *
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
@@ -155,7 +170,7 @@ export default class DataSchema {
 	}
 
 	/**
-	 * Add new data schema definition for inline element.
+	 * Add new data schema definition describing inline element.
 	 *
 	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
@@ -163,6 +178,15 @@ export default class DataSchema {
 		this._definitions.set( definition.model, { ...definition, isInline: true } );
 	}
 
+	/**
+	 * Add new data schema definition to extend existing editor's model block element.
+	 *
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+	 */
+	extendBlockElement( definition ) {
+		this.registerBlockElement( { ...definition, extend: true } );
+	}
+
 	/**
 	 * Returns all definitions matching the given view name.
 	 *
@@ -250,6 +274,7 @@ function testViewName( pattern, viewName ) {
  *
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
  * @property {String} model Name of the model.
+ * @property {Boolean} [extend=false] Indicates if data schema should extend existing model definition.
  */
 
 /**
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index f5c020507bf..8cb456a4bc7 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -380,6 +380,24 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal( '<section><p>foo</p></section>' );
 		} );
+
+		it( 'should only set attributes on existing model range', () => {
+			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowAttributes( { name: 'p', attributes: { 'data-foo': 'foo' } } );
+
+			editor.conversion.for( 'upcast' ).add( dispatcher => {
+				dispatcher.on( 'element:p', ( evt, data ) => {
+					data.modelRange = null;
+				} );
+			} );
+
+			editor.setData( '<p data-foo="foo">foo</p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>foo</paragraph>',
+				attributes: {}
+			} );
+		} );
 	} );
 
 	describe( 'inline', () => {
@@ -763,6 +781,122 @@ describe( 'DataFilter', () => {
 		expect( editor.getData() ).to.equal( '<p><span style="color:blue;"><span>foobar</span></span></p>' );
 	} );
 
+	describe( 'existing features', () => {
+		it( 'should allow additional attributes', () => {
+			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowAttributes( { name: 'p', attributes: { 'data-foo': 'foo' } } );
+
+			editor.setData( '<p data-foo="foo">foo</p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph htmlAttributes="(1)">foo</paragraph>',
+				attributes: {
+					1: {
+						attributes: { 'data-foo': 'foo' }
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p data-foo="foo">foo</p>' );
+		} );
+
+		it( 'should allow additional attributes (classes)', () => {
+			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowAttributes( { name: 'p', classes: /[\s\S]+/ } );
+
+			editor.setData( '<p class="foo">foo</p><p class="bar">bar</p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph htmlAttributes="(1)">foo</paragraph><paragraph htmlAttributes="(2)">bar</paragraph>',
+				attributes: {
+					1: {
+						classes: [ 'foo' ]
+					},
+					2: {
+						classes: [ 'bar' ]
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p class="foo">foo</p><p class="bar">bar</p>' );
+		} );
+
+		it( 'should allow additional attributes (styles)', () => {
+			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowAttributes( { name: 'p', styles: { 'color': /[\s\S]+/ } } );
+
+			editor.setData( '<p style="color:red;">foo</p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph htmlAttributes="(1)">foo</paragraph>',
+				attributes: {
+					1: {
+						styles: { color: 'red' }
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p style="color:red;">foo</p>' );
+		} );
+
+		it( 'should disallow attributes', () => {
+			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowAttributes( { name: 'p', attributes: { 'data-foo': /[\s\S]+/ } } );
+			dataFilter.disallowAttributes( { name: 'p', attributes: { 'data-foo': 'bar' } } );
+
+			editor.setData( '<p data-foo="foo">foo</p><p data-foo="bar">bar</p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph htmlAttributes="(1)">foo</paragraph><paragraph>bar</paragraph>',
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': 'foo'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p data-foo="foo">foo</p><p>bar</p>' );
+		} );
+
+		it( 'should disallow attributes (styles)', () => {
+			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowAttributes( { name: 'p', styles: { color: /[\s\S]+/ } } );
+			dataFilter.disallowAttributes( { name: 'p', styles: { color: 'red' } } );
+
+			editor.setData( '<p style="color:blue;">foo</p><p style="color:red">bar</p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph htmlAttributes="(1)">foo</paragraph><paragraph>bar</paragraph>',
+				attributes: {
+					1: {
+						styles: {
+							color: 'blue'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p style="color:blue;">foo</p><p>bar</p>' );
+		} );
+
+		it( 'should disallow attributes (classes)', () => {
+			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowAttributes( { name: 'p', classes: [ 'foo', 'bar' ] } );
+			dataFilter.disallowAttributes( { name: 'p', classes: [ 'bar' ] } );
+
+			editor.setData( '<p class="foo bar">foo</p><p class="bar">bar</p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>foo</paragraph><paragraph>bar</paragraph>',
+				attributes: {}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p>foo</p><p>bar</p>' );
+		} );
+	} );
+
 	it( 'should preserve attributes not used by other features', () => {
 		dataFilter.allowElement( { name: 'span' } );
 		dataFilter.allowAttributes( { name: 'span', styles: { 'color': /[\s\S]+/ } } );
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index 273f9e1d25d..45cdce0f7a0 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -4,11 +4,14 @@
  */
 
 import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
+import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import DataSchema from '../src/dataschema';
 
 describe( 'DataSchema', () => {
 	let editor, dataSchema;
 
+	testUtils.createSinonSandbox();
+
 	beforeEach( () => {
 		return VirtualTestEditor
 			.create()
@@ -23,7 +26,7 @@ describe( 'DataSchema', () => {
 		return editor.destroy();
 	} );
 
-	describe( 'registerInlineElement', () => {
+	describe( 'registerInlineElement()', () => {
 		it( 'should register proper definition', () => {
 			dataSchema.registerInlineElement( { model: 'htmlDef', view: 'def' } );
 
@@ -58,7 +61,7 @@ describe( 'DataSchema', () => {
 		} );
 	} );
 
-	describe( 'registerBlockElement', () => {
+	describe( 'registerBlockElement()', () => {
 		const fakeDefinitions = [
 			{
 				view: 'def1',
@@ -190,4 +193,27 @@ describe( 'DataSchema', () => {
 			return getFakeDefinitions( ...viewNames ).map( def => ( { ...def, isBlock: true } ) );
 		}
 	} );
+
+	describe( 'extendBlockElement()', () => {
+		it( 'should register proper definition', () => {
+			dataSchema.extendBlockElement( { model: 'paragraph', view: 'p' } );
+
+			const result = dataSchema.getDefinitionsForView( 'p' );
+
+			expect( Array.from( result ) ).to.deep.equal( [ {
+				model: 'paragraph',
+				view: 'p',
+				isBlock: true,
+				extend: true
+			} ] );
+		} );
+
+		it( 'should use registerBlockElement()', () => {
+			const spy = sinon.spy( dataSchema, 'registerBlockElement' );
+
+			dataSchema.extendBlockElement( { model: 'paragraph', view: 'p' } );
+
+			expect( spy.calledOnce ).to.be.true;
+		} );
+	} );
 } );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.html
index e64de28457f..544c1e8728d 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.html
@@ -4,8 +4,8 @@
 
 <div id="editor">
 	<article>
-		<section id="section1"><p>Section #1</p></section>
-		<section id="_section2"><p>Section #2</p></section>
+		<section id="section1"><p data-foo="foo">Section #1</p></section>
+		<section id="_section2"><p style="background-color: violet;">Section #2</p></section>
 		<section id="section3" style="color: red" class="special_section"><p>Section #3</p></section>
 	</article>
 
@@ -23,16 +23,27 @@
 
 	<xyz><p>XYZ</p></xyz>
 
-	<p>
+	<p data-foo="foo">
 		<span data-foo="foo">Nested cite: <cite style="color:blue;">I'm blue!</cite></span>
 	</p>
-	<p>
+	<p data-foo="bar">
 		<span data-foo="foo">Nested span: <span style="color:blue;">I'm blue!</span></span>
 	</p>
 
 	<p><cite>Deeply<cite> nested<cite> cite<span style="color:blue;"> with span!</span></cite></cite></cite></p>
 
-	<p><span>Span with no attributes!</span></p>
+	<p style="background-color: violet;"><span>Span with no attributes!</span></p>
 
 	<p><span style="color:blue;"><span style="color:green;">Span with nested styles!</span></span></p>
+
+	<blockquote style="color: red;">Red quote!</blockquote>
+
+	<ul>
+		<li style="color: blue;">Blue!</li>
+		<li style="color: red;">Red!</li>
+		<li style="color: violet;">Violet!</li>
+		<ul>
+			<li style="color: yellow;">Yellow!</li>
+		</ul>
+	</ul>
 </div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
index dd3604a16a6..37fb9e6ad95 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
@@ -65,6 +65,17 @@ class ExtendHTMLSupport extends Plugin {
 		dataFilter.allowAttributes( { name: /^(span|cite)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
 		dataFilter.allowAttributes( { name: /^(span|cite)$/, styles: { color: /[\s\S]+/ } } );
 		dataFilter.disallowAttributes( { name: /^(span|cite)$/, styles: { color: 'red' } } );
+
+		// Allow existing features.
+		dataFilter.allowElement( { name: 'p' } );
+		dataFilter.allowAttributes( { name: 'p', attributes: { 'data-foo': /[\s\S]+/ } } );
+		dataFilter.allowAttributes( { name: 'p', styles: { 'background-color': /[\s\S]+/ } } );
+
+		dataFilter.allowElement( { name: 'blockquote' } );
+		dataFilter.allowAttributes( { name: 'blockquote', styles: { 'color': /[\s\S]+/ } } );
+
+		dataFilter.allowElement( { name: 'li' } );
+		dataFilter.allowAttributes( { name: 'li', styles: { 'color': /[\s\S]+/ } } );
 	}
 }
 

From 7f81ef038e7b211ac48ebf4bf976579dbba87bd8 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 6 Apr 2021 10:00:50 +0200
Subject: [PATCH 096/217] Rewording.

---
 packages/ckeditor5-content-compatibility/src/dataschema.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 3d119f33578..078970fad30 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -274,7 +274,7 @@ function testViewName( pattern, viewName ) {
  *
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
  * @property {String} model Name of the model.
- * @property {Boolean} [extend=false] Indicates if data schema should extend existing model definition.
+ * @property {Boolean} [extend=false] Indicates if data schema should extend existing editor element.
  */
 
 /**

From 7dd2494ceda484587d5c394d7e513c1dedb2751e Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 8 Apr 2021 08:46:37 +0200
Subject: [PATCH 097/217] Renaming.

---
 .../src/datafilter.js                              |  2 +-
 .../src/dataschema.js                              | 14 +++++++-------
 .../tests/dataschema.js                            |  8 ++++----
 3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 8cba235cd0a..a6c7472f31b 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -143,7 +143,7 @@ export default class DataFilter {
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
 	_defineBlockElement( definition ) {
-		if ( !definition.extend ) {
+		if ( !definition.isFeature ) {
 			this._defineBlockElementSchema( definition );
 			this._addBlockElementToElementConversion( definition );
 		}
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 078970fad30..bfadf2f56ce 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -49,17 +49,17 @@ export default class DataSchema {
 		this._definitions = new Map();
 
 		// Block elements.
-		this.extendBlockElement( {
+		this.registerBlockElementFeature( {
 			model: 'paragraph',
 			view: 'p'
 		} );
 
-		this.extendBlockElement( {
+		this.registerBlockElementFeature( {
 			model: 'blockQuote',
 			view: 'blockquote'
 		} );
 
-		this.extendBlockElement( {
+		this.registerBlockElementFeature( {
 			model: 'listItem',
 			view: 'li'
 		} );
@@ -179,12 +179,12 @@ export default class DataSchema {
 	}
 
 	/**
-	 * Add new data schema definition to extend existing editor's model block element.
+	 * Add new data schema definition to extend existing editor's model block element feature.
 	 *
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
-	extendBlockElement( definition ) {
-		this.registerBlockElement( { ...definition, extend: true } );
+	registerBlockElementFeature( definition ) {
+		this.registerBlockElement( { ...definition, isFeature: true } );
 	}
 
 	/**
@@ -274,7 +274,7 @@ function testViewName( pattern, viewName ) {
  *
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
  * @property {String} model Name of the model.
- * @property {Boolean} [extend=false] Indicates if data schema should extend existing editor element.
+ * @property {Boolean} [isFeature=false] Indicates if data schema should extend existing editor feature.
  */
 
 /**
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index 45cdce0f7a0..eed56377e6f 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -194,9 +194,9 @@ describe( 'DataSchema', () => {
 		}
 	} );
 
-	describe( 'extendBlockElement()', () => {
+	describe( 'registerBlockElementFeature()', () => {
 		it( 'should register proper definition', () => {
-			dataSchema.extendBlockElement( { model: 'paragraph', view: 'p' } );
+			dataSchema.registerBlockElementFeature( { model: 'paragraph', view: 'p' } );
 
 			const result = dataSchema.getDefinitionsForView( 'p' );
 
@@ -204,14 +204,14 @@ describe( 'DataSchema', () => {
 				model: 'paragraph',
 				view: 'p',
 				isBlock: true,
-				extend: true
+				isFeature: true
 			} ] );
 		} );
 
 		it( 'should use registerBlockElement()', () => {
 			const spy = sinon.spy( dataSchema, 'registerBlockElement' );
 
-			dataSchema.extendBlockElement( { model: 'paragraph', view: 'p' } );
+			dataSchema.registerBlockElementFeature( { model: 'paragraph', view: 'p' } );
 
 			expect( spy.calledOnce ).to.be.true;
 		} );

From 8b326e99bf1708590af74c33ec827e551d0a4c56 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 8 Apr 2021 08:57:48 +0200
Subject: [PATCH 098/217] Ensure that model is not registered early.

---
 .../src/datafilter.js                            |  8 +++-----
 .../tests/datafilter.js                          | 16 ++++++++++++++++
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index a6c7472f31b..cc7887e872e 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -143,7 +143,9 @@ export default class DataFilter {
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
 	_defineBlockElement( definition ) {
-		if ( !definition.isFeature ) {
+		const schema = this.editor.model.schema;
+
+		if ( !definition.isFeature && !schema.isRegistered( definition.model ) ) {
 			this._defineBlockElementSchema( definition );
 			this._addBlockElementToElementConversion( definition );
 		}
@@ -184,10 +186,6 @@ export default class DataFilter {
 	_defineBlockElementSchema( definition ) {
 		const schema = this.editor.model.schema;
 
-		if ( schema.isRegistered( definition.model ) ) {
-			return;
-		}
-
 		schema.register( definition.model, definition.modelSchema );
 
 		const allowedChildren = toArray( definition.allowChildren || [] );
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 8cb456a4bc7..26fbd9cc4af 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -398,6 +398,22 @@ describe( 'DataFilter', () => {
 				attributes: {}
 			} );
 		} );
+
+		it( 'should not register converters if element definition was already registered', () => {
+			dataSchema.registerBlockElement( {
+				model: 'htmlXyz',
+				view: 'xyz',
+				modelSchema: { inheritAllFrom: '$block' }
+			} );
+
+			editor.model.schema.register( 'htmlXyz', { inheritAllFrom: '$block' } );
+
+			dataFilter.allowElement( { name: 'xyz' } );
+
+			editor.setData( '<xyz>foo</xyz>' );
+
+			expect( getModelData( model, { withoutSelection: true } ) ).to.equal( '<paragraph>foo</paragraph>' );
+		} );
 	} );
 
 	describe( 'inline', () => {

From 5028c38929e915f9493a71ab1c3fd3e794159d80 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 8 Apr 2021 09:22:37 +0200
Subject: [PATCH 099/217] Return early for attribute filters also.

---
 .../ckeditor5-content-compatibility/src/datafilter.js     | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index cc7887e872e..ff63c02a91d 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -145,7 +145,13 @@ export default class DataFilter {
 	_defineBlockElement( definition ) {
 		const schema = this.editor.model.schema;
 
-		if ( !definition.isFeature && !schema.isRegistered( definition.model ) ) {
+		if ( !definition.isFeature ) {
+			// Early return, so if definition has been already registered,
+			// attribute filters also will be skipped.
+			if ( schema.isRegistered( definition.model ) ) {
+				return;
+			}
+
 			this._defineBlockElementSchema( definition );
 			this._addBlockElementToElementConversion( definition );
 		}

From d5219fbd41c84bf901d53d068f20dfdd22f806e7 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 8 Apr 2021 09:28:49 +0200
Subject: [PATCH 100/217] Reworded test to use real case scenario.

---
 .../tests/datafilter.js                           | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 26fbd9cc4af..a9e1a4469fa 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -6,6 +6,7 @@
 import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
 import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
 import FontColorEditing from '@ckeditor/ckeditor5-font/src/fontcolor/fontcolorediting';
+import ListEditing from '@ckeditor/ckeditor5-list/src/listediting';
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import { expectToThrowCKEditorError } from '@ckeditor/ckeditor5-utils/tests/_utils/utils';
 import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
@@ -21,7 +22,7 @@ describe( 'DataFilter', () => {
 	beforeEach( () => {
 		return VirtualTestEditor
 			.create( {
-				plugins: [ Paragraph, FontColorEditing ]
+				plugins: [ Paragraph, FontColorEditing, ListEditing ]
 			} )
 			.then( newEditor => {
 				editor = newEditor;
@@ -382,16 +383,12 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should only set attributes on existing model range', () => {
-			dataFilter.allowElement( { name: 'p' } );
-			dataFilter.allowAttributes( { name: 'p', attributes: { 'data-foo': 'foo' } } );
+			dataSchema.registerBlockElementFeature( { view: 'xyz', model: 'modelXyz' } );
 
-			editor.conversion.for( 'upcast' ).add( dispatcher => {
-				dispatcher.on( 'element:p', ( evt, data ) => {
-					data.modelRange = null;
-				} );
-			} );
+			dataFilter.allowElement( { name: 'xyz' } );
+			dataFilter.allowAttributes( { name: 'xyz', attributes: { 'data-foo': 'foo' } } );
 
-			editor.setData( '<p data-foo="foo">foo</p>' );
+			editor.setData( '<xyz>foo</xyz>' );
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>foo</paragraph>',

From 26869819178a0967be8dba0e526e1e7e3bf314bc Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 8 Apr 2021 09:31:39 +0200
Subject: [PATCH 101/217] Removed dead code.

---
 packages/ckeditor5-content-compatibility/tests/datafilter.js | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index a9e1a4469fa..3ee12db8b3d 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -6,7 +6,6 @@
 import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
 import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
 import FontColorEditing from '@ckeditor/ckeditor5-font/src/fontcolor/fontcolorediting';
-import ListEditing from '@ckeditor/ckeditor5-list/src/listediting';
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import { expectToThrowCKEditorError } from '@ckeditor/ckeditor5-utils/tests/_utils/utils';
 import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
@@ -22,7 +21,7 @@ describe( 'DataFilter', () => {
 	beforeEach( () => {
 		return VirtualTestEditor
 			.create( {
-				plugins: [ Paragraph, FontColorEditing, ListEditing ]
+				plugins: [ Paragraph, FontColorEditing ]
 			} )
 			.then( newEditor => {
 				editor = newEditor;

From c1b734d0d1350a3f74b7a3368277031f5d1a1c7b Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 8 Apr 2021 10:51:04 +0200
Subject: [PATCH 102/217] Minor refactoring, commenting.

---
 .../src/datafilter.js                         | 22 ++++++++++---------
 .../tests/datafilter.js                       |  6 ++++-
 2 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index ff63c02a91d..18b8a6355a7 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -117,9 +117,9 @@ export default class DataFilter {
 	 */
 	_registerElement( definition ) {
 		if ( definition.isInline ) {
-			this._defineInlineElement( definition );
+			this._registerInlineElement( definition );
 		} else if ( definition.isBlock ) {
-			this._defineBlockElement( definition );
+			this._registerBlockElement( definition );
 		} else {
 			/**
 			 * Only a definition marked as inline or block can be allowed.
@@ -142,7 +142,7 @@ export default class DataFilter {
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
-	_defineBlockElement( definition ) {
+	_registerBlockElement( definition ) {
 		const schema = this.editor.model.schema;
 
 		if ( !definition.isFeature ) {
@@ -152,10 +152,12 @@ export default class DataFilter {
 				return;
 			}
 
-			this._defineBlockElementSchema( definition );
+			this._registerBlockElementSchema( definition );
 			this._addBlockElementToElementConversion( definition );
 		}
 
+		// TODO So far we are not able to detect if feature converters has been already added,
+		// so this code may result in duplicated converters and additional conversion overheat.
 		this._addDisallowedAttributeConversion( definition );
 		this._addBlockElementAttributeConversion( definition );
 	}
@@ -168,7 +170,7 @@ export default class DataFilter {
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
-	_defineInlineElement( definition ) {
+	_registerInlineElement( definition ) {
 		const schema = this.editor.model.schema;
 
 		schema.extend( '$text', {
@@ -189,7 +191,7 @@ export default class DataFilter {
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
-	_defineBlockElementSchema( definition ) {
+	_registerBlockElementSchema( definition ) {
 		const schema = this.editor.model.schema;
 
 		schema.register( definition.model, definition.modelSchema );
@@ -206,7 +208,7 @@ export default class DataFilter {
 	}
 
 	/**
-	 * Registers element to element converters for the given block element definition.
+	 * Adds element to element converters for the given block element definition.
 	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
@@ -233,7 +235,7 @@ export default class DataFilter {
 	}
 
 	/**
-	 * Registers attribute converters for the given block element definition.
+	 * Adds attribute converters for the given block element definition.
 	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
@@ -276,7 +278,7 @@ export default class DataFilter {
 	}
 
 	/**
-	 * Registers converters for the given inline element definition.
+	 * Adds converters for the given inline element definition.
 	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
@@ -328,7 +330,7 @@ export default class DataFilter {
 	}
 
 	/**
-	 * Registers converters responsible for consuming disallowed view attributes.
+	 * Adds converters responsible for consuming disallowed view attributes.
 	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 3ee12db8b3d..93c3c013449 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -381,12 +381,16 @@ describe( 'DataFilter', () => {
 			expect( editor.getData() ).to.equal( '<section><p>foo</p></section>' );
 		} );
 
-		it( 'should only set attributes on existing model range', () => {
+		it( 'should not convert attributes if the model schema item definition is not registered', () => {
 			dataSchema.registerBlockElementFeature( { view: 'xyz', model: 'modelXyz' } );
 
 			dataFilter.allowElement( { name: 'xyz' } );
 			dataFilter.allowAttributes( { name: 'xyz', attributes: { 'data-foo': 'foo' } } );
 
+			// We are not registering model schema anywhere, to check if upcast
+			// converter will be able to detect this case.
+			// editor.model.schema.register( 'modelXyz', { ... } );
+
 			editor.setData( '<xyz>foo</xyz>' );
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {

From b4d1af9b404c3728c35125d613c51141fcaf622f Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 12 Apr 2021 17:26:51 +0200
Subject: [PATCH 103/217] Added inline elements priority support, simplified
 code.

---
 .../package.json                              |  1 +
 .../src/datafilter.js                         |  2 +-
 .../src/dataschema.js                         | 55 +++++++++++++------
 .../tests/datafilter.js                       | 28 +++++++++-
 .../tests/dataschema.js                       | 39 ++++++-------
 .../tests/manual/generichtmlsupport.html      | 12 ++++
 .../tests/manual/generichtmlsupport.js        | 18 ++++++
 7 files changed, 112 insertions(+), 43 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/package.json b/packages/ckeditor5-content-compatibility/package.json
index 67b600df95c..97cc03ad01a 100644
--- a/packages/ckeditor5-content-compatibility/package.json
+++ b/packages/ckeditor5-content-compatibility/package.json
@@ -26,6 +26,7 @@
     "@ckeditor/ckeditor5-engine": "^27.0.0",
     "@ckeditor/ckeditor5-essentials": "^27.0.0",
     "@ckeditor/ckeditor5-font": "^27.0.0",
+    "@ckeditor/ckeditor5-link": "^27.0.0",
     "@ckeditor/ckeditor5-list": "^27.0.0",
     "@ckeditor/ckeditor5-paragraph": "^27.0.0",
     "@ckeditor/ckeditor5-utils": "^27.0.0",
diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 18b8a6355a7..9d94489582a 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -320,7 +320,7 @@ export default class DataFilter {
 				}
 
 				const { writer } = conversionApi;
-				const viewElement = writer.createAttributeElement( viewName );
+				const viewElement = writer.createAttributeElement( viewName, null, { priority: definition.priority } );
 
 				setViewElementAttributes( writer, attributeValue, viewElement );
 
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index bfadf2f56ce..b80378b5921 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -49,19 +49,22 @@ export default class DataSchema {
 		this._definitions = new Map();
 
 		// Block elements.
-		this.registerBlockElementFeature( {
+		this.registerBlockElement( {
 			model: 'paragraph',
-			view: 'p'
+			view: 'p',
+			isFeature: true
 		} );
 
-		this.registerBlockElementFeature( {
+		this.registerBlockElement( {
 			model: 'blockQuote',
-			view: 'blockquote'
+			view: 'blockquote',
+			isFeature: true
 		} );
 
-		this.registerBlockElementFeature( {
+		this.registerBlockElement( {
 			model: 'listItem',
-			view: 'li'
+			view: 'li',
+			isFeature: true
 		} );
 
 		this.registerBlockElement( {
@@ -143,6 +146,27 @@ export default class DataSchema {
 		} );
 
 		// Inline elements.
+		this.registerInlineElement( {
+			view: 'a',
+			model: 'htmlA',
+			priority: 5
+		} );
+
+		this.registerInlineElement( {
+			view: 'strong',
+			model: 'htmlStrong'
+		} );
+
+		this.registerInlineElement( {
+			view: 'i',
+			model: 'htmlI'
+		} );
+
+		this.registerInlineElement( {
+			view: 's',
+			model: 'htmlS'
+		} );
+
 		this.registerInlineElement( {
 			view: 'span',
 			model: 'htmlSpan',
@@ -175,16 +199,11 @@ export default class DataSchema {
 	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
 	registerInlineElement( definition ) {
-		this._definitions.set( definition.model, { ...definition, isInline: true } );
-	}
-
-	/**
-	 * Add new data schema definition to extend existing editor's model block element feature.
-	 *
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
-	 */
-	registerBlockElementFeature( definition ) {
-		this.registerBlockElement( { ...definition, isFeature: true } );
+		this._definitions.set( definition.model, {
+			priority: 10,
+			...definition,
+			isInline: true
+		} );
 	}
 
 	/**
@@ -274,7 +293,6 @@ function testViewName( pattern, viewName ) {
  *
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
  * @property {String} model Name of the model.
- * @property {Boolean} [isFeature=false] Indicates if data schema should extend existing editor feature.
  */
 
 /**
@@ -285,6 +303,7 @@ function testViewName( pattern, viewName ) {
  * @property {module:engine/model/schema~SchemaItemDefinition} [modelSchema] The model schema item definition describing registered model.
  * @property {String|Array.<String>} [allowChildren] Extends the given children list to allow definition model.
  * @property {Boolean} isBlock Indicates that the definition describes block element.
+ * @property {Boolean} [isFeature=false] Indicates if data schema should extend existing editor feature.
  * Set by {@link module:content-compatibility/dataschema~DataSchema#registerBlockElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */
@@ -296,6 +315,8 @@ function testViewName( pattern, viewName ) {
  * @property {String} view Name of the view element.
  * @property {module:engine/model/schema~AttributeProperties} [attributeProperties] Additional metadata describing the model attribute.
  * @property {Boolean} isInline Indicates that the definition descibes inline element.
+ * @property {Number} [priority=10] Element priority. Decides in what order elements are wrapped by
+ * {@link module:engine/view/downcastwriter~DowncastWriter}.
  * Set by {@link module:content-compatibility/dataschema~DataSchema#registerInlineElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 93c3c013449..4037433cfe2 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -5,6 +5,7 @@
 
 import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
 import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
+import LinkEditing from '@ckeditor/ckeditor5-link/src/linkediting';
 import FontColorEditing from '@ckeditor/ckeditor5-font/src/fontcolor/fontcolorediting';
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import { expectToThrowCKEditorError } from '@ckeditor/ckeditor5-utils/tests/_utils/utils';
@@ -21,7 +22,7 @@ describe( 'DataFilter', () => {
 	beforeEach( () => {
 		return VirtualTestEditor
 			.create( {
-				plugins: [ Paragraph, FontColorEditing ]
+				plugins: [ Paragraph, FontColorEditing, LinkEditing ]
 			} )
 			.then( newEditor => {
 				editor = newEditor;
@@ -382,7 +383,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should not convert attributes if the model schema item definition is not registered', () => {
-			dataSchema.registerBlockElementFeature( { view: 'xyz', model: 'modelXyz' } );
+			dataSchema.registerBlockElement( { view: 'xyz', model: 'modelXyz', isFeature: true } );
 
 			dataFilter.allowElement( { name: 'xyz' } );
 			dataFilter.allowAttributes( { name: 'xyz', attributes: { 'data-foo': 'foo' } } );
@@ -760,6 +761,29 @@ describe( 'DataFilter', () => {
 
 			editor.getData( '<p>foobar</p>' );
 		} );
+
+		it( 'should use correct priority level for existing features', () => {
+			// 'a' element is registered by data schema with priority 5.
+			// We are checking if this element will be correctly nested due to different
+			// AttributeElement priority than default.
+			dataFilter.allowElement( { name: 'a' } );
+			dataFilter.allowAttributes( { name: 'a', attributes: { 'data-foo': 'foo' } } );
+
+			editor.setData( '<p><a href="example.com" data-foo="foo">link</a></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlA="(1)" linkHref="example.com">link</$text></paragraph>',
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': 'foo'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><a href="example.com" data-foo="foo">link</a></p>' );
+		} );
 	} );
 
 	it( 'should correctly resolve attributes nesting order', () => {
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index eed56377e6f..8c589a00cc0 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -35,6 +35,7 @@ describe( 'DataSchema', () => {
 			expect( Array.from( result ) ).to.deep.equal( [ {
 				model: 'htmlDef',
 				view: 'def',
+				priority: 10,
 				isInline: true
 			} ] );
 		} );
@@ -53,12 +54,26 @@ describe( 'DataSchema', () => {
 			expect( Array.from( result ) ).to.deep.equal( [ {
 				model: 'htmlDef',
 				view: 'def',
+				priority: 10,
 				attributeProperties: {
 					copyOnEnter: true
 				},
 				isInline: true
 			} ] );
 		} );
+
+		it( 'should preserve custom priority', () => {
+			dataSchema.registerInlineElement( { model: 'htmlDef', view: 'def', priority: 7 } );
+
+			const result = dataSchema.getDefinitionsForView( 'def' );
+
+			expect( Array.from( result ) ).to.deep.equal( [ {
+				model: 'htmlDef',
+				view: 'def',
+				priority: 7,
+				isInline: true
+			} ] );
+		} );
 	} );
 
 	describe( 'registerBlockElement()', () => {
@@ -81,6 +96,7 @@ describe( 'DataSchema', () => {
 			{
 				view: 'def3',
 				model: 'htmlDef3',
+				isFeature: true,
 				modelSchema: {
 					inheritTypesFrom: 'htmlDef2'
 				}
@@ -193,27 +209,4 @@ describe( 'DataSchema', () => {
 			return getFakeDefinitions( ...viewNames ).map( def => ( { ...def, isBlock: true } ) );
 		}
 	} );
-
-	describe( 'registerBlockElementFeature()', () => {
-		it( 'should register proper definition', () => {
-			dataSchema.registerBlockElementFeature( { model: 'paragraph', view: 'p' } );
-
-			const result = dataSchema.getDefinitionsForView( 'p' );
-
-			expect( Array.from( result ) ).to.deep.equal( [ {
-				model: 'paragraph',
-				view: 'p',
-				isBlock: true,
-				isFeature: true
-			} ] );
-		} );
-
-		it( 'should use registerBlockElement()', () => {
-			const spy = sinon.spy( dataSchema, 'registerBlockElement' );
-
-			dataSchema.registerBlockElementFeature( { model: 'paragraph', view: 'p' } );
-
-			expect( spy.calledOnce ).to.be.true;
-		} );
-	} );
 } );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.html
index 544c1e8728d..491f00db3be 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.html
@@ -46,4 +46,16 @@
 			<li style="color: yellow;">Yellow!</li>
 		</ul>
 	</ul>
+	<p>
+		<a href="example.com" style="background-color:#5de">Link with different background color.</a>
+	</p>
+	<p>
+		<strong style="font-weight:400">Strong with font weight 400</strong>
+	</p>
+	<p>
+		<i data-foo="foo" style="color: green;">Italic with custom attributes</i>
+	</p>
+	<p>
+		<s style="color: red;">Red strike</s>
+	</p>
 </div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
index 37fb9e6ad95..5821e3c578a 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
@@ -14,6 +14,7 @@ import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
 import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
 import BlockQuote from '@ckeditor/ckeditor5-block-quote/src/blockquote';
 import List from '@ckeditor/ckeditor5-list/src/list';
+import Link from '@ckeditor/ckeditor5-link/src/link';
 
 import DataSchema from '../../src/dataschema';
 import DataFilter from '../../src/datafilter';
@@ -66,6 +67,9 @@ class ExtendHTMLSupport extends Plugin {
 		dataFilter.allowAttributes( { name: /^(span|cite)$/, styles: { color: /[\s\S]+/ } } );
 		dataFilter.disallowAttributes( { name: /^(span|cite)$/, styles: { color: 'red' } } );
 
+		dataFilter.allowAttributes( { name: /^(span|cite)$/, attributes: { 'data-order-id': /[\s\S]+/ } } );
+		dataFilter.allowAttributes( { name: /^(span|cite)$/, attributes: { 'data-item-id': /[\s\S]+/ } } );
+
 		// Allow existing features.
 		dataFilter.allowElement( { name: 'p' } );
 		dataFilter.allowAttributes( { name: 'p', attributes: { 'data-foo': /[\s\S]+/ } } );
@@ -76,12 +80,26 @@ class ExtendHTMLSupport extends Plugin {
 
 		dataFilter.allowElement( { name: 'li' } );
 		dataFilter.allowAttributes( { name: 'li', styles: { 'color': /[\s\S]+/ } } );
+
+		dataFilter.allowElement( { name: 'a' } );
+		dataFilter.allowAttributes( { name: 'a', styles: { 'background-color': /[\s\S]+/ } } );
+
+		dataFilter.allowElement( { name: 'strong' } );
+		dataFilter.allowAttributes( { name: 'strong', styles: { 'font-weight': /[\s\S]+/ } } );
+
+		dataFilter.allowElement( { name: 'i' } );
+		dataFilter.allowAttributes( { name: 'i', styles: { 'color': /[\s\S]+/ } } );
+		dataFilter.allowAttributes( { name: 'i', attributes: { 'data-foo': /[\s\S]+/ } } );
+
+		dataFilter.allowElement( { name: 's' } );
+		dataFilter.allowAttributes( { name: 's', styles: { 'color': /[\s\S]+/ } } );
 	}
 }
 
 ClassicEditor
 	.create( document.querySelector( '#editor' ), {
 		plugins: [
+			Link,
 			BlockQuote,
 			Bold,
 			Essentials,

From 37bf728581f7e838bc559174f0f16a743d2fc9b1 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 14 Apr 2021 10:14:18 +0200
Subject: [PATCH 104/217] Used model schema instead of isFeature, ensured that
 GHS is initialized at the correct moment.

---
 .../src/datafilter.js                         | 59 +++++++++++++++----
 .../src/dataschema.js                         | 10 +---
 .../src/generalhtmlsupport.js                 | 49 +++++++++++++++
 .../tests/datafilter.js                       | 13 ++--
 .../tests/dataschema.js                       |  1 -
 .../tests/manual/generichtmlsupport.js        | 18 ++----
 6 files changed, 114 insertions(+), 36 deletions(-)
 create mode 100644 packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 9d94489582a..7c8c3421f81 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -73,6 +73,45 @@ export default class DataFilter {
 		 * @member {module:engine/view/matcher~Matcher} #_disallowedAttributes
 		 */
 		this._disallowedAttributes = new Matcher();
+
+		/**
+		 * Allowed element definitions by {@link module:content-compatibility/datafilter~DataFilter#allowElement} method.
+		 *
+		 * @readonly
+		 * @private
+		 * @param {Set.<module:content-compatibility/dataschema~DataSchemaDefinition>} #_allowedElements
+		*/
+		this._allowedElements = new Set();
+
+		/**
+		 * Indicates if {@link module:core/editor~Editor#data editor's data controller} data has been already initialized.
+		 *
+		 * @private
+		 * @param {Boolean} #_dataInitialized
+		*/
+		this._dataInitialized = false;
+
+		this._registerElementsAfterInit();
+	}
+
+	/**
+	 * Registers elements allowed by {@link module:content-compatibility/datafilter~DataFilter#allowElement} method
+	 * once {@link module:core/editor~Editor#data editor's data controller} is initialized.
+	 *
+	 * @private
+	*/
+	_registerElementsAfterInit() {
+		this.editor.data.on( 'init', () => {
+			this._dataInitialized = true;
+
+			for ( const definition of this._allowedElements ) {
+				this._registerElement( definition );
+			}
+		}, {
+			// With high priority listener we are able to register elements right before
+			// running data conversion.
+			priority: 'high'
+		} );
 	}
 
 	/**
@@ -85,7 +124,15 @@ export default class DataFilter {
 	 */
 	allowElement( config ) {
 		for ( const definition of this._dataSchema.getDefinitionsForView( config.name, true ) ) {
-			this._registerElement( definition );
+			if ( this._allowedElements.has( definition ) ) {
+				continue;
+			}
+
+			this._allowedElements.add( definition );
+
+			if ( this._dataInitialized ) {
+				this._registerElement( definition );
+			}
 		}
 
 		this.allowAttributes( config );
@@ -145,19 +192,11 @@ export default class DataFilter {
 	_registerBlockElement( definition ) {
 		const schema = this.editor.model.schema;
 
-		if ( !definition.isFeature ) {
-			// Early return, so if definition has been already registered,
-			// attribute filters also will be skipped.
-			if ( schema.isRegistered( definition.model ) ) {
-				return;
-			}
-
+		if ( !schema.isRegistered( definition.model ) ) {
 			this._registerBlockElementSchema( definition );
 			this._addBlockElementToElementConversion( definition );
 		}
 
-		// TODO So far we are not able to detect if feature converters has been already added,
-		// so this code may result in duplicated converters and additional conversion overheat.
 		this._addDisallowedAttributeConversion( definition );
 		this._addBlockElementAttributeConversion( definition );
 	}
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index b80378b5921..cbcd6ea6bf0 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -51,20 +51,17 @@ export default class DataSchema {
 		// Block elements.
 		this.registerBlockElement( {
 			model: 'paragraph',
-			view: 'p',
-			isFeature: true
+			view: 'p'
 		} );
 
 		this.registerBlockElement( {
 			model: 'blockQuote',
-			view: 'blockquote',
-			isFeature: true
+			view: 'blockquote'
 		} );
 
 		this.registerBlockElement( {
 			model: 'listItem',
-			view: 'li',
-			isFeature: true
+			view: 'li'
 		} );
 
 		this.registerBlockElement( {
@@ -303,7 +300,6 @@ function testViewName( pattern, viewName ) {
  * @property {module:engine/model/schema~SchemaItemDefinition} [modelSchema] The model schema item definition describing registered model.
  * @property {String|Array.<String>} [allowChildren] Extends the given children list to allow definition model.
  * @property {Boolean} isBlock Indicates that the definition describes block element.
- * @property {Boolean} [isFeature=false] Indicates if data schema should extend existing editor feature.
  * Set by {@link module:content-compatibility/dataschema~DataSchema#registerBlockElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */
diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
new file mode 100644
index 00000000000..bae367309b0
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
@@ -0,0 +1,49 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module content-compatibility/generalhtmlsupport
+ */
+
+import { Plugin } from 'ckeditor5/src/core';
+
+import DataSchema from './dataschema';
+import DataFilter from './datafilter';
+
+/**
+ * The General HTML Support feature.
+ *
+ * This is a "glue" plugin which initializes the {@link module:content-compatibility/dataschema~DataSchema data schema}
+ * and {@link module:content-compatibility/datafilter~DataFilter data filter} features.
+ *
+ * @extends module:core/plugin~Plugin
+ */
+export default class GeneralHtmlSupport extends Plugin {
+	constructor( editor ) {
+		super( editor );
+
+		/**
+		 * An instance of the {@link module:content-compatibility/dataschema~DataSchema}.
+		 *
+		 * @readonly
+		 * @member {module:content-compatibility/dataschema~DataSchema} #dataSchema
+		 */
+		this.dataSchema = new DataSchema();
+
+		/**
+		 * An instance of the {@link module:content-compatibility/datafilter~DataFilter}.
+		 *
+		 * @readonly
+		 * @member {module:content-compatibility/datafilter~DataFilter} #dataFilter
+		 */
+		this.dataFilter = new DataFilter( editor, this.dataSchema );
+	}
+	/**
+	 * @inheritDoc
+	 */
+	static get pluginName() {
+		return 'GeneralHtmlSupport';
+	}
+}
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 4037433cfe2..742f27b8769 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -11,8 +11,7 @@ import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import { expectToThrowCKEditorError } from '@ckeditor/ckeditor5-utils/tests/_utils/utils';
 import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
 
-import DataSchema from '../src/dataschema';
-import DataFilter from '../src/datafilter';
+import GeneralHtmlSupport from '../src/generalhtmlsupport';
 
 describe( 'DataFilter', () => {
 	let editor, model, dataFilter, dataSchema;
@@ -22,14 +21,16 @@ describe( 'DataFilter', () => {
 	beforeEach( () => {
 		return VirtualTestEditor
 			.create( {
-				plugins: [ Paragraph, FontColorEditing, LinkEditing ]
+				plugins: [ Paragraph, FontColorEditing, LinkEditing, GeneralHtmlSupport ]
 			} )
 			.then( newEditor => {
 				editor = newEditor;
 				model = editor.model;
 
-				dataSchema = new DataSchema();
-				dataFilter = new DataFilter( editor, dataSchema );
+				const plugin = editor.plugins.get( GeneralHtmlSupport );
+
+				dataFilter = plugin.dataFilter;
+				dataSchema = plugin.dataSchema;
 			} );
 	} );
 
@@ -383,7 +384,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should not convert attributes if the model schema item definition is not registered', () => {
-			dataSchema.registerBlockElement( { view: 'xyz', model: 'modelXyz', isFeature: true } );
+			dataSchema.registerBlockElement( { view: 'xyz', model: 'modelXyz' } );
 
 			dataFilter.allowElement( { name: 'xyz' } );
 			dataFilter.allowAttributes( { name: 'xyz', attributes: { 'data-foo': 'foo' } } );
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index 8c589a00cc0..2e701974db5 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -96,7 +96,6 @@ describe( 'DataSchema', () => {
 			{
 				view: 'def3',
 				model: 'htmlDef3',
-				isFeature: true,
 				modelSchema: {
 					inheritTypesFrom: 'htmlDef2'
 				}
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
index 5821e3c578a..7603b63a6a8 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
@@ -16,20 +16,18 @@ import BlockQuote from '@ckeditor/ckeditor5-block-quote/src/blockquote';
 import List from '@ckeditor/ckeditor5-list/src/list';
 import Link from '@ckeditor/ckeditor5-link/src/link';
 
-import DataSchema from '../../src/dataschema';
-import DataFilter from '../../src/datafilter';
+import GeneralHtmlSupport from '../../src/generalhtmlsupport';
 
 /**
  * Client custom plugin extending HTML support for compatibility.
  */
 class ExtendHTMLSupport extends Plugin {
+	static get requires() {
+		return [ GeneralHtmlSupport ];
+	}
+
 	init() {
-		// Create data schema object including default configuration based on CKE4
-		// DTD elements, missing dedicated feature in CKEditor 5.
-		// Data schema only behaves as container for DTD definitions, it doesn't change
-		// anything inside the editor itself. Registered elements are not extending editor
-		// model schema at this point.
-		const dataSchema = new DataSchema();
+		const { dataSchema, dataFilter } = this.editor.plugins.get( GeneralHtmlSupport );
 
 		// Extend schema with custom `xyz` element.
 		dataSchema.registerBlockElement( {
@@ -40,10 +38,6 @@ class ExtendHTMLSupport extends Plugin {
 			}
 		} );
 
-		// Create data filter which will register editor model schema and converters required
-		// to allow elements and filter attributes.
-		const dataFilter = new DataFilter( this.editor, dataSchema );
-
 		// Allow some elements, at this point model schema will include information about view-model mapping
 		// e.g. article -> ghsArticle
 		dataFilter.allowElement( { name: 'article' } );

From e90852e3d707ecef36fb82c450f140885e069a8e Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 14 Apr 2021 10:16:43 +0200
Subject: [PATCH 105/217] Renaming generic to general.

---
 .../ckeditor5-content-compatibility/src/generalhtmlsupport.js    | 1 +
 .../manual/{generichtmlsupport.html => generalhtmlsupport.html}  | 0
 .../manual/{generichtmlsupport.js => generalhtmlsupport.js}      | 0
 .../manual/{generichtmlsupport.md => generalhtmlsupport.md}      | 0
 4 files changed, 1 insertion(+)
 rename packages/ckeditor5-content-compatibility/tests/manual/{generichtmlsupport.html => generalhtmlsupport.html} (100%)
 rename packages/ckeditor5-content-compatibility/tests/manual/{generichtmlsupport.js => generalhtmlsupport.js} (100%)
 rename packages/ckeditor5-content-compatibility/tests/manual/{generichtmlsupport.md => generalhtmlsupport.md} (100%)

diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
index bae367309b0..a5e11bc0bbb 100644
--- a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
@@ -40,6 +40,7 @@ export default class GeneralHtmlSupport extends Plugin {
 		 */
 		this.dataFilter = new DataFilter( editor, this.dataSchema );
 	}
+
 	/**
 	 * @inheritDoc
 	 */
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.html
rename to packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.js
rename to packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.md b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.md
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/generichtmlsupport.md
rename to packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.md

From c7a592fed7443ed6c5d05c7e7b14204d62fbc9f1 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 14 Apr 2021 12:09:40 +0200
Subject: [PATCH 106/217] Added test coverage for initializing ghs from plugin.

---
 .../tests/datafilter.js                       | 73 +++++++++++++++++++
 1 file changed, 73 insertions(+)

diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 742f27b8769..ebc2c078db0 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -4,6 +4,7 @@
  */
 
 import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
+import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
 import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
 import LinkEditing from '@ckeditor/ckeditor5-link/src/linkediting';
 import FontColorEditing from '@ckeditor/ckeditor5-font/src/fontcolor/fontcolorediting';
@@ -38,6 +39,78 @@ describe( 'DataFilter', () => {
 		return editor.destroy();
 	} );
 
+	describe( 'initialization', () => {
+		let initEditor, initModel;
+
+		beforeEach( () => {
+			return VirtualTestEditor
+				.create( {
+					plugins: [ Paragraph, FakeExtentedHtmlPlugin, GeneralHtmlSupport ]
+				} )
+				.then( newEditor => {
+					initEditor = newEditor;
+					initModel = newEditor.model;
+				} );
+		} );
+
+		afterEach( () => {
+			return initEditor.destroy();
+		} );
+
+		it( 'should allow element registered in init() method', () => {
+			initEditor.setData( '<article><p>foobar</p></article>' );
+
+			expect( getModelData( initModel, { withoutSelection: true } ) ).to.equal(
+				'<htmlArticle><paragraph>foobar</paragraph></htmlArticle>'
+			);
+
+			expect( initEditor.getData() ).to.equal( '<article><p>foobar</p></article>' );
+		} );
+
+		it( 'should allow element registered in afterInit() method', () => {
+			initEditor.setData( '<section><p>foobar</p></section>' );
+
+			expect( getModelData( initModel, { withoutSelection: true } ) ).to.equal(
+				'<htmlSection><paragraph>foobar</paragraph></htmlSection>'
+			);
+
+			expect( initEditor.getData() ).to.equal( '<section><p>foobar</p></section>' );
+		} );
+
+		it( 'should allow element registered after editor initialization', () => {
+			const { dataFilter } = initEditor.plugins.get( GeneralHtmlSupport );
+
+			dataFilter.allowElement( { name: 'span' } );
+
+			initEditor.setData( '<p><span>foobar</span></p>' );
+
+			expect( getModelDataWithAttributes( initModel, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlSpan="(1)">foobar</$text></paragraph>',
+				attributes: {
+					1: {}
+				}
+			} );
+
+			expect( initEditor.getData() ).to.equal( '<p><span>foobar</span></p>' );
+		} );
+
+		class FakeExtentedHtmlPlugin extends Plugin {
+			static get requires() {
+				return [ GeneralHtmlSupport ];
+			}
+
+			init() {
+				const { dataFilter } = this.editor.plugins.get( GeneralHtmlSupport );
+				dataFilter.allowElement( { name: 'article' } );
+			}
+
+			afterInit() {
+				const { dataFilter } = this.editor.plugins.get( GeneralHtmlSupport );
+				dataFilter.allowElement( { name: 'section' } );
+			}
+		}
+	} );
+
 	describe( 'block', () => {
 		it( 'should allow element', () => {
 			dataFilter.allowElement( { name: 'article' } );

From 723ad211c60137425faebd3c01f0ec7a619b1c4d Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 14 Apr 2021 12:24:02 +0200
Subject: [PATCH 107/217] Updated defaults.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 7c8c3421f81..2fe4edd0d41 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -87,7 +87,7 @@ export default class DataFilter {
 		 * Indicates if {@link module:core/editor~Editor#data editor's data controller} data has been already initialized.
 		 *
 		 * @private
-		 * @param {Boolean} #_dataInitialized
+		 * @param {Boolean} [#_dataInitialized=false]
 		*/
 		this._dataInitialized = false;
 

From 76be19c1ae001de4129d8bf26bf63ac888b2cd24 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 15 Apr 2021 11:53:16 +0200
Subject: [PATCH 108/217] Refactoring.

---
 .../src/datafilter.js                         | 48 ++++++++++---------
 1 file changed, 26 insertions(+), 22 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 2fe4edd0d41..d5c831e666e 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -79,7 +79,7 @@ export default class DataFilter {
 		 *
 		 * @readonly
 		 * @private
-		 * @param {Set.<module:content-compatibility/dataschema~DataSchemaDefinition>} #_allowedElements
+		 * @member {Set.<module:content-compatibility/dataschema~DataSchemaDefinition>} #_allowedElements
 		*/
 		this._allowedElements = new Set();
 
@@ -87,33 +87,13 @@ export default class DataFilter {
 		 * Indicates if {@link module:core/editor~Editor#data editor's data controller} data has been already initialized.
 		 *
 		 * @private
-		 * @param {Boolean} [#_dataInitialized=false]
+		 * @member {Boolean} [#_dataInitialized=false]
 		*/
 		this._dataInitialized = false;
 
 		this._registerElementsAfterInit();
 	}
 
-	/**
-	 * Registers elements allowed by {@link module:content-compatibility/datafilter~DataFilter#allowElement} method
-	 * once {@link module:core/editor~Editor#data editor's data controller} is initialized.
-	 *
-	 * @private
-	*/
-	_registerElementsAfterInit() {
-		this.editor.data.on( 'init', () => {
-			this._dataInitialized = true;
-
-			for ( const definition of this._allowedElements ) {
-				this._registerElement( definition );
-			}
-		}, {
-			// With high priority listener we are able to register elements right before
-			// running data conversion.
-			priority: 'high'
-		} );
-	}
-
 	/**
 	 * Allow the given element in the editor context.
 	 *
@@ -130,6 +110,10 @@ export default class DataFilter {
 
 			this._allowedElements.add( definition );
 
+			// We need to wait for all features to be initialized before we can register
+			// element, so we can access existing features model schemas.
+			// If the data has not been initialized yet, _registerElementsAfterInit() method will take care of
+			// registering elements.
 			if ( this._dataInitialized ) {
 				this._registerElement( definition );
 			}
@@ -156,6 +140,26 @@ export default class DataFilter {
 		this._disallowedAttributes.add( config );
 	}
 
+	/**
+	 * Registers elements allowed by {@link module:content-compatibility/datafilter~DataFilter#allowElement} method
+	 * once {@link module:core/editor~Editor#data editor's data controller} is initialized.
+	 *
+	 * @private
+	*/
+	_registerElementsAfterInit() {
+		this.editor.data.on( 'init', () => {
+			this._dataInitialized = true;
+
+			for ( const definition of this._allowedElements ) {
+				this._registerElement( definition );
+			}
+		}, {
+			// With high priority listener we are able to register elements right before
+			// running data conversion.
+			priority: 'high'
+		} );
+	}
+
 	/**
 	 * Registers element and attribute converters for the given data schema definition.
 	 *

From 26033e1904bc9253952d1605ee94ce70ce24c4a5 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 15 Apr 2021 11:54:44 +0200
Subject: [PATCH 109/217] Avoid specifying default priority.

---
 .../ckeditor5-content-compatibility/src/dataschema.js     | 8 ++------
 .../ckeditor5-content-compatibility/tests/dataschema.js   | 2 --
 2 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index cbcd6ea6bf0..11a3062679b 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -196,11 +196,7 @@ export default class DataSchema {
 	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
 	registerInlineElement( definition ) {
-		this._definitions.set( definition.model, {
-			priority: 10,
-			...definition,
-			isInline: true
-		} );
+		this._definitions.set( definition.model, { ...definition, isInline: true } );
 	}
 
 	/**
@@ -311,7 +307,7 @@ function testViewName( pattern, viewName ) {
  * @property {String} view Name of the view element.
  * @property {module:engine/model/schema~AttributeProperties} [attributeProperties] Additional metadata describing the model attribute.
  * @property {Boolean} isInline Indicates that the definition descibes inline element.
- * @property {Number} [priority=10] Element priority. Decides in what order elements are wrapped by
+ * @property {Number} [priority] Element priority. Decides in what order elements are wrapped by
  * {@link module:engine/view/downcastwriter~DowncastWriter}.
  * Set by {@link module:content-compatibility/dataschema~DataSchema#registerInlineElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index 2e701974db5..49523214515 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -35,7 +35,6 @@ describe( 'DataSchema', () => {
 			expect( Array.from( result ) ).to.deep.equal( [ {
 				model: 'htmlDef',
 				view: 'def',
-				priority: 10,
 				isInline: true
 			} ] );
 		} );
@@ -54,7 +53,6 @@ describe( 'DataSchema', () => {
 			expect( Array.from( result ) ).to.deep.equal( [ {
 				model: 'htmlDef',
 				view: 'def',
-				priority: 10,
 				attributeProperties: {
 					copyOnEnter: true
 				},

From 3e12ab7b55f72f754e8ff70a6f94f6489dcaeb98 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 15 Apr 2021 11:57:38 +0200
Subject: [PATCH 110/217] Added missing jsdoc.

---
 .../ckeditor5-content-compatibility/src/generalhtmlsupport.js  | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
index a5e11bc0bbb..0954f2789aa 100644
--- a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
@@ -21,6 +21,9 @@ import DataFilter from './datafilter';
  * @extends module:core/plugin~Plugin
  */
 export default class GeneralHtmlSupport extends Plugin {
+	/**
+	 * @param {module:core/editor/editor~Editor} editor
+	*/
 	constructor( editor ) {
 		super( editor );
 

From 397258d1331eba7d2aa766cccb119d0849d87194 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 15 Apr 2021 13:42:13 +0200
Subject: [PATCH 111/217] Listen on priority higher than RTC.

---
 .../src/datafilter.js                             |  5 +++--
 .../tests/datafilter.js                           | 15 ++++++++++++++-
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index d5c831e666e..373bcd85f10 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -155,8 +155,9 @@ export default class DataFilter {
 			}
 		}, {
 			// With high priority listener we are able to register elements right before
-			// running data conversion.
-			priority: 'high'
+			// running data conversion. Make also sure that priority is higher than the one
+			// used by `RealTimeCollaborationClient`, as RTC is stopping event propagation.
+			priority: priorities.get( 'high' ) + 1
 		} );
 	}
 
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index ebc2c078db0..d391eecd298 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -45,7 +45,8 @@ describe( 'DataFilter', () => {
 		beforeEach( () => {
 			return VirtualTestEditor
 				.create( {
-					plugins: [ Paragraph, FakeExtentedHtmlPlugin, GeneralHtmlSupport ]
+					// Keep FakeRTCPlugin before FakeExtentedHtmlPlugin, so it's registered first.
+					plugins: [ Paragraph, FakeRTCPlugin, FakeExtentedHtmlPlugin ]
 				} )
 				.then( newEditor => {
 					initEditor = newEditor;
@@ -94,6 +95,18 @@ describe( 'DataFilter', () => {
 			expect( initEditor.getData() ).to.equal( '<p><span>foobar</span></p>' );
 		} );
 
+		class FakeRTCPlugin extends Plugin {
+			constructor( editor ) {
+				super( editor );
+
+				// Fake listener to simulate RTC one. Registering in constructor to
+				// register it before DataFilter listener.
+				this.editor.data.on( 'init', evt => {
+					evt.stop();
+				}, { priority: 'high' } );
+			}
+		}
+
 		class FakeExtentedHtmlPlugin extends Plugin {
 			static get requires() {
 				return [ GeneralHtmlSupport ];

From df22ed43a203d38b39957f750eea2fe684ae4145 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 6 May 2021 10:23:36 +0200
Subject: [PATCH 112/217] Updated package.json to the latest CKE5 release.

---
 .../package.json                              | 26 +++++++++----------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/package.json b/packages/ckeditor5-content-compatibility/package.json
index 97cc03ad01a..93340377001 100644
--- a/packages/ckeditor5-content-compatibility/package.json
+++ b/packages/ckeditor5-content-compatibility/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@ckeditor/ckeditor5-content-compatibility",
-  "version": "27.0.0",
+  "version": "27.1.0",
   "description": "Content compatibility feature",
   "private": true,
   "keywords": [
@@ -15,21 +15,21 @@
   ],
   "main": "src/index.js",
   "dependencies": {
-    "ckeditor5": "^27.0.0",
+    "ckeditor5": "^27.1.0",
     "lodash-es": "^4.17.15"
   },
   "devDependencies": {
-    "@ckeditor/ckeditor5-basic-styles": "^27.0.0",
-    "@ckeditor/ckeditor5-block-quote": "^27.0.0",
-    "@ckeditor/ckeditor5-core": "^27.0.0",
-    "@ckeditor/ckeditor5-editor-classic": "^27.0.0",
-    "@ckeditor/ckeditor5-engine": "^27.0.0",
-    "@ckeditor/ckeditor5-essentials": "^27.0.0",
-    "@ckeditor/ckeditor5-font": "^27.0.0",
-    "@ckeditor/ckeditor5-link": "^27.0.0",
-    "@ckeditor/ckeditor5-list": "^27.0.0",
-    "@ckeditor/ckeditor5-paragraph": "^27.0.0",
-    "@ckeditor/ckeditor5-utils": "^27.0.0",
+    "@ckeditor/ckeditor5-basic-styles": "^27.1.0",
+    "@ckeditor/ckeditor5-block-quote": "^27.1.0",
+    "@ckeditor/ckeditor5-core": "^27.1.0",
+    "@ckeditor/ckeditor5-editor-classic": "^27.1.0",
+    "@ckeditor/ckeditor5-engine": "^27.1.0",
+    "@ckeditor/ckeditor5-essentials": "^27.1.0",
+    "@ckeditor/ckeditor5-font": "^27.1.0",
+    "@ckeditor/ckeditor5-link": "^27.1.0",
+    "@ckeditor/ckeditor5-list": "^27.1.0",
+    "@ckeditor/ckeditor5-paragraph": "^27.1.0",
+    "@ckeditor/ckeditor5-utils": "^27.1.0",
     "webpack": "^4.43.0",
     "webpack-cli": "^3.3.11"
   },

From a0700a4789a126d3cbf791b8a5f7af5b32b34670 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 6 May 2021 09:33:39 +0200
Subject: [PATCH 113/217] Initial implementation for object elements.

---
 .../package.json                              |   1 +
 .../src/datafilter.js                         | 138 +++++++++++++-----
 .../src/dataschema.js                         | 127 ++++++++++++++++
 .../tests/manual/objects.html                 |  72 +++++++++
 .../tests/manual/objects.js                   |  91 ++++++++++++
 .../tests/manual/objects.md                   |   1 +
 .../theme/datafilter.css                      |  48 ++++++
 7 files changed, 444 insertions(+), 34 deletions(-)
 create mode 100644 packages/ckeditor5-content-compatibility/tests/manual/objects.html
 create mode 100644 packages/ckeditor5-content-compatibility/tests/manual/objects.js
 create mode 100644 packages/ckeditor5-content-compatibility/tests/manual/objects.md
 create mode 100644 packages/ckeditor5-content-compatibility/theme/datafilter.css

diff --git a/packages/ckeditor5-content-compatibility/package.json b/packages/ckeditor5-content-compatibility/package.json
index 93340377001..352c286da55 100644
--- a/packages/ckeditor5-content-compatibility/package.json
+++ b/packages/ckeditor5-content-compatibility/package.json
@@ -29,6 +29,7 @@
     "@ckeditor/ckeditor5-link": "^27.1.0",
     "@ckeditor/ckeditor5-list": "^27.1.0",
     "@ckeditor/ckeditor5-paragraph": "^27.1.0",
+    "@ckeditor/ckeditor5-table": "^27.1.0",
     "@ckeditor/ckeditor5-utils": "^27.1.0",
     "webpack": "^4.43.0",
     "webpack-cli": "^3.3.11"
diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 373bcd85f10..b2b64b69eb6 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -7,12 +7,13 @@
  * @module content-compatibility/datafilter
  */
 
-import { Matcher } from 'ckeditor5/src/engine';
-import { priorities, toArray, CKEditorError } from 'ckeditor5/src/utils';
+import { Matcher, enablePlaceholder } from 'ckeditor5/src/engine';
+import { priorities, CKEditorError } from 'ckeditor5/src/utils';
+import { toWidget } from 'ckeditor5/src/widget';
+import { Template } from 'ckeditor5/src/ui';
+import { cloneDeep, capitalize } from 'lodash-es';
 
-import { cloneDeep } from 'lodash-es';
-
-const DATA_SCHEMA_ATTRIBUTE_KEY = 'htmlAttributes';
+import '../theme/datafilter.css';
 
 /**
  * Allows to validate elements and element attributes registered by {@link module:content-compatibility/dataschema~DataSchema}.
@@ -172,6 +173,8 @@ export default class DataFilter {
 			this._registerInlineElement( definition );
 		} else if ( definition.isBlock ) {
 			this._registerBlockElement( definition );
+		} else if ( definition.isObject ) {
+			this._registerObjectElement( definition );
 		} else {
 			/**
 			 * Only a definition marked as inline or block can be allowed.
@@ -186,6 +189,30 @@ export default class DataFilter {
 		}
 	}
 
+	_registerObjectElement( definition ) {
+		const schema = this.editor.model.schema;
+
+		schema.register( definition.model, definition.modelSchema );
+
+		this._addObjectElementToElementConversion( definition );
+		this._addDisallowedAttributeConversion( definition );
+		this._addAllowedAttributeConversion( definition );
+	}
+
+	_createObjectElementView( modelName, writer ) {
+		if ( this.editor.model.schema.isInline( modelName ) ) {
+			return writer.createContainerElement( 'span', {
+				class: 'ck-widget__compatibility ck-widget__compatibility-inline'
+			}, {
+				isAllowedInsideAttributeElement: true
+			} );
+		}
+
+		return writer.createContainerElement( 'div', {
+			class: 'ck-widget__compatibility ck-widget__compatibility-block'
+		} );
+	}
+
 	/**
 	 * Registers block element and attribute converters for the given data schema definition.
 	 *
@@ -198,12 +225,12 @@ export default class DataFilter {
 		const schema = this.editor.model.schema;
 
 		if ( !schema.isRegistered( definition.model ) ) {
-			this._registerBlockElementSchema( definition );
+			this.editor.model.schema.register( definition.model, definition.modelSchema );
 			this._addBlockElementToElementConversion( definition );
 		}
 
 		this._addDisallowedAttributeConversion( definition );
-		this._addBlockElementAttributeConversion( definition );
+		this._addAllowedAttributeConversion( definition );
 	}
 
 	/**
@@ -229,28 +256,6 @@ export default class DataFilter {
 		this._addInlineElementConversion( definition );
 	}
 
-	/**
-	 * Registers model schema definition for the given block element definition.
-	 *
-	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
-	 */
-	_registerBlockElementSchema( definition ) {
-		const schema = this.editor.model.schema;
-
-		schema.register( definition.model, definition.modelSchema );
-
-		const allowedChildren = toArray( definition.allowChildren || [] );
-
-		for ( const child of allowedChildren ) {
-			if ( schema.isRegistered( child ) ) {
-				schema.extend( child, {
-					allowIn: definition.model
-				} );
-			}
-		}
-	}
-
 	/**
 	 * Adds element to element converters for the given block element definition.
 	 *
@@ -279,12 +284,12 @@ export default class DataFilter {
 	}
 
 	/**
-	 * Adds attribute converters for the given block element definition.
+	 * Adds attribute converters for the given element definition.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
-	_addBlockElementAttributeConversion( { model: modelName, view: viewName } ) {
+	_addAllowedAttributeConversion( { model: modelName, view: viewName } ) {
 		const conversion = this.editor.conversion;
 
 		if ( !viewName ) {
@@ -300,13 +305,13 @@ export default class DataFilter {
 				const viewAttributes = this._matchAndConsumeAllowedAttributes( data.viewItem, conversionApi );
 
 				if ( viewAttributes ) {
-					conversionApi.writer.setAttribute( DATA_SCHEMA_ATTRIBUTE_KEY, viewAttributes, data.modelRange );
+					conversionApi.writer.setAttribute( 'htmlAttributes', viewAttributes, data.modelRange );
 				}
 			}, { priority: 'low' } );
 		} );
 
 		conversion.for( 'downcast' ).add( dispatcher => {
-			dispatcher.on( `attribute:${ DATA_SCHEMA_ATTRIBUTE_KEY }:${ modelName }`, ( evt, data, conversionApi ) => {
+			dispatcher.on( `attribute:htmlAttributes:${ modelName }`, ( evt, data, conversionApi ) => {
 				const viewAttributes = data.attributeNewValue;
 
 				if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
@@ -394,6 +399,46 @@ export default class DataFilter {
 		} );
 	}
 
+	_addObjectElementToElementConversion( definition ) {
+		const conversion = this.editor.conversion;
+		const { view: viewName, model: modelName } = definition;
+
+		conversion.for( 'upcast' ).elementToElement( {
+			model: modelName,
+			view: viewName
+		} );
+
+		conversion.for( 'editingDowncast' ).elementToElement( {
+			model: modelName,
+			view: ( modelElement, { writer } ) => {
+				const widgetWrapper = this._createObjectElementView( modelName, writer );
+				const title = createHtmlObjectTitle( viewName );
+
+				enablePlaceholder( {
+					view: this.editor.editing.view,
+					element: widgetWrapper,
+					text: title
+				} );
+
+				const widgetLabel = createObjectElementWidgetUILabel( title, writer );
+
+				writer.insert( writer.createPositionAt( widgetWrapper, 'end' ), widgetLabel );
+
+				return toWidget( widgetWrapper, writer );
+			}
+
+		} );
+
+		conversion.for( 'dataDowncast' ).elementToElement( {
+			model: modelName,
+			view: ( modelItem, { writer } ) => {
+				return writer.createContainerElement( viewName, null, {
+					isAllowedInsideAttributeElement: this.editor.model.schema.isInline( modelName )
+				} );
+			}
+		} );
+	}
+
 	/**
 	 * Matches and consumes allowed view attributes.
 	 *
@@ -542,3 +587,28 @@ function mergeViewElementAttributes( oldValue, newValue ) {
 
 	return result;
 }
+
+function createHtmlObjectTitle( viewName ) {
+	return 'HTML ' + capitalize( viewName );
+}
+
+function createObjectElementWidgetUILabel( title, writer ) {
+	return writer.createUIElement( 'div', {
+		class: 'ck ck-reset_all ck-widget__compatibility-type'
+	}, function( domDocument ) {
+		const wrapperDomElement = this.toDomElement( domDocument );
+
+		const labelTemplate = new Template( {
+			attributes: {
+				class: [
+					'ck',
+					'ck-widget__compatibility-type__label'
+				]
+			},
+			text: title
+		} );
+		wrapperDomElement.appendChild( labelTemplate.render() );
+
+		return wrapperDomElement;
+	} );
+}
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 11a3062679b..bfeb75317b7 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -142,6 +142,129 @@ export default class DataSchema {
 			}
 		} );
 
+		this.registerObjectElement( {
+			view: 'object',
+			model: 'htmlObject',
+			modelSchema: {
+				isObject: true,
+				isInline: true,
+				allowWhere: '$text',
+				allowAttributesOf: '$text'
+			}
+		} );
+
+		this.registerObjectElement( {
+			view: 'param',
+			model: 'htmlParam',
+			modelSchema: {
+				isObject: true,
+				isInline: true,
+				allowIn: 'htmlObject'
+			}
+		} );
+
+		this.registerObjectElement( {
+			view: 'embed',
+			model: 'htmlEmbed',
+			modelSchema: {
+				isObject: true,
+				isInline: true,
+				allowIn: 'htmlObject'
+			}
+		} );
+
+		this.registerObjectElement( {
+			view: 'iframe',
+			model: 'htmlIframe',
+			modelSchema: {
+				isObject: true,
+				isInline: true,
+				allowWhere: '$text',
+				allowAttributesOf: '$text'
+			}
+		} );
+
+		this.registerObjectElement( {
+			view: 'form',
+			model: 'htmlForm',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock',
+				allowContentOf: '$root',
+				isObject: true
+			}
+		} );
+
+		this.registerObjectElement( {
+			view: 'input',
+			model: 'htmlInput',
+			modelSchema: {
+				allowIn: [ '$block', '$form' ],
+				isObject: true,
+				isInline: true
+			}
+		} );
+
+		this.registerObjectElement( {
+			view: 'textarea',
+			model: 'htmlTextarea',
+			modelSchema: {
+				allowIn: '$block',
+				allowChildren: '$text',
+				isObject: true,
+				isInline: true
+			}
+		} );
+
+		this.registerObjectElement( {
+			view: 'select',
+			model: 'htmlSelect',
+			modelSchema: {
+				allowIn: '$block',
+				isObject: true,
+				isInline: true
+			}
+		} );
+
+		this.registerObjectElement( {
+			view: 'option',
+			model: 'htmlOption',
+			modelSchema: {
+				allowIn: 'htmlSelect',
+				isObject: true,
+				isInline: true
+			}
+		} );
+
+		this.registerObjectElement( {
+			view: 'video',
+			model: 'htmlVideo',
+			modelSchema: {
+				allowIn: '$block',
+				isObject: true,
+				isInline: true
+			}
+		} );
+
+		this.registerObjectElement( {
+			view: 'audio',
+			model: 'htmlAudio',
+			modelSchema: {
+				allowIn: '$block',
+				isObject: true,
+				isInline: true
+			}
+		} );
+
+		this.registerObjectElement( {
+			view: 'source',
+			model: 'htmlSource',
+			modelSchema: {
+				allowIn: [ 'htmlVideo', 'htmlAudio' ],
+				isObject: true,
+				isInline: true
+			}
+		} );
+
 		// Inline elements.
 		this.registerInlineElement( {
 			view: 'a',
@@ -199,6 +322,10 @@ export default class DataSchema {
 		this._definitions.set( definition.model, { ...definition, isInline: true } );
 	}
 
+	registerObjectElement( definition ) {
+		this._definitions.set( definition.model, { ...definition, isObject: true } );
+	}
+
 	/**
 	 * Returns all definitions matching the given view name.
 	 *
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.html b/packages/ckeditor5-content-compatibility/tests/manual/objects.html
new file mode 100644
index 00000000000..f53be64d54e
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.html
@@ -0,0 +1,72 @@
+<head>
+	<meta http-equiv="Content-Security-Policy" content="script-src 'self' https://ckeditor.com 'unsafe-inline' 'unsafe-eval'">
+</head>
+
+<div id="editor">
+	<p>
+	<object classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,40,0">
+		<param name="allowFullScreen" value="true" />
+		<param name="quality" value="high" />
+		<param name="movie" value="example.com" />
+		<embed allowfullscreen="true" pluginspage="http://www.macromedia.com/go/getflashplayer" quality="high" src="example.com" type="application/x-shockwave-flash"></embed>
+	</object>
+	</p>
+	<p><iframe frameborder="0" scrolling="no" src="example.com"></iframe></p>
+	<form action="controller/register" method="post" name="foobar">
+		<p><input name="checkbox" type="checkbox" value="10" /></p>
+
+		<p><input name="radio" type="radio" value="10" /></p>
+
+		<p><input name="text field" type="text" value="10" /></p>
+
+		<p><textarea name="textarea">10</textarea></p>
+
+		<p><select name="selection field"><option value="1">a1</option><option selected="selected" value="2">a2</option><option value="3">a3</option></select></p>
+
+		<p><input name="button" type="button" value="click me" /></p>
+
+		<p><input alt="" src="https://via.placeholder.com/100" type="image" /></p>
+
+		<p><input name="hidden field" type="hidden" value="aaa" /></p>
+
+		<p>some custom text</p>
+
+		<table border="1" cellpadding="1" cellspacing="1" style="width:500px;">
+			<tbody>
+				<tr>
+					<td>&nbsp;</td>
+					<td>&nbsp;</td>
+				</tr>
+				<tr>
+					<td>&nbsp;</td>
+					<td>&nbsp;</td>
+				</tr>
+				<tr>
+					<td>&nbsp;</td>
+					<td>&nbsp;</td>
+				</tr>
+			</tbody>
+		</table>
+
+		<p>looks like form can include anything</p>
+	</form>
+	<p><input name="checkbox" type="checkbox" value="10" /></p>
+
+	<p><input name="radio" type="radio" value="10" /></p>
+
+	<p><input name="text field" type="text" value="10" /></p>
+
+	<p><input name="button" type="button" value="click me" /></p>
+
+	<p><input alt="" src="https://via.placeholder.com/100" type="image" /></p>
+
+	<p><input name="hidden field" type="hidden" value="aaa" /></p>
+
+	<p><textarea name="textarea">some text in textarea</textarea></p>
+
+	<p><select name="selection field"><option value="1">a1</option><option selected="selected" value="2">a2</option><option value="3">a3</option></select></p>
+
+	<p><video controls="" height="240" width="320"><source src="movie.mp4" type="video/mp4" /> <source src="movie.ogg" type="video/ogg" /> Your browser does not support the video tag.</video></p>
+
+	<p><audio controls=""><source src="horse.ogg" type="audio/ogg" /> <source src="horse.mp3" type="audio/mpeg" /> Your browser does not support the audio element.</audio></p>
+</div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.js b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
new file mode 100644
index 00000000000..f80f4f24919
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
@@ -0,0 +1,91 @@
+/**
+ * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/* globals console:false, window, document */
+
+import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
+import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials';
+import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
+import Bold from '@ckeditor/ckeditor5-basic-styles/src/bold';
+import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
+import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
+import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
+import BlockQuote from '@ckeditor/ckeditor5-block-quote/src/blockquote';
+import List from '@ckeditor/ckeditor5-list/src/list';
+import Link from '@ckeditor/ckeditor5-link/src/link';
+import Table from '@ckeditor/ckeditor5-table/src/table';
+
+import GeneralHtmlSupport from '../../src/generalhtmlsupport';
+
+/**
+ * Client custom plugin extending HTML support for compatibility.
+ */
+class ExtendHTMLSupport extends Plugin {
+	static get requires() {
+		return [ GeneralHtmlSupport ];
+	}
+
+	init() {
+		const { dataFilter } = this.editor.plugins.get( GeneralHtmlSupport );
+
+		const definitions = [
+			{ name: 'object', attributes: [ 'classid', 'codebase' ] },
+			{ name: 'param', attributes: [ 'name', 'value' ] },
+			{ name: 'embed', attributes: [ 'allowfullscreen', 'pluginspage', 'quality', 'src', 'type' ] },
+			{ name: 'iframe', attributes: [ 'frameborder', 'scrolling', 'src' ] },
+			{ name: 'form', attributes: [ 'action', 'method', 'name' ] },
+			{ name: 'input', attributes: [ 'name', 'type', 'value', 'alt', 'src' ] },
+			{ name: 'textarea', attributes: [ 'name' ] },
+			{ name: 'select', attributes: [ 'name' ] },
+			{ name: 'option', attributes: [ 'value', 'selected' ] },
+			{ name: 'video', attributes: [ 'height', 'width', 'controls' ] },
+			{ name: 'audio', attributes: [ 'controls' ] },
+			{ name: 'source', attributes: [ 'src', 'type' ] }
+		];
+
+		for ( const definition of definitions ) {
+			dataFilter.allowElement( { name: definition.name } );
+
+			for ( const key of definition.attributes ) {
+				const attributes = {};
+				attributes[ key ] = /[\s\S]+/;
+
+				dataFilter.allowAttributes( { name: definition.name, attributes } );
+			}
+		}
+	}
+}
+
+ClassicEditor
+	.create( document.querySelector( '#editor' ), {
+		plugins: [
+			Table,
+			Link,
+			BlockQuote,
+			Bold,
+			Essentials,
+			ExtendHTMLSupport,
+			Italic,
+			List,
+			Paragraph,
+			Strikethrough
+		],
+		toolbar: [
+			'bold',
+			'italic',
+			'strikethrough',
+			'|',
+			'numberedList',
+			'bulletedList',
+			'|',
+			'blockquote'
+		]
+	} )
+	.then( editor => {
+		window.editor = editor;
+	} )
+	.catch( err => {
+		console.error( err.stack );
+	} );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.md b/packages/ckeditor5-content-compatibility/tests/manual/objects.md
new file mode 100644
index 00000000000..4b123939219
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.md
@@ -0,0 +1 @@
+# Object elements support
diff --git a/packages/ckeditor5-content-compatibility/theme/datafilter.css b/packages/ckeditor5-content-compatibility/theme/datafilter.css
new file mode 100644
index 00000000000..42ddf3ce9e1
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/theme/datafilter.css
@@ -0,0 +1,48 @@
+:root {
+	--ck-widget__compatibility-base-background: var(--ck-color-widget-blurred-border)
+}
+
+.ck .ck-widget {
+	&.ck-widget__compatibility {
+		padding: 20px 0 15px 0;
+		min-height: 20px;
+
+		& .ck-widget__compatibility-type {
+			opacity: 0;
+			font-size: var(--ck-font-size-tiny);
+			padding: 0 5px;
+			background: var(--ck-widget-compatibility-base-background);
+			display: block;
+			position: absolute;
+			overflow: hidden;
+			z-index: var(--ck-z-default);
+			/* Place it in the middle of the outline */
+			top: calc(-0.5 * var(--ck-widget-outline-thickness));
+			right: min(10%, 30px);
+			transform: translateY(-50%);
+		}
+
+		&.ck-widget_selected > .ck-widget__compatibility-type {
+			opacity: 1;
+			color: var(--ck-color-base-background);
+			background-color: var(--ck-color-focus-border);
+		}
+
+		&:not(.ck-widget_selected):hover > .ck-widget__compatibility-type {
+			opacity: 1;
+			color: var(--ck-color-base-background);
+			background: var(--ck-color-widget-hover-border);
+		}
+	}
+
+	&.ck-widget__compatibility-inline {
+		display: inline-block;
+		min-width: 100px;
+	}
+}
+
+.ck.ck-editor__editable.ck-blurred .ck-widget.ck-widget__compatibility.ck-widget_selected >
+.ck-widget__compatibility-type {
+	color: hsl(0,0%,60%);
+	background: var(--ck-widget-compatibility-base-background);
+}

From 09d528bbb8bf6ae77c1416eb9e6cdf45b5aff9e2 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 6 May 2021 10:09:55 +0200
Subject: [PATCH 114/217] Styling, small bug fix.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js    | 4 ++++
 packages/ckeditor5-content-compatibility/theme/datafilter.css | 1 +
 2 files changed, 5 insertions(+)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index b2b64b69eb6..2f7c8c15cf3 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -314,6 +314,10 @@ export default class DataFilter {
 			dispatcher.on( `attribute:htmlAttributes:${ modelName }`, ( evt, data, conversionApi ) => {
 				const viewAttributes = data.attributeNewValue;
 
+				if ( !viewAttributes ) {
+					return;
+				}
+
 				if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
 					return;
 				}
diff --git a/packages/ckeditor5-content-compatibility/theme/datafilter.css b/packages/ckeditor5-content-compatibility/theme/datafilter.css
index 42ddf3ce9e1..7cd9d5b5d2e 100644
--- a/packages/ckeditor5-content-compatibility/theme/datafilter.css
+++ b/packages/ckeditor5-content-compatibility/theme/datafilter.css
@@ -6,6 +6,7 @@
 	&.ck-widget__compatibility {
 		padding: 20px 0 15px 0;
 		min-height: 20px;
+		border: 1px dotted hsl(15, 100%, 43%);
 
 		& .ck-widget__compatibility-type {
 			opacity: 0;

From 0bcb80845c9bdf85b1ef10ab862b67c50164b4fb Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 6 May 2021 10:50:54 +0200
Subject: [PATCH 115/217] Fixed allowChildren API, docs.

---
 .../src/datafilter.js                         | 13 +++++++++++
 .../src/dataschema.js                         | 23 +++++++++++++++----
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 2f7c8c15cf3..3884b604957 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -189,6 +189,14 @@ export default class DataFilter {
 		}
 	}
 
+	/**
+	 * Registers object element and attribute converters for the given data schema definition.
+	 *
+	 * If the element model schema is already registered, this method will do nothing.
+	 *
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
+	 */
 	_registerObjectElement( definition ) {
 		const schema = this.editor.model.schema;
 
@@ -199,6 +207,9 @@ export default class DataFilter {
 		this._addAllowedAttributeConversion( definition );
 	}
 
+	/**
+	 * TODO
+	*/
 	_createObjectElementView( modelName, writer ) {
 		if ( this.editor.model.schema.isInline( modelName ) ) {
 			return writer.createContainerElement( 'span', {
@@ -592,10 +603,12 @@ function mergeViewElementAttributes( oldValue, newValue ) {
 	return result;
 }
 
+// TODO
 function createHtmlObjectTitle( viewName ) {
 	return 'HTML ' + capitalize( viewName );
 }
 
+// TODO
 function createObjectElementWidgetUILabel( title, writer ) {
 	return writer.createUIElement( 'div', {
 		class: 'ck ck-reset_all ck-widget__compatibility-type'
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index bfeb75317b7..96f10699b10 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -66,8 +66,8 @@ export default class DataSchema {
 
 		this.registerBlockElement( {
 			model: '$htmlBlock',
-			allowChildren: '$block',
 			modelSchema: {
+				allowChildren: '$block',
 				allowIn: [ '$root', '$htmlBlock' ],
 				isBlock: true
 			}
@@ -101,8 +101,8 @@ export default class DataSchema {
 
 		this.registerBlockElement( {
 			model: '$htmlDatalist',
-			allowChildren: '$block',
 			modelSchema: {
+				allowChildren: '$block',
 				allowIn: 'htmlDl',
 				isBlock: true
 			}
@@ -136,8 +136,8 @@ export default class DataSchema {
 		this.registerBlockElement( {
 			view: 'summary',
 			model: 'htmlSummary',
-			allowChildren: '$text',
 			modelSchema: {
+				allowChildren: '$text',
 				allowIn: 'htmlDetails'
 			}
 		} );
@@ -322,6 +322,11 @@ export default class DataSchema {
 		this._definitions.set( definition.model, { ...definition, isInline: true } );
 	}
 
+	/**
+	 * Add new data schema definition describing inline element.
+	 *
+	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
+	 */
 	registerObjectElement( definition ) {
 		this._definitions.set( definition.model, { ...definition, isObject: true } );
 	}
@@ -421,12 +426,22 @@ function testViewName( pattern, viewName ) {
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
  * @property {String} [view] Name of the view element.
  * @property {module:engine/model/schema~SchemaItemDefinition} [modelSchema] The model schema item definition describing registered model.
- * @property {String|Array.<String>} [allowChildren] Extends the given children list to allow definition model.
  * @property {Boolean} isBlock Indicates that the definition describes block element.
  * Set by {@link module:content-compatibility/dataschema~DataSchema#registerBlockElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */
 
+/**
+ * A definition of {@link module:content-compatibility/dataschema~DataSchema data schema} for object elements.
+ *
+ * @typedef {Object} module:content-compatibility/dataschema~DataSchemaObjectElementDefinition
+ * @property {String} view Name of the view element.
+ * @property {module:engine/model/schema~SchemaItemDefinition} modelSchema The model schema item definition describing registered model.
+ * @property {Boolean} isObject Indicates that the definition describes object element.
+ * Set by {@link module:content-compatibility/dataschema~DataSchema#registerObjectElement} method.
+ * @extends module:content-compatibility/dataschema~DataSchemaDefinition
+ */
+
 /**
  * A definition of {@link module:content-compatibility/dataschema~DataSchema data schema} for inline elements.
  *

From 832195132050426fca1ae095a0518804010486ad Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 6 May 2021 11:13:33 +0200
Subject: [PATCH 116/217] Refactoring, css fix.

---
 .../src/datafilter.js                         | 34 +++++++++----------
 .../theme/datafilter.css                      |  7 ++--
 2 files changed, 20 insertions(+), 21 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 3884b604957..7bdbc226b02 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -207,23 +207,6 @@ export default class DataFilter {
 		this._addAllowedAttributeConversion( definition );
 	}
 
-	/**
-	 * TODO
-	*/
-	_createObjectElementView( modelName, writer ) {
-		if ( this.editor.model.schema.isInline( modelName ) ) {
-			return writer.createContainerElement( 'span', {
-				class: 'ck-widget__compatibility ck-widget__compatibility-inline'
-			}, {
-				isAllowedInsideAttributeElement: true
-			} );
-		}
-
-		return writer.createContainerElement( 'div', {
-			class: 'ck-widget__compatibility ck-widget__compatibility-block'
-		} );
-	}
-
 	/**
 	 * Registers block element and attribute converters for the given data schema definition.
 	 *
@@ -454,6 +437,23 @@ export default class DataFilter {
 		} );
 	}
 
+	/**
+	 * TODO
+	*/
+	_createObjectElementView( modelName, writer ) {
+		if ( this.editor.model.schema.isInline( modelName ) ) {
+			return writer.createContainerElement( 'span', {
+				class: 'ck-widget__compatibility ck-widget__compatibility-inline'
+			}, {
+				isAllowedInsideAttributeElement: true
+			} );
+		}
+
+		return writer.createContainerElement( 'div', {
+			class: 'ck-widget__compatibility ck-widget__compatibility-block'
+		} );
+	}
+
 	/**
 	 * Matches and consumes allowed view attributes.
 	 *
diff --git a/packages/ckeditor5-content-compatibility/theme/datafilter.css b/packages/ckeditor5-content-compatibility/theme/datafilter.css
index 7cd9d5b5d2e..c773f619028 100644
--- a/packages/ckeditor5-content-compatibility/theme/datafilter.css
+++ b/packages/ckeditor5-content-compatibility/theme/datafilter.css
@@ -1,5 +1,5 @@
 :root {
-	--ck-widget__compatibility-base-background: var(--ck-color-widget-blurred-border)
+	--ck-widget-compatibility-base-background: var(--ck-color-widget-blurred-border)
 }
 
 .ck .ck-widget {
@@ -26,7 +26,7 @@
 		&.ck-widget_selected > .ck-widget__compatibility-type {
 			opacity: 1;
 			color: var(--ck-color-base-background);
-			background-color: var(--ck-color-focus-border);
+			background: var(--ck-color-focus-border);
 		}
 
 		&:not(.ck-widget_selected):hover > .ck-widget__compatibility-type {
@@ -42,8 +42,7 @@
 	}
 }
 
-.ck.ck-editor__editable.ck-blurred .ck-widget.ck-widget__compatibility.ck-widget_selected >
-.ck-widget__compatibility-type {
+.ck.ck-editor__editable.ck-blurred .ck-widget.ck-widget__compatibility.ck-widget_selected > .ck-widget__compatibility-type {
 	color: hsl(0,0%,60%);
 	background: var(--ck-widget-compatibility-base-background);
 }

From 94ded58bb2e5cded0ccca59a8f86e08e3052e2d0 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Sun, 9 May 2021 11:44:27 +0200
Subject: [PATCH 117/217] Rewritten implementation to embed whole objects
 instead.

---
 .../src/datafilter.js                         | 176 +++++++++---------
 .../src/dataschema.js                         | 120 +++---------
 .../tests/manual/objects.html                 |  10 +-
 .../tests/manual/objects.js                   |   6 +-
 .../theme/datafilter.css                      |  66 +++----
 5 files changed, 150 insertions(+), 228 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 7bdbc226b02..1fff7576ae4 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -7,11 +7,10 @@
  * @module content-compatibility/datafilter
  */
 
-import { Matcher, enablePlaceholder } from 'ckeditor5/src/engine';
+import { Matcher } from 'ckeditor5/src/engine';
 import { priorities, CKEditorError } from 'ckeditor5/src/utils';
 import { toWidget } from 'ckeditor5/src/widget';
-import { Template } from 'ckeditor5/src/ui';
-import { cloneDeep, capitalize } from 'lodash-es';
+import { cloneDeep } from 'lodash-es';
 
 import '../theme/datafilter.css';
 
@@ -192,19 +191,27 @@ export default class DataFilter {
 	/**
 	 * Registers object element and attribute converters for the given data schema definition.
 	 *
-	 * If the element model schema is already registered, this method will do nothing.
-	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
 	 */
 	_registerObjectElement( definition ) {
 		const schema = this.editor.model.schema;
 
-		schema.register( definition.model, definition.modelSchema );
+		// All object elements are represented by a single widget.
+		if ( !schema.isRegistered( 'htmlObjectEmbed' ) ) {
+			schema.register( 'htmlObjectEmbed', {
+				isObject: true,
+				isInline: true,
+				allowWhere: '$text',
+				allowAttributesOf: '$text',
+				allowAttributes: [ 'value', 'view', 'htmlAttributes' ]
+			} );
+
+			this._addHtmlObjectEmbedConversion();
+		}
 
-		this._addObjectElementToElementConversion( definition );
 		this._addDisallowedAttributeConversion( definition );
-		this._addAllowedAttributeConversion( definition );
+		this._addObjectElementToElementConversion( definition );
 	}
 
 	/**
@@ -224,7 +231,7 @@ export default class DataFilter {
 		}
 
 		this._addDisallowedAttributeConversion( definition );
-		this._addAllowedAttributeConversion( definition );
+		this._addBlockElementAttributeConversion( definition );
 	}
 
 	/**
@@ -250,6 +257,40 @@ export default class DataFilter {
 		this._addInlineElementConversion( definition );
 	}
 
+	_addHtmlObjectEmbedConversion() {
+		const editor = this.editor;
+		const conversion = editor.conversion;
+		const t = editor.t;
+
+		conversion.for( 'dataDowncast' ).elementToElement( {
+			model: 'htmlObjectEmbed',
+			view: createObjectViewElement
+		} );
+
+		conversion.for( 'editingDowncast' ).elementToElement( {
+			model: 'htmlObjectEmbed',
+			view: ( modelElement, conversionApi ) => {
+				const { writer } = conversionApi;
+
+				const viewContainer = writer.createContainerElement( 'span', {
+					class: 'html-object-embed',
+					'data-html-object-embed-label': t( 'HTML object' )
+				}, {
+					isAllowedInsideAttributeElement: true
+				} );
+
+				const viewElement = createObjectViewElement( modelElement, conversionApi );
+				writer.addClass( 'html-object-embed__content', viewElement );
+
+				writer.insert( writer.createPositionAt( viewContainer, 0 ), viewElement );
+
+				return toWidget( viewContainer, writer, {
+					widgetLabel: t( 'HTML object' )
+				} );
+			}
+		} );
+	}
+
 	/**
 	 * Adds element to element converters for the given block element definition.
 	 *
@@ -283,7 +324,7 @@ export default class DataFilter {
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
-	_addAllowedAttributeConversion( { model: modelName, view: viewName } ) {
+	_addBlockElementAttributeConversion( { model: modelName, view: viewName } ) {
 		const conversion = this.editor.conversion;
 
 		if ( !viewName ) {
@@ -308,10 +349,6 @@ export default class DataFilter {
 			dispatcher.on( `attribute:htmlAttributes:${ modelName }`, ( evt, data, conversionApi ) => {
 				const viewAttributes = data.attributeNewValue;
 
-				if ( !viewAttributes ) {
-					return;
-				}
-
 				if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
 					return;
 				}
@@ -397,63 +434,31 @@ export default class DataFilter {
 		} );
 	}
 
-	_addObjectElementToElementConversion( definition ) {
+	_addObjectElementToElementConversion( { view: viewName } ) {
 		const conversion = this.editor.conversion;
-		const { view: viewName, model: modelName } = definition;
 
-		conversion.for( 'upcast' ).elementToElement( {
-			model: modelName,
-			view: viewName
+		// Object element content will be hidden under `value` property and restored by
+		// `htmlObjectEmbed` downcast converters.
+		this.editor.data.registerRawContentMatcher( {
+			name: viewName
 		} );
 
-		conversion.for( 'editingDowncast' ).elementToElement( {
-			model: modelName,
-			view: ( modelElement, { writer } ) => {
-				const widgetWrapper = this._createObjectElementView( modelName, writer );
-				const title = createHtmlObjectTitle( viewName );
-
-				enablePlaceholder( {
-					view: this.editor.editing.view,
-					element: widgetWrapper,
-					text: title
-				} );
-
-				const widgetLabel = createObjectElementWidgetUILabel( title, writer );
-
-				writer.insert( writer.createPositionAt( widgetWrapper, 'end' ), widgetLabel );
-
-				return toWidget( widgetWrapper, writer );
-			}
-
-		} );
+		// We just need to add upcast conversion for specific view. Downcast is handled by
+		// `htmlObjectEmbed` itself.
+		conversion.for( 'upcast' ).elementToElement( {
+			view: viewName,
+			model: ( viewElement, conversionApi ) => {
+				const htmlAttributes = this._matchAndConsumeAllowedAttributes( viewElement, conversionApi );
 
-		conversion.for( 'dataDowncast' ).elementToElement( {
-			model: modelName,
-			view: ( modelItem, { writer } ) => {
-				return writer.createContainerElement( viewName, null, {
-					isAllowedInsideAttributeElement: this.editor.model.schema.isInline( modelName )
+				return conversionApi.writer.createElement( 'htmlObjectEmbed', {
+					value: viewElement.getCustomProperty( '$rawContent' ),
+					view: viewName,
+					...( htmlAttributes && { htmlAttributes } )
 				} );
 			}
 		} );
 	}
 
-	/**
-	 * TODO
-	*/
-	_createObjectElementView( modelName, writer ) {
-		if ( this.editor.model.schema.isInline( modelName ) ) {
-			return writer.createContainerElement( 'span', {
-				class: 'ck-widget__compatibility ck-widget__compatibility-inline'
-			}, {
-				isAllowedInsideAttributeElement: true
-			} );
-		}
-
-		return writer.createContainerElement( 'div', {
-			class: 'ck-widget__compatibility ck-widget__compatibility-block'
-		} );
-	}
-
 	/**
 	 * Matches and consumes allowed view attributes.
 	 *
@@ -537,6 +542,28 @@ function setViewElementAttributes( writer, viewAttributes, viewElement ) {
 	}
 }
 
+// Creates object view element from the given model element.
+//
+// @private
+// @param {module:engine/model/element~Element} modelElement
+// @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
+// @returns {module:engine/view/element~Element} viewElement
+function createObjectViewElement( modelElement, { writer } ) {
+	const viewName = modelElement.getAttribute( 'view' );
+	const viewAttributes = modelElement.getAttribute( 'htmlAttributes' );
+	const viewContent = modelElement.getAttribute( 'value' );
+
+	const viewElement = writer.createRawElement( viewName, null, function( domElement ) {
+		domElement.innerHTML = viewContent;
+	} );
+
+	if ( viewAttributes ) {
+		setViewElementAttributes( writer, viewAttributes, viewElement );
+	}
+
+	return viewElement;
+}
+
 // Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
 //
 // @private
@@ -602,30 +629,3 @@ function mergeViewElementAttributes( oldValue, newValue ) {
 
 	return result;
 }
-
-// TODO
-function createHtmlObjectTitle( viewName ) {
-	return 'HTML ' + capitalize( viewName );
-}
-
-// TODO
-function createObjectElementWidgetUILabel( title, writer ) {
-	return writer.createUIElement( 'div', {
-		class: 'ck ck-reset_all ck-widget__compatibility-type'
-	}, function( domDocument ) {
-		const wrapperDomElement = this.toDomElement( domDocument );
-
-		const labelTemplate = new Template( {
-			attributes: {
-				class: [
-					'ck',
-					'ck-widget__compatibility-type__label'
-				]
-			},
-			text: title
-		} );
-		wrapperDomElement.appendChild( labelTemplate.render() );
-
-		return wrapperDomElement;
-	} );
-}
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 96f10699b10..aeeedb027a1 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -89,6 +89,14 @@ export default class DataSchema {
 			}
 		} );
 
+		this.registerBlockElement( {
+			view: 'form',
+			model: 'htmlForm',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		} );
+
 		// Add data list elements.
 		this.registerBlockElement( {
 			view: 'dl',
@@ -144,125 +152,42 @@ export default class DataSchema {
 
 		this.registerObjectElement( {
 			view: 'object',
-			model: 'htmlObject',
-			modelSchema: {
-				isObject: true,
-				isInline: true,
-				allowWhere: '$text',
-				allowAttributesOf: '$text'
-			}
-		} );
-
-		this.registerObjectElement( {
-			view: 'param',
-			model: 'htmlParam',
-			modelSchema: {
-				isObject: true,
-				isInline: true,
-				allowIn: 'htmlObject'
-			}
-		} );
-
-		this.registerObjectElement( {
-			view: 'embed',
-			model: 'htmlEmbed',
-			modelSchema: {
-				isObject: true,
-				isInline: true,
-				allowIn: 'htmlObject'
-			}
+			model: 'htmlObject'
 		} );
 
 		this.registerObjectElement( {
 			view: 'iframe',
-			model: 'htmlIframe',
-			modelSchema: {
-				isObject: true,
-				isInline: true,
-				allowWhere: '$text',
-				allowAttributesOf: '$text'
-			}
+			model: 'htmlIframe'
 		} );
 
 		this.registerObjectElement( {
-			view: 'form',
-			model: 'htmlForm',
-			modelSchema: {
-				inheritAllFrom: '$htmlBlock',
-				allowContentOf: '$root',
-				isObject: true
-			}
+			view: 'input',
+			model: 'htmlInput'
 		} );
 
 		this.registerObjectElement( {
-			view: 'input',
-			model: 'htmlInput',
-			modelSchema: {
-				allowIn: [ '$block', '$form' ],
-				isObject: true,
-				isInline: true
-			}
+			view: 'button',
+			model: 'htmlButton'
 		} );
 
 		this.registerObjectElement( {
 			view: 'textarea',
-			model: 'htmlTextarea',
-			modelSchema: {
-				allowIn: '$block',
-				allowChildren: '$text',
-				isObject: true,
-				isInline: true
-			}
+			model: 'htmlTextarea'
 		} );
 
 		this.registerObjectElement( {
 			view: 'select',
-			model: 'htmlSelect',
-			modelSchema: {
-				allowIn: '$block',
-				isObject: true,
-				isInline: true
-			}
-		} );
-
-		this.registerObjectElement( {
-			view: 'option',
-			model: 'htmlOption',
-			modelSchema: {
-				allowIn: 'htmlSelect',
-				isObject: true,
-				isInline: true
-			}
+			model: 'htmlSelect'
 		} );
 
 		this.registerObjectElement( {
 			view: 'video',
-			model: 'htmlVideo',
-			modelSchema: {
-				allowIn: '$block',
-				isObject: true,
-				isInline: true
-			}
+			model: 'htmlVideo'
 		} );
 
 		this.registerObjectElement( {
 			view: 'audio',
-			model: 'htmlAudio',
-			modelSchema: {
-				allowIn: '$block',
-				isObject: true,
-				isInline: true
-			}
-		} );
-
-		this.registerObjectElement( {
-			view: 'source',
-			model: 'htmlSource',
-			modelSchema: {
-				allowIn: [ 'htmlVideo', 'htmlAudio' ],
-				isObject: true,
-				isInline: true
-			}
+			model: 'htmlAudio'
 		} );
 
 		// Inline elements.
@@ -302,6 +227,14 @@ export default class DataSchema {
 				copyOnEnter: true
 			}
 		} );
+
+		this.registerInlineElement( {
+			view: 'label',
+			model: 'htmlLabel',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		} );
 	}
 
 	/**
@@ -436,7 +369,6 @@ function testViewName( pattern, viewName ) {
  *
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaObjectElementDefinition
  * @property {String} view Name of the view element.
- * @property {module:engine/model/schema~SchemaItemDefinition} modelSchema The model schema item definition describing registered model.
  * @property {Boolean} isObject Indicates that the definition describes object element.
  * Set by {@link module:content-compatibility/dataschema~DataSchema#registerObjectElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.html b/packages/ckeditor5-content-compatibility/tests/manual/objects.html
index f53be64d54e..d69e187ab83 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/objects.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.html
@@ -25,9 +25,9 @@
 
 		<p><input name="button" type="button" value="click me" /></p>
 
-		<p><input alt="" src="https://via.placeholder.com/100" type="image" /></p>
+		<p><button>Click me!</button></p>
 
-		<p><input name="hidden field" type="hidden" value="aaa" /></p>
+		<p><input alt="" src="https://via.placeholder.com/100" type="image" /></p>
 
 		<p>some custom text</p>
 
@@ -60,13 +60,13 @@
 
 	<p><input alt="" src="https://via.placeholder.com/100" type="image" /></p>
 
-	<p><input name="hidden field" type="hidden" value="aaa" /></p>
-
 	<p><textarea name="textarea">some text in textarea</textarea></p>
 
 	<p><select name="selection field"><option value="1">a1</option><option selected="selected" value="2">a2</option><option value="3">a3</option></select></p>
 
-	<p><video controls="" height="240" width="320"><source src="movie.mp4" type="video/mp4" /> <source src="movie.ogg" type="video/ogg" /> Your browser does not support the video tag.</video></p>
+	<p><video controls="" height="240" width="320"><source src="http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/ElephantsDream.mp4" type="video/mp4" /> Your browser does not support the video tag.</video></p>
 
 	<p><audio controls=""><source src="horse.ogg" type="audio/ogg" /> <source src="horse.mp3" type="audio/mpeg" /> Your browser does not support the audio element.</audio></p>
+
+	<p><label><input> text</label></p>
 </div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.js b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
index f80f4f24919..e8e88c41eb3 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/objects.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
@@ -42,13 +42,15 @@ class ExtendHTMLSupport extends Plugin {
 			{ name: 'option', attributes: [ 'value', 'selected' ] },
 			{ name: 'video', attributes: [ 'height', 'width', 'controls' ] },
 			{ name: 'audio', attributes: [ 'controls' ] },
-			{ name: 'source', attributes: [ 'src', 'type' ] }
+			{ name: 'source', attributes: [ 'src', 'type' ] },
+			{ name: 'button' },
+			{ name: 'label' }
 		];
 
 		for ( const definition of definitions ) {
 			dataFilter.allowElement( { name: definition.name } );
 
-			for ( const key of definition.attributes ) {
+			for ( const key of ( definition.attributes || [] ) ) {
 				const attributes = {};
 				attributes[ key ] = /[\s\S]+/;
 
diff --git a/packages/ckeditor5-content-compatibility/theme/datafilter.css b/packages/ckeditor5-content-compatibility/theme/datafilter.css
index c773f619028..806402e6e77 100644
--- a/packages/ckeditor5-content-compatibility/theme/datafilter.css
+++ b/packages/ckeditor5-content-compatibility/theme/datafilter.css
@@ -1,48 +1,36 @@
 :root {
-	--ck-widget-compatibility-base-background: var(--ck-color-widget-blurred-border)
+	--ck-html-object-embed-unfocused-outline-width: 1px;
 }
 
-.ck .ck-widget {
-	&.ck-widget__compatibility {
-		padding: 20px 0 15px 0;
-		min-height: 20px;
-		border: 1px dotted hsl(15, 100%, 43%);
+.ck-widget.html-object-embed {
+	display: inline-block;
+	font-size: var(--ck-font-size-base);
+	background-color: var(--ck-color-base-foreground);
+	padding: var(--ck-spacing-small);
+	/* Leave space for label */
+	padding-top: calc(var(--ck-font-size-tiny) + var(--ck-spacing-large));
+	min-width: calc(76px + var(--ck-spacing-standard));
 
-		& .ck-widget__compatibility-type {
-			opacity: 0;
-			font-size: var(--ck-font-size-tiny);
-			padding: 0 5px;
-			background: var(--ck-widget-compatibility-base-background);
-			display: block;
-			position: absolute;
-			overflow: hidden;
-			z-index: var(--ck-z-default);
-			/* Place it in the middle of the outline */
-			top: calc(-0.5 * var(--ck-widget-outline-thickness));
-			right: min(10%, 30px);
-			transform: translateY(-50%);
-		}
-
-		&.ck-widget_selected > .ck-widget__compatibility-type {
-			opacity: 1;
-			color: var(--ck-color-base-background);
-			background: var(--ck-color-focus-border);
-		}
-
-		&:not(.ck-widget_selected):hover > .ck-widget__compatibility-type {
-			opacity: 1;
-			color: var(--ck-color-base-background);
-			background: var(--ck-color-widget-hover-border);
-		}
+	&:not(.ck-widget_selected):not(:hover) {
+		outline: var(--ck-html-object-embed-unfocused-outline-width) dashed var(--ck-color-widget-blurred-border);
 	}
 
-	&.ck-widget__compatibility-inline {
-		display: inline-block;
-		min-width: 100px;
+	&::before {
+		position: absolute;
+		content: attr(data-html-object-embed-label);
+		top: 0;
+		left: var(--ck-spacing-standard);
+		background: hsl(0deg 0% 60%);
+		transition: background var(--ck-widget-handler-animation-duration) var(--ck-widget-handler-animation-curve);
+		padding: calc(var(--ck-spacing-tiny) + var(--ck-html-object-embed-unfocused-outline-width)) var(--ck-spacing-small) var(--ck-spacing-tiny);
+		border-radius: 0 0 var(--ck-border-radius) var(--ck-border-radius);
+		color: var(--ck-color-base-background);
+		font-size: var(--ck-font-size-tiny);
+		font-family: var(--ck-font-face);
 	}
-}
 
-.ck.ck-editor__editable.ck-blurred .ck-widget.ck-widget__compatibility.ck-widget_selected > .ck-widget__compatibility-type {
-	color: hsl(0,0%,60%);
-	background: var(--ck-widget-compatibility-base-background);
+	& .html-object-embed__content {
+		/* Disable user interation with embed content */
+		pointer-events: none;
+	}
 }

From 0af201057bd87705c35ab89bd81da8ed7c83be49 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Sun, 9 May 2021 11:53:25 +0200
Subject: [PATCH 118/217] Corrected audio example.

---
 .../ckeditor5-content-compatibility/tests/manual/objects.html   | 2 +-
 .../ckeditor5-content-compatibility/tests/manual/objects.js     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.html b/packages/ckeditor5-content-compatibility/tests/manual/objects.html
index d69e187ab83..c849f8a401b 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/objects.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.html
@@ -66,7 +66,7 @@
 
 	<p><video controls="" height="240" width="320"><source src="http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/ElephantsDream.mp4" type="video/mp4" /> Your browser does not support the video tag.</video></p>
 
-	<p><audio controls=""><source src="horse.ogg" type="audio/ogg" /> <source src="horse.mp3" type="audio/mpeg" /> Your browser does not support the audio element.</audio></p>
+	<p><audio controls=""><source src="https://www.soundhelix.com/examples/mp3/SoundHelix-Song-1.mp3" type="audio/mpeg" /> Your browser does not support the audio element.</audio></p>
 
 	<p><label><input> text</label></p>
 </div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.js b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
index e8e88c41eb3..0926be61f06 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/objects.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
@@ -52,7 +52,7 @@ class ExtendHTMLSupport extends Plugin {
 
 			for ( const key of ( definition.attributes || [] ) ) {
 				const attributes = {};
-				attributes[ key ] = /[\s\S]+/;
+				attributes[ key ] = true;
 
 				dataFilter.allowAttributes( { name: definition.name, attributes } );
 			}

From 9f41cfb98ab319c896ca24fe21cde9f16a236b6d Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 10 May 2021 09:44:00 +0200
Subject: [PATCH 119/217] Added support for object block elements.

---
 .../src/datafilter.js                         | 141 ++++++++++++------
 .../src/dataschema.js                         |   5 +-
 .../theme/datafilter.css                      |  14 +-
 3 files changed, 108 insertions(+), 52 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 1fff7576ae4..979af765d09 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -168,15 +168,15 @@ export default class DataFilter {
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
 	_registerElement( definition ) {
-		if ( definition.isInline ) {
+		if ( definition.isObject ) {
+			this._registerObjectElement( definition );
+		} else if ( definition.isInline ) {
 			this._registerInlineElement( definition );
 		} else if ( definition.isBlock ) {
 			this._registerBlockElement( definition );
-		} else if ( definition.isObject ) {
-			this._registerObjectElement( definition );
 		} else {
 			/**
-			 * Only a definition marked as inline or block can be allowed.
+			 * Only a definition marked as inline, block or object can be allowed.
 			 *
 			 * @error data-filter-invalid-definition-type
 			 */
@@ -191,27 +191,48 @@ export default class DataFilter {
 	/**
 	 * Registers object element and attribute converters for the given data schema definition.
 	 *
+	 * This method will embed element inside a `htmlObjectEmbedBlock` or `htmlObjectEmbedInline` widget
+	 * depending on {@link module:content-compatibility/dataschema~DataSchemaObjectElementDefinition#isBlock}
+	 * property.
+	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
 	 */
 	_registerObjectElement( definition ) {
-		const schema = this.editor.model.schema;
+		const t = this.editor.t;
+
+		if ( definition.isBlock ) {
+			this._registerObjectElementWidget( 'htmlObjectEmbedBlock', {
+				isObject: true,
+				isBlock: true,
+				allowWhere: '$block',
+				allowAttributes: [ 'value', 'view', 'htmlAttributes' ]
+			}, writer => {
+				return writer.createContainerElement( 'div', {
+					class: 'html-object-embed html-object-embed-block',
+					'data-html-object-embed-label': t( 'HTML object' )
+				} );
+			} );
 
-		// All object elements are represented by a single widget.
-		if ( !schema.isRegistered( 'htmlObjectEmbed' ) ) {
-			schema.register( 'htmlObjectEmbed', {
+			this._addObjectElementToElementUpcastConversion( definition, 'htmlObjectEmbedBlock' );
+		} else {
+			this._registerObjectElementWidget( 'htmlObjectEmbedInline', {
 				isObject: true,
 				isInline: true,
 				allowWhere: '$text',
 				allowAttributesOf: '$text',
 				allowAttributes: [ 'value', 'view', 'htmlAttributes' ]
+			}, writer => {
+				return writer.createContainerElement( 'span', {
+					class: 'html-object-embed html-object-embed-inline',
+					'data-html-object-embed-label': t( 'HTML object' )
+				}, {
+					isAllowedInsideAttributeElement: true
+				} );
 			} );
 
-			this._addHtmlObjectEmbedConversion();
+			this._addObjectElementToElementUpcastConversion( definition, 'htmlObjectEmbedInline' );
 		}
-
-		this._addDisallowedAttributeConversion( definition );
-		this._addObjectElementToElementConversion( definition );
 	}
 
 	/**
@@ -257,27 +278,42 @@ export default class DataFilter {
 		this._addInlineElementConversion( definition );
 	}
 
-	_addHtmlObjectEmbedConversion() {
-		const editor = this.editor;
-		const conversion = editor.conversion;
-		const t = editor.t;
+	/**
+	 * Registers widget used to embed object elements.
+	 *
+	 * You should provide `createViewContainer` function used to create widget wrapper element.
+	 *
+	 *		this._registerObjectElementWidget( 'customWidgetModel', widgetSchema, writer => {
+	 *			return writer.createContainerElement( 'div', { class: 'widget' } );
+	 *		} );
+	 *
+	 * @private
+	 * @param {String} widgetName
+	 * @param {module:engine/model/schema~SchemaItemDefinition} widgetSchema
+	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
+	 */
+	_registerObjectElementWidget( widgetName, widgetSchema, createViewContainer ) {
+		const t = this.editor.t;
+		const schema = this.editor.model.schema;
+		const conversion = this.editor.conversion;
+
+		if ( schema.isRegistered( widgetName ) ) {
+			return;
+		}
+
+		schema.register( widgetName, widgetSchema );
 
 		conversion.for( 'dataDowncast' ).elementToElement( {
-			model: 'htmlObjectEmbed',
+			model: widgetName,
 			view: createObjectViewElement
 		} );
 
 		conversion.for( 'editingDowncast' ).elementToElement( {
-			model: 'htmlObjectEmbed',
+			model: widgetName,
 			view: ( modelElement, conversionApi ) => {
 				const { writer } = conversionApi;
 
-				const viewContainer = writer.createContainerElement( 'span', {
-					class: 'html-object-embed',
-					'data-html-object-embed-label': t( 'HTML object' )
-				}, {
-					isAllowedInsideAttributeElement: true
-				} );
+				const viewContainer = createViewContainer( writer );
 
 				const viewElement = createObjectViewElement( modelElement, conversionApi );
 				writer.addClass( 'html-object-embed__content', viewElement );
@@ -291,6 +327,38 @@ export default class DataFilter {
 		} );
 	}
 
+	/**
+	 * Registers object element to element upcast conversion for the given data schema definition.
+	 *
+	 * This function will embed view element inside widget element provided as a second argument.
+	 *
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
+	 * @param {String} widgetName
+	 */
+	_addObjectElementToElementUpcastConversion( { view: viewName }, widgetName ) {
+		const conversion = this.editor.conversion;
+
+		// Object element content will be hidden under `value` property and restored by
+		// `htmlObjectEmbedInline` downcast converters.
+		this.editor.data.registerRawContentMatcher( {
+			name: viewName
+		} );
+
+		conversion.for( 'upcast' ).elementToElement( {
+			view: viewName,
+			model: ( viewElement, conversionApi ) => {
+				const htmlAttributes = this._matchAndConsumeAllowedAttributes( viewElement, conversionApi );
+
+				return conversionApi.writer.createElement( widgetName, {
+					value: viewElement.getCustomProperty( '$rawContent' ),
+					view: viewName,
+					...( htmlAttributes && { htmlAttributes } )
+				} );
+			}
+		} );
+	}
+
 	/**
 	 * Adds element to element converters for the given block element definition.
 	 *
@@ -434,31 +502,6 @@ export default class DataFilter {
 		} );
 	}
 
-	_addObjectElementToElementConversion( { view: viewName } ) {
-		const conversion = this.editor.conversion;
-
-		// Object element content will be hidden under `value` property and restored by
-		// `htmlObjectEmbed` downcast converters.
-		this.editor.data.registerRawContentMatcher( {
-			name: viewName
-		} );
-
-		// We just need to add upcast conversion for specific view. Downcast is handled by
-		// `htmlObjectEmbed` itself.
-		conversion.for( 'upcast' ).elementToElement( {
-			view: viewName,
-			model: ( viewElement, conversionApi ) => {
-				const htmlAttributes = this._matchAndConsumeAllowedAttributes( viewElement, conversionApi );
-
-				return conversionApi.writer.createElement( 'htmlObjectEmbed', {
-					value: viewElement.getCustomProperty( '$rawContent' ),
-					view: viewName,
-					...( htmlAttributes && { htmlAttributes } )
-				} );
-			}
-		} );
-	}
-
 	/**
 	 * Matches and consumes allowed view attributes.
 	 *
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index aeeedb027a1..a0806479495 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -256,7 +256,7 @@ export default class DataSchema {
 	}
 
 	/**
-	 * Add new data schema definition describing inline element.
+	 * Add new data schema definition describing object element.
 	 *
 	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
 	 */
@@ -359,7 +359,7 @@ function testViewName( pattern, viewName ) {
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
  * @property {String} [view] Name of the view element.
  * @property {module:engine/model/schema~SchemaItemDefinition} [modelSchema] The model schema item definition describing registered model.
- * @property {Boolean} isBlock Indicates that the definition describes block element.
+ * @property {Boolean} isInline Indicates that the definition descibes inline element.
  * Set by {@link module:content-compatibility/dataschema~DataSchema#registerBlockElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */
@@ -370,6 +370,7 @@ function testViewName( pattern, viewName ) {
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaObjectElementDefinition
  * @property {String} view Name of the view element.
  * @property {Boolean} isObject Indicates that the definition describes object element.
+ * @property {Boolean} [isBlock] Indicates that the definition describes block element.
  * Set by {@link module:content-compatibility/dataschema~DataSchema#registerObjectElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */
diff --git a/packages/ckeditor5-content-compatibility/theme/datafilter.css b/packages/ckeditor5-content-compatibility/theme/datafilter.css
index 806402e6e77..f242c70d7bf 100644
--- a/packages/ckeditor5-content-compatibility/theme/datafilter.css
+++ b/packages/ckeditor5-content-compatibility/theme/datafilter.css
@@ -3,7 +3,6 @@
 }
 
 .ck-widget.html-object-embed {
-	display: inline-block;
 	font-size: var(--ck-font-size-base);
 	background-color: var(--ck-color-base-foreground);
 	padding: var(--ck-spacing-small);
@@ -11,6 +10,19 @@
 	padding-top: calc(var(--ck-font-size-tiny) + var(--ck-spacing-large));
 	min-width: calc(76px + var(--ck-spacing-standard));
 
+	&.html-object-embed-block {
+		margin: 1em auto;
+	}
+
+	/* Make space for label but it only collides in LTR languages */
+	& .ck-widget__type-around .ck-widget__type-around__button.ck-widget__type-around__button_before {
+		margin-left: 50px;
+	}
+
+	&.html-object-embed-inline {
+		display: inline-block;
+	}
+
 	&:not(.ck-widget_selected):not(:hover) {
 		outline: var(--ck-html-object-embed-unfocused-outline-width) dashed var(--ck-color-widget-blurred-border);
 	}

From 4e11c308d1267fe30fdd210593afbe904a00b948 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 10 May 2021 13:12:28 +0200
Subject: [PATCH 120/217] Small fixes, test coverage.

---
 .../src/datafilter.js                         |   7 +-
 .../tests/datafilter.js                       | 196 ++++++++++++++++++
 2 files changed, 201 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 979af765d09..5b2eca072b1 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -200,6 +200,7 @@ export default class DataFilter {
 	 */
 	_registerObjectElement( definition ) {
 		const t = this.editor.t;
+		const label = t( 'HTML object' );
 
 		if ( definition.isBlock ) {
 			this._registerObjectElementWidget( 'htmlObjectEmbedBlock', {
@@ -210,7 +211,7 @@ export default class DataFilter {
 			}, writer => {
 				return writer.createContainerElement( 'div', {
 					class: 'html-object-embed html-object-embed-block',
-					'data-html-object-embed-label': t( 'HTML object' )
+					'data-html-object-embed-label': label
 				} );
 			} );
 
@@ -225,7 +226,7 @@ export default class DataFilter {
 			}, writer => {
 				return writer.createContainerElement( 'span', {
 					class: 'html-object-embed html-object-embed-inline',
-					'data-html-object-embed-label': t( 'HTML object' )
+					'data-html-object-embed-label': label
 				}, {
 					isAllowedInsideAttributeElement: true
 				} );
@@ -233,6 +234,8 @@ export default class DataFilter {
 
 			this._addObjectElementToElementUpcastConversion( definition, 'htmlObjectEmbedInline' );
 		}
+
+		this._addDisallowedAttributeConversion( definition );
 	}
 
 	/**
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index d391eecd298..8d786f65867 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -124,6 +124,202 @@ describe( 'DataFilter', () => {
 		}
 	} );
 
+	describe( 'object', () => {
+		it( 'should allow element', () => {
+			dataFilter.allowElement( { name: 'input' } );
+
+			editor.setData( '<p><input></p>' );
+
+			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
+				'<paragraph>' +
+				'<htmlObjectEmbedInline' +
+				' value=""' +
+				' view="input">' +
+				'</htmlObjectEmbedInline>' +
+				'</paragraph>'
+			);
+
+			expect( editor.getData() ).to.equal( '<p><input></p>' );
+		} );
+
+		it( 'should allow element content', () => {
+			dataFilter.allowElement( { name: 'video' } );
+
+			editor.setData( '<p><video>' +
+				'<source src="https://example.com/video.mp4" type="video/mp4">' +
+				' Your browser does not support the video tag.</video>' +
+				'</p>' );
+
+			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
+				'<paragraph>' +
+				'<htmlObjectEmbedInline' +
+				' value="<source src="https://example.com/video.mp4" type="video/mp4"> Your browser does not support the video tag."' +
+				' view="video">' +
+				'</htmlObjectEmbedInline>' +
+				'</paragraph>'
+			);
+
+			expect( editor.getData() ).to.equal( '<p><video>' +
+				'<source src="https://example.com/video.mp4" type="video/mp4">' +
+				' Your browser does not support the video tag.</video>' +
+				'</p>'
+			);
+		} );
+
+		it( 'should recognize block elements', () => {
+			dataSchema.registerObjectElement( {
+				model: 'htmlXyz',
+				view: 'xyz',
+				isBlock: true
+			} );
+
+			dataFilter.allowElement( { name: 'xyz' } );
+
+			editor.setData( '<xyz>foobar</xyz>' );
+
+			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
+				'<htmlObjectEmbedBlock' +
+				' value="foobar"' +
+				' view="xyz">' +
+				'</htmlObjectEmbedBlock>'
+			);
+
+			expect( editor.getData() ).to.equal( '<xyz>foobar</xyz>' );
+		} );
+
+		it( 'should allow attributes', () => {
+			dataFilter.allowElement( { name: 'input' } );
+			dataFilter.allowAttributes( { name: 'input', attributes: { type: true } } );
+
+			editor.setData( '<p><input type="text"></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><htmlObjectEmbedInline htmlAttributes="(1)" value="" view="input"></htmlObjectEmbedInline></paragraph>',
+				attributes: {
+					1: {
+						attributes: {
+							type: 'text'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><input type="text"></p>' );
+		} );
+
+		it( 'should allow attributes (styles)', () => {
+			dataFilter.allowElement( { name: 'input' } );
+			dataFilter.allowAttributes( { name: 'input', styles: { color: 'red' } } );
+
+			editor.setData( '<p><input style="color:red;"></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><htmlObjectEmbedInline htmlAttributes="(1)" value="" view="input"></htmlObjectEmbedInline></paragraph>',
+				attributes: {
+					1: {
+						styles: {
+							color: 'red'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><input style="color:red;"></p>' );
+		} );
+
+		it( 'should allow attributes (classes)', () => {
+			dataFilter.allowElement( { name: 'input' } );
+			dataFilter.allowAttributes( { name: 'input', classes: [ 'foobar' ] } );
+
+			editor.setData( '<p><input class="foobar"></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><htmlObjectEmbedInline htmlAttributes="(1)" value="" view="input"></htmlObjectEmbedInline></paragraph>',
+				attributes: {
+					1: {
+						classes: [ 'foobar' ]
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><input class="foobar"></p>' );
+		} );
+
+		it( 'should disallow attributes', () => {
+			dataFilter.allowElement( { name: 'input' } );
+			dataFilter.allowAttributes( { name: 'input', attributes: { type: true } } );
+			dataFilter.disallowAttributes( { name: 'input', attributes: { type: 'hidden' } } );
+
+			editor.setData( '<p><input type="text"><input type="hidden"></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+				'<htmlObjectEmbedInline htmlAttributes="(1)" value="" view="input"></htmlObjectEmbedInline>' +
+				'<htmlObjectEmbedInline value="" view="input"></htmlObjectEmbedInline>' +
+				'</paragraph>',
+				attributes: {
+					1: {
+						attributes: {
+							type: 'text'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><input type="text"><input></p>' );
+		} );
+
+		it( 'should disallow attributes (styles)', () => {
+			dataFilter.allowElement( { name: 'input' } );
+			dataFilter.allowAttributes( { name: 'input', styles: { color: /^(red|blue)$/ } } );
+			dataFilter.disallowAttributes( { name: 'input', styles: { color: 'red' } } );
+
+			editor.setData( '<p><input style="color:blue;"><input style="color:red;"</p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+				'<htmlObjectEmbedInline htmlAttributes="(1)" value="" view="input"></htmlObjectEmbedInline>' +
+				'<htmlObjectEmbedInline value="" view="input"></htmlObjectEmbedInline>' +
+				'</paragraph>',
+				attributes: {
+					1: {
+						styles: {
+							color: 'blue'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><input style="color:blue;"><input></p>' );
+		} );
+
+		it( 'should disallow attributes (classes)', () => {
+			dataFilter.allowElement( { name: 'input' } );
+			dataFilter.allowAttributes( { name: 'input', classes: [ 'foo', 'bar' ] } );
+			dataFilter.disallowAttributes( { name: 'input', classes: [ 'bar' ] } );
+
+			editor.setData( '<p><input class="foo bar"><input class="bar"></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+				'<htmlObjectEmbedInline value="" view="input"></htmlObjectEmbedInline>' +
+				'<htmlObjectEmbedInline value="" view="input"></htmlObjectEmbedInline>' +
+				'</paragraph>',
+				attributes: {}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><input><input></p>' );
+		} );
+
+		it( 'should register embed widget only once', () => {
+			dataFilter.allowElement( { name: 'video' } );
+
+			expect( () => {
+				dataFilter.allowElement( { name: 'audio' } );
+			} ).to.not.throw();
+		} );
+	} );
+
 	describe( 'block', () => {
 		it( 'should allow element', () => {
 			dataFilter.allowElement( { name: 'article' } );

From 35942349633cc7b172ea265b792d86e7eae6e158 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 10 May 2021 14:12:37 +0200
Subject: [PATCH 121/217] Added block object manual test.

---
 .../tests/manual/objects.html                              | 2 ++
 .../tests/manual/objects.js                                | 7 +++++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.html b/packages/ckeditor5-content-compatibility/tests/manual/objects.html
index c849f8a401b..7567ff7607f 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/objects.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.html
@@ -69,4 +69,6 @@
 	<p><audio controls=""><source src="https://www.soundhelix.com/examples/mp3/SoundHelix-Song-1.mp3" type="audio/mpeg" /> Your browser does not support the audio element.</audio></p>
 
 	<p><label><input> text</label></p>
+
+	<p><xyz data-foo="foo">Hello, world!</xyz></p>
 </div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.js b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
index 0926be61f06..9989ef3653f 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/objects.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
@@ -28,7 +28,9 @@ class ExtendHTMLSupport extends Plugin {
 	}
 
 	init() {
-		const { dataFilter } = this.editor.plugins.get( GeneralHtmlSupport );
+		const { dataFilter, dataSchema } = this.editor.plugins.get( GeneralHtmlSupport );
+
+		dataSchema.registerObjectElement( { model: 'htmlXyz', view: 'xyz', isBlock: true } );
 
 		const definitions = [
 			{ name: 'object', attributes: [ 'classid', 'codebase' ] },
@@ -44,7 +46,8 @@ class ExtendHTMLSupport extends Plugin {
 			{ name: 'audio', attributes: [ 'controls' ] },
 			{ name: 'source', attributes: [ 'src', 'type' ] },
 			{ name: 'button' },
-			{ name: 'label' }
+			{ name: 'label' },
+			{ name: 'xyz', attributes: [ 'data-foo' ] }
 		];
 
 		for ( const definition of definitions ) {

From db8824f3f85f15b8e1388db827b4a05be86f368f Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 10 May 2021 14:24:52 +0200
Subject: [PATCH 122/217] Respect UI language.

---
 .../src/datafilter.js                             |  6 ++++--
 .../theme/datafilter.css                          | 15 ++++++++++-----
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 5b2eca072b1..7de492110fe 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -211,7 +211,8 @@ export default class DataFilter {
 			}, writer => {
 				return writer.createContainerElement( 'div', {
 					class: 'html-object-embed html-object-embed-block',
-					'data-html-object-embed-label': label
+					'data-html-object-embed-label': label,
+					dir: this.editor.locale.uiLanguageDirection
 				} );
 			} );
 
@@ -226,7 +227,8 @@ export default class DataFilter {
 			}, writer => {
 				return writer.createContainerElement( 'span', {
 					class: 'html-object-embed html-object-embed-inline',
-					'data-html-object-embed-label': label
+					'data-html-object-embed-label': label,
+					dir: this.editor.locale.uiLanguageDirection
 				}, {
 					isAllowedInsideAttributeElement: true
 				} );
diff --git a/packages/ckeditor5-content-compatibility/theme/datafilter.css b/packages/ckeditor5-content-compatibility/theme/datafilter.css
index f242c70d7bf..e251a60fbc6 100644
--- a/packages/ckeditor5-content-compatibility/theme/datafilter.css
+++ b/packages/ckeditor5-content-compatibility/theme/datafilter.css
@@ -14,11 +14,6 @@
 		margin: 1em auto;
 	}
 
-	/* Make space for label but it only collides in LTR languages */
-	& .ck-widget__type-around .ck-widget__type-around__button.ck-widget__type-around__button_before {
-		margin-left: 50px;
-	}
-
 	&.html-object-embed-inline {
 		display: inline-block;
 	}
@@ -41,6 +36,16 @@
 		font-family: var(--ck-font-face);
 	}
 
+	&[dir="rtl"]::before {
+		left: auto;
+		right: var(--ck-spacing-standard);
+	}
+
+	/* Make space for label but it only collides in LTR languages */
+	&[dir="ltr"] .ck-widget__type-around .ck-widget__type-around__button.ck-widget__type-around__button_before {
+		margin-left: 50px;
+	}
+
 	& .html-object-embed__content {
 		/* Disable user interation with embed content */
 		pointer-events: none;

From bc48865c243b868f929da69acc3a79f172978f35 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 10 May 2021 14:50:06 +0200
Subject: [PATCH 123/217] Refactoring.

---
 .../src/datafilter.js                         | 89 +++++++++++--------
 1 file changed, 51 insertions(+), 38 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 7de492110fe..ababc393e24 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -199,42 +199,10 @@ export default class DataFilter {
 	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
 	 */
 	_registerObjectElement( definition ) {
-		const t = this.editor.t;
-		const label = t( 'HTML object' );
-
 		if ( definition.isBlock ) {
-			this._registerObjectElementWidget( 'htmlObjectEmbedBlock', {
-				isObject: true,
-				isBlock: true,
-				allowWhere: '$block',
-				allowAttributes: [ 'value', 'view', 'htmlAttributes' ]
-			}, writer => {
-				return writer.createContainerElement( 'div', {
-					class: 'html-object-embed html-object-embed-block',
-					'data-html-object-embed-label': label,
-					dir: this.editor.locale.uiLanguageDirection
-				} );
-			} );
-
-			this._addObjectElementToElementUpcastConversion( definition, 'htmlObjectEmbedBlock' );
+			this._registerBlockObjectElement( definition );
 		} else {
-			this._registerObjectElementWidget( 'htmlObjectEmbedInline', {
-				isObject: true,
-				isInline: true,
-				allowWhere: '$text',
-				allowAttributesOf: '$text',
-				allowAttributes: [ 'value', 'view', 'htmlAttributes' ]
-			}, writer => {
-				return writer.createContainerElement( 'span', {
-					class: 'html-object-embed html-object-embed-inline',
-					'data-html-object-embed-label': label,
-					dir: this.editor.locale.uiLanguageDirection
-				}, {
-					isAllowedInsideAttributeElement: true
-				} );
-			} );
-
-			this._addObjectElementToElementUpcastConversion( definition, 'htmlObjectEmbedInline' );
+			this._registerInlineObjectElement( definition );
 		}
 
 		this._addDisallowedAttributeConversion( definition );
@@ -283,6 +251,55 @@ export default class DataFilter {
 		this._addInlineElementConversion( definition );
 	}
 
+	/**
+	 * Registers block object element and attribute converters for the given data schema definition.
+	 *
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	*/
+	_registerBlockObjectElement( definition ) {
+		this._registerObjectElementWidget( 'htmlObjectEmbedBlock', {
+			isObject: true,
+			isBlock: true,
+			allowWhere: '$block',
+			allowAttributes: [ 'value', 'view', 'htmlAttributes' ]
+		}, writer => {
+			return writer.createContainerElement( 'div', {
+				class: 'html-object-embed html-object-embed-block',
+				'data-html-object-embed-label': this.editor.t( 'HTML object' ),
+				dir: this.editor.locale.uiLanguageDirection
+			} );
+		} );
+
+		this._addObjectElementToElementUpcastConversion( definition, 'htmlObjectEmbedBlock' );
+	}
+
+	/**
+	 * Registers inline object element and attribute converters for the given data schema definition.
+	 *
+	 * @private
+	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	*/
+	_registerInlineObjectElement( definition ) {
+		this._registerObjectElementWidget( 'htmlObjectEmbedInline', {
+			isObject: true,
+			isInline: true,
+			allowWhere: '$text',
+			allowAttributesOf: '$text',
+			allowAttributes: [ 'value', 'view', 'htmlAttributes' ]
+		}, writer => {
+			return writer.createContainerElement( 'span', {
+				class: 'html-object-embed html-object-embed-inline',
+				'data-html-object-embed-label': this.editor.t( 'HTML object' ),
+				dir: this.editor.locale.uiLanguageDirection
+			}, {
+				isAllowedInsideAttributeElement: true
+			} );
+		} );
+
+		this._addObjectElementToElementUpcastConversion( definition, 'htmlObjectEmbedInline' );
+	}
+
 	/**
 	 * Registers widget used to embed object elements.
 	 *
@@ -335,8 +352,6 @@ export default class DataFilter {
 	/**
 	 * Registers object element to element upcast conversion for the given data schema definition.
 	 *
-	 * This function will embed view element inside widget element provided as a second argument.
-	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
 	 * @param {String} widgetName
@@ -344,8 +359,6 @@ export default class DataFilter {
 	_addObjectElementToElementUpcastConversion( { view: viewName }, widgetName ) {
 		const conversion = this.editor.conversion;
 
-		// Object element content will be hidden under `value` property and restored by
-		// `htmlObjectEmbedInline` downcast converters.
 		this.editor.data.registerRawContentMatcher( {
 			name: viewName
 		} );

From 4ac3c04a2024b72c768e019e259b06cca9711803 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 10 May 2021 14:52:11 +0200
Subject: [PATCH 124/217] Sanity check for dataschema API.

---
 .../tests/dataschema.js                            | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index 49523214515..a31c01b039d 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -26,6 +26,20 @@ describe( 'DataSchema', () => {
 		return editor.destroy();
 	} );
 
+	describe( 'registerObjectElement()', () => {
+		it( 'should register proper definition', () => {
+			dataSchema.registerObjectElement( { model: 'htmlDef', view: 'def' } );
+
+			const result = dataSchema.getDefinitionsForView( 'def' );
+
+			expect( Array.from( result ) ).to.deep.equal( [ {
+				model: 'htmlDef',
+				view: 'def',
+				isObject: true
+			} ] );
+		} );
+	} );
+
 	describe( 'registerInlineElement()', () => {
 		it( 'should register proper definition', () => {
 			dataSchema.registerInlineElement( { model: 'htmlDef', view: 'def' } );

From bb7ed346ce0dc4d29425723c1d1787c1fadac383 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 10 May 2021 15:08:00 +0200
Subject: [PATCH 125/217] Docs update.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 7 ++++---
 packages/ckeditor5-content-compatibility/src/dataschema.js | 2 +-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index ababc393e24..d2aa258f237 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -255,7 +255,7 @@ export default class DataFilter {
 	 * Registers block object element and attribute converters for the given data schema definition.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
 	*/
 	_registerBlockObjectElement( definition ) {
 		this._registerObjectElementWidget( 'htmlObjectEmbedBlock', {
@@ -278,7 +278,7 @@ export default class DataFilter {
 	 * Registers inline object element and attribute converters for the given data schema definition.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
 	*/
 	_registerInlineObjectElement( definition ) {
 		this._registerObjectElementWidget( 'htmlObjectEmbedInline', {
@@ -312,13 +312,14 @@ export default class DataFilter {
 	 * @private
 	 * @param {String} widgetName
 	 * @param {module:engine/model/schema~SchemaItemDefinition} widgetSchema
-	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
+	 * @param {Function} createViewContainer
 	 */
 	_registerObjectElementWidget( widgetName, widgetSchema, createViewContainer ) {
 		const t = this.editor.t;
 		const schema = this.editor.model.schema;
 		const conversion = this.editor.conversion;
 
+		// Object element widget should be registered only once, as it's used to embed different views.
 		if ( schema.isRegistered( widgetName ) ) {
 			return;
 		}
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index a0806479495..20af84cea2f 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -359,7 +359,7 @@ function testViewName( pattern, viewName ) {
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
  * @property {String} [view] Name of the view element.
  * @property {module:engine/model/schema~SchemaItemDefinition} [modelSchema] The model schema item definition describing registered model.
- * @property {Boolean} isInline Indicates that the definition descibes inline element.
+ * @property {Boolean} isBlock Indicates that the definition describes block element.
  * Set by {@link module:content-compatibility/dataschema~DataSchema#registerBlockElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */

From d715d777b7a3bef904b634e097a407a0375ecefc Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 10 May 2021 15:38:21 +0200
Subject: [PATCH 126/217] Refactoring.

---
 .../src/datafilter.js                         | 49 +++++++++----------
 1 file changed, 24 insertions(+), 25 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index d2aa258f237..7960c1915a0 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -261,15 +261,10 @@ export default class DataFilter {
 		this._registerObjectElementWidget( 'htmlObjectEmbedBlock', {
 			isObject: true,
 			isBlock: true,
-			allowWhere: '$block',
-			allowAttributes: [ 'value', 'view', 'htmlAttributes' ]
-		}, writer => {
-			return writer.createContainerElement( 'div', {
-				class: 'html-object-embed html-object-embed-block',
-				'data-html-object-embed-label': this.editor.t( 'HTML object' ),
-				dir: this.editor.locale.uiLanguageDirection
-			} );
-		} );
+			allowWhere: '$block'
+		}, writer => writer.createContainerElement( 'div',
+			{ class: 'html-object-embed-block' } )
+		);
 
 		this._addObjectElementToElementUpcastConversion( definition, 'htmlObjectEmbedBlock' );
 	}
@@ -285,17 +280,11 @@ export default class DataFilter {
 			isObject: true,
 			isInline: true,
 			allowWhere: '$text',
-			allowAttributesOf: '$text',
-			allowAttributes: [ 'value', 'view', 'htmlAttributes' ]
-		}, writer => {
-			return writer.createContainerElement( 'span', {
-				class: 'html-object-embed html-object-embed-inline',
-				'data-html-object-embed-label': this.editor.t( 'HTML object' ),
-				dir: this.editor.locale.uiLanguageDirection
-			}, {
-				isAllowedInsideAttributeElement: true
-			} );
-		} );
+			allowAttributesOf: '$text'
+		}, writer => writer.createContainerElement( 'span',
+			{ class: 'html-object-embed-inline' },
+			{ isAllowedInsideAttributeElement: true } )
+		);
 
 		this._addObjectElementToElementUpcastConversion( definition, 'htmlObjectEmbedInline' );
 	}
@@ -315,7 +304,6 @@ export default class DataFilter {
 	 * @param {Function} createViewContainer
 	 */
 	_registerObjectElementWidget( widgetName, widgetSchema, createViewContainer ) {
-		const t = this.editor.t;
 		const schema = this.editor.model.schema;
 		const conversion = this.editor.conversion;
 
@@ -324,7 +312,11 @@ export default class DataFilter {
 			return;
 		}
 
-		schema.register( widgetName, widgetSchema );
+		schema.register( widgetName, {
+			// Extend with attributes required by conversion.
+			allowAttributes: [ 'value', 'view', 'htmlAttributes' ],
+			...widgetSchema
+		} );
 
 		conversion.for( 'dataDowncast' ).elementToElement( {
 			model: widgetName,
@@ -335,17 +327,24 @@ export default class DataFilter {
 			model: widgetName,
 			view: ( modelElement, conversionApi ) => {
 				const { writer } = conversionApi;
+				const widgetLabel = this.editor.t( 'HTML object' );
 
+				// Widget cannot be a raw element because the widget system would not be able
+				// to add its UI to it. Thus, we need separate view container.
 				const viewContainer = createViewContainer( writer );
 
+				// Add required attributes here, so we don't have to duplicate this logic between
+				// #_registerInlineObjectElement() and #_registerBlockObjectElement() methods.
+				writer.addClass( 'html-object-embed', viewContainer );
+				writer.setAttribute( 'data-html-object-embed-label', widgetLabel, viewContainer );
+				writer.setAttribute( 'dir', this.editor.locale.uiLanguageDirection, viewContainer );
+
 				const viewElement = createObjectViewElement( modelElement, conversionApi );
 				writer.addClass( 'html-object-embed__content', viewElement );
 
 				writer.insert( writer.createPositionAt( viewContainer, 0 ), viewElement );
 
-				return toWidget( viewContainer, writer, {
-					widgetLabel: t( 'HTML object' )
-				} );
+				return toWidget( viewContainer, writer, { widgetLabel } );
 			}
 		} );
 	}

From 6510ebab1ec855c5b1fb43691b938f0d3bc03f1b Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 10 May 2021 15:41:27 +0200
Subject: [PATCH 127/217] Reverted unnecessary docs change.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 7960c1915a0..94df33ba53e 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -405,10 +405,10 @@ export default class DataFilter {
 	}
 
 	/**
-	 * Adds attribute converters for the given element definition.
+	 * Adds attribute converters for the given block element definition.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
 	_addBlockElementAttributeConversion( { model: modelName, view: viewName } ) {
 		const conversion = this.editor.conversion;

From a5b013dbb0ad80054ab195be307431b5e30afb12 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 11 May 2021 09:05:56 +0200
Subject: [PATCH 128/217] Fixed manual test.

---
 .../tests/manual/objects.html                               | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.html b/packages/ckeditor5-content-compatibility/tests/manual/objects.html
index 7567ff7607f..fdef8f3855a 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/objects.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.html
@@ -7,11 +7,11 @@
 	<object classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,40,0">
 		<param name="allowFullScreen" value="true" />
 		<param name="quality" value="high" />
-		<param name="movie" value="example.com" />
-		<embed allowfullscreen="true" pluginspage="http://www.macromedia.com/go/getflashplayer" quality="high" src="example.com" type="application/x-shockwave-flash"></embed>
+		<param name="movie" value="https://example.com" />
+		<embed allowfullscreen="true" pluginspage="http://www.macromedia.com/go/getflashplayer" quality="high" src="https://example.com" type="application/x-shockwave-flash"></embed>
 	</object>
 	</p>
-	<p><iframe frameborder="0" scrolling="no" src="example.com"></iframe></p>
+	<p><iframe frameborder="0" scrolling="no" src="https://example.com"></iframe></p>
 	<form action="controller/register" method="post" name="foobar">
 		<p><input name="checkbox" type="checkbox" value="10" /></p>
 

From c019ad93e8e93f8ce932d170ab783e2ec77e96bc Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 11 May 2021 10:54:57 +0200
Subject: [PATCH 129/217] Ensure that widget label is not changing by basic
 styles.

---
 .../package.json                              |  1 +
 .../tests/manual/objects.js                   | 21 ++++++++++++++++---
 .../theme/datafilter.css                      |  2 ++
 3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/package.json b/packages/ckeditor5-content-compatibility/package.json
index 352c286da55..396610351f9 100644
--- a/packages/ckeditor5-content-compatibility/package.json
+++ b/packages/ckeditor5-content-compatibility/package.json
@@ -26,6 +26,7 @@
     "@ckeditor/ckeditor5-engine": "^27.1.0",
     "@ckeditor/ckeditor5-essentials": "^27.1.0",
     "@ckeditor/ckeditor5-font": "^27.1.0",
+    "@ckeditor/ckeditor5-highlight": "^27.1.0",
     "@ckeditor/ckeditor5-link": "^27.1.0",
     "@ckeditor/ckeditor5-list": "^27.1.0",
     "@ckeditor/ckeditor5-paragraph": "^27.1.0",
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.js b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
index 9989ef3653f..8effa30f8b3 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/objects.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
@@ -11,11 +11,16 @@ import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
 import Bold from '@ckeditor/ckeditor5-basic-styles/src/bold';
 import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
 import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
+import Underline from '@ckeditor/ckeditor5-basic-styles/src/underline';
+import Subscript from '@ckeditor/ckeditor5-basic-styles/src/subscript';
+import Superscript from '@ckeditor/ckeditor5-basic-styles/src/superscript';
+import Code from '@ckeditor/ckeditor5-basic-styles/src/code';
 import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
 import BlockQuote from '@ckeditor/ckeditor5-block-quote/src/blockquote';
 import List from '@ckeditor/ckeditor5-list/src/list';
 import Link from '@ckeditor/ckeditor5-link/src/link';
 import Table from '@ckeditor/ckeditor5-table/src/table';
+import Highlight from '@ckeditor/ckeditor5-highlight/src/highlight';
 
 import GeneralHtmlSupport from '../../src/generalhtmlsupport';
 
@@ -66,21 +71,31 @@ class ExtendHTMLSupport extends Plugin {
 ClassicEditor
 	.create( document.querySelector( '#editor' ), {
 		plugins: [
-			Table,
-			Link,
 			BlockQuote,
 			Bold,
+			Code,
 			Essentials,
 			ExtendHTMLSupport,
+			Highlight,
 			Italic,
+			Link,
 			List,
 			Paragraph,
-			Strikethrough
+			Strikethrough,
+			Subscript,
+			Superscript,
+			Table,
+			Underline
 		],
 		toolbar: [
 			'bold',
 			'italic',
 			'strikethrough',
+			'underline',
+			'code',
+			'subscript',
+			'superscript',
+			'highlight',
 			'|',
 			'numberedList',
 			'bulletedList',
diff --git a/packages/ckeditor5-content-compatibility/theme/datafilter.css b/packages/ckeditor5-content-compatibility/theme/datafilter.css
index e251a60fbc6..5a2a0b913f8 100644
--- a/packages/ckeditor5-content-compatibility/theme/datafilter.css
+++ b/packages/ckeditor5-content-compatibility/theme/datafilter.css
@@ -23,6 +23,8 @@
 	}
 
 	&::before {
+		font-weight: normal;
+		font-style: normal;
 		position: absolute;
 		content: attr(data-html-object-embed-label);
 		top: 0;

From 637ccb8fdff0370d8f4c3ffa40740bb91a2499af Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 12 May 2021 09:44:11 +0200
Subject: [PATCH 130/217] Simplified implementation to use original definition
 model.

---
 .../src/datafilter.js                         | 152 +++++-----------
 .../src/dataschema.js                         | 172 +++++++++++-------
 .../tests/datafilter.js                       |  43 ++---
 .../tests/dataschema.js                       |  14 --
 .../tests/manual/objects.js                   |   8 +-
 .../theme/datafilter.css                      |  17 +-
 6 files changed, 182 insertions(+), 224 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 94df33ba53e..e0319b05d93 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -191,20 +191,17 @@ export default class DataFilter {
 	/**
 	 * Registers object element and attribute converters for the given data schema definition.
 	 *
-	 * This method will embed element inside a `htmlObjectEmbedBlock` or `htmlObjectEmbedInline` widget
-	 * depending on {@link module:content-compatibility/dataschema~DataSchemaObjectElementDefinition#isBlock}
-	 * property.
-	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
 	_registerObjectElement( definition ) {
-		if ( definition.isBlock ) {
-			this._registerBlockObjectElement( definition );
-		} else {
-			this._registerInlineObjectElement( definition );
+		const schema = this.editor.model.schema;
+
+		if ( !schema.isRegistered( definition.model ) ) {
+			schema.register( definition.model, definition.modelSchema );
 		}
 
+		this._addObjectElementConversion( definition );
 		this._addDisallowedAttributeConversion( definition );
 	}
 
@@ -252,94 +249,62 @@ export default class DataFilter {
 	}
 
 	/**
-	 * Registers block object element and attribute converters for the given data schema definition.
-	 *
-	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
-	*/
-	_registerBlockObjectElement( definition ) {
-		this._registerObjectElementWidget( 'htmlObjectEmbedBlock', {
-			isObject: true,
-			isBlock: true,
-			allowWhere: '$block'
-		}, writer => writer.createContainerElement( 'div',
-			{ class: 'html-object-embed-block' } )
-		);
-
-		this._addObjectElementToElementUpcastConversion( definition, 'htmlObjectEmbedBlock' );
-	}
-
-	/**
-	 * Registers inline object element and attribute converters for the given data schema definition.
-	 *
-	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
-	*/
-	_registerInlineObjectElement( definition ) {
-		this._registerObjectElementWidget( 'htmlObjectEmbedInline', {
-			isObject: true,
-			isInline: true,
-			allowWhere: '$text',
-			allowAttributesOf: '$text'
-		}, writer => writer.createContainerElement( 'span',
-			{ class: 'html-object-embed-inline' },
-			{ isAllowedInsideAttributeElement: true } )
-		);
-
-		this._addObjectElementToElementUpcastConversion( definition, 'htmlObjectEmbedInline' );
-	}
-
-	/**
-	 * Registers widget used to embed object elements.
-	 *
-	 * You should provide `createViewContainer` function used to create widget wrapper element.
-	 *
-	 *		this._registerObjectElementWidget( 'customWidgetModel', widgetSchema, writer => {
-	 *			return writer.createContainerElement( 'div', { class: 'widget' } );
-	 *		} );
+	 * Adds converters for the given data schema definition marked as
+	 * {@link module:content-compatibility/dataschema~DataSchemaDefinition#isObject isObject}.
 	 *
 	 * @private
-	 * @param {String} widgetName
-	 * @param {module:engine/model/schema~SchemaItemDefinition} widgetSchema
-	 * @param {Function} createViewContainer
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
-	_registerObjectElementWidget( widgetName, widgetSchema, createViewContainer ) {
-		const schema = this.editor.model.schema;
+	_addObjectElementConversion( definition ) {
+		const { view: viewName, model: modelName } = definition;
 		const conversion = this.editor.conversion;
 
-		// Object element widget should be registered only once, as it's used to embed different views.
-		if ( schema.isRegistered( widgetName ) ) {
+		if ( !viewName ) {
 			return;
 		}
 
-		schema.register( widgetName, {
-			// Extend with attributes required by conversion.
-			allowAttributes: [ 'value', 'view', 'htmlAttributes' ],
-			...widgetSchema
+		// Store element content in special `$rawContent` custom property to
+		// avoid editor's data filtering mechanism.
+		this.editor.data.registerRawContentMatcher( {
+			name: viewName
+		} );
+
+		conversion.for( 'upcast' ).elementToElement( {
+			view: viewName,
+			model: ( viewElement, conversionApi ) => {
+				const htmlAttributes = this._matchAndConsumeAllowedAttributes( viewElement, conversionApi );
+
+				// Let's keep element HTML and its attributes, so we can rebuild element in downcast conversions.
+				return conversionApi.writer.createElement( modelName, {
+					value: viewElement.getCustomProperty( '$rawContent' ),
+					...( htmlAttributes && { htmlAttributes } )
+				} );
+			}
 		} );
 
 		conversion.for( 'dataDowncast' ).elementToElement( {
-			model: widgetName,
-			view: createObjectViewElement
+			model: modelName,
+			view: ( modelElement, { writer } ) => {
+				return createObjectViewElement( viewName, modelElement, writer );
+			}
 		} );
 
 		conversion.for( 'editingDowncast' ).elementToElement( {
-			model: widgetName,
-			view: ( modelElement, conversionApi ) => {
-				const { writer } = conversionApi;
+			model: modelName,
+			view: ( modelElement, { writer } ) => {
 				const widgetLabel = this.editor.t( 'HTML object' );
 
 				// Widget cannot be a raw element because the widget system would not be able
 				// to add its UI to it. Thus, we need separate view container.
-				const viewContainer = createViewContainer( writer );
-
-				// Add required attributes here, so we don't have to duplicate this logic between
-				// #_registerInlineObjectElement() and #_registerBlockObjectElement() methods.
-				writer.addClass( 'html-object-embed', viewContainer );
-				writer.setAttribute( 'data-html-object-embed-label', widgetLabel, viewContainer );
-				writer.setAttribute( 'dir', this.editor.locale.uiLanguageDirection, viewContainer );
+				const viewContainer = writer.createContainerElement( definition.isInline ? 'span' : 'div', {
+					class: 'html-object-embed',
+					'data-html-object-embed-label': widgetLabel,
+					dir: this.editor.locale.uiLanguageDirection
+				}, {
+					isAllowedInsideAttributeElement: definition.isInline
+				} );
 
-				const viewElement = createObjectViewElement( modelElement, conversionApi );
+				const viewElement = createObjectViewElement( viewName, modelElement, writer );
 				writer.addClass( 'html-object-embed__content', viewElement );
 
 				writer.insert( writer.createPositionAt( viewContainer, 0 ), viewElement );
@@ -349,34 +314,6 @@ export default class DataFilter {
 		} );
 	}
 
-	/**
-	 * Registers object element to element upcast conversion for the given data schema definition.
-	 *
-	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
-	 * @param {String} widgetName
-	 */
-	_addObjectElementToElementUpcastConversion( { view: viewName }, widgetName ) {
-		const conversion = this.editor.conversion;
-
-		this.editor.data.registerRawContentMatcher( {
-			name: viewName
-		} );
-
-		conversion.for( 'upcast' ).elementToElement( {
-			view: viewName,
-			model: ( viewElement, conversionApi ) => {
-				const htmlAttributes = this._matchAndConsumeAllowedAttributes( viewElement, conversionApi );
-
-				return conversionApi.writer.createElement( widgetName, {
-					value: viewElement.getCustomProperty( '$rawContent' ),
-					view: viewName,
-					...( htmlAttributes && { htmlAttributes } )
-				} );
-			}
-		} );
-	}
-
 	/**
 	 * Adds element to element converters for the given block element definition.
 	 *
@@ -609,8 +546,7 @@ function setViewElementAttributes( writer, viewAttributes, viewElement ) {
 // @param {module:engine/model/element~Element} modelElement
 // @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
 // @returns {module:engine/view/element~Element} viewElement
-function createObjectViewElement( modelElement, { writer } ) {
-	const viewName = modelElement.getAttribute( 'view' );
+function createObjectViewElement( viewName, modelElement, writer ) {
 	const viewAttributes = modelElement.getAttribute( 'htmlAttributes' );
 	const viewContent = modelElement.getAttribute( 'value' );
 
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 20af84cea2f..eb179b35b4f 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -49,6 +49,15 @@ export default class DataSchema {
 		this._definitions = new Map();
 
 		// Block elements.
+		this.registerBlockElement( {
+			model: '$htmlBlock',
+			modelSchema: {
+				allowChildren: '$block',
+				allowIn: [ '$root', '$htmlBlock' ],
+				isBlock: true
+			}
+		} );
+
 		this.registerBlockElement( {
 			model: 'paragraph',
 			view: 'p'
@@ -64,15 +73,6 @@ export default class DataSchema {
 			view: 'li'
 		} );
 
-		this.registerBlockElement( {
-			model: '$htmlBlock',
-			modelSchema: {
-				allowChildren: '$block',
-				allowIn: [ '$root', '$htmlBlock' ],
-				isBlock: true
-			}
-		} );
-
 		this.registerBlockElement( {
 			view: 'article',
 			model: 'htmlArticle',
@@ -150,44 +150,15 @@ export default class DataSchema {
 			}
 		} );
 
-		this.registerObjectElement( {
-			view: 'object',
-			model: 'htmlObject'
-		} );
-
-		this.registerObjectElement( {
-			view: 'iframe',
-			model: 'htmlIframe'
-		} );
-
-		this.registerObjectElement( {
-			view: 'input',
-			model: 'htmlInput'
-		} );
-
-		this.registerObjectElement( {
-			view: 'button',
-			model: 'htmlButton'
-		} );
-
-		this.registerObjectElement( {
-			view: 'textarea',
-			model: 'htmlTextarea'
-		} );
-
-		this.registerObjectElement( {
-			view: 'select',
-			model: 'htmlSelect'
-		} );
-
-		this.registerObjectElement( {
-			view: 'video',
-			model: 'htmlVideo'
-		} );
-
-		this.registerObjectElement( {
-			view: 'audio',
-			model: 'htmlAudio'
+		// Block objects.
+		this.registerBlockElement( {
+			model: '$htmlObjectBlock',
+			isObject: true,
+			modelSchema: {
+				isObject: true,
+				isBlock: true,
+				allowWhere: '$block'
+			}
 		} );
 
 		// Inline elements.
@@ -235,6 +206,90 @@ export default class DataSchema {
 				copyOnEnter: true
 			}
 		} );
+
+		// Inline objects
+		this.registerInlineElement( {
+			model: '$htmlObjectInline',
+			isObject: true,
+			modelSchema: {
+				isObject: true,
+				isInline: true,
+				allowWhere: '$text',
+				allowAttributesOf: '$text'
+			}
+		} );
+
+		this.registerInlineElement( {
+			view: 'object',
+			model: 'htmlObject',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		} );
+
+		this.registerInlineElement( {
+			view: 'iframe',
+			model: 'htmlIframe',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		} );
+
+		this.registerInlineElement( {
+			view: 'input',
+			model: 'htmlInput',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		} );
+
+		this.registerInlineElement( {
+			view: 'button',
+			model: 'htmlButton',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		} );
+
+		this.registerInlineElement( {
+			view: 'textarea',
+			model: 'htmlTextarea',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		} );
+
+		this.registerInlineElement( {
+			view: 'select',
+			model: 'htmlSelect',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		} );
+
+		this.registerInlineElement( {
+			view: 'video',
+			model: 'htmlVideo',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		} );
+
+		this.registerInlineElement( {
+			view: 'audio',
+			model: 'htmlAudio',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		} );
 	}
 
 	/**
@@ -255,15 +310,6 @@ export default class DataSchema {
 		this._definitions.set( definition.model, { ...definition, isInline: true } );
 	}
 
-	/**
-	 * Add new data schema definition describing object element.
-	 *
-	 * @param {module:content-compatibility/dataschema~DataSchemaObjectElementDefinition} definition
-	 */
-	registerObjectElement( definition ) {
-		this._definitions.set( definition.model, { ...definition, isObject: true } );
-	}
-
 	/**
 	 * Returns all definitions matching the given view name.
 	 *
@@ -351,6 +397,8 @@ function testViewName( pattern, viewName ) {
  *
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
  * @property {String} model Name of the model.
+ * @property {Boolean} [isObject] Indicates that the definition describes object element.
+ * @property {module:engine/model/schema~SchemaItemDefinition} [modelSchema] The model schema item definition describing registered model.
  */
 
 /**
@@ -358,23 +406,11 @@ function testViewName( pattern, viewName ) {
  *
  * @typedef {Object} module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
  * @property {String} [view] Name of the view element.
- * @property {module:engine/model/schema~SchemaItemDefinition} [modelSchema] The model schema item definition describing registered model.
  * @property {Boolean} isBlock Indicates that the definition describes block element.
  * Set by {@link module:content-compatibility/dataschema~DataSchema#registerBlockElement} method.
  * @extends module:content-compatibility/dataschema~DataSchemaDefinition
  */
 
-/**
- * A definition of {@link module:content-compatibility/dataschema~DataSchema data schema} for object elements.
- *
- * @typedef {Object} module:content-compatibility/dataschema~DataSchemaObjectElementDefinition
- * @property {String} view Name of the view element.
- * @property {Boolean} isObject Indicates that the definition describes object element.
- * @property {Boolean} [isBlock] Indicates that the definition describes block element.
- * Set by {@link module:content-compatibility/dataschema~DataSchema#registerObjectElement} method.
- * @extends module:content-compatibility/dataschema~DataSchemaDefinition
- */
-
 /**
  * A definition of {@link module:content-compatibility/dataschema~DataSchema data schema} for inline elements.
  *
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 8d786f65867..766295c05e6 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -131,12 +131,7 @@ describe( 'DataFilter', () => {
 			editor.setData( '<p><input></p>' );
 
 			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
-				'<paragraph>' +
-				'<htmlObjectEmbedInline' +
-				' value=""' +
-				' view="input">' +
-				'</htmlObjectEmbedInline>' +
-				'</paragraph>'
+				'<paragraph><htmlInput value=""></htmlInput></paragraph>'
 			);
 
 			expect( editor.getData() ).to.equal( '<p><input></p>' );
@@ -152,10 +147,8 @@ describe( 'DataFilter', () => {
 
 			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
 				'<paragraph>' +
-				'<htmlObjectEmbedInline' +
-				' value="<source src="https://example.com/video.mp4" type="video/mp4"> Your browser does not support the video tag."' +
-				' view="video">' +
-				'</htmlObjectEmbedInline>' +
+				'<htmlVideo value="<source src="https://example.com/video.mp4" type="video/mp4">' +
+				' Your browser does not support the video tag."></htmlVideo>' +
 				'</paragraph>'
 			);
 
@@ -167,10 +160,13 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should recognize block elements', () => {
-			dataSchema.registerObjectElement( {
+			dataSchema.registerBlockElement( {
 				model: 'htmlXyz',
 				view: 'xyz',
-				isBlock: true
+				isObject: true,
+				modelSchema: {
+					inheritAllFrom: '$htmlObjectBlock'
+				}
 			} );
 
 			dataFilter.allowElement( { name: 'xyz' } );
@@ -178,10 +174,7 @@ describe( 'DataFilter', () => {
 			editor.setData( '<xyz>foobar</xyz>' );
 
 			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
-				'<htmlObjectEmbedBlock' +
-				' value="foobar"' +
-				' view="xyz">' +
-				'</htmlObjectEmbedBlock>'
+				'<htmlXyz value="foobar"></htmlXyz>'
 			);
 
 			expect( editor.getData() ).to.equal( '<xyz>foobar</xyz>' );
@@ -194,7 +187,7 @@ describe( 'DataFilter', () => {
 			editor.setData( '<p><input type="text"></p>' );
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph><htmlObjectEmbedInline htmlAttributes="(1)" value="" view="input"></htmlObjectEmbedInline></paragraph>',
+				data: '<paragraph><htmlInput htmlAttributes="(1)" value=""></htmlInput></paragraph>',
 				attributes: {
 					1: {
 						attributes: {
@@ -214,7 +207,7 @@ describe( 'DataFilter', () => {
 			editor.setData( '<p><input style="color:red;"></p>' );
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph><htmlObjectEmbedInline htmlAttributes="(1)" value="" view="input"></htmlObjectEmbedInline></paragraph>',
+				data: '<paragraph><htmlInput htmlAttributes="(1)" value=""></htmlInput></paragraph>',
 				attributes: {
 					1: {
 						styles: {
@@ -234,7 +227,7 @@ describe( 'DataFilter', () => {
 			editor.setData( '<p><input class="foobar"></p>' );
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph><htmlObjectEmbedInline htmlAttributes="(1)" value="" view="input"></htmlObjectEmbedInline></paragraph>',
+				data: '<paragraph><htmlInput htmlAttributes="(1)" value=""></htmlInput></paragraph>',
 				attributes: {
 					1: {
 						classes: [ 'foobar' ]
@@ -254,8 +247,8 @@ describe( 'DataFilter', () => {
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-				'<htmlObjectEmbedInline htmlAttributes="(1)" value="" view="input"></htmlObjectEmbedInline>' +
-				'<htmlObjectEmbedInline value="" view="input"></htmlObjectEmbedInline>' +
+				'<htmlInput htmlAttributes="(1)" value=""></htmlInput>' +
+				'<htmlInput value=""></htmlInput>' +
 				'</paragraph>',
 				attributes: {
 					1: {
@@ -278,8 +271,8 @@ describe( 'DataFilter', () => {
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-				'<htmlObjectEmbedInline htmlAttributes="(1)" value="" view="input"></htmlObjectEmbedInline>' +
-				'<htmlObjectEmbedInline value="" view="input"></htmlObjectEmbedInline>' +
+				'<htmlInput htmlAttributes="(1)" value=""></htmlInput>' +
+				'<htmlInput value=""></htmlInput>' +
 				'</paragraph>',
 				attributes: {
 					1: {
@@ -302,8 +295,8 @@ describe( 'DataFilter', () => {
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-				'<htmlObjectEmbedInline value="" view="input"></htmlObjectEmbedInline>' +
-				'<htmlObjectEmbedInline value="" view="input"></htmlObjectEmbedInline>' +
+				'<htmlInput value=""></htmlInput>' +
+				'<htmlInput value=""></htmlInput>' +
 				'</paragraph>',
 				attributes: {}
 			} );
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index a31c01b039d..49523214515 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -26,20 +26,6 @@ describe( 'DataSchema', () => {
 		return editor.destroy();
 	} );
 
-	describe( 'registerObjectElement()', () => {
-		it( 'should register proper definition', () => {
-			dataSchema.registerObjectElement( { model: 'htmlDef', view: 'def' } );
-
-			const result = dataSchema.getDefinitionsForView( 'def' );
-
-			expect( Array.from( result ) ).to.deep.equal( [ {
-				model: 'htmlDef',
-				view: 'def',
-				isObject: true
-			} ] );
-		} );
-	} );
-
 	describe( 'registerInlineElement()', () => {
 		it( 'should register proper definition', () => {
 			dataSchema.registerInlineElement( { model: 'htmlDef', view: 'def' } );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.js b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
index 8effa30f8b3..04766df7129 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/objects.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
@@ -35,7 +35,13 @@ class ExtendHTMLSupport extends Plugin {
 	init() {
 		const { dataFilter, dataSchema } = this.editor.plugins.get( GeneralHtmlSupport );
 
-		dataSchema.registerObjectElement( { model: 'htmlXyz', view: 'xyz', isBlock: true } );
+		dataSchema.registerBlockElement( { model: 'htmlXyz',
+			view: 'xyz',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectBlock'
+			}
+		} );
 
 		const definitions = [
 			{ name: 'object', attributes: [ 'classid', 'codebase' ] },
diff --git a/packages/ckeditor5-content-compatibility/theme/datafilter.css b/packages/ckeditor5-content-compatibility/theme/datafilter.css
index 5a2a0b913f8..647e4f7cccc 100644
--- a/packages/ckeditor5-content-compatibility/theme/datafilter.css
+++ b/packages/ckeditor5-content-compatibility/theme/datafilter.css
@@ -10,14 +10,6 @@
 	padding-top: calc(var(--ck-font-size-tiny) + var(--ck-spacing-large));
 	min-width: calc(76px + var(--ck-spacing-standard));
 
-	&.html-object-embed-block {
-		margin: 1em auto;
-	}
-
-	&.html-object-embed-inline {
-		display: inline-block;
-	}
-
 	&:not(.ck-widget_selected):not(:hover) {
 		outline: var(--ck-html-object-embed-unfocused-outline-width) dashed var(--ck-color-widget-blurred-border);
 	}
@@ -53,3 +45,12 @@
 		pointer-events: none;
 	}
 }
+
+div.ck-widget.html-object-embed {
+	margin: 1em auto;
+}
+
+span.ck-widget.html-object-embed {
+	display: inline-block;
+}
+

From fd1c79def2d0d55a0d748e40f52e3b019c4a5819 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 12 May 2021 11:12:45 +0200
Subject: [PATCH 131/217] Transformed data filter and data schema into plugins.

---
 .../src/datafilter.js                         | 34 +++++++++-----
 .../src/dataschema.js                         | 25 ++++++++++-
 .../src/generalhtmlsupport.js                 | 31 +++----------
 .../tests/datafilter.js                       | 45 ++++++++++---------
 .../tests/manual/objects.js                   |  3 +-
 5 files changed, 79 insertions(+), 59 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index e0319b05d93..e7c0b624fef 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -7,10 +7,12 @@
  * @module content-compatibility/datafilter
  */
 
+import { Plugin } from 'ckeditor5/src/core';
 import { Matcher } from 'ckeditor5/src/engine';
 import { priorities, CKEditorError } from 'ckeditor5/src/utils';
-import { toWidget } from 'ckeditor5/src/widget';
+import { toWidget, Widget } from 'ckeditor5/src/widget';
 import { cloneDeep } from 'lodash-es';
+import DataSchema from './dataschema';
 
 import '../theme/datafilter.css';
 
@@ -40,10 +42,12 @@ import '../theme/datafilter.css';
  *				color: /[\s\S]+/
  *			}
  *		} );
+ *
+ * @extends module:core/plugin~Plugin
  */
-export default class DataFilter {
-	constructor( editor, dataSchema ) {
-		this.editor = editor;
+export default class DataFilter extends Plugin {
+	constructor( editor ) {
+		super( editor );
 
 		/**
 		 * An instance of the {@link module:content-compatibility/dataschema~DataSchema}.
@@ -52,7 +56,7 @@ export default class DataFilter {
 		 * @private
 		 * @member {module:content-compatibility/dataschema~DataSchema} #_dataSchema
 		 */
-		this._dataSchema = dataSchema;
+		this._dataSchema = editor.plugins.get( 'DataSchema' );
 
 		/**
 		 * {@link module:engine/view/matcher~Matcher Matcher} instance describing rules upon which
@@ -94,6 +98,20 @@ export default class DataFilter {
 		this._registerElementsAfterInit();
 	}
 
+	/**
+	 * @inheritDoc
+	 */
+	static get pluginName() {
+		return 'DataFilter';
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	static get requires() {
+		return [ DataSchema, Widget ];
+	}
+
 	/**
 	 * Allow the given element in the editor context.
 	 *
@@ -195,11 +213,7 @@ export default class DataFilter {
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
 	_registerObjectElement( definition ) {
-		const schema = this.editor.model.schema;
-
-		if ( !schema.isRegistered( definition.model ) ) {
-			schema.register( definition.model, definition.modelSchema );
-		}
+		this.editor.model.schema.register( definition.model, definition.modelSchema );
 
 		this._addObjectElementConversion( definition );
 		this._addDisallowedAttributeConversion( definition );
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index eb179b35b4f..f1757deb0fe 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -7,6 +7,7 @@
  * @module content-compatibility/dataschema
  */
 
+import { Plugin } from 'ckeditor5/src/core';
 import { toArray } from 'ckeditor5/src/utils';
 
 /**
@@ -36,9 +37,13 @@ import { toArray } from 'ckeditor5/src/utils';
  *				copyOnEnter: true
  *			}
  *		} );
+ *
+ * @extends module:core/plugin~Plugin
  */
-export default class DataSchema {
-	constructor() {
+export default class DataSchema extends Plugin {
+	constructor( editor ) {
+		super( editor );
+
 		/**
 		 * A map of registered data schema definitions via {@link #register} method.
 		 *
@@ -48,6 +53,22 @@ export default class DataSchema {
 		 */
 		this._definitions = new Map();
 
+		this._registerDefaultDefinitions();
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	static get pluginName() {
+		return 'DataSchema';
+	}
+
+	/**
+	 * Registers default data schema definitions.
+	 *
+	 * @private
+	*/
+	_registerDefaultDefinitions() {
 		// Block elements.
 		this.registerBlockElement( {
 			model: '$htmlBlock',
diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
index 0954f2789aa..ce614f769e0 100644
--- a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
@@ -8,9 +8,8 @@
  */
 
 import { Plugin } from 'ckeditor5/src/core';
-
-import DataSchema from './dataschema';
 import DataFilter from './datafilter';
+import DataSchema from './dataschema';
 
 /**
  * The General HTML Support feature.
@@ -22,32 +21,16 @@ import DataFilter from './datafilter';
  */
 export default class GeneralHtmlSupport extends Plugin {
 	/**
-	 * @param {module:core/editor/editor~Editor} editor
-	*/
-	constructor( editor ) {
-		super( editor );
-
-		/**
-		 * An instance of the {@link module:content-compatibility/dataschema~DataSchema}.
-		 *
-		 * @readonly
-		 * @member {module:content-compatibility/dataschema~DataSchema} #dataSchema
-		 */
-		this.dataSchema = new DataSchema();
-
-		/**
-		 * An instance of the {@link module:content-compatibility/datafilter~DataFilter}.
-		 *
-		 * @readonly
-		 * @member {module:content-compatibility/datafilter~DataFilter} #dataFilter
-		 */
-		this.dataFilter = new DataFilter( editor, this.dataSchema );
+	 * @inheritDoc
+	 */
+	static get pluginName() {
+		return 'GeneralHtmlSupport';
 	}
 
 	/**
 	 * @inheritDoc
 	 */
-	static get pluginName() {
-		return 'GeneralHtmlSupport';
+	static get requires() {
+		return [ DataFilter, DataSchema ];
 	}
 }
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 766295c05e6..0564ae815a3 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -3,11 +3,12 @@
  * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
  */
 
-import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
+import ClassicTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/classictesteditor';
 import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
 import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
 import LinkEditing from '@ckeditor/ckeditor5-link/src/linkediting';
 import FontColorEditing from '@ckeditor/ckeditor5-font/src/fontcolor/fontcolorediting';
+import DataFilter from '../src/datafilter';
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import { expectToThrowCKEditorError } from '@ckeditor/ckeditor5-utils/tests/_utils/utils';
 import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
@@ -15,36 +16,42 @@ import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-util
 import GeneralHtmlSupport from '../src/generalhtmlsupport';
 
 describe( 'DataFilter', () => {
-	let editor, model, dataFilter, dataSchema;
+	let editor, model, editorElement, dataFilter, dataSchema;
 
 	testUtils.createSinonSandbox();
 
 	beforeEach( () => {
-		return VirtualTestEditor
-			.create( {
+		editorElement = document.createElement( 'div' );
+		document.body.appendChild( editorElement );
+
+		return ClassicTestEditor
+			.create( editorElement, {
 				plugins: [ Paragraph, FontColorEditing, LinkEditing, GeneralHtmlSupport ]
 			} )
 			.then( newEditor => {
 				editor = newEditor;
 				model = editor.model;
 
-				const plugin = editor.plugins.get( GeneralHtmlSupport );
-
-				dataFilter = plugin.dataFilter;
-				dataSchema = plugin.dataSchema;
+				dataFilter = editor.plugins.get( 'DataFilter' );
+				dataSchema = editor.plugins.get( 'DataSchema' );
 			} );
 	} );
 
 	afterEach( () => {
+		editorElement.remove();
+
 		return editor.destroy();
 	} );
 
 	describe( 'initialization', () => {
-		let initEditor, initModel;
+		let initEditor, initEditorElement, initModel;
 
 		beforeEach( () => {
-			return VirtualTestEditor
-				.create( {
+			initEditorElement = document.createElement( 'div' );
+			document.body.appendChild( initEditorElement );
+
+			return ClassicTestEditor
+				.create( initEditorElement, {
 					// Keep FakeRTCPlugin before FakeExtentedHtmlPlugin, so it's registered first.
 					plugins: [ Paragraph, FakeRTCPlugin, FakeExtentedHtmlPlugin ]
 				} )
@@ -55,6 +62,8 @@ describe( 'DataFilter', () => {
 		} );
 
 		afterEach( () => {
+			initEditorElement.remove();
+
 			return initEditor.destroy();
 		} );
 
@@ -79,7 +88,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow element registered after editor initialization', () => {
-			const { dataFilter } = initEditor.plugins.get( GeneralHtmlSupport );
+			const dataFilter = initEditor.plugins.get( DataFilter );
 
 			dataFilter.allowElement( { name: 'span' } );
 
@@ -113,12 +122,12 @@ describe( 'DataFilter', () => {
 			}
 
 			init() {
-				const { dataFilter } = this.editor.plugins.get( GeneralHtmlSupport );
+				const dataFilter = this.editor.plugins.get( DataFilter );
 				dataFilter.allowElement( { name: 'article' } );
 			}
 
 			afterInit() {
-				const { dataFilter } = this.editor.plugins.get( GeneralHtmlSupport );
+				const dataFilter = this.editor.plugins.get( DataFilter );
 				dataFilter.allowElement( { name: 'section' } );
 			}
 		}
@@ -303,14 +312,6 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal( '<p><input><input></p>' );
 		} );
-
-		it( 'should register embed widget only once', () => {
-			dataFilter.allowElement( { name: 'video' } );
-
-			expect( () => {
-				dataFilter.allowElement( { name: 'audio' } );
-			} ).to.not.throw();
-		} );
 	} );
 
 	describe( 'block', () => {
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.js b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
index 04766df7129..cdabcd5531d 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/objects.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
@@ -33,7 +33,8 @@ class ExtendHTMLSupport extends Plugin {
 	}
 
 	init() {
-		const { dataFilter, dataSchema } = this.editor.plugins.get( GeneralHtmlSupport );
+		const dataFilter = this.editor.plugins.get( 'DataFilter' );
+		const dataSchema = this.editor.plugins.get( 'DataSchema' );
 
 		dataSchema.registerBlockElement( { model: 'htmlXyz',
 			view: 'xyz',

From c60409dd5ef9cc39b8fa38fe13e660fb924c0668 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 12 May 2021 11:18:08 +0200
Subject: [PATCH 132/217] Docs.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js   | 5 +++--
 packages/ckeditor5-content-compatibility/tests/datafilter.js | 2 ++
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index e7c0b624fef..af230b58b90 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -557,9 +557,10 @@ function setViewElementAttributes( writer, viewAttributes, viewElement ) {
 // Creates object view element from the given model element.
 //
 // @private
+// @param {String} viewName
 // @param {module:engine/model/element~Element} modelElement
-// @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
-// @returns {module:engine/view/element~Element} viewElement
+// @param {module:engine/view/downcastwriter~DowncastWriter} writer
+// @returns {module:engine/view/element~Element}
 function createObjectViewElement( viewName, modelElement, writer ) {
 	const viewAttributes = modelElement.getAttribute( 'htmlAttributes' );
 	const viewContent = modelElement.getAttribute( 'value' );
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 0564ae815a3..428810ea290 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -15,6 +15,8 @@ import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-util
 
 import GeneralHtmlSupport from '../src/generalhtmlsupport';
 
+/* global document */
+
 describe( 'DataFilter', () => {
 	let editor, model, editorElement, dataFilter, dataSchema;
 

From 78af6e86b680e9dc4a457c6cae1ac7fbd138a2d1 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 12 May 2021 11:44:02 +0200
Subject: [PATCH 133/217] Fixed manual test.

---
 .../tests/manual/generalhtmlsupport.js                         | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 7603b63a6a8..ed4ffec1934 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -27,7 +27,8 @@ class ExtendHTMLSupport extends Plugin {
 	}
 
 	init() {
-		const { dataSchema, dataFilter } = this.editor.plugins.get( GeneralHtmlSupport );
+		const dataFilter = this.editor.plugins.get( 'DataFilter' );
+		const dataSchema = this.editor.plugins.get( 'DataSchema' );
 
 		// Extend schema with custom `xyz` element.
 		dataSchema.registerBlockElement( {

From f2e23caba77daf0adf4e6bd18ca94f42b6570264 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 14 May 2021 10:33:34 +0200
Subject: [PATCH 134/217] Codeblock support, huge refactoring.

---
 .../package.json                              |   1 +
 .../src/conversionutils.js                    | 158 ++++++
 .../src/converters.js                         | 274 ++++++++++
 .../src/datafilter.js                         | 516 +++++-------------
 .../src/dataschema.js                         |  10 +
 .../tests/manual/codeblock.html               |  11 +
 .../tests/manual/codeblock.js                 |  59 ++
 .../tests/manual/codeblock.md                 |   0
 8 files changed, 649 insertions(+), 380 deletions(-)
 create mode 100644 packages/ckeditor5-content-compatibility/src/conversionutils.js
 create mode 100644 packages/ckeditor5-content-compatibility/src/converters.js
 create mode 100644 packages/ckeditor5-content-compatibility/tests/manual/codeblock.html
 create mode 100644 packages/ckeditor5-content-compatibility/tests/manual/codeblock.js
 create mode 100644 packages/ckeditor5-content-compatibility/tests/manual/codeblock.md

diff --git a/packages/ckeditor5-content-compatibility/package.json b/packages/ckeditor5-content-compatibility/package.json
index 396610351f9..a349d9eee8d 100644
--- a/packages/ckeditor5-content-compatibility/package.json
+++ b/packages/ckeditor5-content-compatibility/package.json
@@ -21,6 +21,7 @@
   "devDependencies": {
     "@ckeditor/ckeditor5-basic-styles": "^27.1.0",
     "@ckeditor/ckeditor5-block-quote": "^27.1.0",
+    "@ckeditor/ckeditor5-code-block": "^27.1.0",
     "@ckeditor/ckeditor5-core": "^27.1.0",
     "@ckeditor/ckeditor5-editor-classic": "^27.1.0",
     "@ckeditor/ckeditor5-engine": "^27.1.0",
diff --git a/packages/ckeditor5-content-compatibility/src/conversionutils.js b/packages/ckeditor5-content-compatibility/src/conversionutils.js
new file mode 100644
index 00000000000..a55dd09b745
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/src/conversionutils.js
@@ -0,0 +1,158 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module content-compatibility/conversionutils
+ */
+
+import { cloneDeep } from 'lodash-es';
+
+/**
+ * Matches and consumes the given view attributes.
+ *
+ * @param {module:engine/view/element~Element} viewElement
+ * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
+ * @param {module:engine/view/matcher~Matcher Matcher} matcher
+ * @returns {Object} [result]
+ * @returns {Object} result.attributes Set with matched attribute names.
+ * @returns {Object} result.styles Set with matched style names.
+ * @returns {Array.<String>} result.classes Set with matched class names.
+ */
+export function consumeViewAttributes( viewElement, conversionApi, matcher ) {
+	const matches = consumeAttributeMatches( viewElement, conversionApi, matcher );
+	const { attributes, styles, classes } = mergeMatchResults( matches );
+	const viewAttributes = {};
+
+	if ( attributes.size ) {
+		viewAttributes.attributes = iterableToObject( attributes, key => viewElement.getAttribute( key ) );
+	}
+
+	if ( styles.size ) {
+		viewAttributes.styles = iterableToObject( styles, key => viewElement.getStyle( key ) );
+	}
+
+	if ( classes.size ) {
+		viewAttributes.classes = Array.from( classes );
+	}
+
+	if ( !Object.keys( viewAttributes ).length ) {
+		return null;
+	}
+
+	return viewAttributes;
+}
+
+/**
+* Helper function for downcast converter. Sets attributes on the given view element.
+*
+* @param {module:engine/view/downcastwriter~DowncastWriter} writer
+* @param {Object} viewAttributes
+* @param {module:engine/view/element~Element} viewElement
+*/
+export function setViewAttributes( writer, viewAttributes, viewElement ) {
+	if ( viewAttributes.attributes ) {
+		for ( const [ key, value ] of Object.entries( viewAttributes.attributes ) ) {
+			writer.setAttribute( key, value, viewElement );
+		}
+	}
+
+	if ( viewAttributes.styles ) {
+		writer.setStyle( viewAttributes.styles, viewElement );
+	}
+
+	if ( viewAttributes.classes ) {
+		writer.addClass( viewAttributes.classes, viewElement );
+	}
+}
+
+/**
+* Merges view element attribute objects.
+*
+* @param {Object} oldValue
+* @param {Object} newValue
+* @returns {Object}
+*/
+export function mergeViewElementAttributes( oldValue, newValue ) {
+	const result = cloneDeep( oldValue );
+
+	for ( const key in newValue ) {
+		// Merge classes.
+		if ( Array.isArray( newValue[ key ] ) ) {
+			result[ key ] = Array.from( new Set( [ ...oldValue[ key ], ...newValue[ key ] ] ) );
+		}
+
+		// Merge attributes or styles.
+		else {
+			result[ key ] = { ...oldValue[ key ], ...newValue[ key ] };
+		}
+	}
+
+	return result;
+}
+
+// Consumes matched attributes.
+//
+// @private
+// @param {module:engine/view/element~Element} viewElement
+// @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
+// @param {module:engine/view/matcher~Matcher Matcher} matcher
+// @returns {Array.<Object>} Array with match information about found attributes.
+function consumeAttributeMatches( viewElement, { consumable }, matcher ) {
+	const matches = matcher.matchAll( viewElement ) || [];
+	const consumedMatches = [];
+
+	for ( const match of matches ) {
+		// We only want to consume attributes, so element can be still processed by other converters.
+		delete match.match.name;
+
+		if ( consumable.consume( viewElement, match.match ) ) {
+			consumedMatches.push( match );
+		}
+	}
+
+	return consumedMatches;
+}
+
+// Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
+//
+// @private
+// @param {Array.<Object>} matches
+// @returns {Object} result
+// @returns {Set.<Object>} result.attributes Set with matched attribute names.
+// @returns {Set.<Object>} result.styles Set with matched style names.
+// @returns {Set.<String>} result.classes Set with matched class names.
+function mergeMatchResults( matches ) {
+	const matchResult = {
+		attributes: new Set(),
+		classes: new Set(),
+		styles: new Set()
+	};
+
+	for ( const match of matches ) {
+		for ( const key in matchResult ) {
+			const values = match.match[ key ] || [];
+
+			values.forEach( value => matchResult[ key ].add( value ) );
+		}
+	}
+
+	return matchResult;
+}
+
+// Converts the given iterable object into an object.
+//
+// @private
+// @param {Iterable.<String>} iterable
+// @param {Function} getValue Should result with value for the given object key.
+// @returns {Object}
+function iterableToObject( iterable, getValue ) {
+	const attributesObject = {};
+
+	for ( const prop of iterable ) {
+		attributesObject[ prop ] = getValue( prop );
+	}
+
+	return attributesObject;
+}
diff --git a/packages/ckeditor5-content-compatibility/src/converters.js b/packages/ckeditor5-content-compatibility/src/converters.js
new file mode 100644
index 00000000000..5ac4d2888cd
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/src/converters.js
@@ -0,0 +1,274 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module content-compatibility/converters
+ */
+
+import { toWidget } from 'ckeditor5/src/widget';
+import { consumeViewAttributes, setViewAttributes, mergeViewElementAttributes } from './conversionutils';
+
+/**
+ * Conversion helper consuming all attributes from the definition view element
+ * matched by the given matcher.
+ *
+ * This converter listenes on `high` priority to ensure that all attributes are consumed
+ * before standard priority converters.
+ *
+ * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+ * @param {module:engine/view/matcher~Matcher} matcher
+ * @returns {Function} Returns a conversion callback.
+*/
+export function consumeViewAttributesConverter( { view: viewName }, matcher ) {
+	return dispatcher => {
+		dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
+			consumeViewAttributes( data.viewItem, conversionApi, matcher );
+		}, { priority: 'high' } );
+	};
+}
+
+/**
+ * View-to-model conversion helper preserving attributes on {@link module:code-block/codeblock~CodeBlock Code Block}
+ * feature model element matched by the given matcher.
+ *
+ * Attributes are preserved as a value of `htmlAttributes` model attribute.
+ *
+ * @param {module:engine/view/matcher~Matcher} matcher
+ * @returns {Function} Returns a conversion callback.
+*/
+export function viewToModelCodeBlockAttributeConverter( matcher ) {
+	return dispatcher => {
+		dispatcher.on( 'element:code', ( evt, data, conversionApi ) => {
+			if ( !data.modelRange ) {
+				return;
+			}
+
+			const viewPreElement = data.viewItem.parent;
+			if ( !isPreElement( viewPreElement ) ) {
+				return;
+			}
+
+			const viewAttributes = consumeViewAttributes( viewPreElement, conversionApi, matcher );
+
+			if ( viewAttributes ) {
+				conversionApi.writer.setAttribute( 'htmlAttributes', viewAttributes, data.modelRange );
+			}
+		}, { conversionPriority: 'low' } );
+	};
+}
+
+/**
+ * Model-to-view conversion helper applying attributes from {@link module:code-block/codeblock~CodeBlock Code Block}
+ * feature model element.
+ *
+ * @returns {Function} Returns a conversion callback.
+*/
+export function modelToViewCodeBlockAttributeConverter() {
+	return dispatcher => {
+		dispatcher.on( 'attribute:htmlAttributes:codeBlock', ( evt, data, conversionApi ) => {
+			if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
+				return;
+			}
+
+			const viewPreElement = conversionApi.mapper.toViewElement( data.item ).parent;
+
+			if ( isPreElement( viewPreElement ) ) {
+				setViewAttributes( conversionApi.writer, data.attributeNewValue, viewPreElement );
+			}
+		} );
+	};
+}
+
+/**
+ * View-to-model conversion helper for object elements.
+ *
+ * Preserves object element content in `value` attribute. Also, all matching attributes
+ * by the given matcher will be preserved on `htmlAttributes` attribute.
+ *
+ * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+ * @param {module:engine/view/matcher~Matcher} matcher
+ * @returns {Function} Returns a conversion callback.
+*/
+export function viewToModelObjectConverter( { model: modelName }, matcher ) {
+	return ( viewElement, conversionApi ) => {
+		const htmlAttributes = consumeViewAttributes( viewElement, conversionApi, matcher );
+
+		// Let's keep element HTML and its attributes, so we can rebuild element in downcast conversions.
+		return conversionApi.writer.createElement( modelName, {
+			value: viewElement.getCustomProperty( '$rawContent' ),
+			...( htmlAttributes && { htmlAttributes } )
+		} );
+	};
+}
+
+/**
+ * Conversion helper converting object element to HTML object widget.
+ *
+ * @param {module:core/editor/editor~Editor} editor
+ * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+ * @returns {Function} Returns a conversion callback.
+*/
+export function toObjectWidgetConverter( editor, { view: viewName, isInline } ) {
+	return ( modelElement, { writer } ) => {
+		const widgetLabel = editor.t( 'HTML object' );
+
+		// Widget cannot be a raw element because the widget system would not be able
+		// to add its UI to it. Thus, we need separate view container.
+		const viewContainer = writer.createContainerElement( isInline ? 'span' : 'div', {
+			class: 'html-object-embed',
+			'data-html-object-embed-label': widgetLabel,
+			dir: editor.locale.uiLanguageDirection
+		}, {
+			isAllowedInsideAttributeElement: isInline
+		} );
+
+		const viewElement = createObjectView( viewName, modelElement, writer );
+		writer.addClass( 'html-object-embed__content', viewElement );
+
+		writer.insert( writer.createPositionAt( viewContainer, 0 ), viewElement );
+
+		return toWidget( viewContainer, writer, { widgetLabel } );
+	};
+}
+
+/**
+* Creates object view element from the given model element.
+*
+* Applies attributes preserved in `htmlAttributes` model attribute.
+*
+* @param {String} viewName
+* @param {module:engine/model/element~Element} modelElement
+* @param {module:engine/view/downcastwriter~DowncastWriter} writer
+* @returns {module:engine/view/element~Element}
+*/
+export function createObjectView( viewName, modelElement, writer ) {
+	const viewAttributes = modelElement.getAttribute( 'htmlAttributes' );
+	const viewContent = modelElement.getAttribute( 'value' );
+
+	const viewElement = writer.createRawElement( viewName, null, function( domElement ) {
+		domElement.innerHTML = viewContent;
+	} );
+
+	if ( viewAttributes ) {
+		setViewAttributes( writer, viewAttributes, viewElement );
+	}
+
+	return viewElement;
+}
+
+/**
+ * View-to-attribute conversion helper preserving inline element attributes on `$text`.
+ *
+ * All element attributes matched by the given matcher will be preserved as a value of
+ * {@link module:content-compatibility/dataschema~DataSchemaInlineElementDefinition~model definition model}
+ * attribute.
+ *
+ * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+ * @param {module:engine/view/matcher~Matcher} matcher
+ * @returns {Function} Returns a conversion callback.
+*/
+export function viewToAttributeInlineConverter( { view: viewName, model: attributeKey }, matcher ) {
+	return dispatcher => {
+		dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
+			const viewAttributes = consumeViewAttributes( data.viewItem, conversionApi, matcher );
+
+			// Since we are converting to attribute we need a range on which we will set the attribute.
+			// If the range is not created yet, we will create it.
+			if ( !data.modelRange ) {
+				data = Object.assign( data, conversionApi.convertChildren( data.viewItem, data.modelCursor ) );
+			}
+
+			// Set attribute on each item in range according to the schema.
+			for ( const node of data.modelRange.getItems() ) {
+				if ( conversionApi.schema.checkAttribute( node, attributeKey ) ) {
+					// Node's children are converted recursively, so node can already include model attribute.
+					// We want to extend it, not replace.
+					const nodeAttributes = node.getAttribute( attributeKey );
+					const attributesToAdd = mergeViewElementAttributes( viewAttributes || {}, nodeAttributes || {} );
+
+					conversionApi.writer.setAttribute( attributeKey, attributesToAdd, node );
+				}
+			}
+		}, { priority: 'low' } );
+	};
+}
+
+/**
+ * Attribute-to-view conversion helper applying attributes to view element preserved on `$text`.
+ *
+ * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+ * @returns {Function} Returns a conversion callback.
+*/
+export function attributeToViewInlineConverter( { priority, view: viewName } ) {
+	return ( attributeValue, conversionApi ) => {
+		if ( !attributeValue ) {
+			return;
+		}
+
+		const { writer } = conversionApi;
+		const viewElement = writer.createAttributeElement( viewName, null, { priority } );
+
+		setViewAttributes( writer, attributeValue, viewElement );
+
+		return viewElement;
+	};
+}
+
+/**
+ * View-to-model conversion helper preserving attributes on block element matched by the given matcher.
+ *
+ * All matched attributes will be preserved on `htmlAttributes` attribute.
+ *
+ * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+ * @param {module:engine/view/matcher~Matcher} matcher
+ * @returns {Function} Returns a conversion callback.
+*/
+export function viewToModelBlockAttributeConverter( { view: viewName }, matcher ) {
+	return dispatcher => {
+		dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
+			if ( !data.modelRange ) {
+				return;
+			}
+
+			const viewAttributes = consumeViewAttributes( data.viewItem, conversionApi, matcher );
+
+			if ( viewAttributes ) {
+				conversionApi.writer.setAttribute( 'htmlAttributes', viewAttributes, data.modelRange );
+			}
+		}, { priority: 'low' } );
+	};
+}
+
+/**
+ * Model-to-view conversion helper applying attributes preserved in `htmlAttributes` attribute
+ * for block elements.
+ *
+ * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+ * @returns {Function} Returns a conversion callback.
+*/
+export function modelToViewBlockAttributeConverter( { model: modelName } ) {
+	return dispatcher => {
+		dispatcher.on( `attribute:htmlAttributes:${ modelName }`, ( evt, data, conversionApi ) => {
+			const viewAttributes = data.attributeNewValue;
+
+			if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
+				return;
+			}
+
+			const viewWriter = conversionApi.writer;
+			const viewElement = conversionApi.mapper.toViewElement( data.item );
+
+			setViewAttributes( viewWriter, viewAttributes, viewElement );
+		} );
+	};
+}
+
+// Checks if the given view element is `pre`.
+//
+// @param {module:engine/view/element~Element} [element]
+// @returns {Boolean}
+function isPreElement( element ) {
+	return element && element.is( 'element', 'pre' );
+}
diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index af230b58b90..faf88bbf87b 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -7,12 +7,28 @@
  * @module content-compatibility/datafilter
  */
 
+import DataSchema from './dataschema';
+
 import { Plugin } from 'ckeditor5/src/core';
 import { Matcher } from 'ckeditor5/src/engine';
 import { priorities, CKEditorError } from 'ckeditor5/src/utils';
-import { toWidget, Widget } from 'ckeditor5/src/widget';
-import { cloneDeep } from 'lodash-es';
-import DataSchema from './dataschema';
+import { Widget } from 'ckeditor5/src/widget';
+import {
+	consumeViewAttributesConverter,
+
+	viewToModelCodeBlockAttributeConverter,
+	modelToViewCodeBlockAttributeConverter,
+
+	viewToModelObjectConverter,
+	toObjectWidgetConverter,
+	createObjectView,
+
+	viewToAttributeInlineConverter,
+	attributeToViewInlineConverter,
+
+	viewToModelBlockAttributeConverter,
+	modelToViewBlockAttributeConverter
+} from './converters';
 
 import '../theme/datafilter.css';
 
@@ -186,92 +202,87 @@ export default class DataFilter extends Plugin {
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
 	_registerElement( definition ) {
-		if ( definition.isObject ) {
-			this._registerObjectElement( definition );
-		} else if ( definition.isInline ) {
-			this._registerInlineElement( definition );
-		} else if ( definition.isBlock ) {
-			this._registerBlockElement( definition );
-		} else {
-			/**
-			 * Only a definition marked as inline, block or object can be allowed.
-			 *
-			 * @error data-filter-invalid-definition-type
-			 */
-			throw new CKEditorError(
-				'data-filter-invalid-definition-type',
-				null,
-				definition
-			);
+		// Note that the order of element handlers is important,
+		// as the handler may interrupt handlers execution in case of returning
+		// anything else than `false` value.
+		const elementHandlers = [
+			this._handleCodeBlockElement,
+			this._handleObjectElement,
+			this._handleInlineElement,
+			this._handleBlockElement
+		];
+
+		for ( const elementHandler of elementHandlers ) {
+			if ( elementHandler.call( this, definition ) !== false ) {
+				return;
+			}
 		}
-	}
-
-	/**
-	 * Registers object element and attribute converters for the given data schema definition.
-	 *
-	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
-	 */
-	_registerObjectElement( definition ) {
-		this.editor.model.schema.register( definition.model, definition.modelSchema );
 
-		this._addObjectElementConversion( definition );
-		this._addDisallowedAttributeConversion( definition );
+		/**
+		 * The definition cannot be handled by the data filter.
+		 *
+		 * Make sure that the registered definition is correct.
+		 *
+		 * @error data-filter-invalid-definition
+		 */
+		throw new CKEditorError(
+			'data-filter-invalid-definition',
+			null,
+			definition
+		);
 	}
 
 	/**
-	 * Registers block element and attribute converters for the given data schema definition.
-	 *
-	 * If the element model schema is already registered, this method will do nothing.
+	 * Registers attribute converters for {@link module:code-block/codeblock~CodeBlock Code Block} feature.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 * @returns {Boolean}
 	 */
-	_registerBlockElement( definition ) {
-		const schema = this.editor.model.schema;
+	_handleCodeBlockElement( definition ) {
+		const editor = this.editor;
 
-		if ( !schema.isRegistered( definition.model ) ) {
-			this.editor.model.schema.register( definition.model, definition.modelSchema );
-			this._addBlockElementToElementConversion( definition );
+		// We should only handle codeBlock model if CodeBlock plugin is available.
+		// Otherwise, let #_handleBlockElement() do the job.
+		if ( !editor.plugins.has( 'CodeBlock' ) || definition.model !== 'codeBlock' ) {
+			return false;
 		}
 
-		this._addDisallowedAttributeConversion( definition );
-		this._addBlockElementAttributeConversion( definition );
-	}
-
-	/**
-	 * Registers inline element and attribute converters for the given data schema definition.
-	 *
-	 * Extends `$text` model schema to allow the given definition model attribute and its properties.
-	 *
-	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
-	 */
-	_registerInlineElement( definition ) {
-		const schema = this.editor.model.schema;
-
-		schema.extend( '$text', {
-			allowAttributes: definition.model
-		} );
+		const schema = editor.model.schema;
+		const conversion = editor.conversion;
 
-		if ( definition.attributeProperties ) {
-			schema.setAttributeProperties( definition.model, definition.attributeProperties );
-		}
+		// CodeBlock plugin is filtering out all attributes on `code` element. Let's add
+		// exception for `htmlCode` required for data filtration mechanism.
+		schema.on( 'checkAttribute', ( evt, [ context, attributeName ] ) => {
+			if ( attributeName === 'htmlCode' && context.endsWith( 'codeBlock $text' ) ) {
+				evt.return = true;
+				evt.stop();
+			}
+		}, { priority: priorities.get( 'high' ) + 1 } );
 
-		this._addDisallowedAttributeConversion( definition );
-		this._addInlineElementConversion( definition );
+		conversion.for( 'upcast' ).add( consumeViewAttributesConverter( definition, this._disallowedAttributes ) );
+		conversion.for( 'upcast' ).add( viewToModelCodeBlockAttributeConverter( this._allowedAttributes ) );
+		conversion.for( 'downcast' ).add( modelToViewCodeBlockAttributeConverter() );
 	}
 
 	/**
-	 * Adds converters for the given data schema definition marked as
-	 * {@link module:content-compatibility/dataschema~DataSchemaDefinition#isObject isObject}.
+	 * Registers object element and attribute converters for the given data schema definition.
 	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 * @returns {Boolean}
 	 */
-	_addObjectElementConversion( definition ) {
+	_handleObjectElement( definition ) {
+		if ( !definition.isObject ) {
+			return false;
+		}
+
+		const editor = this.editor;
+		const schema = editor.model.schema;
+		const conversion = editor.conversion;
 		const { view: viewName, model: modelName } = definition;
-		const conversion = this.editor.conversion;
+
+		schema.register( definition.model, definition.modelSchema );
 
 		if ( !viewName ) {
 			return;
@@ -279,365 +290,110 @@ export default class DataFilter extends Plugin {
 
 		// Store element content in special `$rawContent` custom property to
 		// avoid editor's data filtering mechanism.
-		this.editor.data.registerRawContentMatcher( {
+		editor.data.registerRawContentMatcher( {
 			name: viewName
 		} );
 
+		conversion.for( 'upcast' ).add( consumeViewAttributesConverter( definition, this._disallowedAttributes ) );
 		conversion.for( 'upcast' ).elementToElement( {
 			view: viewName,
-			model: ( viewElement, conversionApi ) => {
-				const htmlAttributes = this._matchAndConsumeAllowedAttributes( viewElement, conversionApi );
-
-				// Let's keep element HTML and its attributes, so we can rebuild element in downcast conversions.
-				return conversionApi.writer.createElement( modelName, {
-					value: viewElement.getCustomProperty( '$rawContent' ),
-					...( htmlAttributes && { htmlAttributes } )
-				} );
-			}
+			model: viewToModelObjectConverter( definition, this._allowedAttributes )
 		} );
 
 		conversion.for( 'dataDowncast' ).elementToElement( {
 			model: modelName,
 			view: ( modelElement, { writer } ) => {
-				return createObjectViewElement( viewName, modelElement, writer );
+				return createObjectView( viewName, modelElement, writer );
 			}
 		} );
-
 		conversion.for( 'editingDowncast' ).elementToElement( {
 			model: modelName,
-			view: ( modelElement, { writer } ) => {
-				const widgetLabel = this.editor.t( 'HTML object' );
-
-				// Widget cannot be a raw element because the widget system would not be able
-				// to add its UI to it. Thus, we need separate view container.
-				const viewContainer = writer.createContainerElement( definition.isInline ? 'span' : 'div', {
-					class: 'html-object-embed',
-					'data-html-object-embed-label': widgetLabel,
-					dir: this.editor.locale.uiLanguageDirection
-				}, {
-					isAllowedInsideAttributeElement: definition.isInline
-				} );
-
-				const viewElement = createObjectViewElement( viewName, modelElement, writer );
-				writer.addClass( 'html-object-embed__content', viewElement );
-
-				writer.insert( writer.createPositionAt( viewContainer, 0 ), viewElement );
-
-				return toWidget( viewContainer, writer, { widgetLabel } );
-			}
+			view: toObjectWidgetConverter( editor, definition )
 		} );
 	}
 
 	/**
-	 * Adds element to element converters for the given block element definition.
+	 * Registers block element and attribute converters for the given data schema definition.
 	 *
-	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
-	 */
-	_addBlockElementToElementConversion( { model: modelName, view: viewName } ) {
-		const conversion = this.editor.conversion;
-
-		if ( !viewName ) {
-			return;
-		}
-
-		conversion.for( 'upcast' ).elementToElement( {
-			model: modelName,
-			view: viewName,
-			// With a `low` priority, `paragraph` plugin auto-paragraphing mechanism is executed. Make sure
-			// this listener is called before it. If not, some elements will be transformed into a paragraph.
-			converterPriority: priorities.get( 'low' ) + 1
-		} );
-
-		conversion.for( 'downcast' ).elementToElement( {
-			model: modelName,
-			view: viewName
-		} );
-	}
-
-	/**
-	 * Adds attribute converters for the given block element definition.
+	 * If the element model schema is already registered, this method will do nothing.
 	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+	 * @returns {Boolean}
 	 */
-	_addBlockElementAttributeConversion( { model: modelName, view: viewName } ) {
-		const conversion = this.editor.conversion;
-
-		if ( !viewName ) {
-			return;
+	_handleBlockElement( definition ) {
+		if ( !definition.isBlock ) {
+			return false;
 		}
 
-		conversion.for( 'upcast' ).add( dispatcher => {
-			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
-				if ( !data.modelRange ) {
-					return;
-				}
-
-				const viewAttributes = this._matchAndConsumeAllowedAttributes( data.viewItem, conversionApi );
-
-				if ( viewAttributes ) {
-					conversionApi.writer.setAttribute( 'htmlAttributes', viewAttributes, data.modelRange );
-				}
-			}, { priority: 'low' } );
-		} );
-
-		conversion.for( 'downcast' ).add( dispatcher => {
-			dispatcher.on( `attribute:htmlAttributes:${ modelName }`, ( evt, data, conversionApi ) => {
-				const viewAttributes = data.attributeNewValue;
+		const editor = this.editor;
+		const schema = editor.model.schema;
+		const conversion = editor.conversion;
+		const { view: viewName, model: modelName } = definition;
 
-				if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
-					return;
-				}
+		if ( !schema.isRegistered( definition.model ) ) {
+			schema.register( definition.model, definition.modelSchema );
 
-				const viewWriter = conversionApi.writer;
-				const viewElement = conversionApi.mapper.toViewElement( data.item );
+			if ( !viewName ) {
+				return;
+			}
 
-				setViewElementAttributes( viewWriter, viewAttributes, viewElement );
+			conversion.for( 'upcast' ).elementToElement( {
+				model: modelName,
+				view: viewName,
+				// With a `low` priority, `paragraph` plugin auto-paragraphing mechanism is executed. Make sure
+				// this listener is called before it. If not, some elements will be transformed into a paragraph.
+				converterPriority: priorities.get( 'low' ) + 1
 			} );
-		} );
-	}
-
-	/**
-	 * Adds converters for the given inline element definition.
-	 *
-	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
-	 */
-	_addInlineElementConversion( definition ) {
-		const conversion = this.editor.conversion;
-		const viewName = definition.view;
-		const attributeKey = definition.model;
-
-		conversion.for( 'upcast' ).add( dispatcher => {
-			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
-				const viewAttributes = this._matchAndConsumeAllowedAttributes( data.viewItem, conversionApi );
-
-				// Since we are converting to attribute we need a range on which we will set the attribute.
-				// If the range is not created yet, we will create it.
-				if ( !data.modelRange ) {
-					data = Object.assign( data, conversionApi.convertChildren( data.viewItem, data.modelCursor ) );
-				}
-
-				// Set attribute on each item in range according to the schema.
-				for ( const node of data.modelRange.getItems() ) {
-					if ( conversionApi.schema.checkAttribute( node, attributeKey ) ) {
-						// Node's children are converted recursively, so node can already include model attribute.
-						// We want to extend it, not replace.
-						const nodeAttributes = node.getAttribute( attributeKey );
-						const attributesToAdd = mergeViewElementAttributes( viewAttributes || {}, nodeAttributes || {} );
-
-						conversionApi.writer.setAttribute( attributeKey, attributesToAdd, node );
-					}
-				}
-			}, { priority: 'low' } );
-		} );
-
-		conversion.for( 'downcast' ).attributeToElement( {
-			model: attributeKey,
-			view: ( attributeValue, conversionApi ) => {
-				if ( !attributeValue ) {
-					return;
-				}
-
-				const { writer } = conversionApi;
-				const viewElement = writer.createAttributeElement( viewName, null, { priority: definition.priority } );
 
-				setViewElementAttributes( writer, attributeValue, viewElement );
-
-				return viewElement;
-			}
-		} );
-	}
-
-	/**
-	 * Adds converters responsible for consuming disallowed view attributes.
-	 *
-	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
-	 */
-	_addDisallowedAttributeConversion( { view: viewName } ) {
-		const conversion = this.editor.conversion;
+			conversion.for( 'downcast' ).elementToElement( {
+				model: modelName,
+				view: viewName
+			} );
+		}
 
 		if ( !viewName ) {
 			return;
 		}
 
-		// Consumes disallowed element attributes to prevent them of being processed by other converters.
-		conversion.for( 'upcast' ).add( dispatcher => {
-			dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
-				consumeAttributeMatches( data.viewItem, conversionApi, this._disallowedAttributes );
-			}, { priority: 'high' } );
-		} );
+		conversion.for( 'upcast' ).add( consumeViewAttributesConverter( definition, this._disallowedAttributes ) );
+		conversion.for( 'upcast' ).add( viewToModelBlockAttributeConverter( definition, this._allowedAttributes ) );
+		conversion.for( 'downcast' ).add( modelToViewBlockAttributeConverter( definition ) );
 	}
 
 	/**
-	 * Matches and consumes allowed view attributes.
+	 * Registers inline element and attribute converters for the given data schema definition.
+	 *
+	 * Extends `$text` model schema to allow the given definition model attribute and its properties.
 	 *
 	 * @private
-	 * @param {module:engine/view/element~Element} viewElement
-	 * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
-	 * @returns {Object} [result]
-	 * @returns {Object} result.attributes Set with matched attribute names.
-	 * @returns {Object} result.styles Set with matched style names.
-	 * @returns {Array.<String>} result.classes Set with matched class names.
+	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 * @returns {Boolean}
 	 */
-	_matchAndConsumeAllowedAttributes( viewElement, conversionApi ) {
-		const matches = consumeAttributeMatches( viewElement, conversionApi, this._allowedAttributes );
-		const { attributes, styles, classes } = mergeMatchResults( matches );
-		const viewAttributes = {};
-
-		if ( attributes.size ) {
-			viewAttributes.attributes = iterableToObject( attributes, key => viewElement.getAttribute( key ) );
-		}
-
-		if ( styles.size ) {
-			viewAttributes.styles = iterableToObject( styles, key => viewElement.getStyle( key ) );
+	_handleInlineElement( definition ) {
+		if ( !definition.isInline ) {
+			return false;
 		}
 
-		if ( classes.size ) {
-			viewAttributes.classes = Array.from( classes );
-		}
-
-		if ( !Object.keys( viewAttributes ).length ) {
-			return null;
-		}
-
-		return viewAttributes;
-	}
-}
-
-// Consumes matched attributes.
-//
-// Returns sucessfully consumed attribute matches.
-//
-// @private
-// @param {module:engine/view/element~Element} viewElement
-// @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
-// @param {module:engine/view/matcher~Matcher Matcher} matcher
-// @returns {Array.<Object>} Array with match information about found attributes.
-function consumeAttributeMatches( viewElement, { consumable }, matcher ) {
-	const matches = matcher.matchAll( viewElement ) || [];
-	const consumedMatches = [];
-
-	for ( const match of matches ) {
-		// We only want to consume attributes, so element can be still processed by other converters.
-		delete match.match.name;
-
-		if ( consumable.consume( viewElement, match.match ) ) {
-			consumedMatches.push( match );
-		}
-	}
-
-	return consumedMatches;
-}
-
-// Helper function for downcast converter. Sets attributes on the given view element.
-//
-// @private
-// @param {module:engine/view/downcastwriter~DowncastWriter} writer
-// @param {Object} viewAttributes
-// @param {module:engine/view/element~Element} viewElement
-function setViewElementAttributes( writer, viewAttributes, viewElement ) {
-	if ( viewAttributes.attributes ) {
-		for ( const [ key, value ] of Object.entries( viewAttributes.attributes ) ) {
-			writer.setAttribute( key, value, viewElement );
-		}
-	}
-
-	if ( viewAttributes.styles ) {
-		writer.setStyle( viewAttributes.styles, viewElement );
-	}
-
-	if ( viewAttributes.classes ) {
-		writer.addClass( viewAttributes.classes, viewElement );
-	}
-}
-
-// Creates object view element from the given model element.
-//
-// @private
-// @param {String} viewName
-// @param {module:engine/model/element~Element} modelElement
-// @param {module:engine/view/downcastwriter~DowncastWriter} writer
-// @returns {module:engine/view/element~Element}
-function createObjectViewElement( viewName, modelElement, writer ) {
-	const viewAttributes = modelElement.getAttribute( 'htmlAttributes' );
-	const viewContent = modelElement.getAttribute( 'value' );
-
-	const viewElement = writer.createRawElement( viewName, null, function( domElement ) {
-		domElement.innerHTML = viewContent;
-	} );
-
-	if ( viewAttributes ) {
-		setViewElementAttributes( writer, viewAttributes, viewElement );
-	}
+		const editor = this.editor;
+		const schema = editor.model.schema;
+		const conversion = editor.conversion;
+		const attributeKey = definition.model;
 
-	return viewElement;
-}
+		schema.extend( '$text', {
+			allowAttributes: attributeKey
+		} );
 
-// Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
-//
-// @private
-// @param {Array.<Object>} matches
-// @returns {Object} result
-// @returns {Set.<Object>} result.attributes Set with matched attribute names.
-// @returns {Set.<Object>} result.styles Set with matched style names.
-// @returns {Set.<String>} result.classes Set with matched class names.
-function mergeMatchResults( matches ) {
-	const matchResult = {
-		attributes: new Set(),
-		classes: new Set(),
-		styles: new Set()
-	};
-
-	for ( const match of matches ) {
-		for ( const key in matchResult ) {
-			const values = match.match[ key ] || [];
-
-			values.forEach( value => matchResult[ key ].add( value ) );
+		if ( definition.attributeProperties ) {
+			schema.setAttributeProperties( attributeKey, definition.attributeProperties );
 		}
-	}
 
-	return matchResult;
-}
-
-// Converts the given iterable object into an object.
-//
-// @private
-// @param {Iterable.<String>} iterable
-// @param {Function} getValue Should result with value for the given object key.
-// @returns {Object}
-function iterableToObject( iterable, getValue ) {
-	const attributesObject = {};
-
-	for ( const prop of iterable ) {
-		attributesObject[ prop ] = getValue( prop );
-	}
+		conversion.for( 'upcast' ).add( consumeViewAttributesConverter( definition, this._disallowedAttributes ) );
+		conversion.for( 'upcast' ).add( viewToAttributeInlineConverter( definition, this._allowedAttributes ) );
 
-	return attributesObject;
-}
-
-// Merges view element attribute objects.
-//
-// @private
-// @param {Object} oldValue
-// @param {Object} newValue
-// @returns {Object}
-function mergeViewElementAttributes( oldValue, newValue ) {
-	const result = cloneDeep( oldValue );
-
-	for ( const key in newValue ) {
-		// Merge classes.
-		if ( Array.isArray( newValue[ key ] ) ) {
-			result[ key ] = Array.from( new Set( [ ...oldValue[ key ], ...newValue[ key ] ] ) );
-		}
-
-		// Merge attributes or styles.
-		else {
-			result[ key ] = { ...oldValue[ key ], ...newValue[ key ] };
-		}
+		conversion.for( 'downcast' ).attributeToElement( {
+			model: attributeKey,
+			view: attributeToViewInlineConverter( definition )
+		} );
 	}
-
-	return result;
 }
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index f1757deb0fe..e81c605c64e 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -79,6 +79,11 @@ export default class DataSchema extends Plugin {
 			}
 		} );
 
+		this.registerBlockElement( {
+			model: 'codeBlock',
+			view: 'pre'
+		} );
+
 		this.registerBlockElement( {
 			model: 'paragraph',
 			view: 'p'
@@ -183,6 +188,11 @@ export default class DataSchema extends Plugin {
 		} );
 
 		// Inline elements.
+		this.registerInlineElement( {
+			view: 'code',
+			model: 'htmlCode'
+		} );
+
 		this.registerInlineElement( {
 			view: 'a',
 			model: 'htmlA',
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/codeblock.html b/packages/ckeditor5-content-compatibility/tests/manual/codeblock.html
new file mode 100644
index 00000000000..8fec2981af6
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/manual/codeblock.html
@@ -0,0 +1,11 @@
+<head>
+	<meta http-equiv="Content-Security-Policy"
+		content="script-src 'self' https://ckeditor.com 'unsafe-inline' 'unsafe-eval'">
+</head>
+
+<div id="editor">
+	<p>Put some text in the :</p>
+	<pre style="background:blue;" class="foo"><code class=\"language-html\" data-foo="foo">Hello world!</code></pre>
+	<p>Then set the font color:</p>
+	<pre style="background:yellow;"><code class=\"language-css\" style="color:red;" data-foo="bar">body { color: red }</code></pre>
+</div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/codeblock.js b/packages/ckeditor5-content-compatibility/tests/manual/codeblock.js
new file mode 100644
index 00000000000..2ce9ed27874
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/manual/codeblock.js
@@ -0,0 +1,59 @@
+/**
+ * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/* globals console:false, window, document */
+
+import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
+import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials';
+import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
+import Bold from '@ckeditor/ckeditor5-basic-styles/src/bold';
+import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
+import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
+import CodeBlock from '@ckeditor/ckeditor5-code-block/src/codeblock';
+import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
+
+import GeneralHtmlSupport from '../../src/generalhtmlsupport';
+
+/**
+ * Client custom plugin extending HTML support for compatibility.
+ */
+class ExtendHTMLSupport extends Plugin {
+	static get requires() {
+		return [ GeneralHtmlSupport ];
+	}
+
+	init() {
+		const dataFilter = this.editor.plugins.get( 'DataFilter' );
+
+		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowAttributes( { name: /^(pre|code)$/, styles: { color: /[\s\S]+/ } } );
+		dataFilter.allowAttributes( { name: /^(pre|code)$/, styles: { background: /[\s\S]+/ } } );
+		dataFilter.allowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
+		dataFilter.allowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
+
+		dataFilter.disallowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': 'bar' } } );
+		dataFilter.disallowAttributes( { name: /^(pre|code)$/, styles: { background: 'yellow' } } );
+	}
+}
+
+ClassicEditor
+	.create( document.querySelector( '#editor' ), {
+		plugins: [
+			Bold,
+			CodeBlock,
+			Essentials,
+			ExtendHTMLSupport,
+			Italic,
+			Paragraph,
+			Strikethrough
+		],
+		toolbar: [ 'codeBlock', '|', 'bold', 'italic', 'strikethrough' ]
+	} )
+	.then( editor => {
+		window.editor = editor;
+	} )
+	.catch( err => {
+		console.error( err.stack );
+	} );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/codeblock.md b/packages/ckeditor5-content-compatibility/tests/manual/codeblock.md
new file mode 100644
index 00000000000..e69de29bb2d

From 3ebc4c60936a25942dbaad1ba5d309b90be10a5f Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 14 May 2021 13:16:17 +0200
Subject: [PATCH 135/217] Added test coverage, removed dead code.

---
 .../src/converters.js                         |  20 +-
 .../tests/datafilter.js                       | 208 +++++++++++++++++-
 2 files changed, 209 insertions(+), 19 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/converters.js b/packages/ckeditor5-content-compatibility/src/converters.js
index 5ac4d2888cd..0056969ff01 100644
--- a/packages/ckeditor5-content-compatibility/src/converters.js
+++ b/packages/ckeditor5-content-compatibility/src/converters.js
@@ -41,12 +41,9 @@ export function consumeViewAttributesConverter( { view: viewName }, matcher ) {
 export function viewToModelCodeBlockAttributeConverter( matcher ) {
 	return dispatcher => {
 		dispatcher.on( 'element:code', ( evt, data, conversionApi ) => {
-			if ( !data.modelRange ) {
-				return;
-			}
-
 			const viewPreElement = data.viewItem.parent;
-			if ( !isPreElement( viewPreElement ) ) {
+
+			if ( !viewPreElement || !viewPreElement.is( 'element', 'pre' ) ) {
 				return;
 			}
 
@@ -73,10 +70,7 @@ export function modelToViewCodeBlockAttributeConverter() {
 			}
 
 			const viewPreElement = conversionApi.mapper.toViewElement( data.item ).parent;
-
-			if ( isPreElement( viewPreElement ) ) {
-				setViewAttributes( conversionApi.writer, data.attributeNewValue, viewPreElement );
-			}
+			setViewAttributes( conversionApi.writer, data.attributeNewValue, viewPreElement );
 		} );
 	};
 }
@@ -264,11 +258,3 @@ export function modelToViewBlockAttributeConverter( { model: modelName } ) {
 		} );
 	};
 }
-
-// Checks if the given view element is `pre`.
-//
-// @param {module:engine/view/element~Element} [element]
-// @returns {Boolean}
-function isPreElement( element ) {
-	return element && element.is( 'element', 'pre' );
-}
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 428810ea290..fe556323579 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -8,6 +8,7 @@ import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
 import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
 import LinkEditing from '@ckeditor/ckeditor5-link/src/linkediting';
 import FontColorEditing from '@ckeditor/ckeditor5-font/src/fontcolor/fontcolorediting';
+import CodeBlock from '@ckeditor/ckeditor5-code-block/src/codeblock';
 import DataFilter from '../src/datafilter';
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import { expectToThrowCKEditorError } from '@ckeditor/ckeditor5-utils/tests/_utils/utils';
@@ -28,7 +29,7 @@ describe( 'DataFilter', () => {
 
 		return ClassicTestEditor
 			.create( editorElement, {
-				plugins: [ Paragraph, FontColorEditing, LinkEditing, GeneralHtmlSupport ]
+				plugins: [ Paragraph, FontColorEditing, LinkEditing, CodeBlock, GeneralHtmlSupport ]
 			} )
 			.then( newEditor => {
 				editor = newEditor;
@@ -135,6 +136,188 @@ describe( 'DataFilter', () => {
 		}
 	} );
 
+	describe( 'codeBlock', () => {
+		it( 'should allow attributes', () => {
+			dataFilter.allowElement( { name: /^(pre|code)$/ } );
+			dataFilter.allowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
+
+			editor.setData( '<pre data-foo="foo"><code data-foo="foo">foobar</code></pre>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<codeBlock htmlAttributes="(1)" language="plaintext"><$text htmlCode="(2)">foobar</$text></codeBlock>',
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': 'foo'
+						}
+					},
+					2: {
+						attributes: {
+							'data-foo': 'foo'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<pre data-foo="foo">' +
+				'<code class="language-plaintext"><code data-foo="foo">foobar</code></code>' +
+				'</pre>' );
+		} );
+
+		it( 'should allow attributes (classes)', () => {
+			dataFilter.allowElement( { name: /^(pre|code)$/ } );
+			dataFilter.allowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
+
+			editor.setData( '<pre class="foo"><code class="foo">foobar</code></pre>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<codeBlock htmlAttributes="(1)" language="plaintext"><$text htmlCode="(2)">foobar</$text></codeBlock>',
+				attributes: {
+					1: {
+						classes: [ 'foo' ]
+					},
+					2: {
+						classes: [ 'foo' ]
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<pre class="foo">' +
+				'<code class="language-plaintext"><code class="foo">foobar</code></code>' +
+				'</pre>' );
+		} );
+
+		it( 'should allow attributes (styles)', () => {
+			dataFilter.allowElement( { name: /^(pre|code)$/ } );
+			dataFilter.allowAttributes( { name: 'pre', styles: { background: 'blue' } } );
+			dataFilter.allowAttributes( { name: 'code', styles: { color: 'red' } } );
+
+			editor.setData( '<pre style="background:blue;"><code style="color:red;">foobar</code></pre>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<codeBlock htmlAttributes="(1)" language="plaintext"><$text htmlCode="(2)">foobar</$text></codeBlock>',
+				attributes: {
+					1: {
+						styles: {
+							background: 'blue'
+						}
+					},
+					2: {
+						styles: {
+							color: 'red'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<pre style="background:blue;">' +
+				'<code class="language-plaintext"><code style="color:red;">foobar</code></code>' +
+				'</pre>' );
+		} );
+
+		it( 'should disallow attributes', () => {
+			dataFilter.allowElement( { name: /^(pre|code)$/ } );
+			dataFilter.allowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
+			dataFilter.disallowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
+
+			editor.setData( '<pre data-foo="foo"><code data-foo="foo">foobar</code></pre>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<codeBlock language="plaintext"><$text htmlCode="(1)">foobar</$text></codeBlock>',
+				attributes: {
+					1: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<pre><code class="language-plaintext"><code>foobar</code></code></pre>' );
+		} );
+
+		it( 'should disallow attributes (classes)', () => {
+			dataFilter.allowElement( { name: /^(pre|code)$/ } );
+			dataFilter.allowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
+			dataFilter.disallowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
+
+			editor.setData( '<pre class="foo"><code class="foo">foobar</code></pre>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<codeBlock language="plaintext"><$text htmlCode="(1)">foobar</$text></codeBlock>',
+				attributes: {
+					1: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<pre><code class="language-plaintext"><code>foobar</code></code></pre>' );
+		} );
+
+		it( 'should allow attributes (styles)', () => {
+			dataFilter.allowElement( { name: /^(pre|code)$/ } );
+
+			dataFilter.allowAttributes( { name: 'pre', styles: { background: 'blue' } } );
+			dataFilter.allowAttributes( { name: 'code', styles: { color: 'red' } } );
+
+			dataFilter.disallowAttributes( { name: 'pre', styles: { background: 'blue' } } );
+			dataFilter.disallowAttributes( { name: 'code', styles: { color: 'red' } } );
+
+			editor.setData( '<pre style="background:blue;"><code style="color:red;">foobar</code></pre>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<codeBlock language="plaintext"><$text htmlCode="(1)">foobar</$text></codeBlock>',
+				attributes: {
+					1: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<pre><code class="language-plaintext"><code>foobar</code></code></pre>' );
+		} );
+
+		it( 'should allow attributes on code element existing alone', () => {
+			dataFilter.allowElement( { name: /^(pre|code)$/ } );
+			dataFilter.allowAttributes( { name: 'code', attributes: { 'data-foo': /[\s\S]+/ } } );
+
+			editor.setData( '<p><code data-foo="foo">foobar</code></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlCode="(1)">foobar</$text></paragraph>',
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': 'foo'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><code data-foo="foo">foobar</code></p>' );
+		} );
+
+		it( 'should not consume attribute already consumed (downcast)', () => {
+			editor.conversion.for( 'downcast' ).add( dispatcher => {
+				dispatcher.on( 'attribute:htmlAttributes:codeBlock', ( evt, data, conversionApi ) => {
+					conversionApi.consumable.consume( data.item, evt.name );
+				}, { priority: 'high' } );
+			} );
+
+			dataFilter.allowElement( { name: 'pre' } );
+			dataFilter.allowAttributes( { name: 'pre', attributes: { 'data-foo': true } } );
+
+			editor.setData( '<pre data-foo><code>foobar</code></section>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<codeBlock htmlAttributes="(1)" language="plaintext">foobar</codeBlock>',
+				// At this point, attribute should still be in the model, as we are testing downcast conversion.
+				attributes: {
+					1: {
+						attributes: {
+							'data-foo': ''
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<pre><code class="language-plaintext">foobar</code></pre>' );
+		} );
+	} );
+
 	describe( 'object', () => {
 		it( 'should allow element', () => {
 			dataFilter.allowElement( { name: 'input' } );
@@ -694,6 +877,27 @@ describe( 'DataFilter', () => {
 
 			expect( getModelData( model, { withoutSelection: true } ) ).to.equal( '<paragraph>foo</paragraph>' );
 		} );
+
+		it( 'should not register view converters for existing features if a view has not been provided', () => {
+			// Skipping `view` property on purpose.
+			dataSchema.registerBlockElement( {
+				model: 'htmlFoo',
+				modelSchema: { inheritAllFrom: '$block' }
+			} );
+
+			dataSchema.registerBlockElement( {
+				model: 'htmlBar',
+				view: 'bar',
+				modelSchema: { inheritAllFrom: 'htmlFoo' }
+			} );
+
+			editor.model.schema.register( 'htmlFoo', { inheritAllFrom: '$block' } );
+
+			// At this point we will be trying to register converter without valid view name.
+			expect( () => {
+				dataFilter.allowElement( { name: 'bar' } );
+			} ).to.not.throw();
+		} );
 	} );
 
 	describe( 'inline', () => {
@@ -1246,7 +1450,7 @@ describe( 'DataFilter', () => {
 
 		expectToThrowCKEditorError( () => {
 			dataFilter.allowElement( { name: 'xyz' } );
-		}, /data-filter-invalid-definition-type/, null, definition );
+		}, /data-filter-invalid-definition/, null, definition );
 	} );
 
 	function getModelDataWithAttributes( model, options ) {

From aa0a93df80b2a2a734164771073e0e55798ff6c5 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 25 May 2021 09:33:12 +0200
Subject: [PATCH 136/217] Refactoring.

---
 .../src/dataschema.js                         | 82 +++++++++----------
 1 file changed, 41 insertions(+), 41 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index e81c605c64e..94641027b67 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -63,6 +63,47 @@ export default class DataSchema extends Plugin {
 		return 'DataSchema';
 	}
 
+	/**
+	 * Add new data schema definition describing block element.
+	 *
+	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+	 */
+	registerBlockElement( definition ) {
+		this._definitions.set( definition.model, { ...definition, isBlock: true } );
+	}
+
+	/**
+	 * Add new data schema definition describing inline element.
+	 *
+	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 */
+	registerInlineElement( definition ) {
+		this._definitions.set( definition.model, { ...definition, isInline: true } );
+	}
+
+	/**
+	 * Returns all definitions matching the given view name.
+	 *
+	 * @param {String|RegExp} viewName
+	 * @param {Boolean} [includeReferences] Indicates if this method should also include definitions of referenced models.
+	 * @returns {Set.<module:content-compatibility/dataschema~DataSchemaDefinition>}
+	 */
+	getDefinitionsForView( viewName, includeReferences ) {
+		const definitions = new Set();
+
+		for ( const definition of this._getMatchingViewDefinitions( viewName ) ) {
+			if ( includeReferences ) {
+				for ( const reference of this._getReferences( definition.model ) ) {
+					definitions.add( reference );
+				}
+			}
+
+			definitions.add( definition );
+		}
+
+		return definitions;
+	}
+
 	/**
 	 * Registers default data schema definitions.
 	 *
@@ -323,47 +364,6 @@ export default class DataSchema extends Plugin {
 		} );
 	}
 
-	/**
-	 * Add new data schema definition describing block element.
-	 *
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
-	 */
-	registerBlockElement( definition ) {
-		this._definitions.set( definition.model, { ...definition, isBlock: true } );
-	}
-
-	/**
-	 * Add new data schema definition describing inline element.
-	 *
-	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
-	 */
-	registerInlineElement( definition ) {
-		this._definitions.set( definition.model, { ...definition, isInline: true } );
-	}
-
-	/**
-	 * Returns all definitions matching the given view name.
-	 *
-	 * @param {String|RegExp} viewName
-	 * @param {Boolean} [includeReferences] Indicates if this method should also include definitions of referenced models.
-	 * @returns {Set.<module:content-compatibility/dataschema~DataSchemaDefinition>}
-	 */
-	getDefinitionsForView( viewName, includeReferences ) {
-		const definitions = new Set();
-
-		for ( const definition of this._getMatchingViewDefinitions( viewName ) ) {
-			if ( includeReferences ) {
-				for ( const reference of this._getReferences( definition.model ) ) {
-					definitions.add( reference );
-				}
-			}
-
-			definitions.add( definition );
-		}
-
-		return definitions;
-	}
-
 	/**
 	 * Returns definitions matching the given view name.
 	 *

From f841e6fd5424e70c2b00d3ac825777312fbdc4b5 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 25 May 2021 13:21:47 +0200
Subject: [PATCH 137/217] Handle registered object elements.

---
 .../src/datafilter.js                             | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index faf88bbf87b..d98d57781c4 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -273,16 +273,21 @@ export default class DataFilter extends Plugin {
 	 * @returns {Boolean}
 	 */
 	_handleObjectElement( definition ) {
-		if ( !definition.isObject ) {
-			return false;
-		}
-
 		const editor = this.editor;
 		const schema = editor.model.schema;
 		const conversion = editor.conversion;
 		const { view: viewName, model: modelName } = definition;
 
-		schema.register( definition.model, definition.modelSchema );
+		if ( !definition.isObject ) {
+			return false;
+		}
+
+		// If feature is already registered, #_handleBlockElement should take care of it.
+		if ( schema.isRegistered( modelName ) ) {
+			return false;
+		}
+
+		schema.register( modelName, definition.modelSchema );
 
 		if ( !viewName ) {
 			return;

From 2b6fc2c5de5667d814c44f2d3b5d4959f328e97c Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 25 May 2021 13:34:13 +0200
Subject: [PATCH 138/217] Added converter priority for object elements.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index d98d57781c4..674c6ae3cdc 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -302,7 +302,10 @@ export default class DataFilter extends Plugin {
 		conversion.for( 'upcast' ).add( consumeViewAttributesConverter( definition, this._disallowedAttributes ) );
 		conversion.for( 'upcast' ).elementToElement( {
 			view: viewName,
-			model: viewToModelObjectConverter( definition, this._allowedAttributes )
+			model: viewToModelObjectConverter( definition, this._allowedAttributes ),
+			// With a `low` priority, `paragraph` plugin auto-paragraphing mechanism is executed. Make sure
+			// this listener is called before it. If not, some elements will be transformed into a paragraph.
+			converterPriority: priorities.get( 'low' ) + 1
 		} );
 
 		conversion.for( 'dataDowncast' ).elementToElement( {

From a76e1038dc36d6eea82b3c25b9b3e36a6a0f9d7c Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 25 May 2021 13:52:58 +0200
Subject: [PATCH 139/217] Register missing schema keys.

---
 .../src/converters.js                         |  6 ++---
 .../src/datafilter.js                         |  8 ++++++
 .../tests/datafilter.js                       | 26 +++++++++----------
 3 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/converters.js b/packages/ckeditor5-content-compatibility/src/converters.js
index 0056969ff01..2be1c9f02b0 100644
--- a/packages/ckeditor5-content-compatibility/src/converters.js
+++ b/packages/ckeditor5-content-compatibility/src/converters.js
@@ -78,7 +78,7 @@ export function modelToViewCodeBlockAttributeConverter() {
 /**
  * View-to-model conversion helper for object elements.
  *
- * Preserves object element content in `value` attribute. Also, all matching attributes
+ * Preserves object element content in `htmlContent` attribute. Also, all matching attributes
  * by the given matcher will be preserved on `htmlAttributes` attribute.
  *
  * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
@@ -91,7 +91,7 @@ export function viewToModelObjectConverter( { model: modelName }, matcher ) {
 
 		// Let's keep element HTML and its attributes, so we can rebuild element in downcast conversions.
 		return conversionApi.writer.createElement( modelName, {
-			value: viewElement.getCustomProperty( '$rawContent' ),
+			htmlContent: viewElement.getCustomProperty( '$rawContent' ),
 			...( htmlAttributes && { htmlAttributes } )
 		} );
 	};
@@ -139,7 +139,7 @@ export function toObjectWidgetConverter( editor, { view: viewName, isInline } )
 */
 export function createObjectView( viewName, modelElement, writer ) {
 	const viewAttributes = modelElement.getAttribute( 'htmlAttributes' );
-	const viewContent = modelElement.getAttribute( 'value' );
+	const viewContent = modelElement.getAttribute( 'htmlContent' );
 
 	const viewElement = writer.createRawElement( viewName, null, function( domElement ) {
 		domElement.innerHTML = viewContent;
diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 674c6ae3cdc..78594c506ba 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -293,6 +293,10 @@ export default class DataFilter extends Plugin {
 			return;
 		}
 
+		schema.extend( definition.model, {
+			allowAttributes: [ 'htmlAttributes', 'htmlContent' ]
+		} );
+
 		// Store element content in special `$rawContent` custom property to
 		// avoid editor's data filtering mechanism.
 		editor.data.registerRawContentMatcher( {
@@ -364,6 +368,10 @@ export default class DataFilter extends Plugin {
 			return;
 		}
 
+		schema.extend( definition.model, {
+			allowAttributes: 'htmlAttributes'
+		} );
+
 		conversion.for( 'upcast' ).add( consumeViewAttributesConverter( definition, this._disallowedAttributes ) );
 		conversion.for( 'upcast' ).add( viewToModelBlockAttributeConverter( definition, this._allowedAttributes ) );
 		conversion.for( 'downcast' ).add( modelToViewBlockAttributeConverter( definition ) );
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index fe556323579..0619cf10eda 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -325,7 +325,7 @@ describe( 'DataFilter', () => {
 			editor.setData( '<p><input></p>' );
 
 			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
-				'<paragraph><htmlInput value=""></htmlInput></paragraph>'
+				'<paragraph><htmlInput htmlContent=""></htmlInput></paragraph>'
 			);
 
 			expect( editor.getData() ).to.equal( '<p><input></p>' );
@@ -341,7 +341,7 @@ describe( 'DataFilter', () => {
 
 			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
 				'<paragraph>' +
-				'<htmlVideo value="<source src="https://example.com/video.mp4" type="video/mp4">' +
+				'<htmlVideo htmlContent="<source src="https://example.com/video.mp4" type="video/mp4">' +
 				' Your browser does not support the video tag."></htmlVideo>' +
 				'</paragraph>'
 			);
@@ -368,7 +368,7 @@ describe( 'DataFilter', () => {
 			editor.setData( '<xyz>foobar</xyz>' );
 
 			expect( getModelData( model, { withoutSelection: true } ) ).to.equal(
-				'<htmlXyz value="foobar"></htmlXyz>'
+				'<htmlXyz htmlContent="foobar"></htmlXyz>'
 			);
 
 			expect( editor.getData() ).to.equal( '<xyz>foobar</xyz>' );
@@ -381,7 +381,7 @@ describe( 'DataFilter', () => {
 			editor.setData( '<p><input type="text"></p>' );
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph><htmlInput htmlAttributes="(1)" value=""></htmlInput></paragraph>',
+				data: '<paragraph><htmlInput htmlAttributes="(1)" htmlContent=""></htmlInput></paragraph>',
 				attributes: {
 					1: {
 						attributes: {
@@ -401,7 +401,7 @@ describe( 'DataFilter', () => {
 			editor.setData( '<p><input style="color:red;"></p>' );
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph><htmlInput htmlAttributes="(1)" value=""></htmlInput></paragraph>',
+				data: '<paragraph><htmlInput htmlAttributes="(1)" htmlContent=""></htmlInput></paragraph>',
 				attributes: {
 					1: {
 						styles: {
@@ -421,7 +421,7 @@ describe( 'DataFilter', () => {
 			editor.setData( '<p><input class="foobar"></p>' );
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph><htmlInput htmlAttributes="(1)" value=""></htmlInput></paragraph>',
+				data: '<paragraph><htmlInput htmlAttributes="(1)" htmlContent=""></htmlInput></paragraph>',
 				attributes: {
 					1: {
 						classes: [ 'foobar' ]
@@ -441,8 +441,8 @@ describe( 'DataFilter', () => {
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-				'<htmlInput htmlAttributes="(1)" value=""></htmlInput>' +
-				'<htmlInput value=""></htmlInput>' +
+				'<htmlInput htmlAttributes="(1)" htmlContent=""></htmlInput>' +
+				'<htmlInput htmlContent=""></htmlInput>' +
 				'</paragraph>',
 				attributes: {
 					1: {
@@ -465,8 +465,8 @@ describe( 'DataFilter', () => {
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-				'<htmlInput htmlAttributes="(1)" value=""></htmlInput>' +
-				'<htmlInput value=""></htmlInput>' +
+				'<htmlInput htmlAttributes="(1)" htmlContent=""></htmlInput>' +
+				'<htmlInput htmlContent=""></htmlInput>' +
 				'</paragraph>',
 				attributes: {
 					1: {
@@ -489,8 +489,8 @@ describe( 'DataFilter', () => {
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-				'<htmlInput value=""></htmlInput>' +
-				'<htmlInput value=""></htmlInput>' +
+				'<htmlInput htmlContent=""></htmlInput>' +
+				'<htmlInput htmlContent=""></htmlInput>' +
 				'</paragraph>',
 				attributes: {}
 			} );
@@ -1465,7 +1465,7 @@ describe( 'DataFilter', () => {
 		let attributes = [];
 		for ( const item of range.getItems() ) {
 			for ( const [ key, value ] of sortAttributes( item.getAttributes() ) ) {
-				if ( key.startsWith( 'html' ) ) {
+				if ( key.startsWith( 'html' ) && key !== 'htmlContent' ) {
 					attributes.push( value );
 				}
 			}

From ef3341497f75938429d6db5c7ac3a53ce0ba35f8 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 25 May 2021 13:54:47 +0200
Subject: [PATCH 140/217] Separated t from editor.

---
 packages/ckeditor5-content-compatibility/src/converters.js | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/converters.js b/packages/ckeditor5-content-compatibility/src/converters.js
index 2be1c9f02b0..781cb7731b1 100644
--- a/packages/ckeditor5-content-compatibility/src/converters.js
+++ b/packages/ckeditor5-content-compatibility/src/converters.js
@@ -105,8 +105,10 @@ export function viewToModelObjectConverter( { model: modelName }, matcher ) {
  * @returns {Function} Returns a conversion callback.
 */
 export function toObjectWidgetConverter( editor, { view: viewName, isInline } ) {
+	const t = editor.t;
+
 	return ( modelElement, { writer } ) => {
-		const widgetLabel = editor.t( 'HTML object' );
+		const widgetLabel = t( 'HTML object' );
 
 		// Widget cannot be a raw element because the widget system would not be able
 		// to add its UI to it. Thus, we need separate view container.

From 957b8f7de9e2f5b0264a6646220bf57907288231 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 25 May 2021 13:57:02 +0200
Subject: [PATCH 141/217] Removed rtl support.

---
 .../ckeditor5-content-compatibility/src/converters.js    | 3 +--
 .../ckeditor5-content-compatibility/theme/datafilter.css | 9 ++-------
 2 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/converters.js b/packages/ckeditor5-content-compatibility/src/converters.js
index 781cb7731b1..d89cd26f26b 100644
--- a/packages/ckeditor5-content-compatibility/src/converters.js
+++ b/packages/ckeditor5-content-compatibility/src/converters.js
@@ -114,8 +114,7 @@ export function toObjectWidgetConverter( editor, { view: viewName, isInline } )
 		// to add its UI to it. Thus, we need separate view container.
 		const viewContainer = writer.createContainerElement( isInline ? 'span' : 'div', {
 			class: 'html-object-embed',
-			'data-html-object-embed-label': widgetLabel,
-			dir: editor.locale.uiLanguageDirection
+			'data-html-object-embed-label': widgetLabel
 		}, {
 			isAllowedInsideAttributeElement: isInline
 		} );
diff --git a/packages/ckeditor5-content-compatibility/theme/datafilter.css b/packages/ckeditor5-content-compatibility/theme/datafilter.css
index 647e4f7cccc..079295f49cc 100644
--- a/packages/ckeditor5-content-compatibility/theme/datafilter.css
+++ b/packages/ckeditor5-content-compatibility/theme/datafilter.css
@@ -30,13 +30,8 @@
 		font-family: var(--ck-font-face);
 	}
 
-	&[dir="rtl"]::before {
-		left: auto;
-		right: var(--ck-spacing-standard);
-	}
-
-	/* Make space for label but it only collides in LTR languages */
-	&[dir="ltr"] .ck-widget__type-around .ck-widget__type-around__button.ck-widget__type-around__button_before {
+	/* Make space for label. */
+	& .ck-widget__type-around .ck-widget__type-around__button.ck-widget__type-around__button_before {
 		margin-left: 50px;
 	}
 

From a74247e86acb9b155680fe1cc33653cf2dac057d Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 25 May 2021 14:05:17 +0200
Subject: [PATCH 142/217] Compose block helper conversions instead of separate
 attribute conversion for objects.

---
 .../src/converters.js                         | 21 ++++---------------
 .../src/datafilter.js                         |  4 +++-
 2 files changed, 7 insertions(+), 18 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/converters.js b/packages/ckeditor5-content-compatibility/src/converters.js
index d89cd26f26b..87d2ff4f997 100644
--- a/packages/ckeditor5-content-compatibility/src/converters.js
+++ b/packages/ckeditor5-content-compatibility/src/converters.js
@@ -82,17 +82,13 @@ export function modelToViewCodeBlockAttributeConverter() {
  * by the given matcher will be preserved on `htmlAttributes` attribute.
  *
  * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
- * @param {module:engine/view/matcher~Matcher} matcher
  * @returns {Function} Returns a conversion callback.
 */
-export function viewToModelObjectConverter( { model: modelName }, matcher ) {
+export function viewToModelObjectConverter( { model: modelName } ) {
 	return ( viewElement, conversionApi ) => {
-		const htmlAttributes = consumeViewAttributes( viewElement, conversionApi, matcher );
-
 		// Let's keep element HTML and its attributes, so we can rebuild element in downcast conversions.
 		return conversionApi.writer.createElement( modelName, {
-			htmlContent: viewElement.getCustomProperty( '$rawContent' ),
-			...( htmlAttributes && { htmlAttributes } )
+			htmlContent: viewElement.getCustomProperty( '$rawContent' )
 		} );
 	};
 }
@@ -139,18 +135,9 @@ export function toObjectWidgetConverter( editor, { view: viewName, isInline } )
 * @returns {module:engine/view/element~Element}
 */
 export function createObjectView( viewName, modelElement, writer ) {
-	const viewAttributes = modelElement.getAttribute( 'htmlAttributes' );
-	const viewContent = modelElement.getAttribute( 'htmlContent' );
-
-	const viewElement = writer.createRawElement( viewName, null, function( domElement ) {
-		domElement.innerHTML = viewContent;
+	return writer.createRawElement( viewName, null, function( domElement ) {
+		domElement.innerHTML = modelElement.getAttribute( 'htmlContent' );
 	} );
-
-	if ( viewAttributes ) {
-		setViewAttributes( writer, viewAttributes, viewElement );
-	}
-
-	return viewElement;
 }
 
 /**
diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 78594c506ba..9317d7990cd 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -306,11 +306,12 @@ export default class DataFilter extends Plugin {
 		conversion.for( 'upcast' ).add( consumeViewAttributesConverter( definition, this._disallowedAttributes ) );
 		conversion.for( 'upcast' ).elementToElement( {
 			view: viewName,
-			model: viewToModelObjectConverter( definition, this._allowedAttributes ),
+			model: viewToModelObjectConverter( definition ),
 			// With a `low` priority, `paragraph` plugin auto-paragraphing mechanism is executed. Make sure
 			// this listener is called before it. If not, some elements will be transformed into a paragraph.
 			converterPriority: priorities.get( 'low' ) + 1
 		} );
+		conversion.for( 'upcast' ).add( viewToModelBlockAttributeConverter( definition, this._allowedAttributes ) );
 
 		conversion.for( 'dataDowncast' ).elementToElement( {
 			model: modelName,
@@ -322,6 +323,7 @@ export default class DataFilter extends Plugin {
 			model: modelName,
 			view: toObjectWidgetConverter( editor, definition )
 		} );
+		conversion.for( 'downcast' ).add( modelToViewBlockAttributeConverter( definition ) );
 	}
 
 	/**

From 186433f5a6a87ed017de45d3ceec04bb3ecde54c Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 26 May 2021 12:23:17 +0200
Subject: [PATCH 143/217] Separate code block from data filter, improve
 conversion

---
 .../src/conversionutils.js                    | 100 ------
 .../src/converters.js                         |  77 +----
 .../src/datafilter.js                         | 286 ++++++++++++------
 .../src/dataschema.js                         |   8 +
 .../src/generalhtmlsupport.js                 |   7 +-
 .../src/integrations/codeblock.js             | 103 +++++++
 .../tests/_utils/utils.js                     |  79 +++++
 .../tests/codeblock.js                        | 219 ++++++++++++++
 .../tests/datafilter.js                       | 248 +--------------
 .../tests/manual/codeblock.html               |   8 +-
 10 files changed, 644 insertions(+), 491 deletions(-)
 create mode 100644 packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
 create mode 100644 packages/ckeditor5-content-compatibility/tests/_utils/utils.js
 create mode 100644 packages/ckeditor5-content-compatibility/tests/codeblock.js

diff --git a/packages/ckeditor5-content-compatibility/src/conversionutils.js b/packages/ckeditor5-content-compatibility/src/conversionutils.js
index a55dd09b745..960d572b40c 100644
--- a/packages/ckeditor5-content-compatibility/src/conversionutils.js
+++ b/packages/ckeditor5-content-compatibility/src/conversionutils.js
@@ -9,41 +9,6 @@
 
 import { cloneDeep } from 'lodash-es';
 
-/**
- * Matches and consumes the given view attributes.
- *
- * @param {module:engine/view/element~Element} viewElement
- * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
- * @param {module:engine/view/matcher~Matcher Matcher} matcher
- * @returns {Object} [result]
- * @returns {Object} result.attributes Set with matched attribute names.
- * @returns {Object} result.styles Set with matched style names.
- * @returns {Array.<String>} result.classes Set with matched class names.
- */
-export function consumeViewAttributes( viewElement, conversionApi, matcher ) {
-	const matches = consumeAttributeMatches( viewElement, conversionApi, matcher );
-	const { attributes, styles, classes } = mergeMatchResults( matches );
-	const viewAttributes = {};
-
-	if ( attributes.size ) {
-		viewAttributes.attributes = iterableToObject( attributes, key => viewElement.getAttribute( key ) );
-	}
-
-	if ( styles.size ) {
-		viewAttributes.styles = iterableToObject( styles, key => viewElement.getStyle( key ) );
-	}
-
-	if ( classes.size ) {
-		viewAttributes.classes = Array.from( classes );
-	}
-
-	if ( !Object.keys( viewAttributes ).length ) {
-		return null;
-	}
-
-	return viewAttributes;
-}
-
 /**
 * Helper function for downcast converter. Sets attributes on the given view element.
 *
@@ -91,68 +56,3 @@ export function mergeViewElementAttributes( oldValue, newValue ) {
 
 	return result;
 }
-
-// Consumes matched attributes.
-//
-// @private
-// @param {module:engine/view/element~Element} viewElement
-// @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
-// @param {module:engine/view/matcher~Matcher Matcher} matcher
-// @returns {Array.<Object>} Array with match information about found attributes.
-function consumeAttributeMatches( viewElement, { consumable }, matcher ) {
-	const matches = matcher.matchAll( viewElement ) || [];
-	const consumedMatches = [];
-
-	for ( const match of matches ) {
-		// We only want to consume attributes, so element can be still processed by other converters.
-		delete match.match.name;
-
-		if ( consumable.consume( viewElement, match.match ) ) {
-			consumedMatches.push( match );
-		}
-	}
-
-	return consumedMatches;
-}
-
-// Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
-//
-// @private
-// @param {Array.<Object>} matches
-// @returns {Object} result
-// @returns {Set.<Object>} result.attributes Set with matched attribute names.
-// @returns {Set.<Object>} result.styles Set with matched style names.
-// @returns {Set.<String>} result.classes Set with matched class names.
-function mergeMatchResults( matches ) {
-	const matchResult = {
-		attributes: new Set(),
-		classes: new Set(),
-		styles: new Set()
-	};
-
-	for ( const match of matches ) {
-		for ( const key in matchResult ) {
-			const values = match.match[ key ] || [];
-
-			values.forEach( value => matchResult[ key ].add( value ) );
-		}
-	}
-
-	return matchResult;
-}
-
-// Converts the given iterable object into an object.
-//
-// @private
-// @param {Iterable.<String>} iterable
-// @param {Function} getValue Should result with value for the given object key.
-// @returns {Object}
-function iterableToObject( iterable, getValue ) {
-	const attributesObject = {};
-
-	for ( const prop of iterable ) {
-		attributesObject[ prop ] = getValue( prop );
-	}
-
-	return attributesObject;
-}
diff --git a/packages/ckeditor5-content-compatibility/src/converters.js b/packages/ckeditor5-content-compatibility/src/converters.js
index 87d2ff4f997..a3a847e0b7a 100644
--- a/packages/ckeditor5-content-compatibility/src/converters.js
+++ b/packages/ckeditor5-content-compatibility/src/converters.js
@@ -8,78 +8,31 @@
  */
 
 import { toWidget } from 'ckeditor5/src/widget';
-import { consumeViewAttributes, setViewAttributes, mergeViewElementAttributes } from './conversionutils';
+import { setViewAttributes, mergeViewElementAttributes } from './conversionutils';
 
 /**
- * Conversion helper consuming all attributes from the definition view element
- * matched by the given matcher.
+ * Conversion helper consuming all disallowed attributes from the definition view element.
  *
  * This converter listenes on `high` priority to ensure that all attributes are consumed
  * before standard priority converters.
  *
  * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
- * @param {module:engine/view/matcher~Matcher} matcher
+ * @param {module:content-compatibility/datafilter~DataFilter} dataFilter
  * @returns {Function} Returns a conversion callback.
 */
-export function consumeViewAttributesConverter( { view: viewName }, matcher ) {
+export function disallowedAttributesConverter( { view: viewName }, dataFilter ) {
 	return dispatcher => {
 		dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
-			consumeViewAttributes( data.viewItem, conversionApi, matcher );
+			dataFilter.consumeDisallowedAttributes( data.viewItem, conversionApi );
 		}, { priority: 'high' } );
 	};
 }
 
-/**
- * View-to-model conversion helper preserving attributes on {@link module:code-block/codeblock~CodeBlock Code Block}
- * feature model element matched by the given matcher.
- *
- * Attributes are preserved as a value of `htmlAttributes` model attribute.
- *
- * @param {module:engine/view/matcher~Matcher} matcher
- * @returns {Function} Returns a conversion callback.
-*/
-export function viewToModelCodeBlockAttributeConverter( matcher ) {
-	return dispatcher => {
-		dispatcher.on( 'element:code', ( evt, data, conversionApi ) => {
-			const viewPreElement = data.viewItem.parent;
-
-			if ( !viewPreElement || !viewPreElement.is( 'element', 'pre' ) ) {
-				return;
-			}
-
-			const viewAttributes = consumeViewAttributes( viewPreElement, conversionApi, matcher );
-
-			if ( viewAttributes ) {
-				conversionApi.writer.setAttribute( 'htmlAttributes', viewAttributes, data.modelRange );
-			}
-		}, { conversionPriority: 'low' } );
-	};
-}
-
-/**
- * Model-to-view conversion helper applying attributes from {@link module:code-block/codeblock~CodeBlock Code Block}
- * feature model element.
- *
- * @returns {Function} Returns a conversion callback.
-*/
-export function modelToViewCodeBlockAttributeConverter() {
-	return dispatcher => {
-		dispatcher.on( 'attribute:htmlAttributes:codeBlock', ( evt, data, conversionApi ) => {
-			if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
-				return;
-			}
-
-			const viewPreElement = conversionApi.mapper.toViewElement( data.item ).parent;
-			setViewAttributes( conversionApi.writer, data.attributeNewValue, viewPreElement );
-		} );
-	};
-}
-
 /**
  * View-to-model conversion helper for object elements.
  *
- * Preserves object element content in `htmlContent` attribute. Also, all matching attributes
- * by the given matcher will be preserved on `htmlAttributes` attribute.
+ * Preserves object element content in `htmlContent` attribute. Also, all allowed attributes
+ * will be preserved on `htmlAttributes` attribute.
  *
  * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
  * @returns {Function} Returns a conversion callback.
@@ -143,18 +96,18 @@ export function createObjectView( viewName, modelElement, writer ) {
 /**
  * View-to-attribute conversion helper preserving inline element attributes on `$text`.
  *
- * All element attributes matched by the given matcher will be preserved as a value of
+ * All allowed element attributes will be preserved as a value of
  * {@link module:content-compatibility/dataschema~DataSchemaInlineElementDefinition~model definition model}
  * attribute.
  *
  * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
- * @param {module:engine/view/matcher~Matcher} matcher
+ * @param {module:content-compatibility/datafilter~DataFilter} dataFilter
  * @returns {Function} Returns a conversion callback.
 */
-export function viewToAttributeInlineConverter( { view: viewName, model: attributeKey }, matcher ) {
+export function viewToAttributeInlineConverter( { view: viewName, model: attributeKey }, dataFilter ) {
 	return dispatcher => {
 		dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
-			const viewAttributes = consumeViewAttributes( data.viewItem, conversionApi, matcher );
+			const viewAttributes = dataFilter.consumeAllowedAttributes( data.viewItem, conversionApi );
 
 			// Since we are converting to attribute we need a range on which we will set the attribute.
 			// If the range is not created yet, we will create it.
@@ -199,22 +152,22 @@ export function attributeToViewInlineConverter( { priority, view: viewName } ) {
 }
 
 /**
- * View-to-model conversion helper preserving attributes on block element matched by the given matcher.
+ * View-to-model conversion helper preserving allowed attributes on block element.
  *
  * All matched attributes will be preserved on `htmlAttributes` attribute.
  *
  * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
- * @param {module:engine/view/matcher~Matcher} matcher
+ * @param {module:content-compatibility/datafilter~DataFilter} dataFilter
  * @returns {Function} Returns a conversion callback.
 */
-export function viewToModelBlockAttributeConverter( { view: viewName }, matcher ) {
+export function viewToModelBlockAttributeConverter( { view: viewName }, dataFilter ) {
 	return dispatcher => {
 		dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
 			if ( !data.modelRange ) {
 				return;
 			}
 
-			const viewAttributes = consumeViewAttributes( data.viewItem, conversionApi, matcher );
+			const viewAttributes = dataFilter.consumeAllowedAttributes( data.viewItem, conversionApi );
 
 			if ( viewAttributes ) {
 				conversionApi.writer.setAttribute( 'htmlAttributes', viewAttributes, data.modelRange );
diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 9317d7990cd..248d2bab0d6 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -14,10 +14,7 @@ import { Matcher } from 'ckeditor5/src/engine';
 import { priorities, CKEditorError } from 'ckeditor5/src/utils';
 import { Widget } from 'ckeditor5/src/widget';
 import {
-	consumeViewAttributesConverter,
-
-	viewToModelCodeBlockAttributeConverter,
-	modelToViewCodeBlockAttributeConverter,
+	disallowedAttributesConverter,
 
 	viewToModelObjectConverter,
 	toObjectWidgetConverter,
@@ -112,6 +109,7 @@ export default class DataFilter extends Plugin {
 		this._dataInitialized = false;
 
 		this._registerElementsAfterInit();
+		this._registerElementHandlers();
 	}
 
 	/**
@@ -149,7 +147,7 @@ export default class DataFilter extends Plugin {
 			// If the data has not been initialized yet, _registerElementsAfterInit() method will take care of
 			// registering elements.
 			if ( this._dataInitialized ) {
-				this._registerElement( definition );
+				this._fireRegisterEvent( definition );
 			}
 		}
 
@@ -174,6 +172,34 @@ export default class DataFilter extends Plugin {
 		this._disallowedAttributes.add( config );
 	}
 
+	/**
+	 * Matches and consumes allowed view attributes.
+	 *
+	 * @param {module:engine/view/element~Element} viewElement
+	 * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
+	 * @returns {Object} [result]
+	 * @returns {Object} result.attributes Set with matched attribute names.
+	 * @returns {Object} result.styles Set with matched style names.
+	 * @returns {Array.<String>} result.classes Set with matched class names.
+	 */
+	consumeAllowedAttributes( viewElement, conversionApi ) {
+		return consumeAttributes( viewElement, conversionApi, this._allowedAttributes );
+	}
+
+	/**
+	 * Matches and consumes disallowed view attributes.
+	 *
+	 * @param {module:engine/view/element~Element} viewElement
+	 * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
+	 * @returns {Object} [result]
+	 * @returns {Object} result.attributes Set with matched attribute names.
+	 * @returns {Object} result.styles Set with matched style names.
+	 * @returns {Array.<String>} result.classes Set with matched class names.
+	 */
+	consumeDisallowedAttributes( viewElement, conversionApi ) {
+		return consumeAttributes( viewElement, conversionApi, this._disallowedAttributes );
+	}
+
 	/**
 	 * Registers elements allowed by {@link module:content-compatibility/datafilter~DataFilter#allowElement} method
 	 * once {@link module:core/editor~Editor#data editor's data controller} is initialized.
@@ -185,7 +211,7 @@ export default class DataFilter extends Plugin {
 			this._dataInitialized = true;
 
 			for ( const definition of this._allowedElements ) {
-				this._registerElement( definition );
+				this._fireRegisterEvent( definition );
 			}
 		}, {
 			// With high priority listener we are able to register elements right before
@@ -196,73 +222,48 @@ export default class DataFilter extends Plugin {
 	}
 
 	/**
-	 * Registers element and attribute converters for the given data schema definition.
+	 * Registers default element handlers.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 */
-	_registerElement( definition ) {
-		// Note that the order of element handlers is important,
-		// as the handler may interrupt handlers execution in case of returning
-		// anything else than `false` value.
-		const elementHandlers = [
-			this._handleCodeBlockElement,
-			this._handleObjectElement,
-			this._handleInlineElement,
-			this._handleBlockElement
-		];
-
-		for ( const elementHandler of elementHandlers ) {
-			if ( elementHandler.call( this, definition ) !== false ) {
-				return;
+	_registerElementHandlers() {
+		this.on( 'register', ( evt, definition ) => {
+			const schema = this.editor.model.schema;
+
+			// Object element should be only registered for new features.
+			if ( definition.isObject && !schema.isRegistered( definition.model ) ) {
+				this._registerObjectElement( definition );
+			} else if ( definition.isBlock ) {
+				this._registerBlockElement( definition );
+			} else if ( definition.isInline ) {
+				this._registerInlineElement( definition );
+			} else {
+				/**
+				 * The definition cannot be handled by the data filter.
+				 *
+				 * Make sure that the registered definition is correct.
+				 *
+				 * @error data-filter-invalid-definition
+				 */
+				throw new CKEditorError(
+					'data-filter-invalid-definition',
+					null,
+					definition
+				);
 			}
-		}
 
-		/**
-		 * The definition cannot be handled by the data filter.
-		 *
-		 * Make sure that the registered definition is correct.
-		 *
-		 * @error data-filter-invalid-definition
-		 */
-		throw new CKEditorError(
-			'data-filter-invalid-definition',
-			null,
-			definition
-		);
+			evt.stop();
+		}, { priority: 'lowest' } );
 	}
 
 	/**
-	 * Registers attribute converters for {@link module:code-block/codeblock~CodeBlock Code Block} feature.
+	 * Fires `register` event for the given element definition.
 	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
-	 * @returns {Boolean}
 	 */
-	_handleCodeBlockElement( definition ) {
-		const editor = this.editor;
-
-		// We should only handle codeBlock model if CodeBlock plugin is available.
-		// Otherwise, let #_handleBlockElement() do the job.
-		if ( !editor.plugins.has( 'CodeBlock' ) || definition.model !== 'codeBlock' ) {
-			return false;
-		}
-
-		const schema = editor.model.schema;
-		const conversion = editor.conversion;
-
-		// CodeBlock plugin is filtering out all attributes on `code` element. Let's add
-		// exception for `htmlCode` required for data filtration mechanism.
-		schema.on( 'checkAttribute', ( evt, [ context, attributeName ] ) => {
-			if ( attributeName === 'htmlCode' && context.endsWith( 'codeBlock $text' ) ) {
-				evt.return = true;
-				evt.stop();
-			}
-		}, { priority: priorities.get( 'high' ) + 1 } );
-
-		conversion.for( 'upcast' ).add( consumeViewAttributesConverter( definition, this._disallowedAttributes ) );
-		conversion.for( 'upcast' ).add( viewToModelCodeBlockAttributeConverter( this._allowedAttributes ) );
-		conversion.for( 'downcast' ).add( modelToViewCodeBlockAttributeConverter() );
+	_fireRegisterEvent( definition ) {
+		this.fire( definition.view ? `register:${ definition.view }` : 'register', definition );
 	}
 
 	/**
@@ -272,21 +273,12 @@ export default class DataFilter extends Plugin {
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
 	 * @returns {Boolean}
 	 */
-	_handleObjectElement( definition ) {
+	_registerObjectElement( definition ) {
 		const editor = this.editor;
 		const schema = editor.model.schema;
 		const conversion = editor.conversion;
 		const { view: viewName, model: modelName } = definition;
 
-		if ( !definition.isObject ) {
-			return false;
-		}
-
-		// If feature is already registered, #_handleBlockElement should take care of it.
-		if ( schema.isRegistered( modelName ) ) {
-			return false;
-		}
-
 		schema.register( modelName, definition.modelSchema );
 
 		if ( !viewName ) {
@@ -303,7 +295,7 @@ export default class DataFilter extends Plugin {
 			name: viewName
 		} );
 
-		conversion.for( 'upcast' ).add( consumeViewAttributesConverter( definition, this._disallowedAttributes ) );
+		conversion.for( 'upcast' ).add( disallowedAttributesConverter( definition, this ) );
 		conversion.for( 'upcast' ).elementToElement( {
 			view: viewName,
 			model: viewToModelObjectConverter( definition ),
@@ -311,7 +303,7 @@ export default class DataFilter extends Plugin {
 			// this listener is called before it. If not, some elements will be transformed into a paragraph.
 			converterPriority: priorities.get( 'low' ) + 1
 		} );
-		conversion.for( 'upcast' ).add( viewToModelBlockAttributeConverter( definition, this._allowedAttributes ) );
+		conversion.for( 'upcast' ).add( viewToModelBlockAttributeConverter( definition, this ) );
 
 		conversion.for( 'dataDowncast' ).elementToElement( {
 			model: modelName,
@@ -329,17 +321,11 @@ export default class DataFilter extends Plugin {
 	/**
 	 * Registers block element and attribute converters for the given data schema definition.
 	 *
-	 * If the element model schema is already registered, this method will do nothing.
-	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
 	 * @returns {Boolean}
 	 */
-	_handleBlockElement( definition ) {
-		if ( !definition.isBlock ) {
-			return false;
-		}
-
+	_registerBlockElement( definition ) {
 		const editor = this.editor;
 		const schema = editor.model.schema;
 		const conversion = editor.conversion;
@@ -374,8 +360,8 @@ export default class DataFilter extends Plugin {
 			allowAttributes: 'htmlAttributes'
 		} );
 
-		conversion.for( 'upcast' ).add( consumeViewAttributesConverter( definition, this._disallowedAttributes ) );
-		conversion.for( 'upcast' ).add( viewToModelBlockAttributeConverter( definition, this._allowedAttributes ) );
+		conversion.for( 'upcast' ).add( disallowedAttributesConverter( definition, this ) );
+		conversion.for( 'upcast' ).add( viewToModelBlockAttributeConverter( definition, this ) );
 		conversion.for( 'downcast' ).add( modelToViewBlockAttributeConverter( definition ) );
 	}
 
@@ -388,11 +374,7 @@ export default class DataFilter extends Plugin {
 	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
 	 * @returns {Boolean}
 	 */
-	_handleInlineElement( definition ) {
-		if ( !definition.isInline ) {
-			return false;
-		}
-
+	_registerInlineElement( definition ) {
 		const editor = this.editor;
 		const schema = editor.model.schema;
 		const conversion = editor.conversion;
@@ -406,12 +388,138 @@ export default class DataFilter extends Plugin {
 			schema.setAttributeProperties( attributeKey, definition.attributeProperties );
 		}
 
-		conversion.for( 'upcast' ).add( consumeViewAttributesConverter( definition, this._disallowedAttributes ) );
-		conversion.for( 'upcast' ).add( viewToAttributeInlineConverter( definition, this._allowedAttributes ) );
+		conversion.for( 'upcast' ).add( disallowedAttributesConverter( definition, this ) );
+		conversion.for( 'upcast' ).add( viewToAttributeInlineConverter( definition, this ) );
 
 		conversion.for( 'downcast' ).attributeToElement( {
 			model: attributeKey,
 			view: attributeToViewInlineConverter( definition )
 		} );
 	}
+
+	/**
+	 * Fired when {@link module:content-compatibility/datafilter~DataFilter} is registering element and attribute
+	 * converters for the {@link module:content-compatibility/dataschema~DataSchemaDefinition element definition}.
+	 *
+	 * The event also accepts {@link module:content-compatibility/dataschema~DataSchemaDefinition#view} value
+	 * as an event namespace, e.g. `register:span`.
+	 *
+	 * 		dataFilter.on( 'register', ( evt, definition ) => {
+	 * 			editor.schema.register( definition.model, definition.modelSchema );
+	 * 			editor.conversion.elementToElement( { model: definition.model, view: definition.view } );
+	 *
+	 * 			evt.stop();
+	 * 		} );
+	 *
+	 * 		dataFilter.on( 'register:span', ( evt, definition ) => {
+	 * 			editor.schema.extend( '$text', { allowAttributes: 'htmlSpan' } );
+	 *
+	 * 			editor.conversion.for( 'upcast' ).elementToAttribute( { view: 'span', model: 'htmlSpan' } );
+	 * 			editor.conversion.for( 'downcast' ).attributeToElement( { view: 'span', model: 'htmlSpan' } );
+	 *
+	 * 			evt.stop();
+	 * 		}, { priority: 'high' } )
+	 *
+	 * @event register
+	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 */
+}
+
+// Matches and consumes the given view attributes.
+//
+// @private
+// @param {module:engine/view/element~Element} viewElement
+// @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
+// @param {module:engine/view/matcher~Matcher Matcher} matcher
+// @returns {Object} [result]
+// @returns {Object} result.attributes Set with matched attribute names.
+// @returns {Object} result.styles Set with matched style names.
+// @returns {Array.<String>} result.classes Set with matched class names.
+function consumeAttributes( viewElement, conversionApi, matcher ) {
+	const matches = consumeAttributeMatches( viewElement, conversionApi, matcher );
+	const { attributes, styles, classes } = mergeMatchResults( matches );
+	const viewAttributes = {};
+
+	if ( attributes.size ) {
+		viewAttributes.attributes = iterableToObject( attributes, key => viewElement.getAttribute( key ) );
+	}
+
+	if ( styles.size ) {
+		viewAttributes.styles = iterableToObject( styles, key => viewElement.getStyle( key ) );
+	}
+
+	if ( classes.size ) {
+		viewAttributes.classes = Array.from( classes );
+	}
+
+	if ( !Object.keys( viewAttributes ).length ) {
+		return null;
+	}
+
+	return viewAttributes;
+}
+
+// Consumes matched attributes.
+//
+// @private
+// @param {module:engine/view/element~Element} viewElement
+// @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
+// @param {module:engine/view/matcher~Matcher Matcher} matcher
+// @returns {Array.<Object>} Array with match information about found attributes.
+function consumeAttributeMatches( viewElement, { consumable }, matcher ) {
+	const matches = matcher.matchAll( viewElement ) || [];
+	const consumedMatches = [];
+
+	for ( const match of matches ) {
+		// We only want to consume attributes, so element can be still processed by other converters.
+		delete match.match.name;
+
+		if ( consumable.consume( viewElement, match.match ) ) {
+			consumedMatches.push( match );
+		}
+	}
+
+	return consumedMatches;
+}
+
+// Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
+//
+// @private
+// @param {Array.<Object>} matches
+// @returns {Object} result
+// @returns {Set.<Object>} result.attributes Set with matched attribute names.
+// @returns {Set.<Object>} result.styles Set with matched style names.
+// @returns {Set.<String>} result.classes Set with matched class names.
+function mergeMatchResults( matches ) {
+	const matchResult = {
+		attributes: new Set(),
+		classes: new Set(),
+		styles: new Set()
+	};
+
+	for ( const match of matches ) {
+		for ( const key in matchResult ) {
+			const values = match.match[ key ] || [];
+
+			values.forEach( value => matchResult[ key ].add( value ) );
+		}
+	}
+
+	return matchResult;
+}
+
+// Converts the given iterable object into an object.
+//
+// @private
+// @param {Iterable.<String>} iterable
+// @param {Function} getValue Should result with value for the given object key.
+// @returns {Object}
+function iterableToObject( iterable, getValue ) {
+	const attributesObject = {};
+
+	for ( const prop of iterable ) {
+		attributesObject[ prop ] = getValue( prop );
+	}
+
+	return attributesObject;
 }
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-content-compatibility/src/dataschema.js
index 94641027b67..2eb74f3cac4 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/src/dataschema.js
@@ -140,6 +140,14 @@ export default class DataSchema extends Plugin {
 			view: 'li'
 		} );
 
+		this.registerBlockElement( {
+			model: 'htmlPre',
+			view: 'pre',
+			modelSchema: {
+				inheritAllFrom: '$block'
+			}
+		} );
+
 		this.registerBlockElement( {
 			view: 'article',
 			model: 'htmlArticle',
diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
index ce614f769e0..9bf7e0c6ced 100644
--- a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
@@ -10,6 +10,7 @@
 import { Plugin } from 'ckeditor5/src/core';
 import DataFilter from './datafilter';
 import DataSchema from './dataschema';
+import CodeBlockHtmlSupport from './integrations/codeblock';
 
 /**
  * The General HTML Support feature.
@@ -31,6 +32,10 @@ export default class GeneralHtmlSupport extends Plugin {
 	 * @inheritDoc
 	 */
 	static get requires() {
-		return [ DataFilter, DataSchema ];
+		return [
+			DataFilter,
+			DataSchema,
+			CodeBlockHtmlSupport
+		];
 	}
 }
diff --git a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js b/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
new file mode 100644
index 00000000000..f8866d25ee1
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
@@ -0,0 +1,103 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module content-compatibility/integrations/codeblock
+ */
+
+import { Plugin } from 'ckeditor5/src/core';
+import { disallowedAttributesConverter } from '../converters';
+import { setViewAttributes } from '../conversionutils.js';
+
+import DataFilter from '../datafilter';
+
+export default class CodeBlockHtmlSupport extends Plugin {
+	static get requires() {
+		return [ DataFilter ];
+	}
+
+	init() {
+		if ( !this.editor.plugins.has( 'CodeBlock' ) ) {
+			return;
+		}
+
+		const dataFilter = this.editor.plugins.get( DataFilter );
+
+		dataFilter.on( 'register:pre', ( evt, definition ) => {
+			if ( definition.model !== 'codeBlock' ) {
+				return;
+			}
+
+			const editor = this.editor;
+			const conversion = editor.conversion;
+
+			conversion.for( 'upcast' ).add( disallowedAttributesConverter( definition, dataFilter ) );
+			conversion.for( 'upcast' ).add( viewToModelCodeBlockAttributeConverter( dataFilter ) );
+			conversion.for( 'downcast' ).add( modelToViewCodeBlockAttributeConverter() );
+
+			evt.stop();
+		} );
+	}
+}
+
+// View-to-model conversion helper preserving allowed attributes on {@link module:code-block/codeblock~CodeBlock Code Block}
+// feature model element.
+//
+// Attributes are preserved as a value of `htmlAttributes` model attribute.
+//
+// @param {module:content-compatibility/datafilter~DataFilter} dataFilter
+// @returns {Function} Returns a conversion callback.
+function viewToModelCodeBlockAttributeConverter( dataFilter ) {
+	return dispatcher => {
+		dispatcher.on( 'element:code', ( evt, data, conversionApi ) => {
+			const viewCodeElement = data.viewItem;
+			const viewPreElement = viewCodeElement.parent;
+
+			if ( !viewPreElement || !viewPreElement.is( 'element', 'pre' ) ) {
+				return;
+			}
+
+			preserveElementAttributes( viewPreElement, 'htmlAttributes' );
+			preserveElementAttributes( viewCodeElement, 'htmlContentAttributes' );
+
+			function preserveElementAttributes( viewElement, attributeName ) {
+				const viewAttributes = dataFilter.consumeAllowedAttributes( viewElement, conversionApi );
+
+				if ( viewAttributes ) {
+					conversionApi.writer.setAttribute( attributeName, viewAttributes, data.modelRange );
+				}
+			}
+		}, { priority: 'low' } );
+	};
+}
+
+// Model-to-view conversion helper applying attributes from {@link module:code-block/codeblock~CodeBlock Code Block}
+// feature model element.
+//
+// @returns {Function} Returns a conversion callback.
+function modelToViewCodeBlockAttributeConverter() {
+	return dispatcher => {
+		dispatcher.on( 'attribute:htmlAttributes:codeBlock', ( evt, data, conversionApi ) => {
+			if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
+				return;
+			}
+
+			const viewCodeElement = conversionApi.mapper.toViewElement( data.item );
+			const viewPreElement = viewCodeElement.parent;
+
+			setViewAttributes( conversionApi.writer, data.attributeNewValue, viewPreElement );
+		} );
+
+		dispatcher.on( 'attribute:htmlContentAttributes:codeBlock', ( evt, data, conversionApi ) => {
+			if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
+				return;
+			}
+
+			const viewCodeElement = conversionApi.mapper.toViewElement( data.item );
+
+			setViewAttributes( conversionApi.writer, data.attributeNewValue, viewCodeElement );
+		} );
+	};
+}
diff --git a/packages/ckeditor5-content-compatibility/tests/_utils/utils.js b/packages/ckeditor5-content-compatibility/tests/_utils/utils.js
new file mode 100644
index 00000000000..3c7ae979f86
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/_utils/utils.js
@@ -0,0 +1,79 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
+
+/**
+ * Writes the content of a model {@link module:engine/model/document~Document document} to an HTML-like string with
+ * indexed HTML Support attributes.
+ *
+ *		getModelDataWithAttributes( editor.model );
+ *		// -> 	{
+ *		//			data: '<paragraph htmlAttributes1="(1)" htmlAttributes2="(2)"><$text htmlSpan="(2)">foobar!</$text></paragraph>',
+ *		//			attributes: {
+ *		//				1: { classes: [ 'foo', 'bar' ] },
+ *		//				2: { attributes: { 'data-foo': 'foo' } }
+ *		//			}
+ *		//		}
+ *
+ * This function will index every attribute starting with `html*` keyword and return it's value in `result.attributes` property.
+ *
+ * @param {module:engine/model/model~Model} model
+ * @param {Object} [options]
+ * @param {Boolean} [options.withoutSelection=false] Whether to write the selection. When set to `true`, the selection will
+ * not be included in the returned string.
+ * @param {String} [options.rootName='main'] The name of the root from which the data should be stringified. If not provided,
+ * the default `main` name will be used.
+ * @param {Boolean} [options.convertMarkers=false] Whether to include markers in the returned string.
+ * @param {Array} [options.excludeAttributes] Attributes to exclude from the result.
+ * @returns {Object} result
+ * @returns {String} result.data The stringified data.
+ * @returns {Object} result.attributes Indexed data attributes.
+ */
+export function getModelDataWithAttributes( model, options ) {
+	// Simplify GHS attributes as they are not very readable at this point due to object structure.
+	let counter = 1;
+	const data = getModelData( model, options ).replace( /(html.*?)="{.*?}"/g, ( fullMatch, attributeName ) => {
+		return `${ attributeName }="(${ counter++ })"`;
+	} );
+
+	const range = model.createRangeIn( model.document.getRoot() );
+	const excludeAttributes = options.excludeAttributes || [];
+
+	let attributes = [];
+	for ( const item of range.getItems() ) {
+		for ( const [ key, value ] of sortAttributes( item.getAttributes() ) ) {
+			if ( key.startsWith( 'html' ) && !excludeAttributes.includes( key ) ) {
+				attributes.push( value );
+			}
+		}
+	}
+
+	attributes = attributes.reduce( ( prev, cur, index ) => {
+		prev[ index + 1 ] = cur;
+		return prev;
+	}, {} );
+
+	return { data, attributes };
+}
+
+function sortAttributes( attributes ) {
+	attributes = Array.from( attributes );
+
+	return attributes.sort( ( attr1, attr2 ) => {
+		const key1 = attr1[ 0 ];
+		const key2 = attr2[ 0 ];
+
+		if ( key1 > key2 ) {
+			return 1;
+		}
+
+		if ( key1 < key2 ) {
+			return -1;
+		}
+
+		return 0;
+	} );
+}
diff --git a/packages/ckeditor5-content-compatibility/tests/codeblock.js b/packages/ckeditor5-content-compatibility/tests/codeblock.js
new file mode 100644
index 00000000000..cbed5810529
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/codeblock.js
@@ -0,0 +1,219 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+import ClassicTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/classictesteditor';
+import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
+import CodeBlock from '@ckeditor/ckeditor5-code-block/src/codeblock';
+import GeneralHtmlSupport from '../src/generalhtmlsupport';
+import { getModelDataWithAttributes } from './_utils/utils';
+
+/* global document */
+
+describe( 'CodeBlockHtmlSupport', () => {
+	let editor, model, editorElement, dataFilter;
+
+	beforeEach( () => {
+		editorElement = document.createElement( 'div' );
+		document.body.appendChild( editorElement );
+
+		return ClassicTestEditor
+			.create( editorElement, {
+				plugins: [ CodeBlock, Paragraph, GeneralHtmlSupport ]
+			} )
+			.then( newEditor => {
+				editor = newEditor;
+				model = editor.model;
+
+				dataFilter = editor.plugins.get( 'DataFilter' );
+			} );
+	} );
+
+	afterEach( () => {
+		editorElement.remove();
+
+		return editor.destroy();
+	} );
+
+	it( 'should allow attributes', () => {
+		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
+
+		editor.setData( '<pre data-foo="foo"><code data-foo="foo">foobar</code></pre>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<codeBlock htmlAttributes="(1)" htmlContentAttributes="(2)" language="plaintext">foobar</codeBlock>',
+			attributes: {
+				1: {
+					attributes: {
+						'data-foo': 'foo'
+					}
+				},
+				2: {
+					attributes: {
+						'data-foo': 'foo'
+					}
+				}
+			}
+		} );
+
+		expect( editor.getData() ).to.equal( '<pre data-foo="foo">' +
+			'<code class="language-plaintext" data-foo="foo">foobar</code>' +
+			'</pre>' );
+	} );
+
+	it( 'should allow attributes (classes)', () => {
+		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
+
+		editor.setData( '<pre class="foo"><code class="foo">foobar</code></pre>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<codeBlock htmlAttributes="(1)" htmlContentAttributes="(2)" language="plaintext">foobar</codeBlock>',
+			attributes: {
+				1: {
+					classes: [ 'foo' ]
+				},
+				2: {
+					classes: [ 'foo' ]
+				}
+			}
+		} );
+
+		expect( editor.getData() ).to.equal( '<pre class="foo">' +
+			'<code class="language-plaintext foo">foobar</code>' +
+			'</pre>' );
+	} );
+
+	it( 'should allow attributes (styles)', () => {
+		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowAttributes( { name: 'pre', styles: { background: 'blue' } } );
+		dataFilter.allowAttributes( { name: 'code', styles: { color: 'red' } } );
+
+		editor.setData( '<pre style="background:blue;"><code style="color:red;">foobar</code></pre>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<codeBlock htmlAttributes="(1)" htmlContentAttributes="(2)" language="plaintext">foobar</codeBlock>',
+			attributes: {
+				1: {
+					styles: {
+						background: 'blue'
+					}
+				},
+				2: {
+					styles: {
+						color: 'red'
+					}
+				}
+			}
+		} );
+
+		expect( editor.getData() ).to.equal( '<pre style="background:blue;">' +
+			'<code class="language-plaintext" style="color:red;">foobar</code>' +
+			'</pre>' );
+	} );
+
+	it( 'should disallow attributes', () => {
+		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
+		dataFilter.disallowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
+
+		editor.setData( '<pre data-foo="foo"><code data-foo="foo">foobar</code></pre>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<codeBlock language="plaintext">foobar</codeBlock>',
+			attributes: {}
+		} );
+
+		expect( editor.getData() ).to.equal( '<pre><code class="language-plaintext">foobar</code></pre>' );
+	} );
+
+	it( 'should disallow attributes (classes)', () => {
+		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
+		dataFilter.disallowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
+
+		editor.setData( '<pre data-foo="foo"><code data-foo="foo">foobar</code></pre>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<codeBlock language="plaintext">foobar</codeBlock>',
+			attributes: {}
+		} );
+
+		expect( editor.getData() ).to.equal( '<pre><code class="language-plaintext">foobar</code></pre>' );
+	} );
+
+	it( 'should disallow attributes (styles)', () => {
+		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+
+		dataFilter.allowAttributes( { name: 'pre', styles: { background: 'blue' } } );
+		dataFilter.allowAttributes( { name: 'code', styles: { color: 'red' } } );
+
+		dataFilter.disallowAttributes( { name: 'pre', styles: { background: 'blue' } } );
+		dataFilter.disallowAttributes( { name: 'code', styles: { color: 'red' } } );
+
+		editor.setData( '<pre style="background:blue;"><code style="color:red;">foobar</code></pre>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<codeBlock language="plaintext">foobar</codeBlock>',
+			attributes: {}
+		} );
+
+		expect( editor.getData() ).to.equal( '<pre><code class="language-plaintext">foobar</code></pre>' );
+	} );
+
+	it( 'should allow attributes on code element existing alone', () => {
+		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowAttributes( { name: 'code', attributes: { 'data-foo': /[\s\S]+/ } } );
+
+		editor.setData( '<p><code data-foo="foo">foobar</code></p>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<paragraph><$text htmlCode="(1)">foobar</$text></paragraph>',
+			attributes: {
+				1: {
+					attributes: {
+						'data-foo': 'foo'
+					}
+				}
+			}
+		} );
+
+		expect( editor.getData() ).to.equal( '<p><code data-foo="foo">foobar</code></p>' );
+	} );
+
+	it( 'should not consume attributes already consumed (downcast)', () => {
+		[ 'htmlAttributes', 'htmlContentAttributes' ].forEach( attributeName => {
+			editor.conversion.for( 'downcast' ).add( dispatcher => {
+				dispatcher.on( `attribute:${ attributeName }:codeBlock`, ( evt, data, conversionApi ) => {
+					conversionApi.consumable.consume( data.item, evt.name );
+				}, { priority: 'high' } );
+			} );
+		} );
+
+		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': true } } );
+
+		editor.setData( '<pre data-foo><code data-foo>foobar</code></section>' );
+
+		expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			data: '<codeBlock htmlAttributes="(1)" htmlContentAttributes="(2)" language="plaintext">foobar</codeBlock>',
+			// At this point, attribute should still be in the model, as we are testing downcast conversion.
+			attributes: {
+				1: {
+					attributes: {
+						'data-foo': ''
+					}
+				},
+				2: {
+					attributes: {
+						'data-foo': ''
+					}
+				}
+			}
+		} );
+
+		expect( editor.getData() ).to.equal( '<pre><code class="language-plaintext">foobar</code></pre>' );
+	} );
+} );
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 0619cf10eda..d5b1f38f521 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -8,11 +8,11 @@ import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
 import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
 import LinkEditing from '@ckeditor/ckeditor5-link/src/linkediting';
 import FontColorEditing from '@ckeditor/ckeditor5-font/src/fontcolor/fontcolorediting';
-import CodeBlock from '@ckeditor/ckeditor5-code-block/src/codeblock';
 import DataFilter from '../src/datafilter';
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import { expectToThrowCKEditorError } from '@ckeditor/ckeditor5-utils/tests/_utils/utils';
 import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
+import { getModelDataWithAttributes } from './_utils/utils';
 
 import GeneralHtmlSupport from '../src/generalhtmlsupport';
 
@@ -29,7 +29,7 @@ describe( 'DataFilter', () => {
 
 		return ClassicTestEditor
 			.create( editorElement, {
-				plugins: [ Paragraph, FontColorEditing, LinkEditing, CodeBlock, GeneralHtmlSupport ]
+				plugins: [ Paragraph, FontColorEditing, LinkEditing, GeneralHtmlSupport ]
 			} )
 			.then( newEditor => {
 				editor = newEditor;
@@ -136,188 +136,6 @@ describe( 'DataFilter', () => {
 		}
 	} );
 
-	describe( 'codeBlock', () => {
-		it( 'should allow attributes', () => {
-			dataFilter.allowElement( { name: /^(pre|code)$/ } );
-			dataFilter.allowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
-
-			editor.setData( '<pre data-foo="foo"><code data-foo="foo">foobar</code></pre>' );
-
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<codeBlock htmlAttributes="(1)" language="plaintext"><$text htmlCode="(2)">foobar</$text></codeBlock>',
-				attributes: {
-					1: {
-						attributes: {
-							'data-foo': 'foo'
-						}
-					},
-					2: {
-						attributes: {
-							'data-foo': 'foo'
-						}
-					}
-				}
-			} );
-
-			expect( editor.getData() ).to.equal( '<pre data-foo="foo">' +
-				'<code class="language-plaintext"><code data-foo="foo">foobar</code></code>' +
-				'</pre>' );
-		} );
-
-		it( 'should allow attributes (classes)', () => {
-			dataFilter.allowElement( { name: /^(pre|code)$/ } );
-			dataFilter.allowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
-
-			editor.setData( '<pre class="foo"><code class="foo">foobar</code></pre>' );
-
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<codeBlock htmlAttributes="(1)" language="plaintext"><$text htmlCode="(2)">foobar</$text></codeBlock>',
-				attributes: {
-					1: {
-						classes: [ 'foo' ]
-					},
-					2: {
-						classes: [ 'foo' ]
-					}
-				}
-			} );
-
-			expect( editor.getData() ).to.equal( '<pre class="foo">' +
-				'<code class="language-plaintext"><code class="foo">foobar</code></code>' +
-				'</pre>' );
-		} );
-
-		it( 'should allow attributes (styles)', () => {
-			dataFilter.allowElement( { name: /^(pre|code)$/ } );
-			dataFilter.allowAttributes( { name: 'pre', styles: { background: 'blue' } } );
-			dataFilter.allowAttributes( { name: 'code', styles: { color: 'red' } } );
-
-			editor.setData( '<pre style="background:blue;"><code style="color:red;">foobar</code></pre>' );
-
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<codeBlock htmlAttributes="(1)" language="plaintext"><$text htmlCode="(2)">foobar</$text></codeBlock>',
-				attributes: {
-					1: {
-						styles: {
-							background: 'blue'
-						}
-					},
-					2: {
-						styles: {
-							color: 'red'
-						}
-					}
-				}
-			} );
-
-			expect( editor.getData() ).to.equal( '<pre style="background:blue;">' +
-				'<code class="language-plaintext"><code style="color:red;">foobar</code></code>' +
-				'</pre>' );
-		} );
-
-		it( 'should disallow attributes', () => {
-			dataFilter.allowElement( { name: /^(pre|code)$/ } );
-			dataFilter.allowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
-			dataFilter.disallowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
-
-			editor.setData( '<pre data-foo="foo"><code data-foo="foo">foobar</code></pre>' );
-
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<codeBlock language="plaintext"><$text htmlCode="(1)">foobar</$text></codeBlock>',
-				attributes: {
-					1: {}
-				}
-			} );
-
-			expect( editor.getData() ).to.equal( '<pre><code class="language-plaintext"><code>foobar</code></code></pre>' );
-		} );
-
-		it( 'should disallow attributes (classes)', () => {
-			dataFilter.allowElement( { name: /^(pre|code)$/ } );
-			dataFilter.allowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
-			dataFilter.disallowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
-
-			editor.setData( '<pre class="foo"><code class="foo">foobar</code></pre>' );
-
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<codeBlock language="plaintext"><$text htmlCode="(1)">foobar</$text></codeBlock>',
-				attributes: {
-					1: {}
-				}
-			} );
-
-			expect( editor.getData() ).to.equal( '<pre><code class="language-plaintext"><code>foobar</code></code></pre>' );
-		} );
-
-		it( 'should allow attributes (styles)', () => {
-			dataFilter.allowElement( { name: /^(pre|code)$/ } );
-
-			dataFilter.allowAttributes( { name: 'pre', styles: { background: 'blue' } } );
-			dataFilter.allowAttributes( { name: 'code', styles: { color: 'red' } } );
-
-			dataFilter.disallowAttributes( { name: 'pre', styles: { background: 'blue' } } );
-			dataFilter.disallowAttributes( { name: 'code', styles: { color: 'red' } } );
-
-			editor.setData( '<pre style="background:blue;"><code style="color:red;">foobar</code></pre>' );
-
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<codeBlock language="plaintext"><$text htmlCode="(1)">foobar</$text></codeBlock>',
-				attributes: {
-					1: {}
-				}
-			} );
-
-			expect( editor.getData() ).to.equal( '<pre><code class="language-plaintext"><code>foobar</code></code></pre>' );
-		} );
-
-		it( 'should allow attributes on code element existing alone', () => {
-			dataFilter.allowElement( { name: /^(pre|code)$/ } );
-			dataFilter.allowAttributes( { name: 'code', attributes: { 'data-foo': /[\s\S]+/ } } );
-
-			editor.setData( '<p><code data-foo="foo">foobar</code></p>' );
-
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph><$text htmlCode="(1)">foobar</$text></paragraph>',
-				attributes: {
-					1: {
-						attributes: {
-							'data-foo': 'foo'
-						}
-					}
-				}
-			} );
-
-			expect( editor.getData() ).to.equal( '<p><code data-foo="foo">foobar</code></p>' );
-		} );
-
-		it( 'should not consume attribute already consumed (downcast)', () => {
-			editor.conversion.for( 'downcast' ).add( dispatcher => {
-				dispatcher.on( 'attribute:htmlAttributes:codeBlock', ( evt, data, conversionApi ) => {
-					conversionApi.consumable.consume( data.item, evt.name );
-				}, { priority: 'high' } );
-			} );
-
-			dataFilter.allowElement( { name: 'pre' } );
-			dataFilter.allowAttributes( { name: 'pre', attributes: { 'data-foo': true } } );
-
-			editor.setData( '<pre data-foo><code>foobar</code></section>' );
-
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<codeBlock htmlAttributes="(1)" language="plaintext">foobar</codeBlock>',
-				// At this point, attribute should still be in the model, as we are testing downcast conversion.
-				attributes: {
-					1: {
-						attributes: {
-							'data-foo': ''
-						}
-					}
-				}
-			} );
-
-			expect( editor.getData() ).to.equal( '<pre><code class="language-plaintext">foobar</code></pre>' );
-		} );
-	} );
-
 	describe( 'object', () => {
 		it( 'should allow element', () => {
 			dataFilter.allowElement( { name: 'input' } );
@@ -380,7 +198,7 @@ describe( 'DataFilter', () => {
 
 			editor.setData( '<p><input type="text"></p>' );
 
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			expect( getObjectModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph><htmlInput htmlAttributes="(1)" htmlContent=""></htmlInput></paragraph>',
 				attributes: {
 					1: {
@@ -400,7 +218,7 @@ describe( 'DataFilter', () => {
 
 			editor.setData( '<p><input style="color:red;"></p>' );
 
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			expect( getObjectModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph><htmlInput htmlAttributes="(1)" htmlContent=""></htmlInput></paragraph>',
 				attributes: {
 					1: {
@@ -420,7 +238,7 @@ describe( 'DataFilter', () => {
 
 			editor.setData( '<p><input class="foobar"></p>' );
 
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			expect( getObjectModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph><htmlInput htmlAttributes="(1)" htmlContent=""></htmlInput></paragraph>',
 				attributes: {
 					1: {
@@ -439,7 +257,7 @@ describe( 'DataFilter', () => {
 
 			editor.setData( '<p><input type="text"><input type="hidden"></p>' );
 
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			expect( getObjectModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
 				'<htmlInput htmlAttributes="(1)" htmlContent=""></htmlInput>' +
 				'<htmlInput htmlContent=""></htmlInput>' +
@@ -463,7 +281,7 @@ describe( 'DataFilter', () => {
 
 			editor.setData( '<p><input style="color:blue;"><input style="color:red;"</p>' );
 
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			expect( getObjectModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
 				'<htmlInput htmlAttributes="(1)" htmlContent=""></htmlInput>' +
 				'<htmlInput htmlContent=""></htmlInput>' +
@@ -487,7 +305,7 @@ describe( 'DataFilter', () => {
 
 			editor.setData( '<p><input class="foo bar"><input class="bar"></p>' );
 
-			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+			expect( getObjectModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
 				'<htmlInput htmlContent=""></htmlInput>' +
 				'<htmlInput htmlContent=""></htmlInput>' +
@@ -497,6 +315,11 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal( '<p><input><input></p>' );
 		} );
+
+		function getObjectModelDataWithAttributes( model, options ) {
+			options.excludeAttributes = [ 'htmlContent' ];
+			return getModelDataWithAttributes( model, options );
+		}
 	} );
 
 	describe( 'block', () => {
@@ -1452,49 +1275,4 @@ describe( 'DataFilter', () => {
 			dataFilter.allowElement( { name: 'xyz' } );
 		}, /data-filter-invalid-definition/, null, definition );
 	} );
-
-	function getModelDataWithAttributes( model, options ) {
-		// Simplify GHS attributes as they are not very readable at this point due to object structure.
-		let counter = 1;
-		const data = getModelData( model, options ).replace( /(html.*?)="{.*?}"/g, ( fullMatch, attributeName ) => {
-			return `${ attributeName }="(${ counter++ })"`;
-		} );
-
-		const range = model.createRangeIn( model.document.getRoot() );
-
-		let attributes = [];
-		for ( const item of range.getItems() ) {
-			for ( const [ key, value ] of sortAttributes( item.getAttributes() ) ) {
-				if ( key.startsWith( 'html' ) && key !== 'htmlContent' ) {
-					attributes.push( value );
-				}
-			}
-		}
-
-		attributes = attributes.reduce( ( prev, cur, index ) => {
-			prev[ index + 1 ] = cur;
-			return prev;
-		}, {} );
-
-		return { data, attributes };
-	}
-
-	function sortAttributes( attributes ) {
-		attributes = Array.from( attributes );
-
-		return attributes.sort( ( attr1, attr2 ) => {
-			const key1 = attr1[ 0 ];
-			const key2 = attr2[ 0 ];
-
-			if ( key1 > key2 ) {
-				return 1;
-			}
-
-			if ( key1 < key2 ) {
-				return -1;
-			}
-
-			return 0;
-		} );
-	}
 } );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/codeblock.html b/packages/ckeditor5-content-compatibility/tests/manual/codeblock.html
index 8fec2981af6..6c928e2cb9c 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/codeblock.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/codeblock.html
@@ -4,8 +4,8 @@
 </head>
 
 <div id="editor">
-	<p>Put some text in the :</p>
-	<pre style="background:blue;" class="foo"><code class=\"language-html\" data-foo="foo">Hello world!</code></pre>
-	<p>Then set the font color:</p>
-	<pre style="background:yellow;"><code class=\"language-css\" style="color:red;" data-foo="bar">body { color: red }</code></pre>
+	<pre style="background:violet;" class="foo"><code class=\"language-html\" data-foo="foo">Code Block with custom properties!</code></pre>
+	<pre style="background:yellow;"><code class=\"language-css\" style="color:red;" data-foo="bar">Code Block with disallowed background!</code></pre>
+	<pre style="background:grey;"><strong>Apes are strong!</strong><br><i>Let's check if inline elements are strong also!</i></pre>
+	<code style="color:blue; background:yellow;">Blue code with disallowed background!</code>
 </div>

From 909f12c2f15562f1397a971763bde6dabb36d9c7 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Wed, 26 May 2021 13:06:49 +0200
Subject: [PATCH 144/217] Docs.

---
 .../src/integrations/codeblock.js                               | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js b/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
index f8866d25ee1..76af492637e 100644
--- a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
+++ b/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
@@ -47,6 +47,7 @@ export default class CodeBlockHtmlSupport extends Plugin {
 //
 // Attributes are preserved as a value of `htmlAttributes` model attribute.
 //
+// @private
 // @param {module:content-compatibility/datafilter~DataFilter} dataFilter
 // @returns {Function} Returns a conversion callback.
 function viewToModelCodeBlockAttributeConverter( dataFilter ) {
@@ -76,6 +77,7 @@ function viewToModelCodeBlockAttributeConverter( dataFilter ) {
 // Model-to-view conversion helper applying attributes from {@link module:code-block/codeblock~CodeBlock Code Block}
 // feature model element.
 //
+// @private
 // @returns {Function} Returns a conversion callback.
 function modelToViewCodeBlockAttributeConverter() {
 	return dispatcher => {

From 854e9182732d3363add8a958f454f868a4799594 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 1 Jun 2021 10:36:31 +0200
Subject: [PATCH 145/217] Docs, small fixes.

---
 .../ckeditor5-content-compatibility/src/datafilter.js    | 9 +++------
 .../src/integrations/codeblock.js                        | 2 +-
 .../ckeditor5-content-compatibility/theme/datafilter.css | 2 +-
 3 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 248d2bab0d6..2871b491400 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -271,7 +271,6 @@ export default class DataFilter extends Plugin {
 	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
-	 * @returns {Boolean}
 	 */
 	_registerObjectElement( definition ) {
 		const editor = this.editor;
@@ -323,7 +322,6 @@ export default class DataFilter extends Plugin {
 	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
-	 * @returns {Boolean}
 	 */
 	_registerBlockElement( definition ) {
 		const editor = this.editor;
@@ -372,7 +370,6 @@ export default class DataFilter extends Plugin {
 	 *
 	 * @private
 	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
-	 * @returns {Boolean}
 	 */
 	_registerInlineElement( definition ) {
 		const editor = this.editor;
@@ -432,9 +429,9 @@ export default class DataFilter extends Plugin {
 // @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
 // @param {module:engine/view/matcher~Matcher Matcher} matcher
 // @returns {Object} [result]
-// @returns {Object} result.attributes Set with matched attribute names.
-// @returns {Object} result.styles Set with matched style names.
-// @returns {Array.<String>} result.classes Set with matched class names.
+// @returns {Object} result.attributes
+// @returns {Object} result.styles
+// @returns {Array.<String>} result.classes
 function consumeAttributes( viewElement, conversionApi, matcher ) {
 	const matches = consumeAttributeMatches( viewElement, conversionApi, matcher );
 	const { attributes, styles, classes } = mergeMatchResults( matches );
diff --git a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js b/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
index 76af492637e..f7e846101c5 100644
--- a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
+++ b/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
@@ -19,7 +19,7 @@ export default class CodeBlockHtmlSupport extends Plugin {
 	}
 
 	init() {
-		if ( !this.editor.plugins.has( 'CodeBlock' ) ) {
+		if ( !this.editor.plugins.has( 'CodeBlockEditing' ) ) {
 			return;
 		}
 
diff --git a/packages/ckeditor5-content-compatibility/theme/datafilter.css b/packages/ckeditor5-content-compatibility/theme/datafilter.css
index 079295f49cc..d84a730fd90 100644
--- a/packages/ckeditor5-content-compatibility/theme/datafilter.css
+++ b/packages/ckeditor5-content-compatibility/theme/datafilter.css
@@ -36,7 +36,7 @@
 	}
 
 	& .html-object-embed__content {
-		/* Disable user interation with embed content */
+		/* Disable user interaction with embed content */
 		pointer-events: none;
 	}
 }

From 81af835ca0f47691c089e8ea8b5677c54a558a53 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 1 Jun 2021 10:40:27 +0200
Subject: [PATCH 146/217] Added codeBlock attributes.

---
 .../src/integrations/codeblock.js                           | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js b/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
index f7e846101c5..1e1a40af21a 100644
--- a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
+++ b/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
@@ -31,8 +31,14 @@ export default class CodeBlockHtmlSupport extends Plugin {
 			}
 
 			const editor = this.editor;
+			const schema = editor.model.schema;
 			const conversion = editor.conversion;
 
+			// Extend codeBlock to allow attributes required by attribute filtration.
+			schema.extend( 'codeBlock', {
+				allowAttributes: [ 'htmlAttributes', 'htmlContentAttributes' ]
+			} );
+
 			conversion.for( 'upcast' ).add( disallowedAttributesConverter( definition, dataFilter ) );
 			conversion.for( 'upcast' ).add( viewToModelCodeBlockAttributeConverter( dataFilter ) );
 			conversion.for( 'downcast' ).add( modelToViewCodeBlockAttributeConverter() );

From 818f9365b5048fc5c006b13606907429069f4bde Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 1 Jun 2021 10:44:29 +0200
Subject: [PATCH 147/217] Removed invalid docs.

---
 packages/ckeditor5-content-compatibility/src/converters.js | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/converters.js b/packages/ckeditor5-content-compatibility/src/converters.js
index a3a847e0b7a..85dd0b93055 100644
--- a/packages/ckeditor5-content-compatibility/src/converters.js
+++ b/packages/ckeditor5-content-compatibility/src/converters.js
@@ -31,8 +31,7 @@ export function disallowedAttributesConverter( { view: viewName }, dataFilter )
 /**
  * View-to-model conversion helper for object elements.
  *
- * Preserves object element content in `htmlContent` attribute. Also, all allowed attributes
- * will be preserved on `htmlAttributes` attribute.
+ * Preserves object element content in `htmlContent` attribute.
  *
  * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
  * @returns {Function} Returns a conversion callback.
@@ -80,8 +79,6 @@ export function toObjectWidgetConverter( editor, { view: viewName, isInline } )
 /**
 * Creates object view element from the given model element.
 *
-* Applies attributes preserved in `htmlAttributes` model attribute.
-*
 * @param {String} viewName
 * @param {module:engine/model/element~Element} modelElement
 * @param {module:engine/view/downcastwriter~DowncastWriter} writer

From 2affa412d255d25249ba3d5d112a184642aa5ca3 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 1 Jun 2021 10:48:12 +0200
Subject: [PATCH 148/217] Improved docs.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 2871b491400..1a6517624a0 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -231,6 +231,8 @@ export default class DataFilter extends Plugin {
 			const schema = this.editor.model.schema;
 
 			// Object element should be only registered for new features.
+			// If the model schema is already registered, it should be handled by
+			// #_registerBlockElement() or #_registerObjectElement() attribute handlers.
 			if ( definition.isObject && !schema.isRegistered( definition.model ) ) {
 				this._registerObjectElement( definition );
 			} else if ( definition.isBlock ) {

From 5891ac44b4523c57aa9f14bf3098456e5822292a Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 1 Jun 2021 11:02:23 +0200
Subject: [PATCH 149/217] Protected API instead of public.

---
 packages/ckeditor5-content-compatibility/src/converters.js  | 6 +++---
 packages/ckeditor5-content-compatibility/src/datafilter.js  | 6 ++++--
 .../src/integrations/codeblock.js                           | 2 +-
 3 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/converters.js b/packages/ckeditor5-content-compatibility/src/converters.js
index 85dd0b93055..aa403cf8b78 100644
--- a/packages/ckeditor5-content-compatibility/src/converters.js
+++ b/packages/ckeditor5-content-compatibility/src/converters.js
@@ -23,7 +23,7 @@ import { setViewAttributes, mergeViewElementAttributes } from './conversionutils
 export function disallowedAttributesConverter( { view: viewName }, dataFilter ) {
 	return dispatcher => {
 		dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
-			dataFilter.consumeDisallowedAttributes( data.viewItem, conversionApi );
+			dataFilter._consumeDisallowedAttributes( data.viewItem, conversionApi );
 		}, { priority: 'high' } );
 	};
 }
@@ -104,7 +104,7 @@ export function createObjectView( viewName, modelElement, writer ) {
 export function viewToAttributeInlineConverter( { view: viewName, model: attributeKey }, dataFilter ) {
 	return dispatcher => {
 		dispatcher.on( `element:${ viewName }`, ( evt, data, conversionApi ) => {
-			const viewAttributes = dataFilter.consumeAllowedAttributes( data.viewItem, conversionApi );
+			const viewAttributes = dataFilter._consumeAllowedAttributes( data.viewItem, conversionApi );
 
 			// Since we are converting to attribute we need a range on which we will set the attribute.
 			// If the range is not created yet, we will create it.
@@ -164,7 +164,7 @@ export function viewToModelBlockAttributeConverter( { view: viewName }, dataFilt
 				return;
 			}
 
-			const viewAttributes = dataFilter.consumeAllowedAttributes( data.viewItem, conversionApi );
+			const viewAttributes = dataFilter._consumeAllowedAttributes( data.viewItem, conversionApi );
 
 			if ( viewAttributes ) {
 				conversionApi.writer.setAttribute( 'htmlAttributes', viewAttributes, data.modelRange );
diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 1a6517624a0..cc7fc13a30a 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -175,6 +175,7 @@ export default class DataFilter extends Plugin {
 	/**
 	 * Matches and consumes allowed view attributes.
 	 *
+	 * @protected
 	 * @param {module:engine/view/element~Element} viewElement
 	 * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
 	 * @returns {Object} [result]
@@ -182,13 +183,14 @@ export default class DataFilter extends Plugin {
 	 * @returns {Object} result.styles Set with matched style names.
 	 * @returns {Array.<String>} result.classes Set with matched class names.
 	 */
-	consumeAllowedAttributes( viewElement, conversionApi ) {
+	_consumeAllowedAttributes( viewElement, conversionApi ) {
 		return consumeAttributes( viewElement, conversionApi, this._allowedAttributes );
 	}
 
 	/**
 	 * Matches and consumes disallowed view attributes.
 	 *
+	 * @protected
 	 * @param {module:engine/view/element~Element} viewElement
 	 * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
 	 * @returns {Object} [result]
@@ -196,7 +198,7 @@ export default class DataFilter extends Plugin {
 	 * @returns {Object} result.styles Set with matched style names.
 	 * @returns {Array.<String>} result.classes Set with matched class names.
 	 */
-	consumeDisallowedAttributes( viewElement, conversionApi ) {
+	_consumeDisallowedAttributes( viewElement, conversionApi ) {
 		return consumeAttributes( viewElement, conversionApi, this._disallowedAttributes );
 	}
 
diff --git a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js b/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
index 1e1a40af21a..c0fbaf273f3 100644
--- a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
+++ b/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
@@ -70,7 +70,7 @@ function viewToModelCodeBlockAttributeConverter( dataFilter ) {
 			preserveElementAttributes( viewCodeElement, 'htmlContentAttributes' );
 
 			function preserveElementAttributes( viewElement, attributeName ) {
-				const viewAttributes = dataFilter.consumeAllowedAttributes( viewElement, conversionApi );
+				const viewAttributes = dataFilter._consumeAllowedAttributes( viewElement, conversionApi );
 
 				if ( viewAttributes ) {
 					conversionApi.writer.setAttribute( attributeName, viewAttributes, data.modelRange );

From 6f5a1cfc5fb101fbd4c90b683f75d4bd529b8ccd Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 7 Jun 2021 11:47:07 +0200
Subject: [PATCH 150/217] Updated docs.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js   | 4 ++--
 .../src/integrations/codeblock.js                            | 5 +++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index cc7fc13a30a..9172972c6dd 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -41,7 +41,7 @@ import '../theme/datafilter.css';
  * You can also allow or disallow specific element attributes:
  *
  *		// Allow `data-foo` attribute on `section` element.
- *		dataFilter.allowedAttributes( {
+ *		dataFilter.allowAttributes( {
  *			name: 'section',
  *			attributes: {
  *				'data-foo': true
@@ -49,7 +49,7 @@ import '../theme/datafilter.css';
  *		} );
  *
  *		// Disallow `color` style attribute on 'section' element.
- *		dataFilter.disallowedAttributes( {
+ *		dataFilter.disallowAttributes( {
  *			name: 'section',
  *			styles: {
  *				color: /[\s\S]+/
diff --git a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js b/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
index c0fbaf273f3..56e64d98c64 100644
--- a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
+++ b/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
@@ -13,6 +13,11 @@ import { setViewAttributes } from '../conversionutils.js';
 
 import DataFilter from '../datafilter';
 
+/**
+ * Provides the General HTML Support integration with {@link module:code-block/codeblock~CodeBlock Code Block} feature.
+ *
+ * @extends module:core/plugin~Plugin
+ */
 export default class CodeBlockHtmlSupport extends Plugin {
 	static get requires() {
 		return [ DataFilter ];

From b56ba535c90396c69af8e194168405c61138954f Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 7 Jun 2021 13:43:00 +0200
Subject: [PATCH 151/217] Deps update to the latest release.

---
 .../package.json                              | 32 +++++++++----------
 1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/package.json b/packages/ckeditor5-content-compatibility/package.json
index a349d9eee8d..93778128863 100644
--- a/packages/ckeditor5-content-compatibility/package.json
+++ b/packages/ckeditor5-content-compatibility/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@ckeditor/ckeditor5-content-compatibility",
-  "version": "27.1.0",
+  "version": "28.0.0",
   "description": "Content compatibility feature",
   "private": true,
   "keywords": [
@@ -15,24 +15,24 @@
   ],
   "main": "src/index.js",
   "dependencies": {
-    "ckeditor5": "^27.1.0",
+    "ckeditor5": "^28.0.0",
     "lodash-es": "^4.17.15"
   },
   "devDependencies": {
-    "@ckeditor/ckeditor5-basic-styles": "^27.1.0",
-    "@ckeditor/ckeditor5-block-quote": "^27.1.0",
-    "@ckeditor/ckeditor5-code-block": "^27.1.0",
-    "@ckeditor/ckeditor5-core": "^27.1.0",
-    "@ckeditor/ckeditor5-editor-classic": "^27.1.0",
-    "@ckeditor/ckeditor5-engine": "^27.1.0",
-    "@ckeditor/ckeditor5-essentials": "^27.1.0",
-    "@ckeditor/ckeditor5-font": "^27.1.0",
-    "@ckeditor/ckeditor5-highlight": "^27.1.0",
-    "@ckeditor/ckeditor5-link": "^27.1.0",
-    "@ckeditor/ckeditor5-list": "^27.1.0",
-    "@ckeditor/ckeditor5-paragraph": "^27.1.0",
-    "@ckeditor/ckeditor5-table": "^27.1.0",
-    "@ckeditor/ckeditor5-utils": "^27.1.0",
+    "@ckeditor/ckeditor5-basic-styles": "^28.0.0",
+    "@ckeditor/ckeditor5-block-quote": "^28.0.0",
+    "@ckeditor/ckeditor5-code-block": "^28.0.0",
+    "@ckeditor/ckeditor5-core": "^28.0.0",
+    "@ckeditor/ckeditor5-editor-classic": "^28.0.0",
+    "@ckeditor/ckeditor5-engine": "^28.0.0",
+    "@ckeditor/ckeditor5-essentials": "^28.0.0",
+    "@ckeditor/ckeditor5-font": "^28.0.0",
+    "@ckeditor/ckeditor5-highlight": "^28.0.0",
+    "@ckeditor/ckeditor5-link": "^28.0.0",
+    "@ckeditor/ckeditor5-list": "^28.0.0",
+    "@ckeditor/ckeditor5-paragraph": "^28.0.0",
+    "@ckeditor/ckeditor5-table": "^28.0.0",
+    "@ckeditor/ckeditor5-utils": "^28.0.0",
     "webpack": "^4.43.0",
     "webpack-cli": "^3.3.11"
   },

From 6368cb744408efeb4d83c45c810f7caf7e95d537 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <j.niegowski@cksource.com>
Date: Mon, 7 Jun 2021 18:10:49 +0200
Subject: [PATCH 152/217] Fixed manual test.

---
 .../tests/manual/codeblock.html                               | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/codeblock.html b/packages/ckeditor5-content-compatibility/tests/manual/codeblock.html
index 6c928e2cb9c..a6cf25bb452 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/codeblock.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/codeblock.html
@@ -4,8 +4,8 @@
 </head>
 
 <div id="editor">
-	<pre style="background:violet;" class="foo"><code class=\"language-html\" data-foo="foo">Code Block with custom properties!</code></pre>
-	<pre style="background:yellow;"><code class=\"language-css\" style="color:red;" data-foo="bar">Code Block with disallowed background!</code></pre>
+	<pre style="background:violet;" class="foo"><code class="language-html" data-foo="foo">Code Block with custom properties!</code></pre>
+	<pre style="background:yellow;"><code class="language-css" style="color:red;" data-foo="bar">Code Block with disallowed background!</code></pre>
 	<pre style="background:grey;"><strong>Apes are strong!</strong><br><i>Let's check if inline elements are strong also!</i></pre>
 	<code style="color:blue; background:yellow;">Blue code with disallowed background!</code>
 </div>

From 423d9c03821e2b79b0b720dffe20293359dfd570 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Thu, 13 May 2021 15:25:24 +0200
Subject: [PATCH 153/217] Add data filter configuration loading.

---
 .../src/datafilter.js                         | 45 +++++++++++-
 .../tests/datafilter.js                       | 69 +++++++++++++++++++
 2 files changed, 111 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 9172972c6dd..2bcbbf8539b 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -11,7 +11,7 @@ import DataSchema from './dataschema';
 
 import { Plugin } from 'ckeditor5/src/core';
 import { Matcher } from 'ckeditor5/src/engine';
-import { priorities, CKEditorError } from 'ckeditor5/src/utils';
+import { priorities, toArray, CKEditorError } from 'ckeditor5/src/utils';
 import { Widget } from 'ckeditor5/src/widget';
 import {
 	disallowedAttributesConverter,
@@ -126,6 +126,26 @@ export default class DataFilter extends Plugin {
 		return [ DataSchema, Widget ];
 	}
 
+	/**
+	 * Load a configuration of one or many elements, where their attributes should be allowed.
+	 *
+	 * @param {Array.<module:engine/view/matcher~MatcherPattern>} config Configuration of elements
+	 * that should have their attributes accepted in the editor.
+	 */
+	loadAllowedConfig( config ) {
+		this._loadConfig( config );
+	}
+
+	/**
+	 * Load a configuration of one or many elements, where their attributes should be disallowed.
+	 *
+	 * @param {Array.<module:engine/view/matcher~MatcherPattern>} config Configuration of elements
+	 * that should have their attributes rejected from the editor.
+	 */
+	loadDisallowedConfig( config ) {
+		this._loadConfig( config, true );
+	}
+
 	/**
 	 * Allow the given element in the editor context.
 	 *
@@ -160,7 +180,7 @@ export default class DataFilter extends Plugin {
 	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all attributes which should be allowed.
 	 */
 	allowAttributes( config ) {
-		this._allowedAttributes.add( config );
+		this._allowedAttributes.add( toArray( config || [] ) );
 	}
 
 	/**
@@ -169,7 +189,26 @@ export default class DataFilter extends Plugin {
 	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all attributes which should be disallowed.
 	 */
 	disallowAttributes( config ) {
-		this._disallowedAttributes.add( config );
+		this._disallowedAttributes.add( toArray( config || [] ) );
+	}
+
+	/**
+	 * Batch load of the filtering configuration.
+	 *
+	 * @private
+	 * @param {Array.<module:engine/view/matcher~MatcherPattern>} config Filtering configuration.
+	 * @param {Boolean} shouldDisallow Provided rules will reject attributes from matched elements instead of accepting them.
+	 */
+	_loadConfig( config, shouldDisallow = false ) {
+		for ( const { element, ...rules } of config ) {
+			this.allowElement( element );
+
+			if ( shouldDisallow ) {
+				this.disallowAttributes( { element, ...rules } );
+			} else {
+				this.allowAttributes( { element, ...rules } );
+			}
+		}
 	}
 
 	/**
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index d5b1f38f521..167c1cfce9b 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -1275,4 +1275,73 @@ describe( 'DataFilter', () => {
 			dataFilter.allowElement( { name: 'xyz' } );
 		}, /data-filter-invalid-definition/, null, definition );
 	} );
+
+	describe.skip( 'fromConfig', () => {
+		// TODO: Better name
+		it( 'should load config', () => {
+			const config = [
+				{
+					element: 'xyz',
+					attributes: {
+						title: 'foo'
+					}
+				}
+			];
+
+			dataSchema.registerBlockElement( { view: 'xyz', model: 'modelXyz' } );
+			dataFilter.fromConfig( config );
+
+			editor.setData( '<xyz>foo</xyz>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>foo</paragraph>',
+				attributes: {}
+			} );
+		} );
+	} );
+
+	function getModelDataWithAttributes( model, options ) {
+		// Simplify GHS attributes as they are not very readable at this point due to object structure.
+		let counter = 1;
+		const data = getModelData( model, options ).replace( /(html.*?)="{.*?}"/g, ( fullMatch, attributeName ) => {
+			return `${ attributeName }="(${ counter++ })"`;
+		} );
+
+		const range = model.createRangeIn( model.document.getRoot() );
+
+		let attributes = [];
+		for ( const item of range.getItems() ) {
+			for ( const [ key, value ] of sortAttributes( item.getAttributes() ) ) {
+				if ( key.startsWith( 'html' ) ) {
+					attributes.push( value );
+				}
+			}
+		}
+
+		attributes = attributes.reduce( ( prev, cur, index ) => {
+			prev[ index + 1 ] = cur;
+			return prev;
+		}, {} );
+
+		return { data, attributes };
+	}
+
+	function sortAttributes( attributes ) {
+		attributes = Array.from( attributes );
+
+		return attributes.sort( ( attr1, attr2 ) => {
+			const key1 = attr1[ 0 ];
+			const key2 = attr2[ 0 ];
+
+			if ( key1 > key2 ) {
+				return 1;
+			}
+
+			if ( key1 < key2 ) {
+				return -1;
+			}
+
+			return 0;
+		} );
+	}
 } );

From f512de362ecc4397170dc59d705d51ae4c34af4c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Mon, 17 May 2021 13:56:08 +0200
Subject: [PATCH 154/217] Add loading config.

---
 .../src/datafilter.js                         |  15 ++-
 .../tests/manual/datafilter.html              |  61 ++++++++++
 .../tests/manual/datafilter.js                | 105 ++++++++++++++++++
 .../tests/manual/datafilter.md                |   1 +
 4 files changed, 178 insertions(+), 4 deletions(-)
 create mode 100644 packages/ckeditor5-content-compatibility/tests/manual/datafilter.html
 create mode 100644 packages/ckeditor5-content-compatibility/tests/manual/datafilter.js
 create mode 100644 packages/ckeditor5-content-compatibility/tests/manual/datafilter.md

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 2bcbbf8539b..2c1e2f5dcd8 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -108,6 +108,9 @@ export default class DataFilter extends Plugin {
 		*/
 		this._dataInitialized = false;
 
+		this.loadAllowedConfig( this.editor.config.get( 'contentCompatibility.allowed' ) || [] );
+		this.loadDisallowedConfig( this.editor.config.get( 'contentCompatibility.disallowed' ) || [] );
+
 		this._registerElementsAfterInit();
 		this._registerElementHandlers();
 	}
@@ -200,13 +203,17 @@ export default class DataFilter extends Plugin {
 	 * @param {Boolean} shouldDisallow Provided rules will reject attributes from matched elements instead of accepting them.
 	 */
 	_loadConfig( config, shouldDisallow = false ) {
-		for ( const { element, ...rules } of config ) {
-			this.allowElement( element );
+		for ( const { name, ...rules } of config ) {
+			this.allowElement( { name } );
+
+			if ( !rules ) {
+				continue;
+			}
 
 			if ( shouldDisallow ) {
-				this.disallowAttributes( { element, ...rules } );
+				this.disallowAttributes( { name, ...rules } );
 			} else {
-				this.allowAttributes( { element, ...rules } );
+				this.allowAttributes( { name, ...rules } );
 			}
 		}
 	}
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/datafilter.html b/packages/ckeditor5-content-compatibility/tests/manual/datafilter.html
new file mode 100644
index 00000000000..491f00db3be
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/manual/datafilter.html
@@ -0,0 +1,61 @@
+<head>
+	<meta http-equiv="Content-Security-Policy" content="script-src 'self' https://ckeditor.com 'unsafe-inline' 'unsafe-eval'">
+</head>
+
+<div id="editor">
+	<article>
+		<section id="section1"><p data-foo="foo">Section #1</p></section>
+		<section id="_section2"><p style="background-color: violet;">Section #2</p></section>
+		<section id="section3" style="color: red" class="special_section"><p>Section #3</p></section>
+	</article>
+
+	<details>
+		<summary>Summary</summary>
+		Hello world
+	</details>
+
+	<dl>
+		<dt><p>dt1</p></dt>
+		<dt><p>dt2</p></dt>
+		<dd><p>dd1</p></dd>
+		<dd><p>dd2</p></dd>
+	</dl>
+
+	<xyz><p>XYZ</p></xyz>
+
+	<p data-foo="foo">
+		<span data-foo="foo">Nested cite: <cite style="color:blue;">I'm blue!</cite></span>
+	</p>
+	<p data-foo="bar">
+		<span data-foo="foo">Nested span: <span style="color:blue;">I'm blue!</span></span>
+	</p>
+
+	<p><cite>Deeply<cite> nested<cite> cite<span style="color:blue;"> with span!</span></cite></cite></cite></p>
+
+	<p style="background-color: violet;"><span>Span with no attributes!</span></p>
+
+	<p><span style="color:blue;"><span style="color:green;">Span with nested styles!</span></span></p>
+
+	<blockquote style="color: red;">Red quote!</blockquote>
+
+	<ul>
+		<li style="color: blue;">Blue!</li>
+		<li style="color: red;">Red!</li>
+		<li style="color: violet;">Violet!</li>
+		<ul>
+			<li style="color: yellow;">Yellow!</li>
+		</ul>
+	</ul>
+	<p>
+		<a href="example.com" style="background-color:#5de">Link with different background color.</a>
+	</p>
+	<p>
+		<strong style="font-weight:400">Strong with font weight 400</strong>
+	</p>
+	<p>
+		<i data-foo="foo" style="color: green;">Italic with custom attributes</i>
+	</p>
+	<p>
+		<s style="color: red;">Red strike</s>
+	</p>
+</div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/datafilter.js b/packages/ckeditor5-content-compatibility/tests/manual/datafilter.js
new file mode 100644
index 00000000000..70d63e1f4c9
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/manual/datafilter.js
@@ -0,0 +1,105 @@
+/**
+ * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/* globals console:false, window, document */
+
+import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
+import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials';
+import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
+import Bold from '@ckeditor/ckeditor5-basic-styles/src/bold';
+import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
+import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
+import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
+import BlockQuote from '@ckeditor/ckeditor5-block-quote/src/blockquote';
+import List from '@ckeditor/ckeditor5-list/src/list';
+import Link from '@ckeditor/ckeditor5-link/src/link';
+
+import GeneralHtmlSupport from '../../src/generalhtmlsupport';
+
+/**
+ * Client custom plugin extending HTML support for compatibility.
+ */
+class ExtendHTMLSupport extends Plugin {
+	static get requires() {
+		return [ GeneralHtmlSupport ];
+	}
+
+	init() {
+		const { dataSchema } = this.editor.plugins.get( GeneralHtmlSupport );
+
+		// Extend schema with custom `xyz` element.
+		dataSchema.registerBlockElement( {
+			view: 'xyz',
+			model: 'htmlXyz',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		} );
+	}
+}
+
+ClassicEditor
+	.create( document.querySelector( '#editor' ), {
+		plugins: [
+			Link,
+			BlockQuote,
+			Bold,
+			Essentials,
+			ExtendHTMLSupport,
+			Italic,
+			List,
+			Paragraph,
+			Strikethrough
+		],
+		toolbar: [
+			'bold',
+			'italic',
+			'strikethrough',
+			'|',
+			'numberedList',
+			'bulletedList',
+			'|',
+			'blockquote'
+		],
+		contentCompatibility: {
+			allowed: [
+				{ name: 'article' },
+
+				{ name: 'section', attributes: { id: /[\s\S]+/ } },
+				{ name: 'section', classes: /[\s\S]+/ },
+				{ name: 'section', styles: { color: 'red' } },
+
+				{ name: /^(details|summary)$/ },
+				{ name: /^(dl|dd|dt)$/ },
+				{ name: 'xyz' },
+
+				{ name: /^(span|cite)$/, attributes: { 'data-foo': /[\s\S]+/ } },
+				{ name: /^(span|cite)$/, styles: { color: /[\s\S]+/ } },
+				{ name: /^(span|cite)$/, attributes: { 'data-order-id': /[\s\S]+/ } },
+				{ name: /^(span|cite)$/, attributes: { 'data-item-id': /[\s\S]+/ } },
+
+				{ name: 'p', attributes: { 'data-foo': /[\s\S]+/ } },
+				{ name: 'p', styles: { 'background-color': /[\s\S]+/ } },
+
+				{ name: 'blockquote', styles: { 'color': /[\s\S]+/ } },
+				{ name: 'li', styles: { 'color': /[\s\S]+/ } },
+				{ name: 'a', styles: { 'background-color': /[\s\S]+/ } },
+				{ name: 'strong', styles: { 'font-weight': /[\s\S]+/ } },
+				{ name: 'i', styles: { 'color': /[\s\S]+/ } },
+				{ name: 'i', attributes: { 'data-foo': /[\s\S]+/ } },
+				{ name: 's', styles: { 'color': /[\s\S]+/ } }
+			],
+			disallowed: [
+				{ name: 'section', attributes: { id: /^_.*/ } },
+				{ name: /^(span|cite)$/, styles: { color: 'red' } }
+			]
+		}
+	} )
+	.then( editor => {
+		window.editor = editor;
+	} )
+	.catch( err => {
+		console.error( err.stack );
+	} );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/datafilter.md b/packages/ckeditor5-content-compatibility/tests/manual/datafilter.md
new file mode 100644
index 00000000000..62e56632586
--- /dev/null
+++ b/packages/ckeditor5-content-compatibility/tests/manual/datafilter.md
@@ -0,0 +1 @@
+# Data Filter

From 3461201d0b7b1ea4c40a7897f5a1f90937ca1f23 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Tue, 18 May 2021 09:10:49 +0200
Subject: [PATCH 155/217] Fix config loading.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js    | 4 ++--
 .../tests/manual/datafilter.html                              | 2 ++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 2c1e2f5dcd8..e2c8ff006f5 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -183,7 +183,7 @@ export default class DataFilter extends Plugin {
 	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all attributes which should be allowed.
 	 */
 	allowAttributes( config ) {
-		this._allowedAttributes.add( toArray( config || [] ) );
+		this._allowedAttributes.add( config );
 	}
 
 	/**
@@ -192,7 +192,7 @@ export default class DataFilter extends Plugin {
 	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all attributes which should be disallowed.
 	 */
 	disallowAttributes( config ) {
-		this._disallowedAttributes.add( toArray( config || [] ) );
+		this._disallowedAttributes.add( config );
 	}
 
 	/**
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/datafilter.html b/packages/ckeditor5-content-compatibility/tests/manual/datafilter.html
index 491f00db3be..0e9925b237c 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/datafilter.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/datafilter.html
@@ -23,6 +23,8 @@
 
 	<xyz><p>XYZ</p></xyz>
 
+	<p><span style="color:red;">Span with styles! This should not be red.</span></p>
+
 	<p data-foo="foo">
 		<span data-foo="foo">Nested cite: <cite style="color:blue;">I'm blue!</cite></span>
 	</p>

From 1fcec51f952c118f733488284c381069a348cf0a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Tue, 18 May 2021 10:52:35 +0200
Subject: [PATCH 156/217] Review fixes.

---
 .../src/datafilter.js                         | 21 +++++----------
 .../src/generalhtmlsupport.js                 | 27 +++++++++++++++++++
 2 files changed, 33 insertions(+), 15 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index e2c8ff006f5..319c754d80e 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -108,9 +108,6 @@ export default class DataFilter extends Plugin {
 		*/
 		this._dataInitialized = false;
 
-		this.loadAllowedConfig( this.editor.config.get( 'contentCompatibility.allowed' ) || [] );
-		this.loadDisallowedConfig( this.editor.config.get( 'contentCompatibility.disallowed' ) || [] );
-
 		this._registerElementsAfterInit();
 		this._registerElementHandlers();
 	}
@@ -136,7 +133,7 @@ export default class DataFilter extends Plugin {
 	 * that should have their attributes accepted in the editor.
 	 */
 	loadAllowedConfig( config ) {
-		this._loadConfig( config );
+		this._loadConfig( config, pattern => this.allowAttributes( pattern ) );
 	}
 
 	/**
@@ -146,7 +143,7 @@ export default class DataFilter extends Plugin {
 	 * that should have their attributes rejected from the editor.
 	 */
 	loadDisallowedConfig( config ) {
-		this._loadConfig( config, true );
+		this._loadConfig( config, pattern => this.disallowAttributes( pattern ) );
 	}
 
 	/**
@@ -155,7 +152,7 @@ export default class DataFilter extends Plugin {
 	 * This method will only allow elements described by the {@link module:content-compatibility/dataschema~DataSchema} used
 	 * to create data filter.
 	 *
-	 * @param {module:engine/view/matcher~MatcherPattern} config Pattern matching all view elements which should be allowed.
+	 * @param {String|RegExp} viewName String or regular expression matching view name.
 	 */
 	allowElement( config ) {
 		for ( const definition of this._dataSchema.getDefinitionsForView( config.name, true ) ) {
@@ -173,8 +170,6 @@ export default class DataFilter extends Plugin {
 				this._fireRegisterEvent( definition );
 			}
 		}
-
-		this.allowAttributes( config );
 	}
 
 	/**
@@ -200,9 +195,9 @@ export default class DataFilter extends Plugin {
 	 *
 	 * @private
 	 * @param {Array.<module:engine/view/matcher~MatcherPattern>} config Filtering configuration.
-	 * @param {Boolean} shouldDisallow Provided rules will reject attributes from matched elements instead of accepting them.
+	 * @param {Function} handleAttributes Callback handling the way the attributes should be processed.
 	 */
-	_loadConfig( config, shouldDisallow = false ) {
+	_loadConfig( config, handleAttributes ) {
 		for ( const { name, ...rules } of config ) {
 			this.allowElement( { name } );
 
@@ -210,11 +205,7 @@ export default class DataFilter extends Plugin {
 				continue;
 			}
 
-			if ( shouldDisallow ) {
-				this.disallowAttributes( { name, ...rules } );
-			} else {
-				this.allowAttributes( { name, ...rules } );
-			}
+			handleAttributes( { name, ...rules } );
 		}
 	}
 
diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
index 9bf7e0c6ced..b4ec6162949 100644
--- a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
@@ -28,6 +28,33 @@ export default class GeneralHtmlSupport extends Plugin {
 		return 'GeneralHtmlSupport';
 	}
 
+	/**
+	 * @param {module:core/editor/editor~Editor} editor
+	 */
+	constructor( editor ) {
+		super( editor );
+
+		/**
+		 * An instance of the {@link module:content-compatibility/dataschema~DataSchema}.
+		 *
+		 * @readonly
+		 * @member {module:content-compatibility/dataschema~DataSchema} #dataSchema
+		 */
+		this.dataSchema = new DataSchema();
+
+		/**
+		 * An instance of the {@link module:content-compatibility/datafilter~DataFilter}.
+		 *
+		 * @readonly
+		 * @member {module:content-compatibility/datafilter~DataFilter} #dataFilter
+		 */
+		this.dataFilter = new DataFilter( editor, this.dataSchema );
+
+		// Load the filtering configuration.
+		this.dataFilter.loadAllowedConfig( this.editor.config.get( 'contentCompatibility.allowed' ) || [] );
+		this.dataFilter.loadDisallowedConfig( this.editor.config.get( 'contentCompatibility.disallowed' ) || [] );
+	}
+
 	/**
 	 * @inheritDoc
 	 */

From a781a74d64bcc803e98ce61668d58a391f843eb8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Tue, 18 May 2021 10:55:47 +0200
Subject: [PATCH 157/217] Merge manual tests.

---
 .../tests/manual/datafilter.html              |  63 -----------
 .../tests/manual/datafilter.js                | 105 ------------------
 .../tests/manual/datafilter.md                |   1 -
 .../tests/manual/generalhtmlsupport.html      |   2 +
 .../tests/manual/generalhtmlsupport.js        |  85 ++++++--------
 5 files changed, 36 insertions(+), 220 deletions(-)
 delete mode 100644 packages/ckeditor5-content-compatibility/tests/manual/datafilter.html
 delete mode 100644 packages/ckeditor5-content-compatibility/tests/manual/datafilter.js
 delete mode 100644 packages/ckeditor5-content-compatibility/tests/manual/datafilter.md

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/datafilter.html b/packages/ckeditor5-content-compatibility/tests/manual/datafilter.html
deleted file mode 100644
index 0e9925b237c..00000000000
--- a/packages/ckeditor5-content-compatibility/tests/manual/datafilter.html
+++ /dev/null
@@ -1,63 +0,0 @@
-<head>
-	<meta http-equiv="Content-Security-Policy" content="script-src 'self' https://ckeditor.com 'unsafe-inline' 'unsafe-eval'">
-</head>
-
-<div id="editor">
-	<article>
-		<section id="section1"><p data-foo="foo">Section #1</p></section>
-		<section id="_section2"><p style="background-color: violet;">Section #2</p></section>
-		<section id="section3" style="color: red" class="special_section"><p>Section #3</p></section>
-	</article>
-
-	<details>
-		<summary>Summary</summary>
-		Hello world
-	</details>
-
-	<dl>
-		<dt><p>dt1</p></dt>
-		<dt><p>dt2</p></dt>
-		<dd><p>dd1</p></dd>
-		<dd><p>dd2</p></dd>
-	</dl>
-
-	<xyz><p>XYZ</p></xyz>
-
-	<p><span style="color:red;">Span with styles! This should not be red.</span></p>
-
-	<p data-foo="foo">
-		<span data-foo="foo">Nested cite: <cite style="color:blue;">I'm blue!</cite></span>
-	</p>
-	<p data-foo="bar">
-		<span data-foo="foo">Nested span: <span style="color:blue;">I'm blue!</span></span>
-	</p>
-
-	<p><cite>Deeply<cite> nested<cite> cite<span style="color:blue;"> with span!</span></cite></cite></cite></p>
-
-	<p style="background-color: violet;"><span>Span with no attributes!</span></p>
-
-	<p><span style="color:blue;"><span style="color:green;">Span with nested styles!</span></span></p>
-
-	<blockquote style="color: red;">Red quote!</blockquote>
-
-	<ul>
-		<li style="color: blue;">Blue!</li>
-		<li style="color: red;">Red!</li>
-		<li style="color: violet;">Violet!</li>
-		<ul>
-			<li style="color: yellow;">Yellow!</li>
-		</ul>
-	</ul>
-	<p>
-		<a href="example.com" style="background-color:#5de">Link with different background color.</a>
-	</p>
-	<p>
-		<strong style="font-weight:400">Strong with font weight 400</strong>
-	</p>
-	<p>
-		<i data-foo="foo" style="color: green;">Italic with custom attributes</i>
-	</p>
-	<p>
-		<s style="color: red;">Red strike</s>
-	</p>
-</div>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/datafilter.js b/packages/ckeditor5-content-compatibility/tests/manual/datafilter.js
deleted file mode 100644
index 70d63e1f4c9..00000000000
--- a/packages/ckeditor5-content-compatibility/tests/manual/datafilter.js
+++ /dev/null
@@ -1,105 +0,0 @@
-/**
- * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
- * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
- */
-
-/* globals console:false, window, document */
-
-import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
-import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials';
-import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
-import Bold from '@ckeditor/ckeditor5-basic-styles/src/bold';
-import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
-import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
-import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
-import BlockQuote from '@ckeditor/ckeditor5-block-quote/src/blockquote';
-import List from '@ckeditor/ckeditor5-list/src/list';
-import Link from '@ckeditor/ckeditor5-link/src/link';
-
-import GeneralHtmlSupport from '../../src/generalhtmlsupport';
-
-/**
- * Client custom plugin extending HTML support for compatibility.
- */
-class ExtendHTMLSupport extends Plugin {
-	static get requires() {
-		return [ GeneralHtmlSupport ];
-	}
-
-	init() {
-		const { dataSchema } = this.editor.plugins.get( GeneralHtmlSupport );
-
-		// Extend schema with custom `xyz` element.
-		dataSchema.registerBlockElement( {
-			view: 'xyz',
-			model: 'htmlXyz',
-			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
-			}
-		} );
-	}
-}
-
-ClassicEditor
-	.create( document.querySelector( '#editor' ), {
-		plugins: [
-			Link,
-			BlockQuote,
-			Bold,
-			Essentials,
-			ExtendHTMLSupport,
-			Italic,
-			List,
-			Paragraph,
-			Strikethrough
-		],
-		toolbar: [
-			'bold',
-			'italic',
-			'strikethrough',
-			'|',
-			'numberedList',
-			'bulletedList',
-			'|',
-			'blockquote'
-		],
-		contentCompatibility: {
-			allowed: [
-				{ name: 'article' },
-
-				{ name: 'section', attributes: { id: /[\s\S]+/ } },
-				{ name: 'section', classes: /[\s\S]+/ },
-				{ name: 'section', styles: { color: 'red' } },
-
-				{ name: /^(details|summary)$/ },
-				{ name: /^(dl|dd|dt)$/ },
-				{ name: 'xyz' },
-
-				{ name: /^(span|cite)$/, attributes: { 'data-foo': /[\s\S]+/ } },
-				{ name: /^(span|cite)$/, styles: { color: /[\s\S]+/ } },
-				{ name: /^(span|cite)$/, attributes: { 'data-order-id': /[\s\S]+/ } },
-				{ name: /^(span|cite)$/, attributes: { 'data-item-id': /[\s\S]+/ } },
-
-				{ name: 'p', attributes: { 'data-foo': /[\s\S]+/ } },
-				{ name: 'p', styles: { 'background-color': /[\s\S]+/ } },
-
-				{ name: 'blockquote', styles: { 'color': /[\s\S]+/ } },
-				{ name: 'li', styles: { 'color': /[\s\S]+/ } },
-				{ name: 'a', styles: { 'background-color': /[\s\S]+/ } },
-				{ name: 'strong', styles: { 'font-weight': /[\s\S]+/ } },
-				{ name: 'i', styles: { 'color': /[\s\S]+/ } },
-				{ name: 'i', attributes: { 'data-foo': /[\s\S]+/ } },
-				{ name: 's', styles: { 'color': /[\s\S]+/ } }
-			],
-			disallowed: [
-				{ name: 'section', attributes: { id: /^_.*/ } },
-				{ name: /^(span|cite)$/, styles: { color: 'red' } }
-			]
-		}
-	} )
-	.then( editor => {
-		window.editor = editor;
-	} )
-	.catch( err => {
-		console.error( err.stack );
-	} );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/datafilter.md b/packages/ckeditor5-content-compatibility/tests/manual/datafilter.md
deleted file mode 100644
index 62e56632586..00000000000
--- a/packages/ckeditor5-content-compatibility/tests/manual/datafilter.md
+++ /dev/null
@@ -1 +0,0 @@
-# Data Filter
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
index 491f00db3be..0e9925b237c 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -23,6 +23,8 @@
 
 	<xyz><p>XYZ</p></xyz>
 
+	<p><span style="color:red;">Span with styles! This should not be red.</span></p>
+
 	<p data-foo="foo">
 		<span data-foo="foo">Nested cite: <cite style="color:blue;">I'm blue!</cite></span>
 	</p>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index ed4ffec1934..26f128b2ec7 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -38,56 +38,6 @@ class ExtendHTMLSupport extends Plugin {
 				inheritAllFrom: '$htmlBlock'
 			}
 		} );
-
-		// Allow some elements, at this point model schema will include information about view-model mapping
-		// e.g. article -> ghsArticle
-		dataFilter.allowElement( { name: 'article' } );
-		dataFilter.allowElement( { name: 'section' } );
-		dataFilter.allowElement( { name: /^(details|summary)$/ } );
-		dataFilter.allowElement( { name: /^(dl|dd|dt)$/ } );
-		dataFilter.allowElement( { name: 'xyz' } );
-
-		// Let's extend 'section' with some attributes. Data filter will take care of
-		// creating proper converters and attribute matchers:
-		dataFilter.allowAttributes( { name: 'section', attributes: { id: /[\s\S]+/ } } );
-		dataFilter.allowAttributes( { name: 'section', classes: /[\s\S]+/ } );
-		dataFilter.allowAttributes( { name: 'section', styles: { color: 'red' } } );
-
-		// but disallow setting id attribute if it start with `_` prefix:
-		dataFilter.disallowAttributes( { name: 'section', attributes: { id: /^_.*/ } } );
-
-		// Let's also add some inline elements support:
-		dataFilter.allowElement( { name: /^(span|cite)$/ } );
-		dataFilter.allowAttributes( { name: /^(span|cite)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
-		dataFilter.allowAttributes( { name: /^(span|cite)$/, styles: { color: /[\s\S]+/ } } );
-		dataFilter.disallowAttributes( { name: /^(span|cite)$/, styles: { color: 'red' } } );
-
-		dataFilter.allowAttributes( { name: /^(span|cite)$/, attributes: { 'data-order-id': /[\s\S]+/ } } );
-		dataFilter.allowAttributes( { name: /^(span|cite)$/, attributes: { 'data-item-id': /[\s\S]+/ } } );
-
-		// Allow existing features.
-		dataFilter.allowElement( { name: 'p' } );
-		dataFilter.allowAttributes( { name: 'p', attributes: { 'data-foo': /[\s\S]+/ } } );
-		dataFilter.allowAttributes( { name: 'p', styles: { 'background-color': /[\s\S]+/ } } );
-
-		dataFilter.allowElement( { name: 'blockquote' } );
-		dataFilter.allowAttributes( { name: 'blockquote', styles: { 'color': /[\s\S]+/ } } );
-
-		dataFilter.allowElement( { name: 'li' } );
-		dataFilter.allowAttributes( { name: 'li', styles: { 'color': /[\s\S]+/ } } );
-
-		dataFilter.allowElement( { name: 'a' } );
-		dataFilter.allowAttributes( { name: 'a', styles: { 'background-color': /[\s\S]+/ } } );
-
-		dataFilter.allowElement( { name: 'strong' } );
-		dataFilter.allowAttributes( { name: 'strong', styles: { 'font-weight': /[\s\S]+/ } } );
-
-		dataFilter.allowElement( { name: 'i' } );
-		dataFilter.allowAttributes( { name: 'i', styles: { 'color': /[\s\S]+/ } } );
-		dataFilter.allowAttributes( { name: 'i', attributes: { 'data-foo': /[\s\S]+/ } } );
-
-		dataFilter.allowElement( { name: 's' } );
-		dataFilter.allowAttributes( { name: 's', styles: { 'color': /[\s\S]+/ } } );
 	}
 }
 
@@ -113,7 +63,40 @@ ClassicEditor
 			'bulletedList',
 			'|',
 			'blockquote'
-		]
+		],
+		contentCompatibility: {
+			allowed: [
+				{ name: 'article' },
+
+				{ name: 'section', attributes: { id: /[\s\S]+/ } },
+				{ name: 'section', classes: /[\s\S]+/ },
+				{ name: 'section', styles: { color: 'red' } },
+
+				{ name: /^(details|summary)$/ },
+				{ name: /^(dl|dd|dt)$/ },
+				{ name: 'xyz' },
+
+				{ name: /^(span|cite)$/, attributes: { 'data-foo': /[\s\S]+/ } },
+				{ name: /^(span|cite)$/, styles: { color: /[\s\S]+/ } },
+				{ name: /^(span|cite)$/, attributes: { 'data-order-id': /[\s\S]+/ } },
+				{ name: /^(span|cite)$/, attributes: { 'data-item-id': /[\s\S]+/ } },
+
+				{ name: 'p', attributes: { 'data-foo': /[\s\S]+/ } },
+				{ name: 'p', styles: { 'background-color': /[\s\S]+/ } },
+
+				{ name: 'blockquote', styles: { 'color': /[\s\S]+/ } },
+				{ name: 'li', styles: { 'color': /[\s\S]+/ } },
+				{ name: 'a', styles: { 'background-color': /[\s\S]+/ } },
+				{ name: 'strong', styles: { 'font-weight': /[\s\S]+/ } },
+				{ name: 'i', styles: { 'color': /[\s\S]+/ } },
+				{ name: 'i', attributes: { 'data-foo': /[\s\S]+/ } },
+				{ name: 's', styles: { 'color': /[\s\S]+/ } }
+			],
+			disallowed: [
+				{ name: 'section', attributes: { id: /^_.*/ } },
+				{ name: /^(span|cite)$/, styles: { color: 'red' } }
+			]
+		}
 	} )
 	.then( editor => {
 		window.editor = editor;

From ee76ffbed8fdc7f2620236b91b910d32d49cf624 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Thu, 20 May 2021 11:51:21 +0200
Subject: [PATCH 158/217] Match when any pattern group is matched.

---
 .../src/datafilter.js                         | 34 ++++++++++---
 .../src/generalhtmlsupport.js                 |  4 +-
 .../tests/manual/generalhtmlsupport.js        | 49 +++++++++++--------
 3 files changed, 58 insertions(+), 29 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 319c754d80e..09397683b10 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -198,15 +198,37 @@ export default class DataFilter extends Plugin {
 	 * @param {Function} handleAttributes Callback handling the way the attributes should be processed.
 	 */
 	_loadConfig( config, handleAttributes ) {
-		for ( const { name, ...rules } of config ) {
-			this.allowElement( { name } );
+		for ( const pattern of config ) {
+			this.allowElement( { name: pattern.name } );
 
-			if ( !rules ) {
-				continue;
-			}
+			this._splitRules( pattern )
+				.forEach( rule => handleAttributes( rule ) );
+		}
+	}
+
+	/**
+	 * Rules are matched in conjunction (AND operation), but we want to have a match if any of the rules is matched (OR operation).
+	 * By splitting the rules we force the latter effect.
+	 *
+	 * @private
+	 * @param {module:engine/view/matcher~MatcherPattern} rules
+	 * @returns {Array.<module:engine/view/matcher~MatcherPattern>}
+	 */
+	_splitRules( rules ) {
+		const { name, attributes, classes, styles } = rules;
+		const splitRules = [];
 
-			handleAttributes( { name, ...rules } );
+		if ( attributes ) {
+			splitRules.push( { name, attributes } );
 		}
+		if ( classes ) {
+			splitRules.push( { name, classes } );
+		}
+		if ( styles ) {
+			splitRules.push( { name, styles } );
+		}
+
+		return splitRules;
 	}
 
 	/**
diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
index b4ec6162949..7cc5dfcb7eb 100644
--- a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
@@ -51,8 +51,8 @@ export default class GeneralHtmlSupport extends Plugin {
 		this.dataFilter = new DataFilter( editor, this.dataSchema );
 
 		// Load the filtering configuration.
-		this.dataFilter.loadAllowedConfig( this.editor.config.get( 'contentCompatibility.allowed' ) || [] );
-		this.dataFilter.loadDisallowedConfig( this.editor.config.get( 'contentCompatibility.disallowed' ) || [] );
+		this.dataFilter.loadAllowedConfig( this.editor.config.get( 'generalHtmlSupport.allowed' ) || [] );
+		this.dataFilter.loadDisallowedConfig( this.editor.config.get( 'generalHtmlSupport.disallowed' ) || [] );
 	}
 
 	/**
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 26f128b2ec7..940b12f8a0d 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -64,33 +64,40 @@ ClassicEditor
 			'|',
 			'blockquote'
 		],
-		contentCompatibility: {
+		generalHtmlSupport: {
 			allowed: [
 				{ name: 'article' },
-
-				{ name: 'section', attributes: { id: /[\s\S]+/ } },
-				{ name: 'section', classes: /[\s\S]+/ },
-				{ name: 'section', styles: { color: 'red' } },
-
+				{ name: 'xyz' },
 				{ name: /^(details|summary)$/ },
 				{ name: /^(dl|dd|dt)$/ },
-				{ name: 'xyz' },
-
-				{ name: /^(span|cite)$/, attributes: { 'data-foo': /[\s\S]+/ } },
-				{ name: /^(span|cite)$/, styles: { color: /[\s\S]+/ } },
-				{ name: /^(span|cite)$/, attributes: { 'data-order-id': /[\s\S]+/ } },
-				{ name: /^(span|cite)$/, attributes: { 'data-item-id': /[\s\S]+/ } },
 
-				{ name: 'p', attributes: { 'data-foo': /[\s\S]+/ } },
-				{ name: 'p', styles: { 'background-color': /[\s\S]+/ } },
+				{ name: 'a', styles: { 'background-color': true } },
+				{ name: 'blockquote', styles: { 'color': true } },
+				{ name: 'li', styles: { 'color': true } },
+				{ name: 's', styles: { 'color': true } },
+				{ name: 'strong', styles: { 'font-weight': true } },
 
-				{ name: 'blockquote', styles: { 'color': /[\s\S]+/ } },
-				{ name: 'li', styles: { 'color': /[\s\S]+/ } },
-				{ name: 'a', styles: { 'background-color': /[\s\S]+/ } },
-				{ name: 'strong', styles: { 'font-weight': /[\s\S]+/ } },
-				{ name: 'i', styles: { 'color': /[\s\S]+/ } },
-				{ name: 'i', attributes: { 'data-foo': /[\s\S]+/ } },
-				{ name: 's', styles: { 'color': /[\s\S]+/ } }
+				{
+					name: 'i',
+					styles: { 'color': true },
+					attributes: { 'data-foo': true }
+				},
+				{
+					name: 'section',
+					attributes: { id: true },
+					classes: true,
+					styles: { color: 'red' }
+				},
+				{
+					name: /^(span|cite)$/,
+					styles: { color: true },
+					attributes: [ 'data-foo', 'data-order-id', 'data-item-id' ]
+				},
+				{
+					name: 'p',
+					attributes: { 'data-foo': true },
+					styles: { 'background-color': true }
+				}
 			],
 			disallowed: [
 				{ name: 'section', attributes: { id: /^_.*/ } },

From 8563013a00ae8718269ad38d0e0a777733b1d288 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Thu, 20 May 2021 14:14:02 +0200
Subject: [PATCH 159/217] Match any pattern inside a rule.

---
 .../src/datafilter.js                         | 41 +++++++++++++--
 .../tests/datafilter.js                       | 52 +++++++++++++++----
 2 files changed, 79 insertions(+), 14 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 09397683b10..dc94d06d639 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -23,9 +23,13 @@ import {
 	viewToAttributeInlineConverter,
 	attributeToViewInlineConverter,
 
+<<<<<<< HEAD
 	viewToModelBlockAttributeConverter,
 	modelToViewBlockAttributeConverter
 } from './converters';
+=======
+import { cloneDeep, isPlainObject } from 'lodash-es';
+>>>>>>> b60cdaaadc (Match any pattern inside a rule.)
 
 import '../theme/datafilter.css';
 
@@ -219,13 +223,13 @@ export default class DataFilter extends Plugin {
 		const splitRules = [];
 
 		if ( attributes ) {
-			splitRules.push( { name, attributes } );
+			splitRules.push( ...this._splitPattern( { name, attributes }, 'attributes' ) );
 		}
 		if ( classes ) {
-			splitRules.push( { name, classes } );
+			splitRules.push( ...this._splitPattern( { name, classes }, 'classes' ) );
 		}
 		if ( styles ) {
-			splitRules.push( { name, styles } );
+			splitRules.push( ...this._splitPattern( { name, styles }, 'styles' ) );
 		}
 
 		return splitRules;
@@ -261,6 +265,37 @@ export default class DataFilter extends Plugin {
 		return consumeAttributes( viewElement, conversionApi, this._disallowedAttributes );
 	}
 
+	/**
+	 * TODO: JSdoc, refactoring.
+	 * Separate multiple patterns into separate rules to make them disjunctive.
+	 *
+	 * @param {*} pattern
+	 * @param {*} attributeName
+	 * @returns
+	 */
+	_splitPattern( pattern, attributeName ) {
+		const { name } = pattern;
+
+		if ( isPlainObject( pattern[ attributeName ] ) ) {
+			return Object.entries( pattern[ attributeName ] ).map(
+				( [ key, value ] ) => ( {
+					name,
+					[ attributeName ]: {
+						[ key ]: value
+					}
+				} ) );
+		} else if ( Array.isArray( pattern[ attributeName ] ) ) {
+			return pattern[ attributeName ].map(
+				value => ( {
+					name,
+					[ attributeName ]: [ value ]
+				} )
+			);
+		}
+
+		return pattern;
+	}
+
 	/**
 	 * Registers elements allowed by {@link module:content-compatibility/datafilter~DataFilter#allowElement} method
 	 * once {@link module:core/editor~Editor#data editor's data controller} is initialized.
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 167c1cfce9b..f2c8584256a 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -1276,27 +1276,57 @@ describe( 'DataFilter', () => {
 		}, /data-filter-invalid-definition/, null, definition );
 	} );
 
-	describe.skip( 'fromConfig', () => {
-		// TODO: Better name
-		it( 'should load config', () => {
+	describe( 'loadAllowedConfig', () => {
+		it( 'should load config with simple allowed rule', () => {
 			const config = [
 				{
-					element: 'xyz',
-					attributes: {
-						title: 'foo'
+					name: 'span',
+					styles: { color: true },
+					classes: [ 'foo' ]
+				}
+			];
+
+			dataFilter.loadAllowedConfig( config );
+
+			editor.setData( '<p><span class="foo">foobar</span></p>' );
+
+			// Font feature should take over color CSS property.
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlSpan="(1)">foobar</$text></paragraph>',
+				attributes: {
+					1: {
+						classes: [ 'foo' ]
 					}
 				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><span class="foo">foobar</span></p>' );
+		} );
+
+		it( 'should load config and match whenever a single match has been found', () => {
+			const config = [
+				{
+					name: 'span',
+					styles: { color: true },
+					classes: [ 'foo', 'bar', 'test' ]
+				}
 			];
 
-			dataSchema.registerBlockElement( { view: 'xyz', model: 'modelXyz' } );
-			dataFilter.fromConfig( config );
+			dataFilter.loadAllowedConfig( config );
 
-			editor.setData( '<xyz>foo</xyz>' );
+			editor.setData( '<p><span style="color:blue; font-weight:400" class="foo bar">foobar</span></p>' );
 
+			// Font feature should take over color CSS property.
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph>foo</paragraph>',
-				attributes: {}
+				data: '<paragraph><$text fontColor="blue" htmlSpan="(1)">foobar</$text></paragraph>',
+				attributes: {
+					1: {
+						classes: [ 'foo', 'bar' ]
+					}
+				}
 			} );
+
+			expect( editor.getData() ).to.equal( '<p><span style="color:blue;"><span class="foo bar">foobar</span></span></p>' );
 		} );
 	} );
 

From d6a96306fd4807a3a32be61ebf64ee2dfde17825 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Thu, 20 May 2021 14:19:56 +0200
Subject: [PATCH 160/217] Return pattern as array in _splitPattern method.

---
 packages/ckeditor5-content-compatibility/src/datafilter.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index dc94d06d639..9b6783196e0 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -293,7 +293,7 @@ export default class DataFilter extends Plugin {
 			);
 		}
 
-		return pattern;
+		return [ pattern ];
 	}
 
 	/**

From 141bdc759c517ef58a424fa442bfe76737716240 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Piotrek=20Koszuli=C5=84ski?= <pkoszulinski@gmail.com>
Date: Thu, 20 May 2021 14:32:34 +0200
Subject: [PATCH 161/217] Display the source content as before passed through
 the editor.

---
 .../tests/manual/generalhtmlsupport.html      | 130 ++++++++++--------
 1 file changed, 72 insertions(+), 58 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
index 0e9925b237c..f7c5bd5a7aa 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -1,63 +1,77 @@
 <head>
 	<meta http-equiv="Content-Security-Policy" content="script-src 'self' https://ckeditor.com 'unsafe-inline' 'unsafe-eval'">
+	<style>
+
+	</style>
 </head>
+<div style="display: flex">
+	<div style="width: 40%; margin-right: 20px">
+		<div id="editor">
+			<article>
+				<section id="section1"><p data-foo="foo">Section #1</p></section>
+				<section id="_section2"><p style="background-color: violet;">Section #2</p></section>
+				<section id="section3" style="color: red" class="special_section"><p>Section #3</p></section>
+			</article>
+
+			<details>
+				<summary>Summary</summary>
+				Hello world
+			</details>
+
+			<dl>
+				<dt><p>dt1</p></dt>
+				<dt><p>dt2</p></dt>
+				<dd><p>dd1</p></dd>
+				<dd><p>dd2</p></dd>
+			</dl>
+
+			<xyz><p>XYZ</p></xyz>
+
+			<p><span style="color:red;">Span with styles! This should not be red (due to disallowed content).</span></p>
+
+			<p data-foo="foo">
+				<span data-foo="foo">Nested cite: <cite style="color:blue;">I'm blue!</cite></span>
+			</p>
+			<p data-foo="bar">
+				<span data-foo="foo">Nested span: <span style="color:blue;">I'm blue!</span></span>
+			</p>
+
+			<p><cite>Deeply<cite> nested<cite> cite<span style="color:blue;"> with span!</span></cite></cite></cite></p>
+
+			<p style="background-color: violet;"><span>Span with no attributes!</span></p>
+
+			<p><span style="color:blue;"><span style="color:green;">Span with nested styles!</span></span></p>
+
+			<blockquote style="color: red;">Red quote!</blockquote>
+
+			<ul>
+				<li style="color: blue;">Blue!</li>
+				<li style="color: red;">Red!</li>
+				<li style="color: violet;">Violet!</li>
+				<ul>
+					<li style="color: yellow;">Yellow!</li>
+				</ul>
+			</ul>
+			<p>
+				<a href="example.com" style="background-color:#5de">Link with different background color.</a>
+			</p>
+			<p>
+				<strong style="font-weight:400">Strong with font weight 400</strong>
+			</p>
+			<p>
+				<i data-foo="foo" style="color: green;">Italic with custom attributes</i>
+			</p>
+			<p>
+				<s style="color: red;">Red strike</s>
+			</p>
+		</div>
+	</div>
 
-<div id="editor">
-	<article>
-		<section id="section1"><p data-foo="foo">Section #1</p></section>
-		<section id="_section2"><p style="background-color: violet;">Section #2</p></section>
-		<section id="section3" style="color: red" class="special_section"><p>Section #3</p></section>
-	</article>
-
-	<details>
-		<summary>Summary</summary>
-		Hello world
-	</details>
-
-	<dl>
-		<dt><p>dt1</p></dt>
-		<dt><p>dt2</p></dt>
-		<dd><p>dd1</p></dd>
-		<dd><p>dd2</p></dd>
-	</dl>
-
-	<xyz><p>XYZ</p></xyz>
-
-	<p><span style="color:red;">Span with styles! This should not be red.</span></p>
-
-	<p data-foo="foo">
-		<span data-foo="foo">Nested cite: <cite style="color:blue;">I'm blue!</cite></span>
-	</p>
-	<p data-foo="bar">
-		<span data-foo="foo">Nested span: <span style="color:blue;">I'm blue!</span></span>
-	</p>
-
-	<p><cite>Deeply<cite> nested<cite> cite<span style="color:blue;"> with span!</span></cite></cite></cite></p>
-
-	<p style="background-color: violet;"><span>Span with no attributes!</span></p>
-
-	<p><span style="color:blue;"><span style="color:green;">Span with nested styles!</span></span></p>
-
-	<blockquote style="color: red;">Red quote!</blockquote>
-
-	<ul>
-		<li style="color: blue;">Blue!</li>
-		<li style="color: red;">Red!</li>
-		<li style="color: violet;">Violet!</li>
-		<ul>
-			<li style="color: yellow;">Yellow!</li>
-		</ul>
-	</ul>
-	<p>
-		<a href="example.com" style="background-color:#5de">Link with different background color.</a>
-	</p>
-	<p>
-		<strong style="font-weight:400">Strong with font weight 400</strong>
-	</p>
-	<p>
-		<i data-foo="foo" style="color: green;">Italic with custom attributes</i>
-	</p>
-	<p>
-		<s style="color: red;">Red strike</s>
-	</p>
+	<div style="width: 40%">
+		<h1 style="margin:12px 0 0 0; padding:0 0 5px 0; font-size: 18px; border-bottom: solid 1px grey">Source content:</h1>
+		<div id="preview"></div>
+	</div>
 </div>
+<script>
+	document.getElementById( 'preview' ).innerHTML = document.getElementById( 'editor' ).innerHTML;
+</script>

From e13e84e73b7d44b78c36778faeb6309ec3feab43 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Piotrek=20Koszuli=C5=84ski?= <pkoszulinski@gmail.com>
Date: Thu, 20 May 2021 14:54:41 +0200
Subject: [PATCH 162/217] Some more examples.

---
 .../tests/manual/generalhtmlsupport.html         | 16 +++++++++++-----
 .../tests/manual/generalhtmlsupport.js           | 12 ++++++++++--
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
index f7c5bd5a7aa..a07a831fe6e 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -8,9 +8,15 @@
 	<div style="width: 40%; margin-right: 20px">
 		<div id="editor">
 			<article>
-				<section id="section1"><p data-foo="foo">Section #1</p></section>
-				<section id="_section2"><p style="background-color: violet;">Section #2</p></section>
-				<section id="section3" style="color: red" class="special_section"><p>Section #3</p></section>
+				<section id="section1" data-section-id="shall-not-pass">
+					<p data-foo="foo">Section #1</p>
+				</section>
+				<section id="_section2" data-section-id="123">
+					<p style="background-color: violet;">Section #2</p>
+				</section>
+				<section id="section3" style="color: red" class="special_section">
+					<p>Section #3</p>
+				</section>
 			</article>
 
 			<details>
@@ -55,10 +61,10 @@
 			<p>
 				<a href="example.com" style="background-color:#5de">Link with different background color.</a>
 			</p>
-			<p>
+			<p data-any-property-name="1">
 				<strong style="font-weight:400">Strong with font weight 400</strong>
 			</p>
-			<p>
+			<p data-any-property-name="2">
 				<i data-foo="foo" style="color: green;">Italic with custom attributes</i>
 			</p>
 			<p>
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 940b12f8a0d..f4ac8ac4b49 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -84,7 +84,10 @@ ClassicEditor
 				},
 				{
 					name: 'section',
-					attributes: { id: true },
+					attributes: {
+						id: true,
+						'data-section-id': /^\d+$/
+					},
 					classes: true,
 					styles: { color: 'red' }
 				},
@@ -95,7 +98,12 @@ ClassicEditor
 				},
 				{
 					name: 'p',
-					attributes: { 'data-foo': true },
+					attributes: [
+						{
+							key: /^data-/,
+							value: true
+						}
+					],
 					styles: { 'background-color': true }
 				}
 			],

From 63797d648012d5f63b82d6b6b56abed82672d78e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Mon, 31 May 2021 16:38:54 +0200
Subject: [PATCH 163/217] Add missing tests and docs.

---
 .../src/datafilter.js                         |  16 +-
 .../src/generalhtmlsupport.js                 |   2 +
 .../tests/datafilter.js                       | 410 +++++++++++++++++-
 .../tests/manual/generalhtmlsupport.js        |   1 -
 4 files changed, 407 insertions(+), 22 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 9b6783196e0..d1c36f84dd9 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -23,13 +23,10 @@ import {
 	viewToAttributeInlineConverter,
 	attributeToViewInlineConverter,
 
-<<<<<<< HEAD
 	viewToModelBlockAttributeConverter,
 	modelToViewBlockAttributeConverter
 } from './converters';
-=======
-import { cloneDeep, isPlainObject } from 'lodash-es';
->>>>>>> b60cdaaadc (Match any pattern inside a rule.)
+import { isPlainObject } from 'lodash-es';
 
 import '../theme/datafilter.css';
 
@@ -266,12 +263,13 @@ export default class DataFilter extends Plugin {
 	}
 
 	/**
-	 * TODO: JSdoc, refactoring.
-	 * Separate multiple patterns into separate rules to make them disjunctive.
+	 * Matcher by default has to match **all** patterns to count it as an actual match. By splitting the pattern
+	 * into separate patterns means that any matched pattern will be count as a match.
 	 *
-	 * @param {*} pattern
-	 * @param {*} attributeName
-	 * @returns
+	 * @private
+	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern to split.
+	 * @param {String} attributeName Name of the attribute to split (e.g. 'attributes', 'classes', 'styles').
+	 * @returns {Array.<module:engine/view/matcher~MatcherPattern>}
 	 */
 	_splitPattern( pattern, attributeName ) {
 		const { name } = pattern;
diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
index 7cc5dfcb7eb..e7eb657620b 100644
--- a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
@@ -49,7 +49,9 @@ export default class GeneralHtmlSupport extends Plugin {
 		 * @member {module:content-compatibility/datafilter~DataFilter} #dataFilter
 		 */
 		this.dataFilter = new DataFilter( editor, this.dataSchema );
+	}
 
+	init() {
 		// Load the filtering configuration.
 		this.dataFilter.loadAllowedConfig( this.editor.config.get( 'generalHtmlSupport.allowed' ) || [] );
 		this.dataFilter.loadDisallowedConfig( this.editor.config.get( 'generalHtmlSupport.disallowed' ) || [] );
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index f2c8584256a..200955117d6 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -1277,56 +1277,442 @@ describe( 'DataFilter', () => {
 	} );
 
 	describe( 'loadAllowedConfig', () => {
-		it( 'should load config with simple allowed rule', () => {
+		it( 'should load config and match whenever a single match has been found', () => {
 			const config = [
 				{
 					name: 'span',
 					styles: { color: true },
-					classes: [ 'foo' ]
+					classes: [ 'foo', 'bar', 'test' ],
+					attributes: [ { key: /data-foo.*/, value: true } ]
 				}
 			];
 
 			dataFilter.loadAllowedConfig( config );
 
-			editor.setData( '<p><span class="foo">foobar</span></p>' );
+			editor.setData(
+				'<p>' +
+					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
+					'<span data-foo="foo data">foo data</span>' +
+					'<span data-bar="bar data">bar data</span>' +
+				'</p>'
+			);
 
 			// Font feature should take over color CSS property.
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph><$text htmlSpan="(1)">foobar</$text></paragraph>',
+				data: '<paragraph>' +
+						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
+						'<$text htmlSpan="(2)">foo data</$text>' +
+						'<$text htmlSpan="(3)">bar data</$text>' +
+					'</paragraph>',
 				attributes: {
 					1: {
-						classes: [ 'foo' ]
+						classes: [ 'foo', 'bar' ]
+					},
+					2: {
+						attributes: {
+							'data-foo': 'foo data'
+						}
+					},
+					3: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span style="color:blue;">' +
+						'<span class="foo bar">foobar</span>' +
+					'</span>' +
+					'<span data-foo="foo data">foo data</span>' +
+					'<span>bar data</span>' +
+				'</p>'
+			);
+		} );
+
+		it( 'should match all values', () => {
+			// Sanity check test for splitting patterns that are not objects nor arrays.
+
+			const config = [
+				{
+					name: 'span',
+					styles: true,
+					classes: true,
+					attributes: true
+				}
+			];
+
+			dataFilter.loadAllowedConfig( config );
+
+			editor.setData(
+				'<p>' +
+					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
+					'<span data-foo="foo data">foo data</span>' +
+					'<span data-bar="bar data">bar data</span>' +
+				'</p>'
+			);
+
+			// Font feature should take over color CSS property.
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
+						'<$text htmlSpan="(2)">foo data</$text>' +
+						'<$text htmlSpan="(3)">bar data</$text>' +
+					'</paragraph>',
+				attributes: {
+					1: {
+						classes: [ 'foo', 'bar' ]
+					},
+					2: {
+						attributes: {
+							'data-foo': 'foo data'
+						}
+					},
+					3: {
+						attributes: {
+							'data-bar': 'bar data'
+						}
 					}
 				}
 			} );
 
-			expect( editor.getData() ).to.equal( '<p><span class="foo">foobar</span></p>' );
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span style="color:blue;">' +
+						'<span class="foo bar">foobar</span>' +
+					'</span>' +
+					'<span data-foo="foo data">foo data</span>' +
+					'<span data-bar="bar data">bar data</span>' +
+				'</p>'
+			);
 		} );
 
-		it( 'should load config and match whenever a single match has been found', () => {
+		it( 'should match attributes', () => {
+			const config = [
+				{
+					name: 'span',
+					attributes: [ { key: /data-foo.*/, value: true } ]
+				}
+			];
+
+			dataFilter.loadAllowedConfig( config );
+
+			editor.setData(
+				'<p>' +
+					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
+					'<span data-foo="foo data">foo data</span>' +
+					'<span data-bar="bar data">bar data</span>' +
+				'</p>'
+			);
+
+			// Font feature should take over color CSS property.
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
+						'<$text htmlSpan="(2)">foo data</$text>' +
+						'<$text htmlSpan="(3)">bar data</$text>' +
+					'</paragraph>',
+				attributes: {
+					1: {},
+					2: {
+						attributes: {
+							'data-foo': 'foo data'
+						}
+					},
+					3: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span style="color:blue;">' +
+						'<span>foobar</span>' +
+					'</span>' +
+					'<span data-foo="foo data">foo data</span>' +
+					'<span>bar data</span>' +
+				'</p>'
+			);
+		} );
+
+		it( 'should match classes', () => {
 			const config = [
 				{
 					name: 'span',
-					styles: { color: true },
 					classes: [ 'foo', 'bar', 'test' ]
 				}
 			];
 
 			dataFilter.loadAllowedConfig( config );
 
-			editor.setData( '<p><span style="color:blue; font-weight:400" class="foo bar">foobar</span></p>' );
+			editor.setData(
+				'<p>' +
+					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
+					'<span data-foo="foo data">foo data</span>' +
+					'<span data-bar="bar data">bar data</span>' +
+				'</p>'
+			);
 
 			// Font feature should take over color CSS property.
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph><$text fontColor="blue" htmlSpan="(1)">foobar</$text></paragraph>',
+				data: '<paragraph>' +
+						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
+						'<$text htmlSpan="(2)">foo databar data</$text>' +
+					'</paragraph>',
 				attributes: {
 					1: {
 						classes: [ 'foo', 'bar' ]
-					}
+					},
+					2: {},
+					3: {}
 				}
 			} );
 
-			expect( editor.getData() ).to.equal( '<p><span style="color:blue;"><span class="foo bar">foobar</span></span></p>' );
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span style="color:blue;">' +
+						'<span class="foo bar">foobar</span>' +
+					'</span>' +
+					'<span>foo databar data</span>' +
+				'</p>'
+			);
+		} );
+
+		it( 'should match styles', () => {
+			const config = [
+				{
+					name: 'span',
+					styles: { color: true }
+				}
+			];
+
+			dataFilter.loadAllowedConfig( config );
+
+			editor.setData(
+				'<p>' +
+					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
+					'<span data-foo="foo data">foo data</span>' +
+					'<span data-bar="bar data">bar data</span>' +
+				'</p>'
+			);
+
+			// Font feature should take over color CSS property.
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
+						'<$text htmlSpan="(2)">foo databar data</$text>' +
+					'</paragraph>',
+				attributes: {
+					1: {},
+					2: {},
+					3: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span style="color:blue;">' +
+						'<span>foobar</span>' +
+					'</span>' +
+					'<span>foo databar data</span>' +
+				'</p>'
+			);
+		} );
+	} );
+
+	describe( 'loadDisallowedConfig', () => {
+		it( 'should load config and match whenever a single match has been found', () => {
+			const config = [
+				{
+					name: 'span',
+					styles: { color: true },
+					classes: [ 'foo', 'bar', 'test' ],
+					attributes: [ { key: /data-foo.*/, value: true } ]
+				}
+			];
+
+			dataFilter.loadDisallowedConfig( config );
+
+			editor.setData(
+				'<p>' +
+					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
+					'<span data-foo="foo data">foo data</span>' +
+					'<span data-bar="bar data">bar data</span>' +
+				'</p>'
+			);
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+						'<$text htmlSpan="(1)">foobarfoo databar data</$text>' +
+					'</paragraph>',
+				attributes: {
+					1: {},
+					2: {},
+					3: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span>foobarfoo databar data</span>' +
+				'</p>'
+			);
+		} );
+
+		it( 'should match all values', () => {
+			// Sanity check test for splitting patterns that are not objects nor arrays.
+
+			const config = [
+				{
+					name: 'span',
+					styles: true,
+					classes: true,
+					attributes: true
+				}
+			];
+
+			dataFilter.loadDisallowedConfig( config );
+
+			editor.setData(
+				'<p>' +
+					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
+					'<span data-foo="foo data">foo data</span>' +
+					'<span data-bar="bar data">bar data</span>' +
+				'</p>'
+			);
+
+			// Font feature should take over color CSS property.
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+						'<$text htmlSpan="(1)">foobarfoo databar data</$text>' +
+					'</paragraph>',
+				attributes: {
+					1: {},
+					2: {},
+					3: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span>foobarfoo databar data</span>' +
+				'</p>'
+			);
+		} );
+
+		it( 'should match attributes', () => {
+			const config = [
+				{
+					name: 'span',
+					attributes: [ { key: /data-foo.*/, value: true } ]
+				}
+			];
+
+			dataFilter.loadDisallowedConfig( config );
+
+			editor.setData(
+				'<p>' +
+					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
+					'<span data-foo="foo data">foo data</span>' +
+					'<span data-bar="bar data">bar data</span>' +
+				'</p>'
+			);
+
+			// Font feature should take over color CSS property.
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
+						'<$text htmlSpan="(2)">foo databar data</$text>' +
+					'</paragraph>',
+				attributes: {
+					1: {},
+					2: {},
+					3: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span style="color:blue;">' +
+						'<span>foobar</span>' +
+					'</span>' +
+					'<span>foo databar data</span>' +
+				'</p>'
+			);
+		} );
+
+		it( 'should match classes', () => {
+			const config = [
+				{
+					name: 'span',
+					classes: [ 'foo', 'bar', 'test' ]
+				}
+			];
+
+			dataFilter.loadDisallowedConfig( config );
+
+			editor.setData(
+				'<p>' +
+					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
+					'<span data-foo="foo data">foo data</span>' +
+					'<span data-bar="bar data">bar data</span>' +
+				'</p>'
+			);
+
+			// Font feature should take over color CSS property.
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
+						'<$text htmlSpan="(2)">foo databar data</$text>' +
+					'</paragraph>',
+				attributes: {
+					1: {},
+					2: {},
+					3: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span style="color:blue;">' +
+						'<span>foobar</span>' +
+					'</span>' +
+					'<span>foo databar data</span>' +
+				'</p>'
+			);
+		} );
+
+		it( 'should match styles', () => {
+			const config = [
+				{
+					name: 'span',
+					styles: { color: true }
+				}
+			];
+
+			dataFilter.loadDisallowedConfig( config );
+
+			editor.setData(
+				'<p>' +
+					'<span style="color:blue;">' +
+					'<span>foobar</span>' +
+					'<span>foo databar data</span>' +
+				'</p>'
+			);
+
+			// Font feature should take over color CSS property.
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+						'<$text htmlSpan="(1)">foobarfoo databar data</$text>' +
+					'</paragraph>',
+				attributes: {
+					1: {},
+					2: {}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span>foobarfoo databar data</span>' +
+				'</p>'
+			);
 		} );
 	} );
 
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index f4ac8ac4b49..0a6bcd468d6 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -67,7 +67,6 @@ ClassicEditor
 		generalHtmlSupport: {
 			allowed: [
 				{ name: 'article' },
-				{ name: 'xyz' },
 				{ name: /^(details|summary)$/ },
 				{ name: /^(dl|dd|dt)$/ },
 

From 87b0b4e858eff2416a8d74c6a43eecd92fcdceb4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Wed, 2 Jun 2021 14:21:14 +0200
Subject: [PATCH 164/217] Review fixes.

---
 .../ckeditor5-content-compatibility/src/datafilter.js     | 3 +--
 .../ckeditor5-content-compatibility/tests/datafilter.js   | 8 ++++----
 .../tests/manual/generalhtmlsupport.js                    | 3 +++
 3 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index d1c36f84dd9..92be8aeec59 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -202,8 +202,7 @@ export default class DataFilter extends Plugin {
 		for ( const pattern of config ) {
 			this.allowElement( { name: pattern.name } );
 
-			this._splitRules( pattern )
-				.forEach( rule => handleAttributes( rule ) );
+			this._splitRules( pattern ).forEach( handleAttributes );
 		}
 	}
 
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 200955117d6..77420a044f3 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -1283,7 +1283,7 @@ describe( 'DataFilter', () => {
 					name: 'span',
 					styles: { color: true },
 					classes: [ 'foo', 'bar', 'test' ],
-					attributes: [ { key: /data-foo.*/, value: true } ]
+					attributes: [ { key: /^data-foo.*$/, value: true } ]
 				}
 			];
 
@@ -1389,7 +1389,7 @@ describe( 'DataFilter', () => {
 			const config = [
 				{
 					name: 'span',
-					attributes: [ { key: /data-foo.*/, value: true } ]
+					attributes: [ { key: /^data-foo.*$/, value: true } ]
 				}
 			];
 
@@ -1524,7 +1524,7 @@ describe( 'DataFilter', () => {
 					name: 'span',
 					styles: { color: true },
 					classes: [ 'foo', 'bar', 'test' ],
-					attributes: [ { key: /data-foo.*/, value: true } ]
+					attributes: [ { key: /^data-foo.*$/, value: true } ]
 				}
 			];
 
@@ -1601,7 +1601,7 @@ describe( 'DataFilter', () => {
 			const config = [
 				{
 					name: 'span',
-					attributes: [ { key: /data-foo.*/, value: true } ]
+					attributes: [ { key: /^data-foo.*$/, value: true } ]
 				}
 			];
 
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index 0a6bcd468d6..defe6d24752 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -38,6 +38,9 @@ class ExtendHTMLSupport extends Plugin {
 				inheritAllFrom: '$htmlBlock'
 			}
 		} );
+
+		// Custom elements need to be filtered using direct API instead of config.
+		dataFilter.allowElement( { name: 'xyz' } );
 	}
 }
 

From 5a8528ea345a98c9baa30f4af06d88e4cf373f15 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Fri, 4 Jun 2021 08:53:31 +0200
Subject: [PATCH 165/217] Update `allowElement()` method and tests.

---
 .../src/datafilter.js                         | 10 +-
 .../tests/datafilter.js                       | 93 ++++++++++---------
 .../tests/manual/generalhtmlsupport.js        |  2 +-
 3 files changed, 54 insertions(+), 51 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 92be8aeec59..bbf63546c38 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -35,9 +35,7 @@ import '../theme/datafilter.css';
  *
  * To enable registered element in the editor, use {@link module:content-compatibility/datafilter~DataFilter#allowElement} method:
  *
- *		dataFilter.allowElement( {
- *			name: 'section'
- *		} );
+ *		dataFilter.allowElement( 'section' );
  *
  * You can also allow or disallow specific element attributes:
  *
@@ -155,8 +153,8 @@ export default class DataFilter extends Plugin {
 	 *
 	 * @param {String|RegExp} viewName String or regular expression matching view name.
 	 */
-	allowElement( config ) {
-		for ( const definition of this._dataSchema.getDefinitionsForView( config.name, true ) ) {
+	allowElement( viewName ) {
+		for ( const definition of this._dataSchema.getDefinitionsForView( viewName, true ) ) {
 			if ( this._allowedElements.has( definition ) ) {
 				continue;
 			}
@@ -200,7 +198,7 @@ export default class DataFilter extends Plugin {
 	 */
 	_loadConfig( config, handleAttributes ) {
 		for ( const pattern of config ) {
-			this.allowElement( { name: pattern.name } );
+			this.allowElement( pattern.name );
 
 			this._splitRules( pattern ).forEach( handleAttributes );
 		}
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 77420a044f3..f17923f07de 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -93,7 +93,7 @@ describe( 'DataFilter', () => {
 		it( 'should allow element registered after editor initialization', () => {
 			const dataFilter = initEditor.plugins.get( DataFilter );
 
-			dataFilter.allowElement( { name: 'span' } );
+			dataFilter.allowElement( 'span' );
 
 			initEditor.setData( '<p><span>foobar</span></p>' );
 
@@ -126,12 +126,12 @@ describe( 'DataFilter', () => {
 
 			init() {
 				const dataFilter = this.editor.plugins.get( DataFilter );
-				dataFilter.allowElement( { name: 'article' } );
+				dataFilter.allowElement( 'article' );
 			}
 
 			afterInit() {
 				const dataFilter = this.editor.plugins.get( DataFilter );
-				dataFilter.allowElement( { name: 'section' } );
+				dataFilter.allowElement( 'section' );
 			}
 		}
 	} );
@@ -324,7 +324,7 @@ describe( 'DataFilter', () => {
 
 	describe( 'block', () => {
 		it( 'should allow element', () => {
-			dataFilter.allowElement( { name: 'article' } );
+			dataFilter.allowElement( 'article' );
 
 			editor.setData( '<article>' +
 				'<section><paragraph>section1</paragraph></section>' +
@@ -339,7 +339,7 @@ describe( 'DataFilter', () => {
 				'<article><p>section1section2</p></article>'
 			);
 
-			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowElement( 'section' );
 
 			editor.setData( '<article>' +
 				'<section><paragraph>section1</paragraph></section>' +
@@ -360,7 +360,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow deeply nested structure', () => {
-			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowElement( 'section' );
 
 			editor.setData(
 				'<section><p>1</p>' +
@@ -385,7 +385,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow attributes', () => {
-			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowElement( 'section' );
 			dataFilter.allowAttributes( {
 				name: 'section',
 				attributes: {
@@ -412,7 +412,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow attributes (styles)', () => {
-			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowElement( 'section' );
 			dataFilter.allowAttributes( {
 				name: 'section',
 				styles: {
@@ -441,7 +441,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow attributes (classes)', () => {
-			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowElement( 'section' );
 			dataFilter.allowAttributes( { name: 'section', classes: [ 'foo', 'bar' ] } );
 
 			editor.setData( '<section class="foo bar"><p>foobar</p></section>' );
@@ -459,7 +459,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow nested attributes', () => {
-			dataFilter.allowElement( { name: /^(article|section)$/ } );
+			dataFilter.allowElement( /^(article|section)$/ );
 			dataFilter.allowAttributes( { name: /[\s\S]+/, attributes: { 'data-foo': /foo|bar/ } } );
 
 			editor.setData( '<article data-foo="foo">' +
@@ -494,7 +494,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow attributes for all allowed definitions', () => {
-			dataFilter.allowElement( { name: /^(section|article)$/ } );
+			dataFilter.allowElement( /^(section|article)$/ );
 
 			dataFilter.allowAttributes( { name: /^(section|article)$/, attributes: { 'data-foo': 'foo' } } );
 			dataFilter.allowAttributes( { name: /^(section|article)$/, attributes: { 'data-bar': 'bar' } } );
@@ -528,7 +528,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should disallow attributes', () => {
-			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowElement( 'section' );
 			dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': /[\s\S]+/ } } );
 			dataFilter.disallowAttributes( { name: 'section', attributes: { 'data-foo': 'bar' } } );
 
@@ -556,7 +556,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should disallow attributes (styles)', () => {
-			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowElement( 'section' );
 			dataFilter.allowAttributes( { name: 'section', styles: { color: /[\s\S]+/ } } );
 			dataFilter.disallowAttributes( { name: 'section', styles: { color: 'red' } } );
 
@@ -584,7 +584,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should disallow attributes (classes)', () => {
-			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowElement( 'section' );
 			dataFilter.allowAttributes( { name: 'section', classes: [ 'foo', 'bar' ] } );
 			dataFilter.disallowAttributes( { name: 'section', classes: [ 'bar' ] } );
 
@@ -616,7 +616,7 @@ describe( 'DataFilter', () => {
 			} );
 
 			expect( () => {
-				dataFilter.allowElement( { name: 'xyz' } );
+				dataFilter.allowElement( 'xyz' );
 			} ).to.not.throw();
 		} );
 
@@ -627,7 +627,7 @@ describe( 'DataFilter', () => {
 				} );
 			} );
 
-			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowElement( 'section' );
 			dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': true } } );
 
 			editor.setData( '<section data-foo><p>foo</p></section>' );
@@ -647,7 +647,7 @@ describe( 'DataFilter', () => {
 				}, { priority: 'high' } );
 			} );
 
-			dataFilter.allowElement( { name: 'section' } );
+			dataFilter.allowElement( 'section' );
 			dataFilter.allowAttributes( { name: 'section', attributes: { 'data-foo': true } } );
 
 			editor.setData( '<section data-foo><p>foo</p></section>' );
@@ -670,7 +670,7 @@ describe( 'DataFilter', () => {
 		it( 'should not convert attributes if the model schema item definition is not registered', () => {
 			dataSchema.registerBlockElement( { view: 'xyz', model: 'modelXyz' } );
 
-			dataFilter.allowElement( { name: 'xyz' } );
+			dataFilter.allowElement( 'xyz' );
 			dataFilter.allowAttributes( { name: 'xyz', attributes: { 'data-foo': 'foo' } } );
 
 			// We are not registering model schema anywhere, to check if upcast
@@ -694,7 +694,7 @@ describe( 'DataFilter', () => {
 
 			editor.model.schema.register( 'htmlXyz', { inheritAllFrom: '$block' } );
 
-			dataFilter.allowElement( { name: 'xyz' } );
+			dataFilter.allowElement( 'xyz' );
 
 			editor.setData( '<xyz>foo</xyz>' );
 
@@ -725,7 +725,7 @@ describe( 'DataFilter', () => {
 
 	describe( 'inline', () => {
 		it( 'should allow element', () => {
-			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowElement( 'cite' );
 
 			editor.setData( '<p><cite>foobar</cite></p>' );
 
@@ -740,7 +740,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow deeply nested structure', () => {
-			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowElement( 'cite' );
 
 			editor.setData( '<p><cite>foo<cite>bar<cite>baz</cite></cite></cite>' );
 
@@ -757,7 +757,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow attributes', () => {
-			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowElement( 'cite' );
 			dataFilter.allowAttributes( {
 				name: 'cite',
 				attributes: {
@@ -782,7 +782,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow attributes (styles)', () => {
-			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowElement( 'cite' );
 			dataFilter.allowAttributes( {
 				name: 'cite',
 				styles: {
@@ -811,7 +811,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow attributes (classes)', () => {
-			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowElement( 'cite' );
 			dataFilter.allowAttributes( { name: 'cite', classes: [ 'foo', 'bar' ] } );
 
 			editor.setData( '<p><cite class="foo bar">foobar</cite></p>' );
@@ -827,7 +827,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow nested attributes', () => {
-			dataFilter.allowElement( { name: /^(span|cite)$/ } );
+			dataFilter.allowElement( /^(span|cite)$/ );
 			dataFilter.allowAttributes( { name: /^(span|cite)$/, attributes: { 'data-foo': 'foo' } } );
 			dataFilter.allowAttributes( { name: /^(span|cite)$/, attributes: { 'data-bar': 'bar' } } );
 
@@ -869,7 +869,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should disallow attributes', () => {
-			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowElement( 'cite' );
 			dataFilter.allowAttributes( { name: 'cite', attributes: { 'data-foo': /[\s\S]+/ } } );
 			dataFilter.disallowAttributes( { name: 'cite', attributes: { 'data-foo': 'bar' } } );
 
@@ -891,7 +891,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should disallow attributes (styles)', () => {
-			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowElement( 'cite' );
 			dataFilter.allowAttributes( { name: 'cite', styles: { color: /[\s\S]+/ } } );
 			dataFilter.disallowAttributes( { name: 'cite', styles: { color: 'red' } } );
 
@@ -920,7 +920,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should disallow attributes (classes)', () => {
-			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowElement( 'cite' );
 			dataFilter.allowAttributes( { name: 'cite', classes: [ 'foo', 'bar' ] } );
 			dataFilter.disallowAttributes( { name: 'cite', classes: [ 'bar' ] } );
 
@@ -949,7 +949,7 @@ describe( 'DataFilter', () => {
 				} );
 			} );
 
-			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowElement( 'cite' );
 			dataFilter.allowAttributes( { name: 'cite', attributes: { 'data-foo': true } } );
 
 			editor.setData( '<p><cite data-foo>foo</cite></p>' );
@@ -971,7 +971,7 @@ describe( 'DataFilter', () => {
 				}, { priority: 'high' } );
 			} );
 
-			dataFilter.allowElement( { name: 'cite' } );
+			dataFilter.allowElement( 'cite' );
 			dataFilter.allowAttributes( { name: 'cite', attributes: { 'data-foo': true } } );
 
 			editor.setData( '<p><cite data-foo>foo</cite></p>' );
@@ -992,7 +992,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should correctly merge class names', () => {
-			dataFilter.allowElement( { name: 'span' } );
+			dataFilter.allowElement( 'span' );
 			dataFilter.allowAttributes( { name: 'span', classes: /[\s\S]+/ } );
 
 			editor.setData( '<p><span class="foo">foo<span class="bar">bar<span class="baz">baz</span></span></span></p>' );
@@ -1027,7 +1027,7 @@ describe( 'DataFilter', () => {
 					}
 				} );
 
-				dataFilter.allowElement( { name: 'xyz' } );
+				dataFilter.allowElement( 'xyz' );
 
 				expect( editor.model.schema.getAttributeProperties( 'htmlXyz' ) ).to.deep.equal( { copyOnEnter: true } );
 			} );
@@ -1038,7 +1038,7 @@ describe( 'DataFilter', () => {
 					model: 'htmlXyz'
 				} );
 
-				dataFilter.allowElement( { name: 'xyz' } );
+				dataFilter.allowElement( 'xyz' );
 
 				expect( editor.model.schema.getAttributeProperties( 'htmlXyz' ) ).to.deep.equal( {} );
 			} );
@@ -1059,7 +1059,7 @@ describe( 'DataFilter', () => {
 				}
 			} );
 
-			dataFilter.allowElement( { name: 'xyz' } );
+			dataFilter.allowElement( 'xyz' );
 
 			editor.setData( '<p><xyz>foobar</xyz></p>' );
 
@@ -1072,7 +1072,7 @@ describe( 'DataFilter', () => {
 			// 'a' element is registered by data schema with priority 5.
 			// We are checking if this element will be correctly nested due to different
 			// AttributeElement priority than default.
-			dataFilter.allowElement( { name: 'a' } );
+			dataFilter.allowElement( 'a' );
 			dataFilter.allowAttributes( { name: 'a', attributes: { 'data-foo': 'foo' } } );
 
 			editor.setData( '<p><a href="example.com" data-foo="foo">link</a></p>' );
@@ -1093,7 +1093,7 @@ describe( 'DataFilter', () => {
 	} );
 
 	it( 'should correctly resolve attributes nesting order', () => {
-		dataFilter.allowElement( { name: 'span' } );
+		dataFilter.allowElement( 'span' );
 		dataFilter.allowAttributes( { name: 'span', styles: { 'font-weight': /[\s\S]+/ } } );
 
 		editor.setData( '<p><span style="font-weight:700;"><span style="font-weight:400;">foobar</span></span>' );
@@ -1111,7 +1111,7 @@ describe( 'DataFilter', () => {
 	} );
 
 	it( 'should allow using attributes by other features', () => {
-		dataFilter.allowElement( { name: 'span' } );
+		dataFilter.allowElement( 'span' );
 		dataFilter.allowAttributes( { name: 'span', styles: { 'color': /[\s\S]+/ } } );
 
 		editor.setData( '<p><span style="color:blue;">foobar</span></p>' );
@@ -1129,7 +1129,7 @@ describe( 'DataFilter', () => {
 
 	describe( 'existing features', () => {
 		it( 'should allow additional attributes', () => {
-			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowElement( 'p' );
 			dataFilter.allowAttributes( { name: 'p', attributes: { 'data-foo': 'foo' } } );
 
 			editor.setData( '<p data-foo="foo">foo</p>' );
@@ -1147,7 +1147,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow additional attributes (classes)', () => {
-			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowElement( 'p' );
 			dataFilter.allowAttributes( { name: 'p', classes: /[\s\S]+/ } );
 
 			editor.setData( '<p class="foo">foo</p><p class="bar">bar</p>' );
@@ -1168,7 +1168,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow additional attributes (styles)', () => {
-			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowElement( 'p' );
 			dataFilter.allowAttributes( { name: 'p', styles: { 'color': /[\s\S]+/ } } );
 
 			editor.setData( '<p style="color:red;">foo</p>' );
@@ -1186,7 +1186,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should disallow attributes', () => {
-			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowElement( 'p' );
 			dataFilter.allowAttributes( { name: 'p', attributes: { 'data-foo': /[\s\S]+/ } } );
 			dataFilter.disallowAttributes( { name: 'p', attributes: { 'data-foo': 'bar' } } );
 
@@ -1207,7 +1207,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should disallow attributes (styles)', () => {
-			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowElement( 'p' );
 			dataFilter.allowAttributes( { name: 'p', styles: { color: /[\s\S]+/ } } );
 			dataFilter.disallowAttributes( { name: 'p', styles: { color: 'red' } } );
 
@@ -1228,7 +1228,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should disallow attributes (classes)', () => {
-			dataFilter.allowElement( { name: 'p' } );
+			dataFilter.allowElement( 'p' );
 			dataFilter.allowAttributes( { name: 'p', classes: [ 'foo', 'bar' ] } );
 			dataFilter.disallowAttributes( { name: 'p', classes: [ 'bar' ] } );
 
@@ -1244,7 +1244,7 @@ describe( 'DataFilter', () => {
 	} );
 
 	it( 'should preserve attributes not used by other features', () => {
-		dataFilter.allowElement( { name: 'span' } );
+		dataFilter.allowElement( 'span' );
 		dataFilter.allowAttributes( { name: 'span', styles: { 'color': /[\s\S]+/ } } );
 		dataFilter.allowAttributes( { name: 'span', classes: [ 'foo', 'bar' ] } );
 
@@ -1272,8 +1272,13 @@ describe( 'DataFilter', () => {
 		sinon.stub( dataSchema, 'getDefinitionsForView' ).returns( new Set( [ definition ] ) );
 
 		expectToThrowCKEditorError( () => {
+<<<<<<< HEAD
 			dataFilter.allowElement( { name: 'xyz' } );
 		}, /data-filter-invalid-definition/, null, definition );
+=======
+			dataFilter.allowElement( 'xyz' );
+		}, /data-filter-invalid-definition-type/, null, definition );
+>>>>>>> 8dd542497f (Update `allowElement()` method and tests.)
 	} );
 
 	describe( 'loadAllowedConfig', () => {
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
index defe6d24752..5863fa3bb29 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
@@ -40,7 +40,7 @@ class ExtendHTMLSupport extends Plugin {
 		} );
 
 		// Custom elements need to be filtered using direct API instead of config.
-		dataFilter.allowElement( { name: 'xyz' } );
+		dataFilter.allowElement( 'xyz' );
 	}
 }
 

From 3df9664cf56dd7e60f0f10f157d1700c7891bd0e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Fri, 4 Jun 2021 12:58:17 +0200
Subject: [PATCH 166/217] Rebase fixes.

---
 .../tests/codeblock.js                        | 16 ++--
 .../tests/datafilter.js                       | 74 +++----------------
 .../tests/manual/codeblock.js                 |  2 +-
 .../tests/manual/objects.js                   |  2 +-
 4 files changed, 22 insertions(+), 72 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/codeblock.js b/packages/ckeditor5-content-compatibility/tests/codeblock.js
index cbed5810529..eab4b694294 100644
--- a/packages/ckeditor5-content-compatibility/tests/codeblock.js
+++ b/packages/ckeditor5-content-compatibility/tests/codeblock.js
@@ -37,7 +37,7 @@ describe( 'CodeBlockHtmlSupport', () => {
 	} );
 
 	it( 'should allow attributes', () => {
-		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowElement( /^(pre|code)$/ );
 		dataFilter.allowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
 
 		editor.setData( '<pre data-foo="foo"><code data-foo="foo">foobar</code></pre>' );
@@ -64,7 +64,7 @@ describe( 'CodeBlockHtmlSupport', () => {
 	} );
 
 	it( 'should allow attributes (classes)', () => {
-		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowElement( /^(pre|code)$/ );
 		dataFilter.allowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
 
 		editor.setData( '<pre class="foo"><code class="foo">foobar</code></pre>' );
@@ -87,7 +87,7 @@ describe( 'CodeBlockHtmlSupport', () => {
 	} );
 
 	it( 'should allow attributes (styles)', () => {
-		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowElement( /^(pre|code)$/ );
 		dataFilter.allowAttributes( { name: 'pre', styles: { background: 'blue' } } );
 		dataFilter.allowAttributes( { name: 'code', styles: { color: 'red' } } );
 
@@ -115,7 +115,7 @@ describe( 'CodeBlockHtmlSupport', () => {
 	} );
 
 	it( 'should disallow attributes', () => {
-		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowElement( /^(pre|code)$/ );
 		dataFilter.allowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
 		dataFilter.disallowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
 
@@ -130,7 +130,7 @@ describe( 'CodeBlockHtmlSupport', () => {
 	} );
 
 	it( 'should disallow attributes (classes)', () => {
-		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowElement( /^(pre|code)$/ );
 		dataFilter.allowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
 		dataFilter.disallowAttributes( { name: /^(pre|code)$/, classes: [ 'foo' ] } );
 
@@ -145,7 +145,7 @@ describe( 'CodeBlockHtmlSupport', () => {
 	} );
 
 	it( 'should disallow attributes (styles)', () => {
-		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowElement( /^(pre|code)$/ );
 
 		dataFilter.allowAttributes( { name: 'pre', styles: { background: 'blue' } } );
 		dataFilter.allowAttributes( { name: 'code', styles: { color: 'red' } } );
@@ -164,7 +164,7 @@ describe( 'CodeBlockHtmlSupport', () => {
 	} );
 
 	it( 'should allow attributes on code element existing alone', () => {
-		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowElement( /^(pre|code)$/ );
 		dataFilter.allowAttributes( { name: 'code', attributes: { 'data-foo': /[\s\S]+/ } } );
 
 		editor.setData( '<p><code data-foo="foo">foobar</code></p>' );
@@ -192,7 +192,7 @@ describe( 'CodeBlockHtmlSupport', () => {
 			} );
 		} );
 
-		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowElement( /^(pre|code)$/ );
 		dataFilter.allowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': true } } );
 
 		editor.setData( '<pre data-foo><code data-foo>foobar</code></section>' );
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index f17923f07de..51d46db9971 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -138,7 +138,7 @@ describe( 'DataFilter', () => {
 
 	describe( 'object', () => {
 		it( 'should allow element', () => {
-			dataFilter.allowElement( { name: 'input' } );
+			dataFilter.allowElement( 'input' );
 
 			editor.setData( '<p><input></p>' );
 
@@ -150,7 +150,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow element content', () => {
-			dataFilter.allowElement( { name: 'video' } );
+			dataFilter.allowElement( 'video' );
 
 			editor.setData( '<p><video>' +
 				'<source src="https://example.com/video.mp4" type="video/mp4">' +
@@ -181,7 +181,7 @@ describe( 'DataFilter', () => {
 				}
 			} );
 
-			dataFilter.allowElement( { name: 'xyz' } );
+			dataFilter.allowElement( 'xyz' );
 
 			editor.setData( '<xyz>foobar</xyz>' );
 
@@ -193,8 +193,8 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow attributes', () => {
-			dataFilter.allowElement( { name: 'input' } );
-			dataFilter.allowAttributes( { name: 'input', attributes: { type: true } } );
+			dataFilter.allowElement( 'input' );
+			dataFilter.allowAttributes( { name: 'input', attributes: { type: 'text' } } );
 
 			editor.setData( '<p><input type="text"></p>' );
 
@@ -213,7 +213,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow attributes (styles)', () => {
-			dataFilter.allowElement( { name: 'input' } );
+			dataFilter.allowElement( 'input' );
 			dataFilter.allowAttributes( { name: 'input', styles: { color: 'red' } } );
 
 			editor.setData( '<p><input style="color:red;"></p>' );
@@ -233,7 +233,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should allow attributes (classes)', () => {
-			dataFilter.allowElement( { name: 'input' } );
+			dataFilter.allowElement( 'input' );
 			dataFilter.allowAttributes( { name: 'input', classes: [ 'foobar' ] } );
 
 			editor.setData( '<p><input class="foobar"></p>' );
@@ -251,7 +251,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should disallow attributes', () => {
-			dataFilter.allowElement( { name: 'input' } );
+			dataFilter.allowElement( 'input' );
 			dataFilter.allowAttributes( { name: 'input', attributes: { type: true } } );
 			dataFilter.disallowAttributes( { name: 'input', attributes: { type: 'hidden' } } );
 
@@ -275,7 +275,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should disallow attributes (styles)', () => {
-			dataFilter.allowElement( { name: 'input' } );
+			dataFilter.allowElement( 'input' );
 			dataFilter.allowAttributes( { name: 'input', styles: { color: /^(red|blue)$/ } } );
 			dataFilter.disallowAttributes( { name: 'input', styles: { color: 'red' } } );
 
@@ -299,7 +299,7 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should disallow attributes (classes)', () => {
-			dataFilter.allowElement( { name: 'input' } );
+			dataFilter.allowElement( 'input' );
 			dataFilter.allowAttributes( { name: 'input', classes: [ 'foo', 'bar' ] } );
 			dataFilter.disallowAttributes( { name: 'input', classes: [ 'bar' ] } );
 
@@ -718,7 +718,7 @@ describe( 'DataFilter', () => {
 
 			// At this point we will be trying to register converter without valid view name.
 			expect( () => {
-				dataFilter.allowElement( { name: 'bar' } );
+				dataFilter.allowElement( 'bar' );
 			} ).to.not.throw();
 		} );
 	} );
@@ -1272,13 +1272,8 @@ describe( 'DataFilter', () => {
 		sinon.stub( dataSchema, 'getDefinitionsForView' ).returns( new Set( [ definition ] ) );
 
 		expectToThrowCKEditorError( () => {
-<<<<<<< HEAD
-			dataFilter.allowElement( { name: 'xyz' } );
-		}, /data-filter-invalid-definition/, null, definition );
-=======
 			dataFilter.allowElement( 'xyz' );
-		}, /data-filter-invalid-definition-type/, null, definition );
->>>>>>> 8dd542497f (Update `allowElement()` method and tests.)
+		}, /data-filter-invalid-definition/, null, definition );
 	} );
 
 	describe( 'loadAllowedConfig', () => {
@@ -1720,49 +1715,4 @@ describe( 'DataFilter', () => {
 			);
 		} );
 	} );
-
-	function getModelDataWithAttributes( model, options ) {
-		// Simplify GHS attributes as they are not very readable at this point due to object structure.
-		let counter = 1;
-		const data = getModelData( model, options ).replace( /(html.*?)="{.*?}"/g, ( fullMatch, attributeName ) => {
-			return `${ attributeName }="(${ counter++ })"`;
-		} );
-
-		const range = model.createRangeIn( model.document.getRoot() );
-
-		let attributes = [];
-		for ( const item of range.getItems() ) {
-			for ( const [ key, value ] of sortAttributes( item.getAttributes() ) ) {
-				if ( key.startsWith( 'html' ) ) {
-					attributes.push( value );
-				}
-			}
-		}
-
-		attributes = attributes.reduce( ( prev, cur, index ) => {
-			prev[ index + 1 ] = cur;
-			return prev;
-		}, {} );
-
-		return { data, attributes };
-	}
-
-	function sortAttributes( attributes ) {
-		attributes = Array.from( attributes );
-
-		return attributes.sort( ( attr1, attr2 ) => {
-			const key1 = attr1[ 0 ];
-			const key2 = attr2[ 0 ];
-
-			if ( key1 > key2 ) {
-				return 1;
-			}
-
-			if ( key1 < key2 ) {
-				return -1;
-			}
-
-			return 0;
-		} );
-	}
 } );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/codeblock.js b/packages/ckeditor5-content-compatibility/tests/manual/codeblock.js
index 2ce9ed27874..bda1ed39ed4 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/codeblock.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/codeblock.js
@@ -27,7 +27,7 @@ class ExtendHTMLSupport extends Plugin {
 	init() {
 		const dataFilter = this.editor.plugins.get( 'DataFilter' );
 
-		dataFilter.allowElement( { name: /^(pre|code)$/ } );
+		dataFilter.allowElement( /^(pre|code)$/ );
 		dataFilter.allowAttributes( { name: /^(pre|code)$/, styles: { color: /[\s\S]+/ } } );
 		dataFilter.allowAttributes( { name: /^(pre|code)$/, styles: { background: /[\s\S]+/ } } );
 		dataFilter.allowAttributes( { name: /^(pre|code)$/, attributes: { 'data-foo': /[\s\S]+/ } } );
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.js b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
index cdabcd5531d..76a6c9b97b4 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/objects.js
+++ b/packages/ckeditor5-content-compatibility/tests/manual/objects.js
@@ -63,7 +63,7 @@ class ExtendHTMLSupport extends Plugin {
 		];
 
 		for ( const definition of definitions ) {
-			dataFilter.allowElement( { name: definition.name } );
+			dataFilter.allowElement( definition.name );
 
 			for ( const key of ( definition.attributes || [] ) ) {
 				const attributes = {};

From f8a2f3988ef9f9c08272c9f55666f6c9fb11751a Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 8 Jun 2021 10:41:54 +0200
Subject: [PATCH 167/217] Fixed loading data filter by ghs plugin.

---
 .../src/generalhtmlsupport.js                 | 36 ++++---------------
 .../tests/dataschema.js                       |  6 ++--
 2 files changed, 11 insertions(+), 31 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
index e7eb657620b..81e615ba2e9 100644
--- a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
@@ -9,14 +9,13 @@
 
 import { Plugin } from 'ckeditor5/src/core';
 import DataFilter from './datafilter';
-import DataSchema from './dataschema';
 import CodeBlockHtmlSupport from './integrations/codeblock';
 
 /**
  * The General HTML Support feature.
  *
- * This is a "glue" plugin which initializes the {@link module:content-compatibility/dataschema~DataSchema data schema}
- * and {@link module:content-compatibility/datafilter~DataFilter data filter} features.
+ * This is a "glue" plugin which initializes the {@link module:content-compatibility/datafilter~DataFilter data filter} configuration
+ * and features integration with the General HTML Support.
  *
  * @extends module:core/plugin~Plugin
  */
@@ -28,33 +27,13 @@ export default class GeneralHtmlSupport extends Plugin {
 		return 'GeneralHtmlSupport';
 	}
 
-	/**
-	 * @param {module:core/editor/editor~Editor} editor
-	 */
-	constructor( editor ) {
-		super( editor );
-
-		/**
-		 * An instance of the {@link module:content-compatibility/dataschema~DataSchema}.
-		 *
-		 * @readonly
-		 * @member {module:content-compatibility/dataschema~DataSchema} #dataSchema
-		 */
-		this.dataSchema = new DataSchema();
-
-		/**
-		 * An instance of the {@link module:content-compatibility/datafilter~DataFilter}.
-		 *
-		 * @readonly
-		 * @member {module:content-compatibility/datafilter~DataFilter} #dataFilter
-		 */
-		this.dataFilter = new DataFilter( editor, this.dataSchema );
-	}
-
 	init() {
+		const editor = this.editor;
+		const dataFilter = editor.plugins.get( DataFilter );
+
 		// Load the filtering configuration.
-		this.dataFilter.loadAllowedConfig( this.editor.config.get( 'generalHtmlSupport.allowed' ) || [] );
-		this.dataFilter.loadDisallowedConfig( this.editor.config.get( 'generalHtmlSupport.disallowed' ) || [] );
+		dataFilter.loadAllowedConfig( editor.config.get( 'generalHtmlSupport.allowed' ) || [] );
+		dataFilter.loadDisallowedConfig( editor.config.get( 'generalHtmlSupport.disallowed' ) || [] );
 	}
 
 	/**
@@ -63,7 +42,6 @@ export default class GeneralHtmlSupport extends Plugin {
 	static get requires() {
 		return [
 			DataFilter,
-			DataSchema,
 			CodeBlockHtmlSupport
 		];
 	}
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-content-compatibility/tests/dataschema.js
index 49523214515..46f4160cebb 100644
--- a/packages/ckeditor5-content-compatibility/tests/dataschema.js
+++ b/packages/ckeditor5-content-compatibility/tests/dataschema.js
@@ -14,11 +14,13 @@ describe( 'DataSchema', () => {
 
 	beforeEach( () => {
 		return VirtualTestEditor
-			.create()
+			.create( {
+				plugins: [ DataSchema ]
+			} )
 			.then( newEditor => {
 				editor = newEditor;
 
-				dataSchema = new DataSchema();
+				dataSchema = editor.plugins.get( DataSchema );
 			} );
 	} );
 

From 9d9adaaa2858ecb2f6ff34bd6a1afed3f61b3b67 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Tue, 8 Jun 2021 13:41:23 +0200
Subject: [PATCH 168/217] Review fixes - more tests.

---
 .../src/datafilter.js                         |   2 +-
 .../tests/datafilter.js                       | 176 +++++++++++++++++-
 2 files changed, 176 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index bbf63546c38..b2ce91b359d 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -11,7 +11,7 @@ import DataSchema from './dataschema';
 
 import { Plugin } from 'ckeditor5/src/core';
 import { Matcher } from 'ckeditor5/src/engine';
-import { priorities, toArray, CKEditorError } from 'ckeditor5/src/utils';
+import { priorities, CKEditorError } from 'ckeditor5/src/utils';
 import { Widget } from 'ckeditor5/src/widget';
 import {
 	disallowedAttributesConverter,
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 51d46db9971..bfc0546e6f9 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -1328,7 +1328,7 @@ describe( 'DataFilter', () => {
 			);
 		} );
 
-		it( 'should match all values', () => {
+		it( 'should match all values - across styles, classes and attributes', () => {
 			// Sanity check test for splitting patterns that are not objects nor arrays.
 
 			const config = [
@@ -1385,6 +1385,180 @@ describe( 'DataFilter', () => {
 			);
 		} );
 
+		it( 'should match all values - array of values', () => {
+			const config = [
+				{
+					name: 'span',
+					classes: [ 'foo', 'bar' ]
+				}
+			];
+
+			dataFilter.loadAllowedConfig( config );
+
+			editor.setData(
+				'<p>' +
+					'<span class="foo bar">foo bar</span>' +
+					'<span class="foo">foo</span>' +
+					'<span class="bar">bar</span>' +
+					'<span class="bar baz">bar baz</span>' +
+				'</p>'
+			);
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+						'<$text htmlSpan="(1)">foo bar</$text>' +
+						'<$text htmlSpan="(2)">foo</$text>' +
+						'<$text htmlSpan="(3)">barbar baz</$text>' +
+					'</paragraph>',
+				attributes: {
+					1: {
+						classes: [ 'foo', 'bar' ]
+					},
+					2: {
+						classes: [ 'foo' ]
+					},
+					3: {
+						classes: [ 'bar' ]
+					},
+					4: {
+						classes: [ 'bar' ]
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span class="foo bar">foo bar</span>' +
+					'<span class="foo">foo</span>' +
+					'<span class="bar">barbar baz</span>' +
+				'</p>'
+			);
+		} );
+
+		it( 'should match all values - array of objects', () => {
+			const config = [
+				{
+					name: 'span',
+					styles: [
+						{ key: 'position', value: true },
+						{ key: 'visibility', value: true }
+					]
+				}
+			];
+
+			dataFilter.loadAllowedConfig( config );
+
+			editor.setData(
+				'<p>' +
+					'<span style="position: absolute; visibility: hidden;">foo bar</span>' +
+					'<span style="position: absolute;">foo</span>' +
+					'<span style="visibility: hidden;">bar</span>' +
+					'<span style="visibility: hidden; margin-left: 1px;">bar baz</span>' +
+				'</p>'
+			);
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+						'<$text htmlSpan="(1)">foo bar</$text>' +
+						'<$text htmlSpan="(2)">foo</$text>' +
+						'<$text htmlSpan="(3)">barbar baz</$text>' +
+					'</paragraph>',
+				attributes: {
+					1: {
+						styles: {
+							position: 'absolute',
+							visibility: 'hidden'
+						}
+					},
+					2: {
+						styles: {
+							position: 'absolute'
+						}
+					},
+					3: {
+						styles: {
+							visibility: 'hidden'
+						}
+					},
+					4: {
+						styles: {
+							visibility: 'hidden'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span style="position:absolute;visibility:hidden;">foo bar</span>' +
+					'<span style="position:absolute;">foo</span>' +
+					'<span style="visibility:hidden;">barbar baz</span>' +
+				'</p>'
+			);
+		} );
+
+		it( 'should match all values - object', () => {
+			const config = [
+				{
+					name: 'span',
+					styles: {
+						position: true,
+						visibility: true
+					}
+				}
+			];
+
+			dataFilter.loadAllowedConfig( config );
+
+			editor.setData(
+				'<p>' +
+					'<span style="position: absolute; visibility: hidden;">foo bar</span>' +
+					'<span style="position: absolute;">foo</span>' +
+					'<span style="visibility: hidden;">bar</span>' +
+					'<span style="visibility: hidden; margin-left: 1px;">bar baz</span>' +
+				'</p>'
+			);
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph>' +
+						'<$text htmlSpan="(1)">foo bar</$text>' +
+						'<$text htmlSpan="(2)">foo</$text>' +
+						'<$text htmlSpan="(3)">barbar baz</$text>' +
+					'</paragraph>',
+				attributes: {
+					1: {
+						styles: {
+							position: 'absolute',
+							visibility: 'hidden'
+						}
+					},
+					2: {
+						styles: {
+							position: 'absolute'
+						}
+					},
+					3: {
+						styles: {
+							visibility: 'hidden'
+						}
+					},
+					4: {
+						styles: {
+							visibility: 'hidden'
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal(
+				'<p>' +
+					'<span style="position:absolute;visibility:hidden;">foo bar</span>' +
+					'<span style="position:absolute;">foo</span>' +
+					'<span style="visibility:hidden;">barbar baz</span>' +
+				'</p>'
+			);
+		} );
+
 		it( 'should match attributes', () => {
 			const config = [
 				{

From 4a444d579e787fe827476b26cd1d71f88c0178e1 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 8 Jun 2021 14:52:26 +0200
Subject: [PATCH 169/217] Allow matching all elements by skipping name.

---
 .../src/datafilter.js                         |  6 +++++-
 .../tests/datafilter.js                       | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index b2ce91b359d..f8a76e74f64 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -198,7 +198,11 @@ export default class DataFilter extends Plugin {
 	 */
 	_loadConfig( config, handleAttributes ) {
 		for ( const pattern of config ) {
-			this.allowElement( pattern.name );
+			// MatcherPattern allows omitting `name` to not narrow searches to specific elements.
+			// Let's keep it consistent and match every element if a `name` has not been provided.
+			const elementName = pattern.name || /[\s\S]+/;
+
+			this.allowElement( elementName );
 
 			this._splitRules( pattern ).forEach( handleAttributes );
 		}
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index bfc0546e6f9..6a5f6d756b6 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -1277,6 +1277,25 @@ describe( 'DataFilter', () => {
 	} );
 
 	describe( 'loadAllowedConfig', () => {
+		it( 'should allow match all elements by ommiting pattern name', () => {
+			dataSchema.registerBlockElement( {
+				model: 'htmlXyz',
+				view: 'xyz',
+				modelSchema: {
+					inheritAllFrom: '$block'
+				}
+			} );
+
+			const config = [ {} ];
+
+			dataFilter.loadAllowedConfig( config );
+
+			editor.setData( '<xyz>foobar</xyz>' );
+
+			expect( getModelData( model, { withoutSelection: true } ) ).to.equal( '<htmlXyz>foobar</htmlXyz>' );
+			expect( editor.getData() ).to.equal( '<xyz>foobar</xyz>' );
+		} );
+
 		it( 'should load config and match whenever a single match has been found', () => {
 			const config = [
 				{

From 4171bfdba1debdd62eb9dc66071d2883a6f8e5c4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Wed, 9 Jun 2021 13:56:56 +0200
Subject: [PATCH 170/217] Move methods outside of a class.

---
 .../src/datafilter.js                         | 112 +++++++++---------
 1 file changed, 54 insertions(+), 58 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index f8a76e74f64..62563c5a9f5 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -204,35 +204,10 @@ export default class DataFilter extends Plugin {
 
 			this.allowElement( elementName );
 
-			this._splitRules( pattern ).forEach( handleAttributes );
+			splitRules( pattern ).forEach( handleAttributes );
 		}
 	}
 
-	/**
-	 * Rules are matched in conjunction (AND operation), but we want to have a match if any of the rules is matched (OR operation).
-	 * By splitting the rules we force the latter effect.
-	 *
-	 * @private
-	 * @param {module:engine/view/matcher~MatcherPattern} rules
-	 * @returns {Array.<module:engine/view/matcher~MatcherPattern>}
-	 */
-	_splitRules( rules ) {
-		const { name, attributes, classes, styles } = rules;
-		const splitRules = [];
-
-		if ( attributes ) {
-			splitRules.push( ...this._splitPattern( { name, attributes }, 'attributes' ) );
-		}
-		if ( classes ) {
-			splitRules.push( ...this._splitPattern( { name, classes }, 'classes' ) );
-		}
-		if ( styles ) {
-			splitRules.push( ...this._splitPattern( { name, styles }, 'styles' ) );
-		}
-
-		return splitRules;
-	}
-
 	/**
 	 * Matches and consumes allowed view attributes.
 	 *
@@ -263,38 +238,6 @@ export default class DataFilter extends Plugin {
 		return consumeAttributes( viewElement, conversionApi, this._disallowedAttributes );
 	}
 
-	/**
-	 * Matcher by default has to match **all** patterns to count it as an actual match. By splitting the pattern
-	 * into separate patterns means that any matched pattern will be count as a match.
-	 *
-	 * @private
-	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern to split.
-	 * @param {String} attributeName Name of the attribute to split (e.g. 'attributes', 'classes', 'styles').
-	 * @returns {Array.<module:engine/view/matcher~MatcherPattern>}
-	 */
-	_splitPattern( pattern, attributeName ) {
-		const { name } = pattern;
-
-		if ( isPlainObject( pattern[ attributeName ] ) ) {
-			return Object.entries( pattern[ attributeName ] ).map(
-				( [ key, value ] ) => ( {
-					name,
-					[ attributeName ]: {
-						[ key ]: value
-					}
-				} ) );
-		} else if ( Array.isArray( pattern[ attributeName ] ) ) {
-			return pattern[ attributeName ].map(
-				value => ( {
-					name,
-					[ attributeName ]: [ value ]
-				} )
-			);
-		}
-
-		return [ pattern ];
-	}
-
 	/**
 	 * Registers elements allowed by {@link module:content-compatibility/datafilter~DataFilter#allowElement} method
 	 * once {@link module:core/editor~Editor#data editor's data controller} is initialized.
@@ -617,3 +560,56 @@ function iterableToObject( iterable, getValue ) {
 
 	return attributesObject;
 }
+
+// Matcher by default has to match **all** patterns to count it as an actual match. By splitting the pattern
+// into separate patterns means that any matched pattern will be count as a match.
+//
+// @private
+// @param {module:engine/view/matcher~MatcherPattern} pattern Pattern to split.
+// @param {String} attributeName Name of the attribute to split (e.g. 'attributes', 'classes', 'styles').
+// @returns {Array.<module:engine/view/matcher~MatcherPattern>}
+function splitPattern( pattern, attributeName ) {
+	const { name } = pattern;
+
+	if ( isPlainObject( pattern[ attributeName ] ) ) {
+		return Object.entries( pattern[ attributeName ] ).map(
+			( [ key, value ] ) => ( {
+				name,
+				[ attributeName ]: {
+					[ key ]: value
+				}
+			} ) );
+	} else if ( Array.isArray( pattern[ attributeName ] ) ) {
+		return pattern[ attributeName ].map(
+			value => ( {
+				name,
+				[ attributeName ]: [ value ]
+			} )
+		);
+	}
+
+	return [ pattern ];
+}
+
+// Rules are matched in conjunction (AND operation), but we want to have a match if *any* of the rules is matched (OR operation).
+// By splitting the rules we force the latter effect.
+//
+// @private
+// @param {module:engine/view/matcher~MatcherPattern} rules
+// @returns {Array.<module:engine/view/matcher~MatcherPattern>}
+function splitRules( rules ) {
+	const { name, attributes, classes, styles } = rules;
+	const splittedRules = [];
+
+	if ( attributes ) {
+		splittedRules.push( ...splitPattern( { name, attributes }, 'attributes' ) );
+	}
+	if ( classes ) {
+		splittedRules.push( ...splitPattern( { name, classes }, 'classes' ) );
+	}
+	if ( styles ) {
+		splittedRules.push( ...splitPattern( { name, styles }, 'styles' ) );
+	}
+
+	return splittedRules;
+}

From a14f1e059e0724297ca1118943304d14ce30db7d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?= <max.barnas@gmail.com>
Date: Thu, 10 Jun 2021 11:02:28 +0200
Subject: [PATCH 171/217] Review fixes.

---
 .../src/datafilter.js                         |   4 +-
 .../tests/datafilter.js                       | 306 ++++++++++--------
 2 files changed, 182 insertions(+), 128 deletions(-)

diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-content-compatibility/src/datafilter.js
index 62563c5a9f5..bfc80152c04 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/src/datafilter.js
@@ -579,7 +579,9 @@ function splitPattern( pattern, attributeName ) {
 					[ key ]: value
 				}
 			} ) );
-	} else if ( Array.isArray( pattern[ attributeName ] ) ) {
+	}
+
+	if ( Array.isArray( pattern[ attributeName ] ) ) {
 		return pattern[ attributeName ].map(
 			value => ( {
 				name,
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-content-compatibility/tests/datafilter.js
index 6a5f6d756b6..085079bfeeb 100644
--- a/packages/ckeditor5-content-compatibility/tests/datafilter.js
+++ b/packages/ckeditor5-content-compatibility/tests/datafilter.js
@@ -1310,18 +1310,18 @@ describe( 'DataFilter', () => {
 
 			editor.setData(
 				'<p>' +
-					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
-					'<span data-foo="foo data">foo data</span>' +
-					'<span data-bar="bar data">bar data</span>' +
+					'<span style="line-height: 1em; font-weight:400" class="foo bar">aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span data-bar="bar data">ccc</span>' +
 				'</p>'
 			);
 
 			// Font feature should take over color CSS property.
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
-						'<$text htmlSpan="(2)">foo data</$text>' +
-						'<$text htmlSpan="(3)">bar data</$text>' +
+						'<$text htmlSpan="(1)">aaa</$text>' +
+						'<$text htmlSpan="(2)">bbb</$text>' +
+						'<$text htmlSpan="(3)">ccc</$text>' +
 					'</paragraph>',
 				attributes: {
 					1: {
@@ -1338,11 +1338,9 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span style="color:blue;">' +
-						'<span class="foo bar">foobar</span>' +
-					'</span>' +
-					'<span data-foo="foo data">foo data</span>' +
-					'<span>bar data</span>' +
+					'<span class="foo bar">aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span>ccc</span>' +
 				'</p>'
 			);
 		} );
@@ -1363,22 +1361,25 @@ describe( 'DataFilter', () => {
 
 			editor.setData(
 				'<p>' +
-					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
-					'<span data-foo="foo data">foo data</span>' +
-					'<span data-bar="bar data">bar data</span>' +
+					'<span style="line-height: 1em; font-weight:400" class="foo bar">aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span data-bar="bar data">ccc</span>' +
 				'</p>'
 			);
 
 			// Font feature should take over color CSS property.
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
-						'<$text htmlSpan="(2)">foo data</$text>' +
-						'<$text htmlSpan="(3)">bar data</$text>' +
+						'<$text htmlSpan="(1)">aaa</$text>' +
+						'<$text htmlSpan="(2)">bbb</$text>' +
+						'<$text htmlSpan="(3)">ccc</$text>' +
 					'</paragraph>',
 				attributes: {
 					1: {
-						classes: [ 'foo', 'bar' ]
+						attributes: {
+							class: 'foo bar',
+							style: 'font-weight:400;line-height:1em;'
+						}
 					},
 					2: {
 						attributes: {
@@ -1395,11 +1396,9 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span style="color:blue;">' +
-						'<span class="foo bar">foobar</span>' +
-					'</span>' +
-					'<span data-foo="foo data">foo data</span>' +
-					'<span data-bar="bar data">bar data</span>' +
+					'<span class="foo bar" style="font-weight:400;line-height:1em;">aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span data-bar="bar data">ccc</span>' +
 				'</p>'
 			);
 		} );
@@ -1416,18 +1415,18 @@ describe( 'DataFilter', () => {
 
 			editor.setData(
 				'<p>' +
-					'<span class="foo bar">foo bar</span>' +
-					'<span class="foo">foo</span>' +
-					'<span class="bar">bar</span>' +
-					'<span class="bar baz">bar baz</span>' +
+					'<span class="foo bar">aaa</span>' +
+					'<span class="foo">bbb</span>' +
+					'<span class="bar">ccc</span>' +
+					'<span class="bar baz">ddd</span>' +
 				'</p>'
 			);
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text htmlSpan="(1)">foo bar</$text>' +
-						'<$text htmlSpan="(2)">foo</$text>' +
-						'<$text htmlSpan="(3)">barbar baz</$text>' +
+						'<$text htmlSpan="(1)">aaa</$text>' +
+						'<$text htmlSpan="(2)">bbb</$text>' +
+						'<$text htmlSpan="(3)">cccddd</$text>' +
 					'</paragraph>',
 				attributes: {
 					1: {
@@ -1447,9 +1446,9 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span class="foo bar">foo bar</span>' +
-					'<span class="foo">foo</span>' +
-					'<span class="bar">barbar baz</span>' +
+					'<span class="foo bar">aaa</span>' +
+					'<span class="foo">bbb</span>' +
+					'<span class="bar">cccddd</span>' +
 				'</p>'
 			);
 		} );
@@ -1469,18 +1468,18 @@ describe( 'DataFilter', () => {
 
 			editor.setData(
 				'<p>' +
-					'<span style="position: absolute; visibility: hidden;">foo bar</span>' +
-					'<span style="position: absolute;">foo</span>' +
-					'<span style="visibility: hidden;">bar</span>' +
-					'<span style="visibility: hidden; margin-left: 1px;">bar baz</span>' +
+					'<span style="position: absolute; visibility: hidden;">aaa</span>' +
+					'<span style="position: absolute;">bbb</span>' +
+					'<span style="visibility: hidden;">ccc</span>' +
+					'<span style="visibility: hidden; margin-left: 1px;">ddd</span>' +
 				'</p>'
 			);
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text htmlSpan="(1)">foo bar</$text>' +
-						'<$text htmlSpan="(2)">foo</$text>' +
-						'<$text htmlSpan="(3)">barbar baz</$text>' +
+						'<$text htmlSpan="(1)">aaa</$text>' +
+						'<$text htmlSpan="(2)">bbb</$text>' +
+						'<$text htmlSpan="(3)">cccddd</$text>' +
 					'</paragraph>',
 				attributes: {
 					1: {
@@ -1509,9 +1508,9 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span style="position:absolute;visibility:hidden;">foo bar</span>' +
-					'<span style="position:absolute;">foo</span>' +
-					'<span style="visibility:hidden;">barbar baz</span>' +
+					'<span style="position:absolute;visibility:hidden;">aaa</span>' +
+					'<span style="position:absolute;">bbb</span>' +
+					'<span style="visibility:hidden;">cccddd</span>' +
 				'</p>'
 			);
 		} );
@@ -1531,18 +1530,18 @@ describe( 'DataFilter', () => {
 
 			editor.setData(
 				'<p>' +
-					'<span style="position: absolute; visibility: hidden;">foo bar</span>' +
-					'<span style="position: absolute;">foo</span>' +
-					'<span style="visibility: hidden;">bar</span>' +
-					'<span style="visibility: hidden; margin-left: 1px;">bar baz</span>' +
+					'<span style="position: absolute; visibility: hidden;">aaa</span>' +
+					'<span style="position: absolute;">bbb</span>' +
+					'<span style="visibility: hidden;">ccc</span>' +
+					'<span style="visibility: hidden; margin-left: 1px;">ddd</span>' +
 				'</p>'
 			);
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text htmlSpan="(1)">foo bar</$text>' +
-						'<$text htmlSpan="(2)">foo</$text>' +
-						'<$text htmlSpan="(3)">barbar baz</$text>' +
+						'<$text htmlSpan="(1)">aaa</$text>' +
+						'<$text htmlSpan="(2)">bbb</$text>' +
+						'<$text htmlSpan="(3)">cccddd</$text>' +
 					'</paragraph>',
 				attributes: {
 					1: {
@@ -1571,9 +1570,9 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span style="position:absolute;visibility:hidden;">foo bar</span>' +
-					'<span style="position:absolute;">foo</span>' +
-					'<span style="visibility:hidden;">barbar baz</span>' +
+					'<span style="position:absolute;visibility:hidden;">aaa</span>' +
+					'<span style="position:absolute;">bbb</span>' +
+					'<span style="visibility:hidden;">cccddd</span>' +
 				'</p>'
 			);
 		} );
@@ -1590,18 +1589,18 @@ describe( 'DataFilter', () => {
 
 			editor.setData(
 				'<p>' +
-					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
-					'<span data-foo="foo data">foo data</span>' +
-					'<span data-bar="bar data">bar data</span>' +
+					'<span style="line-height: 1em; font-weight:400" class="foo bar">aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span data-bar="bar data">ccc</span>' +
 				'</p>'
 			);
 
 			// Font feature should take over color CSS property.
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
-						'<$text htmlSpan="(2)">foo data</$text>' +
-						'<$text htmlSpan="(3)">bar data</$text>' +
+						'<$text htmlSpan="(1)">aaa</$text>' +
+						'<$text htmlSpan="(2)">bbb</$text>' +
+						'<$text htmlSpan="(3)">ccc</$text>' +
 					'</paragraph>',
 				attributes: {
 					1: {},
@@ -1616,11 +1615,9 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span style="color:blue;">' +
-						'<span>foobar</span>' +
-					'</span>' +
-					'<span data-foo="foo data">foo data</span>' +
-					'<span>bar data</span>' +
+					'<span>aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span>ccc</span>' +
 				'</p>'
 			);
 		} );
@@ -1637,17 +1634,17 @@ describe( 'DataFilter', () => {
 
 			editor.setData(
 				'<p>' +
-					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
-					'<span data-foo="foo data">foo data</span>' +
-					'<span data-bar="bar data">bar data</span>' +
+					'<span style="line-height: 1em; font-weight:400" class="foo bar">aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span data-bar="bar data">ccc</span>' +
 				'</p>'
 			);
 
 			// Font feature should take over color CSS property.
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
-						'<$text htmlSpan="(2)">foo databar data</$text>' +
+						'<$text htmlSpan="(1)">aaa</$text>' +
+						'<$text htmlSpan="(2)">bbbccc</$text>' +
 					'</paragraph>',
 				attributes: {
 					1: {
@@ -1660,10 +1657,8 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span style="color:blue;">' +
-						'<span class="foo bar">foobar</span>' +
-					'</span>' +
-					'<span>foo databar data</span>' +
+					'<span class="foo bar">aaa</span>' +
+					'<span>bbbccc</span>' +
 				'</p>'
 			);
 		} );
@@ -1672,7 +1667,7 @@ describe( 'DataFilter', () => {
 			const config = [
 				{
 					name: 'span',
-					styles: { color: true }
+					styles: { 'line-height': true }
 				}
 			];
 
@@ -1680,31 +1675,38 @@ describe( 'DataFilter', () => {
 
 			editor.setData(
 				'<p>' +
-					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
-					'<span data-foo="foo data">foo data</span>' +
-					'<span data-bar="bar data">bar data</span>' +
+					'<span style="line-height: 1em; font-weight:400" class="foo bar">aaa</span>' +
+					'<span style="font-weight: 400;">bbb</span>' +
+					'<span style="line-height: 2em;">ccc</span>' +
 				'</p>'
 			);
 
-			// Font feature should take over color CSS property.
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
-						'<$text htmlSpan="(2)">foo databar data</$text>' +
+						'<$text htmlSpan="(1)">aaa</$text>' +
+						'<$text htmlSpan="(2)">bbb</$text>' +
+						'<$text htmlSpan="(3)">ccc</$text>' +
 					'</paragraph>',
 				attributes: {
-					1: {},
+					1: {
+						styles: {
+							'line-height': '1em'
+						}
+					},
 					2: {},
-					3: {}
+					3: {
+						styles: {
+							'line-height': '2em'
+						}
+					}
 				}
 			} );
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span style="color:blue;">' +
-						'<span>foobar</span>' +
-					'</span>' +
-					'<span>foo databar data</span>' +
+					'<span style="line-height:1em;">aaa</span>' +
+					'<span>bbb</span>' +
+					'<span style="line-height:2em;">ccc</span>' +
 				'</p>'
 			);
 		} );
@@ -1721,19 +1723,23 @@ describe( 'DataFilter', () => {
 				}
 			];
 
+			// First, allow all the elements matching config.
+			dataFilter.loadAllowedConfig( config );
+
+			// Then, disallow and verify it's actually working.
 			dataFilter.loadDisallowedConfig( config );
 
 			editor.setData(
 				'<p>' +
-					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
-					'<span data-foo="foo data">foo data</span>' +
-					'<span data-bar="bar data">bar data</span>' +
+					'<span style="line-height: 1em; font-weight:400" class="foo bar">aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span data-bar="bar data">ccc</span>' +
 				'</p>'
 			);
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text htmlSpan="(1)">foobarfoo databar data</$text>' +
+						'<$text htmlSpan="(1)">aaabbbccc</$text>' +
 					'</paragraph>',
 				attributes: {
 					1: {},
@@ -1744,7 +1750,7 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span>foobarfoo databar data</span>' +
+					'<span>aaabbbccc</span>' +
 				'</p>'
 			);
 		} );
@@ -1761,20 +1767,24 @@ describe( 'DataFilter', () => {
 				}
 			];
 
+			// First, allow all the elements matching config.
+			dataFilter.loadAllowedConfig( config );
+
+			// Then, disallow and verify it's actually working.
 			dataFilter.loadDisallowedConfig( config );
 
 			editor.setData(
 				'<p>' +
-					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
-					'<span data-foo="foo data">foo data</span>' +
-					'<span data-bar="bar data">bar data</span>' +
+					'<span style="line-height: 1em; font-weight:400" class="foo bar">aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span data-bar="bar data">ccc</span>' +
 				'</p>'
 			);
 
 			// Font feature should take over color CSS property.
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text htmlSpan="(1)">foobarfoo databar data</$text>' +
+						'<$text htmlSpan="(1)">aaabbbccc</$text>' +
 					'</paragraph>',
 				attributes: {
 					1: {},
@@ -1785,7 +1795,7 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span>foobarfoo databar data</span>' +
+					'<span>aaabbbccc</span>' +
 				'</p>'
 			);
 		} );
@@ -1798,21 +1808,24 @@ describe( 'DataFilter', () => {
 				}
 			];
 
+			// First, allow all the elements matching config.
+			dataFilter.loadAllowedConfig( config );
+
+			// Then, disallow and verify it's actually working.
 			dataFilter.loadDisallowedConfig( config );
 
 			editor.setData(
 				'<p>' +
-					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
-					'<span data-foo="foo data">foo data</span>' +
-					'<span data-bar="bar data">bar data</span>' +
+					'<span style="line-height: 1em; font-weight:400" class="foo bar">aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span data-bar="bar data">ccc</span>' +
 				'</p>'
 			);
 
 			// Font feature should take over color CSS property.
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
-						'<$text htmlSpan="(2)">foo databar data</$text>' +
+						'<$text htmlSpan="(1)">aaabbbccc</$text>' +
 					'</paragraph>',
 				attributes: {
 					1: {},
@@ -1823,87 +1836,126 @@ describe( 'DataFilter', () => {
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span style="color:blue;">' +
-						'<span>foobar</span>' +
-					'</span>' +
-					'<span>foo databar data</span>' +
+					'<span>aaabbbccc</span>' +
 				'</p>'
 			);
 		} );
 
 		it( 'should match classes', () => {
-			const config = [
+			const allowedConfig = [
+				{
+					name: 'span',
+					attributes: true,
+					// Allow it to really verify that the disallowing works.
+					classes: [ 'foo', 'bar', 'test' ]
+				}
+			];
+			const disallowedConfig = [
 				{
 					name: 'span',
 					classes: [ 'foo', 'bar', 'test' ]
 				}
 			];
 
-			dataFilter.loadDisallowedConfig( config );
+			dataFilter.loadAllowedConfig( allowedConfig );
+			dataFilter.loadDisallowedConfig( disallowedConfig );
 
 			editor.setData(
 				'<p>' +
-					'<span style="color:blue; font-weight:400" class="foo bar">foobar</span>' +
-					'<span data-foo="foo data">foo data</span>' +
-					'<span data-bar="bar data">bar data</span>' +
+					'<span style="line-height: 1em; font-weight:400" class="foo bar">aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span data-bar="bar data">ccc</span>' +
 				'</p>'
 			);
 
 			// Font feature should take over color CSS property.
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text fontColor="blue" htmlSpan="(1)">foobar</$text>' +
-						'<$text htmlSpan="(2)">foo databar data</$text>' +
+						'<$text htmlSpan="(1)">aaa</$text>' +
+						'<$text htmlSpan="(2)">bbb</$text>' +
+						'<$text htmlSpan="(3)">ccc</$text>' +
 					'</paragraph>',
 				attributes: {
 					1: {},
-					2: {},
-					3: {}
+					2: {
+						attributes: {
+							'data-foo': 'foo data'
+						}
+					},
+					3: {
+						attributes: {
+							'data-bar': 'bar data'
+						}
+					}
 				}
 			} );
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span style="color:blue;">' +
-						'<span>foobar</span>' +
-					'</span>' +
-					'<span>foo databar data</span>' +
+					'<span>aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span data-bar="bar data">ccc</span>' +
 				'</p>'
 			);
 		} );
 
 		it( 'should match styles', () => {
-			const config = [
+			const allowedConfig = [
+				{
+					name: 'span',
+					attributes: true,
+					// Allow it to really verify that the disallowing works.
+					styles: { 'line-height': true }
+				}
+			];
+			const disallowedConfig = [
 				{
 					name: 'span',
-					styles: { color: true }
+					styles: { 'line-height': true }
 				}
 			];
 
-			dataFilter.loadDisallowedConfig( config );
+			// First, allow all the elements matching config.
+			dataFilter.loadAllowedConfig( allowedConfig );
+
+			// Then, disallow and verify it's actually working.
+			dataFilter.loadDisallowedConfig( disallowedConfig );
 
 			editor.setData(
 				'<p>' +
-					'<span style="color:blue;">' +
-					'<span>foobar</span>' +
-					'<span>foo databar data</span>' +
+					'<span style="line-height:1em;">aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span data-bar="bar data">ccc</span>' +
 				'</p>'
 			);
 
 			// Font feature should take over color CSS property.
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-						'<$text htmlSpan="(1)">foobarfoo databar data</$text>' +
+						'<$text htmlSpan="(1)">aaa</$text>' +
+						'<$text htmlSpan="(2)">bbb</$text>' +
+						'<$text htmlSpan="(3)">ccc</$text>' +
 					'</paragraph>',
 				attributes: {
 					1: {},
-					2: {}
+					2: {
+						attributes: {
+							'data-foo': 'foo data'
+						}
+					},
+					3: {
+						attributes: {
+							'data-bar': 'bar data'
+						}
+					}
 				}
 			} );
 
 			expect( editor.getData() ).to.equal(
 				'<p>' +
-					'<span>foobarfoo databar data</span>' +
+					'<span>aaa</span>' +
+					'<span data-foo="foo data">bbb</span>' +
+					'<span data-bar="bar data">ccc</span>' +
 				'</p>'
 			);
 		} );

From b93e929e033d5a16d1d3b2be1cc1f436834901a2 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 10 Jun 2021 12:47:50 +0200
Subject: [PATCH 172/217] Corrected sample.

---
 .../tests/manual/generalhtmlsupport.html                        | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
index a07a831fe6e..36c562b8946 100644
--- a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
@@ -48,7 +48,7 @@
 
 			<p><span style="color:blue;"><span style="color:green;">Span with nested styles!</span></span></p>
 
-			<blockquote style="color: red;">Red quote!</blockquote>
+			<blockquote style="color: red;"><p>Red quote!</p></blockquote>
 
 			<ul>
 				<li style="color: blue;">Blue!</li>

From 5d963b966a56cd09c5c48c667df9138d0e9820b7 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 11 Jun 2021 08:50:50 +0200
Subject: [PATCH 173/217] Package renaming.

---
 .../package.json                              |  2 +-
 .../src/conversionutils.js                    |  2 +-
 .../src/converters.js                         | 24 ++++++------
 .../src/datafilter.js                         | 34 ++++++++---------
 .../src/dataschema.js                         | 38 +++++++++----------
 .../src/generalhtmlsupport.js                 |  4 +-
 .../src/integrations/codeblock.js             |  4 +-
 .../tests/_utils/utils.js                     |  0
 .../tests/codeblock.js                        |  0
 .../tests/datafilter.js                       |  0
 .../tests/dataschema.js                       |  0
 .../tests/manual/codeblock.html               |  0
 .../tests/manual/codeblock.js                 |  0
 .../tests/manual/codeblock.md                 |  0
 .../tests/manual/generalhtmlsupport.html      |  0
 .../tests/manual/generalhtmlsupport.js        |  0
 .../tests/manual/generalhtmlsupport.md        |  0
 .../tests/manual/objects.html                 |  0
 .../tests/manual/objects.js                   |  0
 .../tests/manual/objects.md                   |  0
 .../theme/datafilter.css                      |  0
 21 files changed, 54 insertions(+), 54 deletions(-)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/package.json (96%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/src/conversionutils.js (96%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/src/converters.js (86%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/src/datafilter.js (92%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/src/dataschema.js (84%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/src/generalhtmlsupport.js (85%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/src/integrations/codeblock.js (96%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/_utils/utils.js (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/codeblock.js (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/datafilter.js (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/dataschema.js (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/manual/codeblock.html (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/manual/codeblock.js (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/manual/codeblock.md (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/manual/generalhtmlsupport.html (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/manual/generalhtmlsupport.js (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/manual/generalhtmlsupport.md (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/manual/objects.html (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/manual/objects.js (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/tests/manual/objects.md (100%)
 rename packages/{ckeditor5-content-compatibility => ckeditor5-html-support}/theme/datafilter.css (100%)

diff --git a/packages/ckeditor5-content-compatibility/package.json b/packages/ckeditor5-html-support/package.json
similarity index 96%
rename from packages/ckeditor5-content-compatibility/package.json
rename to packages/ckeditor5-html-support/package.json
index 93778128863..4b292806e3c 100644
--- a/packages/ckeditor5-content-compatibility/package.json
+++ b/packages/ckeditor5-html-support/package.json
@@ -1,5 +1,5 @@
 {
-  "name": "@ckeditor/ckeditor5-content-compatibility",
+  "name": "@ckeditor/ckeditor5-html-support",
   "version": "28.0.0",
   "description": "Content compatibility feature",
   "private": true,
diff --git a/packages/ckeditor5-content-compatibility/src/conversionutils.js b/packages/ckeditor5-html-support/src/conversionutils.js
similarity index 96%
rename from packages/ckeditor5-content-compatibility/src/conversionutils.js
rename to packages/ckeditor5-html-support/src/conversionutils.js
index 960d572b40c..b844a2e613e 100644
--- a/packages/ckeditor5-content-compatibility/src/conversionutils.js
+++ b/packages/ckeditor5-html-support/src/conversionutils.js
@@ -4,7 +4,7 @@
  */
 
 /**
- * @module content-compatibility/conversionutils
+ * @module html-support/conversionutils
  */
 
 import { cloneDeep } from 'lodash-es';
diff --git a/packages/ckeditor5-content-compatibility/src/converters.js b/packages/ckeditor5-html-support/src/converters.js
similarity index 86%
rename from packages/ckeditor5-content-compatibility/src/converters.js
rename to packages/ckeditor5-html-support/src/converters.js
index aa403cf8b78..6f2662031f9 100644
--- a/packages/ckeditor5-content-compatibility/src/converters.js
+++ b/packages/ckeditor5-html-support/src/converters.js
@@ -4,7 +4,7 @@
  */
 
 /**
- * @module content-compatibility/converters
+ * @module html-support/converters
  */
 
 import { toWidget } from 'ckeditor5/src/widget';
@@ -16,8 +16,8 @@ import { setViewAttributes, mergeViewElementAttributes } from './conversionutils
  * This converter listenes on `high` priority to ensure that all attributes are consumed
  * before standard priority converters.
  *
- * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
- * @param {module:content-compatibility/datafilter~DataFilter} dataFilter
+ * @param {module:html-support/dataschema~DataSchemaDefinition} definition
+ * @param {module:html-support/datafilter~DataFilter} dataFilter
  * @returns {Function} Returns a conversion callback.
 */
 export function disallowedAttributesConverter( { view: viewName }, dataFilter ) {
@@ -33,7 +33,7 @@ export function disallowedAttributesConverter( { view: viewName }, dataFilter )
  *
  * Preserves object element content in `htmlContent` attribute.
  *
- * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+ * @param {module:html-support/dataschema~DataSchemaDefinition} definition
  * @returns {Function} Returns a conversion callback.
 */
 export function viewToModelObjectConverter( { model: modelName } ) {
@@ -49,7 +49,7 @@ export function viewToModelObjectConverter( { model: modelName } ) {
  * Conversion helper converting object element to HTML object widget.
  *
  * @param {module:core/editor/editor~Editor} editor
- * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+ * @param {module:html-support/dataschema~DataSchemaInlineElementDefinition} definition
  * @returns {Function} Returns a conversion callback.
 */
 export function toObjectWidgetConverter( editor, { view: viewName, isInline } ) {
@@ -94,11 +94,11 @@ export function createObjectView( viewName, modelElement, writer ) {
  * View-to-attribute conversion helper preserving inline element attributes on `$text`.
  *
  * All allowed element attributes will be preserved as a value of
- * {@link module:content-compatibility/dataschema~DataSchemaInlineElementDefinition~model definition model}
+ * {@link module:html-support/dataschema~DataSchemaInlineElementDefinition~model definition model}
  * attribute.
  *
- * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
- * @param {module:content-compatibility/datafilter~DataFilter} dataFilter
+ * @param {module:html-support/dataschema~DataSchemaInlineElementDefinition} definition
+ * @param {module:html-support/datafilter~DataFilter} dataFilter
  * @returns {Function} Returns a conversion callback.
 */
 export function viewToAttributeInlineConverter( { view: viewName, model: attributeKey }, dataFilter ) {
@@ -130,7 +130,7 @@ export function viewToAttributeInlineConverter( { view: viewName, model: attribu
 /**
  * Attribute-to-view conversion helper applying attributes to view element preserved on `$text`.
  *
- * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+ * @param {module:html-support/dataschema~DataSchemaInlineElementDefinition} definition
  * @returns {Function} Returns a conversion callback.
 */
 export function attributeToViewInlineConverter( { priority, view: viewName } ) {
@@ -153,8 +153,8 @@ export function attributeToViewInlineConverter( { priority, view: viewName } ) {
  *
  * All matched attributes will be preserved on `htmlAttributes` attribute.
  *
- * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
- * @param {module:content-compatibility/datafilter~DataFilter} dataFilter
+ * @param {module:html-support/dataschema~DataSchemaBlockElementDefinition} definition
+ * @param {module:html-support/datafilter~DataFilter} dataFilter
  * @returns {Function} Returns a conversion callback.
 */
 export function viewToModelBlockAttributeConverter( { view: viewName }, dataFilter ) {
@@ -177,7 +177,7 @@ export function viewToModelBlockAttributeConverter( { view: viewName }, dataFilt
  * Model-to-view conversion helper applying attributes preserved in `htmlAttributes` attribute
  * for block elements.
  *
- * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+ * @param {module:html-support/dataschema~DataSchemaBlockElementDefinition} definition
  * @returns {Function} Returns a conversion callback.
 */
 export function modelToViewBlockAttributeConverter( { model: modelName } ) {
diff --git a/packages/ckeditor5-content-compatibility/src/datafilter.js b/packages/ckeditor5-html-support/src/datafilter.js
similarity index 92%
rename from packages/ckeditor5-content-compatibility/src/datafilter.js
rename to packages/ckeditor5-html-support/src/datafilter.js
index bfc80152c04..f5856727cb8 100644
--- a/packages/ckeditor5-content-compatibility/src/datafilter.js
+++ b/packages/ckeditor5-html-support/src/datafilter.js
@@ -4,7 +4,7 @@
  */
 
 /**
- * @module content-compatibility/datafilter
+ * @module html-support/datafilter
  */
 
 import DataSchema from './dataschema';
@@ -31,9 +31,9 @@ import { isPlainObject } from 'lodash-es';
 import '../theme/datafilter.css';
 
 /**
- * Allows to validate elements and element attributes registered by {@link module:content-compatibility/dataschema~DataSchema}.
+ * Allows to validate elements and element attributes registered by {@link module:html-support/dataschema~DataSchema}.
  *
- * To enable registered element in the editor, use {@link module:content-compatibility/datafilter~DataFilter#allowElement} method:
+ * To enable registered element in the editor, use {@link module:html-support/datafilter~DataFilter#allowElement} method:
  *
  *		dataFilter.allowElement( 'section' );
  *
@@ -62,11 +62,11 @@ export default class DataFilter extends Plugin {
 		super( editor );
 
 		/**
-		 * An instance of the {@link module:content-compatibility/dataschema~DataSchema}.
+		 * An instance of the {@link module:html-support/dataschema~DataSchema}.
 		 *
 		 * @readonly
 		 * @private
-		 * @member {module:content-compatibility/dataschema~DataSchema} #_dataSchema
+		 * @member {module:html-support/dataschema~DataSchema} #_dataSchema
 		 */
 		this._dataSchema = editor.plugins.get( 'DataSchema' );
 
@@ -91,11 +91,11 @@ export default class DataFilter extends Plugin {
 		this._disallowedAttributes = new Matcher();
 
 		/**
-		 * Allowed element definitions by {@link module:content-compatibility/datafilter~DataFilter#allowElement} method.
+		 * Allowed element definitions by {@link module:html-support/datafilter~DataFilter#allowElement} method.
 		 *
 		 * @readonly
 		 * @private
-		 * @member {Set.<module:content-compatibility/dataschema~DataSchemaDefinition>} #_allowedElements
+		 * @member {Set.<module:html-support/dataschema~DataSchemaDefinition>} #_allowedElements
 		*/
 		this._allowedElements = new Set();
 
@@ -148,7 +148,7 @@ export default class DataFilter extends Plugin {
 	/**
 	 * Allow the given element in the editor context.
 	 *
-	 * This method will only allow elements described by the {@link module:content-compatibility/dataschema~DataSchema} used
+	 * This method will only allow elements described by the {@link module:html-support/dataschema~DataSchema} used
 	 * to create data filter.
 	 *
 	 * @param {String|RegExp} viewName String or regular expression matching view name.
@@ -239,7 +239,7 @@ export default class DataFilter extends Plugin {
 	}
 
 	/**
-	 * Registers elements allowed by {@link module:content-compatibility/datafilter~DataFilter#allowElement} method
+	 * Registers elements allowed by {@link module:html-support/datafilter~DataFilter#allowElement} method
 	 * once {@link module:core/editor~Editor#data editor's data controller} is initialized.
 	 *
 	 * @private
@@ -300,7 +300,7 @@ export default class DataFilter extends Plugin {
 	 * Fires `register` event for the given element definition.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 * @param {module:html-support/dataschema~DataSchemaDefinition} definition
 	 */
 	_fireRegisterEvent( definition ) {
 		this.fire( definition.view ? `register:${ definition.view }` : 'register', definition );
@@ -310,7 +310,7 @@ export default class DataFilter extends Plugin {
 	 * Registers object element and attribute converters for the given data schema definition.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 * @param {module:html-support/dataschema~DataSchemaDefinition} definition
 	 */
 	_registerObjectElement( definition ) {
 		const editor = this.editor;
@@ -361,7 +361,7 @@ export default class DataFilter extends Plugin {
 	 * Registers block element and attribute converters for the given data schema definition.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+	 * @param {module:html-support/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
 	_registerBlockElement( definition ) {
 		const editor = this.editor;
@@ -409,7 +409,7 @@ export default class DataFilter extends Plugin {
 	 * Extends `$text` model schema to allow the given definition model attribute and its properties.
 	 *
 	 * @private
-	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 * @param {module:html-support/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
 	_registerInlineElement( definition ) {
 		const editor = this.editor;
@@ -435,10 +435,10 @@ export default class DataFilter extends Plugin {
 	}
 
 	/**
-	 * Fired when {@link module:content-compatibility/datafilter~DataFilter} is registering element and attribute
-	 * converters for the {@link module:content-compatibility/dataschema~DataSchemaDefinition element definition}.
+	 * Fired when {@link module:html-support/datafilter~DataFilter} is registering element and attribute
+	 * converters for the {@link module:html-support/dataschema~DataSchemaDefinition element definition}.
 	 *
-	 * The event also accepts {@link module:content-compatibility/dataschema~DataSchemaDefinition#view} value
+	 * The event also accepts {@link module:html-support/dataschema~DataSchemaDefinition#view} value
 	 * as an event namespace, e.g. `register:span`.
 	 *
 	 * 		dataFilter.on( 'register', ( evt, definition ) => {
@@ -458,7 +458,7 @@ export default class DataFilter extends Plugin {
 	 * 		}, { priority: 'high' } )
 	 *
 	 * @event register
-	 * @param {module:content-compatibility/dataschema~DataSchemaDefinition} definition
+	 * @param {module:html-support/dataschema~DataSchemaDefinition} definition
 	 */
 }
 
diff --git a/packages/ckeditor5-content-compatibility/src/dataschema.js b/packages/ckeditor5-html-support/src/dataschema.js
similarity index 84%
rename from packages/ckeditor5-content-compatibility/src/dataschema.js
rename to packages/ckeditor5-html-support/src/dataschema.js
index 2eb74f3cac4..d53ef461a0c 100644
--- a/packages/ckeditor5-content-compatibility/src/dataschema.js
+++ b/packages/ckeditor5-html-support/src/dataschema.js
@@ -4,7 +4,7 @@
  */
 
 /**
- * @module content-compatibility/dataschema
+ * @module html-support/dataschema
  */
 
 import { Plugin } from 'ckeditor5/src/core';
@@ -17,7 +17,7 @@ import { toArray } from 'ckeditor5/src/utils';
  * Data schema is represented by data schema definitions.
  *
  * To add new definition for block element,
- * use {@link module:content-compatibility/dataschema~DataSchema#registerBlockElement} method:
+ * use {@link module:html-support/dataschema~DataSchema#registerBlockElement} method:
  *
  *		dataSchema.registerBlockElement( {
  *			view: 'section',
@@ -28,7 +28,7 @@ import { toArray } from 'ckeditor5/src/utils';
  *		} );
  *
  * To add new definition for inline element,
- * use {@link module:content-compatibility/dataschema~DataSchema#registerInlineElement} method:
+ * use {@link module:html-support/dataschema~DataSchema#registerInlineElement} method:
  *
  *		dataSchema.registerInlineElement( {
  *			view: 'span',
@@ -49,7 +49,7 @@ export default class DataSchema extends Plugin {
 		 *
 		 * @readonly
 		 * @private
-		 * @member {Map.<String, module:content-compatibility/dataschema~DataSchemaDefinition>} #_definitions
+		 * @member {Map.<String, module:html-support/dataschema~DataSchemaDefinition>} #_definitions
 		 */
 		this._definitions = new Map();
 
@@ -66,7 +66,7 @@ export default class DataSchema extends Plugin {
 	/**
 	 * Add new data schema definition describing block element.
 	 *
-	 * @param {module:content-compatibility/dataschema~DataSchemaBlockElementDefinition} definition
+	 * @param {module:html-support/dataschema~DataSchemaBlockElementDefinition} definition
 	 */
 	registerBlockElement( definition ) {
 		this._definitions.set( definition.model, { ...definition, isBlock: true } );
@@ -75,7 +75,7 @@ export default class DataSchema extends Plugin {
 	/**
 	 * Add new data schema definition describing inline element.
 	 *
-	 * @param {module:content-compatibility/dataschema~DataSchemaInlineElementDefinition} definition
+	 * @param {module:html-support/dataschema~DataSchemaInlineElementDefinition} definition
 	 */
 	registerInlineElement( definition ) {
 		this._definitions.set( definition.model, { ...definition, isInline: true } );
@@ -86,7 +86,7 @@ export default class DataSchema extends Plugin {
 	 *
 	 * @param {String|RegExp} viewName
 	 * @param {Boolean} [includeReferences] Indicates if this method should also include definitions of referenced models.
-	 * @returns {Set.<module:content-compatibility/dataschema~DataSchemaDefinition>}
+	 * @returns {Set.<module:html-support/dataschema~DataSchemaDefinition>}
 	 */
 	getDefinitionsForView( viewName, includeReferences ) {
 		const definitions = new Set();
@@ -377,7 +377,7 @@ export default class DataSchema extends Plugin {
 	 *
 	 * @private
 	 * @param {String|RegExp} viewName
-	 * @returns {Array.<module:content-compatibility/dataschema~DataSchemaDefinition>}
+	 * @returns {Array.<module:html-support/dataschema~DataSchemaDefinition>}
 	 */
 	_getMatchingViewDefinitions( viewName ) {
 		return Array.from( this._definitions.values() )
@@ -389,7 +389,7 @@ export default class DataSchema extends Plugin {
 	 *
 	 * @private
 	 * @param {String} modelName Data schema model name.
-	 * @returns {Iterable.<module:content-compatibility/dataschema~DataSchemaDefinition>}
+	 * @returns {Iterable.<module:html-support/dataschema~DataSchemaDefinition>}
 	 */
 	* _getReferences( modelName ) {
 		const { modelSchema } = this._definitions.get( modelName );
@@ -432,33 +432,33 @@ function testViewName( pattern, viewName ) {
 }
 
 /**
- * A base definition of {@link module:content-compatibility/dataschema~DataSchema data schema}.
+ * A base definition of {@link module:html-support/dataschema~DataSchema data schema}.
  *
- * @typedef {Object} module:content-compatibility/dataschema~DataSchemaDefinition
+ * @typedef {Object} module:html-support/dataschema~DataSchemaDefinition
  * @property {String} model Name of the model.
  * @property {Boolean} [isObject] Indicates that the definition describes object element.
  * @property {module:engine/model/schema~SchemaItemDefinition} [modelSchema] The model schema item definition describing registered model.
  */
 
 /**
- * A definition of {@link module:content-compatibility/dataschema~DataSchema data schema} for block elements.
+ * A definition of {@link module:html-support/dataschema~DataSchema data schema} for block elements.
  *
- * @typedef {Object} module:content-compatibility/dataschema~DataSchemaBlockElementDefinition
+ * @typedef {Object} module:html-support/dataschema~DataSchemaBlockElementDefinition
  * @property {String} [view] Name of the view element.
  * @property {Boolean} isBlock Indicates that the definition describes block element.
- * Set by {@link module:content-compatibility/dataschema~DataSchema#registerBlockElement} method.
- * @extends module:content-compatibility/dataschema~DataSchemaDefinition
+ * Set by {@link module:html-support/dataschema~DataSchema#registerBlockElement} method.
+ * @extends module:html-support/dataschema~DataSchemaDefinition
  */
 
 /**
- * A definition of {@link module:content-compatibility/dataschema~DataSchema data schema} for inline elements.
+ * A definition of {@link module:html-support/dataschema~DataSchema data schema} for inline elements.
  *
- * @typedef {Object} module:content-compatibility/dataschema~DataSchemaInlineElementDefinition
+ * @typedef {Object} module:html-support/dataschema~DataSchemaInlineElementDefinition
  * @property {String} view Name of the view element.
  * @property {module:engine/model/schema~AttributeProperties} [attributeProperties] Additional metadata describing the model attribute.
  * @property {Boolean} isInline Indicates that the definition descibes inline element.
  * @property {Number} [priority] Element priority. Decides in what order elements are wrapped by
  * {@link module:engine/view/downcastwriter~DowncastWriter}.
- * Set by {@link module:content-compatibility/dataschema~DataSchema#registerInlineElement} method.
- * @extends module:content-compatibility/dataschema~DataSchemaDefinition
+ * Set by {@link module:html-support/dataschema~DataSchema#registerInlineElement} method.
+ * @extends module:html-support/dataschema~DataSchemaDefinition
  */
diff --git a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js b/packages/ckeditor5-html-support/src/generalhtmlsupport.js
similarity index 85%
rename from packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
rename to packages/ckeditor5-html-support/src/generalhtmlsupport.js
index 81e615ba2e9..4048a8c2244 100644
--- a/packages/ckeditor5-content-compatibility/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-html-support/src/generalhtmlsupport.js
@@ -4,7 +4,7 @@
  */
 
 /**
- * @module content-compatibility/generalhtmlsupport
+ * @module html-support/generalhtmlsupport
  */
 
 import { Plugin } from 'ckeditor5/src/core';
@@ -14,7 +14,7 @@ import CodeBlockHtmlSupport from './integrations/codeblock';
 /**
  * The General HTML Support feature.
  *
- * This is a "glue" plugin which initializes the {@link module:content-compatibility/datafilter~DataFilter data filter} configuration
+ * This is a "glue" plugin which initializes the {@link module:html-support/datafilter~DataFilter data filter} configuration
  * and features integration with the General HTML Support.
  *
  * @extends module:core/plugin~Plugin
diff --git a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js b/packages/ckeditor5-html-support/src/integrations/codeblock.js
similarity index 96%
rename from packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
rename to packages/ckeditor5-html-support/src/integrations/codeblock.js
index 56e64d98c64..e0cca88cbff 100644
--- a/packages/ckeditor5-content-compatibility/src/integrations/codeblock.js
+++ b/packages/ckeditor5-html-support/src/integrations/codeblock.js
@@ -4,7 +4,7 @@
  */
 
 /**
- * @module content-compatibility/integrations/codeblock
+ * @module html-support/integrations/codeblock
  */
 
 import { Plugin } from 'ckeditor5/src/core';
@@ -59,7 +59,7 @@ export default class CodeBlockHtmlSupport extends Plugin {
 // Attributes are preserved as a value of `htmlAttributes` model attribute.
 //
 // @private
-// @param {module:content-compatibility/datafilter~DataFilter} dataFilter
+// @param {module:html-support/datafilter~DataFilter} dataFilter
 // @returns {Function} Returns a conversion callback.
 function viewToModelCodeBlockAttributeConverter( dataFilter ) {
 	return dispatcher => {
diff --git a/packages/ckeditor5-content-compatibility/tests/_utils/utils.js b/packages/ckeditor5-html-support/tests/_utils/utils.js
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/_utils/utils.js
rename to packages/ckeditor5-html-support/tests/_utils/utils.js
diff --git a/packages/ckeditor5-content-compatibility/tests/codeblock.js b/packages/ckeditor5-html-support/tests/codeblock.js
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/codeblock.js
rename to packages/ckeditor5-html-support/tests/codeblock.js
diff --git a/packages/ckeditor5-content-compatibility/tests/datafilter.js b/packages/ckeditor5-html-support/tests/datafilter.js
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/datafilter.js
rename to packages/ckeditor5-html-support/tests/datafilter.js
diff --git a/packages/ckeditor5-content-compatibility/tests/dataschema.js b/packages/ckeditor5-html-support/tests/dataschema.js
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/dataschema.js
rename to packages/ckeditor5-html-support/tests/dataschema.js
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/codeblock.html b/packages/ckeditor5-html-support/tests/manual/codeblock.html
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/codeblock.html
rename to packages/ckeditor5-html-support/tests/manual/codeblock.html
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/codeblock.js b/packages/ckeditor5-html-support/tests/manual/codeblock.js
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/codeblock.js
rename to packages/ckeditor5-html-support/tests/manual/codeblock.js
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/codeblock.md b/packages/ckeditor5-html-support/tests/manual/codeblock.md
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/codeblock.md
rename to packages/ckeditor5-html-support/tests/manual/codeblock.md
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.html
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.html
rename to packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.html
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.js
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.js
rename to packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.js
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.md b/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.md
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/generalhtmlsupport.md
rename to packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.md
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.html b/packages/ckeditor5-html-support/tests/manual/objects.html
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/objects.html
rename to packages/ckeditor5-html-support/tests/manual/objects.html
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.js b/packages/ckeditor5-html-support/tests/manual/objects.js
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/objects.js
rename to packages/ckeditor5-html-support/tests/manual/objects.js
diff --git a/packages/ckeditor5-content-compatibility/tests/manual/objects.md b/packages/ckeditor5-html-support/tests/manual/objects.md
similarity index 100%
rename from packages/ckeditor5-content-compatibility/tests/manual/objects.md
rename to packages/ckeditor5-html-support/tests/manual/objects.md
diff --git a/packages/ckeditor5-content-compatibility/theme/datafilter.css b/packages/ckeditor5-html-support/theme/datafilter.css
similarity index 100%
rename from packages/ckeditor5-content-compatibility/theme/datafilter.css
rename to packages/ckeditor5-html-support/theme/datafilter.css

From c0b07ba4304d2633925b96d49a652d8425b431dc Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 11 Jun 2021 08:55:11 +0200
Subject: [PATCH 174/217] Renamed config.

---
 packages/ckeditor5-html-support/src/generalhtmlsupport.js   | 4 ++--
 .../tests/manual/generalhtmlsupport.js                      | 6 +++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/generalhtmlsupport.js b/packages/ckeditor5-html-support/src/generalhtmlsupport.js
index 4048a8c2244..9c7aa3caf32 100644
--- a/packages/ckeditor5-html-support/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-html-support/src/generalhtmlsupport.js
@@ -32,8 +32,8 @@ export default class GeneralHtmlSupport extends Plugin {
 		const dataFilter = editor.plugins.get( DataFilter );
 
 		// Load the filtering configuration.
-		dataFilter.loadAllowedConfig( editor.config.get( 'generalHtmlSupport.allowed' ) || [] );
-		dataFilter.loadDisallowedConfig( editor.config.get( 'generalHtmlSupport.disallowed' ) || [] );
+		dataFilter.loadAllowedConfig( editor.config.get( 'htmlSupport.allow' ) || [] );
+		dataFilter.loadDisallowedConfig( editor.config.get( 'htmlSupport.disallow' ) || [] );
 	}
 
 	/**
diff --git a/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.js
index 5863fa3bb29..81a1f326591 100644
--- a/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.js
@@ -67,8 +67,8 @@ ClassicEditor
 			'|',
 			'blockquote'
 		],
-		generalHtmlSupport: {
-			allowed: [
+		htmlSupport: {
+			allow: [
 				{ name: 'article' },
 				{ name: /^(details|summary)$/ },
 				{ name: /^(dl|dd|dt)$/ },
@@ -109,7 +109,7 @@ ClassicEditor
 					styles: { 'background-color': true }
 				}
 			],
-			disallowed: [
+			disallow: [
 				{ name: 'section', attributes: { id: /^_.*/ } },
 				{ name: /^(span|cite)$/, styles: { color: 'red' } }
 			]

From 8cf0364e65fa6115ffb7e08655f06a28c9d74985 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 11 Jun 2021 09:06:42 +0200
Subject: [PATCH 175/217] Added missing renaming.

---
 packages/ckeditor5-html-support/package.json                    | 2 +-
 packages/ckeditor5-html-support/src/dataschema.js               | 2 +-
 .../ckeditor5-html-support/tests/manual/generalhtmlsupport.md   | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-html-support/package.json b/packages/ckeditor5-html-support/package.json
index 4b292806e3c..d0b6e7d8655 100644
--- a/packages/ckeditor5-html-support/package.json
+++ b/packages/ckeditor5-html-support/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@ckeditor/ckeditor5-html-support",
   "version": "28.0.0",
-  "description": "Content compatibility feature",
+  "description": "HTML Support feature",
   "private": true,
   "keywords": [
     "ckeditor",
diff --git a/packages/ckeditor5-html-support/src/dataschema.js b/packages/ckeditor5-html-support/src/dataschema.js
index d53ef461a0c..c245fc3a7d5 100644
--- a/packages/ckeditor5-html-support/src/dataschema.js
+++ b/packages/ckeditor5-html-support/src/dataschema.js
@@ -12,7 +12,7 @@ import { toArray } from 'ckeditor5/src/utils';
 
 /**
  * Holds representation of the extended HTML document type definitions to be used by the
- * editor in content compatibility support.
+ * editor in HTML support.
  *
  * Data schema is represented by data schema definitions.
  *
diff --git a/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.md b/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.md
index 4f09838d7e4..c357cf7f28a 100644
--- a/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.md
+++ b/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.md
@@ -1 +1 @@
-# Content compatibility
+# General HTML Support

From 4191bf4c8a6ba7d9542a987c1cfd4e9cefe8adac Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 15 Jun 2021 13:53:30 +0200
Subject: [PATCH 176/217] Updated docs, package.json.

---
 packages/ckeditor5-html-support/package.json  | 23 +++++--
 .../ckeditor5-html-support/src/converters.js  |  4 --
 .../ckeditor5-html-support/src/datafilter.js  |  5 +-
 .../ckeditor5-html-support/src/dataschema.js  |  5 +-
 .../src/generalhtmlsupport.js                 | 65 +++++++++++++++++++
 packages/ckeditor5-html-support/src/index.js  | 12 ++++
 6 files changed, 99 insertions(+), 15 deletions(-)
 create mode 100644 packages/ckeditor5-html-support/src/index.js

diff --git a/packages/ckeditor5-html-support/package.json b/packages/ckeditor5-html-support/package.json
index d0b6e7d8655..2835d584301 100644
--- a/packages/ckeditor5-html-support/package.json
+++ b/packages/ckeditor5-html-support/package.json
@@ -1,8 +1,7 @@
 {
   "name": "@ckeditor/ckeditor5-html-support",
   "version": "28.0.0",
-  "description": "HTML Support feature",
-  "private": true,
+  "description": "HTML Support feature for CKEditor 5.",
   "keywords": [
     "ckeditor",
     "ckeditor5",
@@ -11,6 +10,7 @@
     "ckeditor5-plugin",
     "compatibility",
     "content compatibility",
+	"html support",
     "generic html support"
   ],
   "main": "src/index.js",
@@ -40,11 +40,22 @@
     "node": ">=12.0.0",
     "npm": ">=5.7.1"
   },
-  "license": "SEE LICENSE IN LICENSE.md",
   "author": "CKSource (http://cksource.com/)",
-  "homepage": "https://ckeditor.com",
+  "license": "GPL-2.0-or-later",
+  "homepage": "https://ckeditor.com/ckeditor-5",
   "bugs": "https://github.com/ckeditor/ckeditor5/issues",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/ckeditor/ckeditor5.git",
+    "directory": "packages/ckeditor5-language"
+  },
   "files": [
-    "src"
-  ]
+    "lang",
+    "src",
+    "theme",
+    "build"
+  ],
+  "scripts": {
+    "dll:build": "webpack"
+  }
 }
diff --git a/packages/ckeditor5-html-support/src/converters.js b/packages/ckeditor5-html-support/src/converters.js
index 6f2662031f9..ee1c87afd53 100644
--- a/packages/ckeditor5-html-support/src/converters.js
+++ b/packages/ckeditor5-html-support/src/converters.js
@@ -93,10 +93,6 @@ export function createObjectView( viewName, modelElement, writer ) {
 /**
  * View-to-attribute conversion helper preserving inline element attributes on `$text`.
  *
- * All allowed element attributes will be preserved as a value of
- * {@link module:html-support/dataschema~DataSchemaInlineElementDefinition~model definition model}
- * attribute.
- *
  * @param {module:html-support/dataschema~DataSchemaInlineElementDefinition} definition
  * @param {module:html-support/datafilter~DataFilter} dataFilter
  * @returns {Function} Returns a conversion callback.
diff --git a/packages/ckeditor5-html-support/src/datafilter.js b/packages/ckeditor5-html-support/src/datafilter.js
index f5856727cb8..d1e5bf2ccd2 100644
--- a/packages/ckeditor5-html-support/src/datafilter.js
+++ b/packages/ckeditor5-html-support/src/datafilter.js
@@ -100,7 +100,8 @@ export default class DataFilter extends Plugin {
 		this._allowedElements = new Set();
 
 		/**
-		 * Indicates if {@link module:core/editor~Editor#data editor's data controller} data has been already initialized.
+		 * Indicates if {@link module:engine/controller/datacontroller~DataController editor's data controller}
+		 * data has been already initialized.
 		 *
 		 * @private
 		 * @member {Boolean} [#_dataInitialized=false]
@@ -240,7 +241,7 @@ export default class DataFilter extends Plugin {
 
 	/**
 	 * Registers elements allowed by {@link module:html-support/datafilter~DataFilter#allowElement} method
-	 * once {@link module:core/editor~Editor#data editor's data controller} is initialized.
+	 * once {@link module:engine/controller/datacontroller~DataController editor's data controller} is initialized.
 	 *
 	 * @private
 	*/
diff --git a/packages/ckeditor5-html-support/src/dataschema.js b/packages/ckeditor5-html-support/src/dataschema.js
index c245fc3a7d5..17db7ac2edb 100644
--- a/packages/ckeditor5-html-support/src/dataschema.js
+++ b/packages/ckeditor5-html-support/src/dataschema.js
@@ -45,7 +45,7 @@ export default class DataSchema extends Plugin {
 		super( editor );
 
 		/**
-		 * A map of registered data schema definitions via {@link #register} method.
+		 * A map of registered data schema definitions.
 		 *
 		 * @readonly
 		 * @private
@@ -436,6 +436,7 @@ function testViewName( pattern, viewName ) {
  *
  * @typedef {Object} module:html-support/dataschema~DataSchemaDefinition
  * @property {String} model Name of the model.
+ * @property {String} [view] Name of the view element.
  * @property {Boolean} [isObject] Indicates that the definition describes object element.
  * @property {module:engine/model/schema~SchemaItemDefinition} [modelSchema] The model schema item definition describing registered model.
  */
@@ -444,7 +445,6 @@ function testViewName( pattern, viewName ) {
  * A definition of {@link module:html-support/dataschema~DataSchema data schema} for block elements.
  *
  * @typedef {Object} module:html-support/dataschema~DataSchemaBlockElementDefinition
- * @property {String} [view] Name of the view element.
  * @property {Boolean} isBlock Indicates that the definition describes block element.
  * Set by {@link module:html-support/dataschema~DataSchema#registerBlockElement} method.
  * @extends module:html-support/dataschema~DataSchemaDefinition
@@ -454,7 +454,6 @@ function testViewName( pattern, viewName ) {
  * A definition of {@link module:html-support/dataschema~DataSchema data schema} for inline elements.
  *
  * @typedef {Object} module:html-support/dataschema~DataSchemaInlineElementDefinition
- * @property {String} view Name of the view element.
  * @property {module:engine/model/schema~AttributeProperties} [attributeProperties] Additional metadata describing the model attribute.
  * @property {Boolean} isInline Indicates that the definition descibes inline element.
  * @property {Number} [priority] Element priority. Decides in what order elements are wrapped by
diff --git a/packages/ckeditor5-html-support/src/generalhtmlsupport.js b/packages/ckeditor5-html-support/src/generalhtmlsupport.js
index 9c7aa3caf32..e8e46b7fb50 100644
--- a/packages/ckeditor5-html-support/src/generalhtmlsupport.js
+++ b/packages/ckeditor5-html-support/src/generalhtmlsupport.js
@@ -46,3 +46,68 @@ export default class GeneralHtmlSupport extends Plugin {
 		];
 	}
 }
+
+/**
+ * The configuration of the General HTML Support feature.
+ * Introduced by the {@link module:html-support/generalhtmlsupport~GeneralHtmlSupport} feature.
+ *
+ * Read more in {@link module:html-support/generalhtmlsupport~GeneralHtmlSupportConfig}.
+ *
+ * @member {module:htmlsupport/generalhtmlsupport~GeneralHtmlSupportConfig} module:core/editor/editorconfig~EditorConfig#htmlSupport
+ */
+
+/**
+ * The configuration of the General HTML Support feature.
+ * The option is used by the {@link module:html-support/generalhtmlsupport~GeneralHtmlSupport} feature.
+ *
+ *		ClassicEditor
+ *			.create( {
+ * 				htmlSupport: ... // General HTML Support feature config.
+ *			} )
+ *			.then( ... )
+ *			.catch( ... );
+ *
+ * See {@link module:core/editor/editorconfig~EditorConfig all editor options}.
+ *
+ * @interface GeneralHtmlSupportConfig
+ */
+
+/**
+ * The configuration of allowed content rules used by General HTML Support.
+ *
+ * Setting this configuration option will enable HTML features that are not explicitly supported by any other dedicated CKEditor 5 features.
+ *
+ * 		const htmlSupportConfig.allow = [
+ * 			{
+ * 				name: 'div',                      // Enable 'div' element support,
+ * 				classes: [ 'special-container' ], // allow 'special-container' class,
+ * 				styles: 'background',             // allow 'background' style,
+ * 				attributes: true                  // allow any attribute (can be empty).
+ * 			},
+ * 			{
+ * 				name: 'p',                                   // Extend existing Paragraph feature,
+ * 				classes: 'highlighted'                       // with 'highlighted' class,
+ * 				attributes: [
+ * 					{ key: 'data-i18n-context, value: true } // and i18n attribute.
+ * 				]
+ * 			}
+ * 		];
+ *
+ * @member {Array.<module:engine/view/matcher~MatcherPattern>} module:html-support/generalhtmlsupport~GeneralHtmlSupportConfig#allow
+ */
+
+/**
+ * The configuration of disallowed content rules used by General HTML Support.
+ *
+ * Setting this configuration option will disable listed HTML features.
+ *
+ * 		const htmlSupportConfig.disallow = [
+ * 			{
+ * 				name: /[\s\S]+/    // For every HTML feature,
+ * 				attributes: {
+ * 					key: /^on.*$/ // disable 'on*' attributes, like 'onClick', 'onError' etc.
+ * 				}
+ * 			}
+ * 		];
+ * @member {Array.<module:engine/view/matcher~MatcherPattern>} module:html-support/generalhtmlsupport~GeneralHtmlSupportConfig#disallow
+ */
diff --git a/packages/ckeditor5-html-support/src/index.js b/packages/ckeditor5-html-support/src/index.js
new file mode 100644
index 00000000000..0b58680969b
--- /dev/null
+++ b/packages/ckeditor5-html-support/src/index.js
@@ -0,0 +1,12 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module html-support
+ */
+
+export { default as GeneralHtmlSupport } from './generalhtmlsupport';
+export { default as DataFilter } from './datafilter';
+export { default as DataSchema } from './dataschema';

From b44e02d6dcf75aba5f8c88467c27112d164e02d9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Smyrek?= <p.smyrek@cksource.com>
Date: Wed, 16 Jun 2021 08:00:44 +0200
Subject: [PATCH 177/217] Added missing `@ckeditor/ckeditor5-html-support`
 dependency

---
 package.json | 1 +
 1 file changed, 1 insertion(+)

diff --git a/package.json b/package.json
index 03381929b2b..f3430ebf199 100644
--- a/package.json
+++ b/package.json
@@ -50,6 +50,7 @@
     "@ckeditor/ckeditor5-highlight": "^28.0.0",
     "@ckeditor/ckeditor5-horizontal-line": "^28.0.0",
     "@ckeditor/ckeditor5-html-embed": "^28.0.0",
+    "@ckeditor/ckeditor5-html-support": "^28.0.0",
     "@ckeditor/ckeditor5-image": "^28.0.0",
     "@ckeditor/ckeditor5-indent": "^28.0.0",
     "@ckeditor/ckeditor5-language": "^28.0.0",

From ac66883e688378f00b9b4ec9804e5b7252ebf7f0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Piotrek=20Koszuli=C5=84ski?= <pkoszulinski@gmail.com>
Date: Mon, 14 Jun 2021 09:23:01 +0200
Subject: [PATCH 178/217] First draft of the docs.

---
 .../features/general-html-support.html        |  22 ++
 .../features/general-html-support.js          | 115 ++++++++++
 docs/_snippets/features/mathtype.js           |   2 +
 docs/features/general-html-support.md         | 215 ++++++++++++++++++
 .../docs/features/source-editing.md           |   3 +-
 5 files changed, 356 insertions(+), 1 deletion(-)
 create mode 100644 docs/_snippets/features/general-html-support.html
 create mode 100644 docs/_snippets/features/general-html-support.js
 create mode 100644 docs/features/general-html-support.md

diff --git a/docs/_snippets/features/general-html-support.html b/docs/_snippets/features/general-html-support.html
new file mode 100644
index 00000000000..3648628f0d3
--- /dev/null
+++ b/docs/_snippets/features/general-html-support.html
@@ -0,0 +1,22 @@
+<div id="snippet-general-html-support">
+	<h2 data-i18n-context="title">General HTML support</h2>
+
+	<div styles="color: red; padding: 10px; text-align: center; border: solid 3px red">
+		<p data-i18n-context="experimental-note">This is an experimental feature.</p>
+
+		<details data-i18n-context="experimental-note">
+			<summary>Read more</summary>
+
+			<p>The General HTML support feature is <strong>experimental and not yet production-ready</strong>.</p>
+			<p>Follow the <a href="https://github.com/ckeditor/ckeditor5/issues/9856">"Stabilize and release a production-ready General HTML support feature"</a> issue for more updates.</p>
+		</details>
+	</div>
+
+	<p data-i18n-context="description">The <abbr title="General HTML Support">GHS</abbr> feature is enabled in this editor and configured to support the following content (in addition to content already support by other editor features):</p>
+
+	<ul>
+		<li data-i18n-context="description"><code>&lt;div></code>, <code>&lt;details></code>, and <code>&lt;summary></code> elements with all kind of attributes,</li>
+		<li data-i18n-context="description">paragraphs and headings with <code>data-*</code> attributes and all classes,</li>
+		<li data-i18n-context="description"><code>&lt;span></code> elements with all inline styles and <code>&lt;abbr></code> elements with `title` attributes.</li>
+	</ul>
+</div>
diff --git a/docs/_snippets/features/general-html-support.js b/docs/_snippets/features/general-html-support.js
new file mode 100644
index 00000000000..2456c18133c
--- /dev/null
+++ b/docs/_snippets/features/general-html-support.js
@@ -0,0 +1,115 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/* globals console, window, document */
+
+import { CS_CONFIG } from '@ckeditor/ckeditor5-cloud-services/tests/_utils/cloud-services-config.js';
+
+import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
+import ArticlePluginSet from '@ckeditor/ckeditor5-core/tests/_utils/articlepluginset';
+import Code from '@ckeditor/ckeditor5-basic-styles/src/code';
+import EasyImage from '@ckeditor/ckeditor5-easy-image/src/easyimage';
+import ImageUpload from '@ckeditor/ckeditor5-image/src/imageupload';
+import CloudServices from '@ckeditor/ckeditor5-cloud-services/src/cloudservices';
+
+import SourceEditing from '@ckeditor/ckeditor5-source-editing/src/sourceediting';
+import GeneralHtmlSupport from '@ckeditor/ckeditor5-content-compatibility/src/generalhtmlsupport';
+
+ClassicEditor
+	.create( document.querySelector( '#snippet-general-html-support' ), {
+		plugins: [
+			ArticlePluginSet,
+			Code,
+			EasyImage,
+			ImageUpload,
+			CloudServices,
+			SourceEditing,
+			GeneralHtmlSupport
+		],
+		toolbar: {
+			items: [
+				'sourceEditing',
+				'|',
+				'heading',
+				'|',
+				'bold',
+				'italic',
+				'code',
+				'bulletedList',
+				'numberedList',
+				'|',
+				'outdent',
+				'indent',
+				'|',
+				'blockQuote',
+				'link',
+				'mediaEmbed',
+				'insertTable',
+				'|',
+				'undo',
+				'redo'
+			],
+			viewportTopOffset: window.getViewportTopOffsetConfig()
+		},
+		image: {
+			toolbar: [
+				'imageStyle:inline',
+				'imageStyle:wrapText',
+				'imageStyle:breakText',
+				'|',
+				'toggleImageCaption',
+				'imageTextAlternative'
+			]
+		},
+		table: {
+			contentToolbar: [ 'tableColumn', 'tableRow', 'mergeTableCells' ]
+		},
+		cloudServices: CS_CONFIG,
+
+		generalHtmlSupport: {
+			allowed: [
+				// Enables <div>, <details>, and <summary> elements with all kind of attributes.
+				{
+					name: /^(div|details|summary)$/,
+					styles: true,
+					classes: true,
+					attributes: true
+				},
+
+				// Extends the existing Paragraph and Heading features
+				// with classes and data-* attributes.
+				{
+					name: /^(p|h[2-4])$/,
+					classes: true,
+					attributes: /^data-/
+				},
+
+				// Enables <span>s with any inline styles.
+				{
+					name: 'span',
+					styles: true
+				},
+
+				// Enables <abbr>s with the title attribute.
+				{
+					name: 'abbr',
+					attributes: [ 'title' ]
+				}
+			]
+		}
+	} )
+	.then( editor => {
+		window.editor = editor;
+
+		window.attachTourBalloon( {
+			target: window.findToolbarItem( editor.ui.view.toolbar,
+				item => item.label && item.label === 'Source' ),
+			text: 'Switch to the source mode to check out the source of the content and play with it.',
+			editor
+		} );
+	} )
+	.catch( err => {
+		console.error( err.stack );
+	} );
diff --git a/docs/_snippets/features/mathtype.js b/docs/_snippets/features/mathtype.js
index 8a8c51bb512..8e8aaed31b3 100644
--- a/docs/_snippets/features/mathtype.js
+++ b/docs/_snippets/features/mathtype.js
@@ -64,6 +64,8 @@ ClassicEditor
 	} )
 
 	.then( editor => {
+		window.editor = editor;
+
 		window.attachTourBalloon( {
 			target: window.findToolbarItem( editor.ui.view.toolbar,
 				item => item.label && item.label === 'Insert a math equation - MathType' ),
diff --git a/docs/features/general-html-support.md b/docs/features/general-html-support.md
new file mode 100644
index 00000000000..c665a04ea89
--- /dev/null
+++ b/docs/features/general-html-support.md
@@ -0,0 +1,215 @@
+---
+category: features
+modified_at: 2021-06-13
+---
+
+# General HTML support
+
+The General HTML support ("GHS") feature allows you to easily enable HTML features that are not supported by any other "specific" CKEditor 5 features.
+
+Some examples of HTML features that can be easily enabled thanks to GHS:
+
+* `<section>`, `<article>`, and `<div>` elements,
+* `<audio>`, `<video>`, and `<iframe>` elements,
+* `<span>` and `<cite>` elements,
+* attributes on existing specific CKEditor 5 features:
+	* `data-*` and `id` attributes on e.g. `<p>` and `<h1-h6>`,
+	* `style` and `classes` on e.g. `<strong>` and `<a>`.
+
+Enabled HTML features can be loaded (via e.g. `editor.setData()`), pasted, output (via e.g. `editor.getData()`), and are visible in the editing area. Such content can also be edited in the editor, although, to a limited extend. Read more in [Level of support](#level-of-support).
+
+<info-box>
+	The General HTML support feature is **experimental and not yet production-ready**.
+
+	Follow the ["Stabilize and release a production-ready General HTML support feature"](https://github.com/ckeditor/ckeditor5/issues/9856) issue for more updates and related issues.
+</info-box>
+
+## Demo
+
+The GHS feature is configured via the `config.generalHtmlSupport` property in which you need to list HTML features that should be handled by GHS.
+
+The demo below uses this configuration:
+
+```js
+import SourceEditing from '@ckeditor/ckeditor5-source-editing/src/sourceediting';
+import GeneralHtmlSupport from '@ckeditor/ckeditor5-html-support/src/generalhtmlsupport';
+
+ClassicEditor
+	.create( document.querySelector( '#editor' ), {
+		plugins: [ SourceEditing, GeneralHtmlSupport, ... ],
+		toolbar: [ 'sourceEditing', ... ],
+		generalHtmlSupport: {
+			allowed: {
+				// Enables <div>, <details>, and <summary> elements with all kind of attributes.
+				{
+					name: /^(div|details|summary)$/,
+					styles: true,
+					classes: true,
+					attributes: true
+				},
+
+				// Extends the existing Paragraph and Heading features
+				// with classes and data-* attributes.
+				{
+					name: /^(p|h[2-4])$/,
+					classes: true,
+					attributes: /^data-/
+				},
+
+				// Enables <span>s with any inline styles.
+				{
+					name: 'span',
+					styles: true
+				},
+
+				// Enables <abbr>s with the title attribute.
+				{
+					name: 'abbr',
+					attributes: [ 'title' ]
+				}
+			}
+		}
+	} )
+	.then( ... )
+	.catch( ... );
+```
+
+{@snippet features/general-html-support}
+
+## Level of support
+
+The difference between specific CKEditor 5 features such as {@link features/basic-styles Basic styles} or {@link features/headings Headings} and HTML features enabled by GHS is that a plugin that support a specific HTML feature provides a complete user experience for that feature, whereas GHS ensures only that such a content is accepted by the editor.
+
+For instance, the specific {@link module:basic-styles/bold~Bold} feature offers a toolbar button to make the selected text bold. Together with the {@link features/autoformat Autoformatting feature} it also allows applying bold by typing `**foo**`. The {@link features/headings Headings} feature offers a dropdown from which the user can choose a heading level and ensures that pressing <kbd>Enter</kbd> at the end of a heading creates a new paragraph (and not another heading).
+
+GHS does not offer any UI for enabled features and takes only basic semantics of a given feature into account. If you enable support for `<div>`s via GHS, the user will not be able to create `<div>`s from the editor UI. The GHS will know that a `<div>` is a container element, so it can wrap other blocks (like paragraphs) but cannot be used inline (next to e.g. a `<strong>` element). But that's it.
+
+Therefore, GHS's main use cases are:
+
+* Ensuring backward content compatibility with legacy systems.
+* Introducing basic support for missing HTML features at a low cost.
+
+<info-box>
+	Taken the nature of GHS, you may consider installing the {@link features/source-editing Source editing} feature alongside it.
+</info-box>
+
+## Configuration
+
+By default, enabling the {@link module:content-compatibility/generalhtmlsupport~GeneralHtmlSupport} plugin does not enable support for any element. The elements to be supported need to be configured via {@link TODOmodule:core/editor/editorconfig~EditorConfig#generalHtmlSupport `config.generalHtmlSupport`} option:
+
+```js
+ClassicEditor.create( document.querySelector( '#editor' ), {
+	generalHtmlSupport: {
+		allowed: [ /* HTML features to allow */ ]
+		disallowed: [ /* HTML features to disallow */ ]
+	}
+} )
+```
+
+The notation of `allowed` and `disallowed` rules looks like this:
+
+<!-- TODO REVIEW THE BELOW. I WROTE IT FROM THE TOP OF MY HEAD. -->
+
+```js
+[
+	{
+		// The element name to enable and/or extend with
+		// the following styles, classes and other attributes.
+		name: string|regexp,
+
+		// Styles to allow (by name, name and value or just all).
+		styles: object<string=>true|string|regexp>|array<string>|true,
+
+		// Classes to allow (by name or just all).
+		classes: array<string|regexp>|true,
+
+		// Other attributes to allow (by name, name and value or just all).
+		attributes: object<string=>true|string|regexp>|array<string>|true,
+	}
+]
+```
+
+Some examples:
+
+```js
+generalHtmlSupport: {
+	allowed: [
+		// Enables plain <div>s.
+		{
+			name: 'div'
+		},
+
+		// Enables plain <div>, <section> and <article> elements.
+		{
+			name: /^(div|section|article)$/
+		},
+
+		// Enables <div>s with all inline styles (but no other attributes).
+		{
+			name: 'div',
+			styles: true
+		},
+
+		// Enables <div>s with foo and bar classes.
+		{
+			name: 'div',
+			classes: [ 'foo', 'bar' ]
+		},
+
+		// Adds support for `foo` and `bar` classes to the already supported
+		// <p> elements (those are enabled by the specific Paragraph feature).
+		{
+			name: 'p',
+			classes: [ 'foo', 'bar' ]
+		},
+
+		// Enables <div>s with foo="true" attribute and bar attribute that
+		// can accept any value (boolean `true` value works as an asterisk).
+		{
+			name: 'div',
+			attributes: {
+				foo: 'true',
+				bar: true
+			}
+		},
+
+		// Adds support for style="color: *" to already supported
+		// <p> and <h2-h4> elements.
+		{
+			name: /^(p|h[2-4])$/',
+			styles: { 'color': true }
+		},
+}
+```
+
+The GHS feature distinguishes a couple of types of content that it treats a bit differently:
+
+* container elements (e.g. `<section>`, `<div>`),
+* inline elements (e.g. `<span>`, `<a>`),
+* and object elements (e.g. `<iframe>`, `<video>`).
+
+Enabled elements will not be available "anywhere" in the content, but still need to adhere to certain rules derived from HTML schema and common sense. Also, the behavior of specific type of elements in the editing area will be different. For instance, object elements will only be selectable as a whole, and inline elements will work as other formatting features supported by CKEditor 5 (e.g. bold, italic).
+
+## Extending specific editor features
+
+It is possible to add support for arbitrary styles, classed and other attributes to existing CKEditor 5 features (such as paragraphs, headings, list items, etc.).
+
+Most of the existing CKEditor 5 features can already be extended this way, however, some cannot yet. This includes:
+
+* Some of the table and image features' markup.
+* The `<ul>` and `<ol>` elements of the list feature.
+
+<!-- TODO link the above points to specific tickets on GH -->
+
+## Related features
+
+There is other source-related CKEditor 5 feature you may want to check:
+
+* {@link features/source-editing Source editing} &ndash; Provides the ability for viewing and editing the source of the document.
+* {@link features/html-embed HTML embed} &ndash; Allows embedding an arbitrary HTML snippet in the editor. It is a more constrained and controllable approach to arbitrary HTML than GHS.
+
+<!-- TODO link to HTML comments features once it's ready. -->
+
+## Contribute
+
+The source code of the feature is available on GitHub in https://github.com/ckeditor/ckeditor5/tree/master/packages/ckeditor5-media-embed.
diff --git a/packages/ckeditor5-source-editing/docs/features/source-editing.md b/packages/ckeditor5-source-editing/docs/features/source-editing.md
index 2954be996e9..79838b31c25 100644
--- a/packages/ckeditor5-source-editing/docs/features/source-editing.md
+++ b/packages/ckeditor5-source-editing/docs/features/source-editing.md
@@ -3,7 +3,6 @@ category: features
 menu-title: Source editing
 modified_at: 2021-05-28
 ---
-
 # Source editing
 
 The {@link module:source-editing/sourceediting~SourceEditing} feature provides the ability for viewing and editing the source of the document. The source editing plugin is a low-level document editing interface, while all the buttons and dropdowns located in a editor's toolbar are high-level ones.
@@ -30,8 +29,10 @@ The source editing plugin also works well with the {@link features/markdown Mark
 
 There is other source-related CKEditor 5 feature you may want to check:
 
+* {@link features/general-html-support General HTML support} &ndash; Allows enabling a generic support for additional HTML features.
 * {@link features/html-embed HTML embed} &ndash; Allows embedding an arbitrary HTML snippet in the editor.
 
+
 ## Installation
 
 To add this feature to your rich-text editor, install the [`@ckeditor/ckeditor5-source-editing`](https://www.npmjs.com/package/@ckeditor/ckeditor5-source-editing) package:

From 2deb33d11bb2ea06b8f722dc2263f5ae41a2f779 Mon Sep 17 00:00:00 2001
From: godai78 <b.biedrzycki@cksource.com>
Date: Mon, 14 Jun 2021 11:27:37 +0200
Subject: [PATCH 179/217] Docs: basic language review.

---
 docs/features/general-html-support.md | 49 ++++++++++++++-------------
 1 file changed, 25 insertions(+), 24 deletions(-)

diff --git a/docs/features/general-html-support.md b/docs/features/general-html-support.md
index c665a04ea89..3d48751c578 100644
--- a/docs/features/general-html-support.md
+++ b/docs/features/general-html-support.md
@@ -1,22 +1,23 @@
 ---
 category: features
 modified_at: 2021-06-13
+updated_at: 2021-06-14
 ---
 
 # General HTML support
 
-The General HTML support ("GHS") feature allows you to easily enable HTML features that are not supported by any other "specific" CKEditor 5 features.
+The general HTML support ("GHS") feature allows the user to easily enable HTML features that are not explicitly supported by any other dedicated CKEditor 5 features.
 
-Some examples of HTML features that can be easily enabled thanks to GHS:
+Some examples of HTML features that can be easily enabled thanks to GHS include:
 
-* `<section>`, `<article>`, and `<div>` elements,
-* `<audio>`, `<video>`, and `<iframe>` elements,
-* `<span>` and `<cite>` elements,
-* attributes on existing specific CKEditor 5 features:
+* The `<section>`, `<article>`, and `<div>` elements,
+* the `<audio>`, `<video>`, and `<iframe>` elements,
+* the `<span>` and `<cite>` elements,
+* some of the attributes on existing dedicated CKEditor 5 features:
 	* `data-*` and `id` attributes on e.g. `<p>` and `<h1-h6>`,
 	* `style` and `classes` on e.g. `<strong>` and `<a>`.
 
-Enabled HTML features can be loaded (via e.g. `editor.setData()`), pasted, output (via e.g. `editor.getData()`), and are visible in the editing area. Such content can also be edited in the editor, although, to a limited extend. Read more in [Level of support](#level-of-support).
+The enabled HTML features can be loaded (e.g. via `editor.setData()`), pasted, output (e.g. via `editor.getData()`), and are visible in the editing area. Such content can also be edited in the editor, although, to a limited extend. Read more about it in the [Level of support](#level-of-support) section.
 
 <info-box>
 	The General HTML support feature is **experimental and not yet production-ready**.
@@ -26,9 +27,9 @@ Enabled HTML features can be loaded (via e.g. `editor.setData()`), pasted, outpu
 
 ## Demo
 
-The GHS feature is configured via the `config.generalHtmlSupport` property in which you need to list HTML features that should be handled by GHS.
+The general HTML support feature is configured via the `config.generalHtmlSupport` property in which you need to list the HTML features that should be handled by GHS.
 
-The demo below uses this configuration:
+The demo below uses the following configuration:
 
 ```js
 import SourceEditing from '@ckeditor/ckeditor5-source-editing/src/sourceediting';
@@ -78,24 +79,24 @@ ClassicEditor
 
 ## Level of support
 
-The difference between specific CKEditor 5 features such as {@link features/basic-styles Basic styles} or {@link features/headings Headings} and HTML features enabled by GHS is that a plugin that support a specific HTML feature provides a complete user experience for that feature, whereas GHS ensures only that such a content is accepted by the editor.
+The difference between specific CKEditor 5 features such as {@link features/basic-styles basic styles} or {@link features/headings headings} and the HTML features enabled by GHS is that a plugin that support a specific HTML feature provides a complete user experience for that feature, whereas GHS ensures only that such a content is accepted by the editor.
 
-For instance, the specific {@link module:basic-styles/bold~Bold} feature offers a toolbar button to make the selected text bold. Together with the {@link features/autoformat Autoformatting feature} it also allows applying bold by typing `**foo**`. The {@link features/headings Headings} feature offers a dropdown from which the user can choose a heading level and ensures that pressing <kbd>Enter</kbd> at the end of a heading creates a new paragraph (and not another heading).
+For instance, the dedicated {@link module:basic-styles/bold~Bold} feature offers a toolbar button used to make the selected text bold. Together with the {@link features/autoformat autoformatting feature}, it also allows for applying bold style to content by typing a Markdown shortcode (`**foo**`). The {@link features/headings headings} feature offers a dropdown from which the user can choose a heading level and ensures that pressing <kbd>Enter</kbd> at the end of a heading creates a new paragraph (and not another heading).
 
-GHS does not offer any UI for enabled features and takes only basic semantics of a given feature into account. If you enable support for `<div>`s via GHS, the user will not be able to create `<div>`s from the editor UI. The GHS will know that a `<div>` is a container element, so it can wrap other blocks (like paragraphs) but cannot be used inline (next to e.g. a `<strong>` element). But that's it.
+General HTML support does not offer any UI for the enabled features and takes only basic semantics of a given feature into account. If you enable support for `<div>`s via GHS, the user will not be able to create `<div>`s from the editor UI. The GHS will know that a `<div>` is a container element, so it can wrap other blocks (like paragraphs) but cannot be used inline (next to e.g. a `<strong>` element). But there is no more.
 
-Therefore, GHS's main use cases are:
+Therefore, GHS's main use cases would be:
 
-* Ensuring backward content compatibility with legacy systems.
+* Ensuring backwards content compatibility with legacy systems.
 * Introducing basic support for missing HTML features at a low cost.
 
 <info-box>
-	Taken the nature of GHS, you may consider installing the {@link features/source-editing Source editing} feature alongside it.
+	Taken the nature of GHS, you may consider installing the {@link features/source-editing source editing} feature alongside with it.
 </info-box>
 
 ## Configuration
 
-By default, enabling the {@link module:content-compatibility/generalhtmlsupport~GeneralHtmlSupport} plugin does not enable support for any element. The elements to be supported need to be configured via {@link TODOmodule:core/editor/editorconfig~EditorConfig#generalHtmlSupport `config.generalHtmlSupport`} option:
+By default, enabling the {@link module:content-compatibility/generalhtmlsupport~GeneralHtmlSupport} plugin does not enable support for any element. The elements the user wants to be supported, need to be configured via the {@link TODOmodule:core/editor/editorconfig~EditorConfig#generalHtmlSupport `config.generalHtmlSupport`} option:
 
 ```js
 ClassicEditor.create( document.querySelector( '#editor' ), {
@@ -106,7 +107,7 @@ ClassicEditor.create( document.querySelector( '#editor' ), {
 } )
 ```
 
-The notation of `allowed` and `disallowed` rules looks like this:
+The notation of the `allowed` and `disallowed` rules looks as follows:
 
 <!-- TODO REVIEW THE BELOW. I WROTE IT FROM THE TOP OF MY HEAD. -->
 
@@ -129,12 +130,12 @@ The notation of `allowed` and `disallowed` rules looks like this:
 ]
 ```
 
-Some examples:
+Several implementation examples:
 
 ```js
 generalHtmlSupport: {
 	allowed: [
-		// Enables plain <div>s.
+		// Enables plain <div> elements.
 		{
 			name: 'div'
 		},
@@ -182,17 +183,17 @@ generalHtmlSupport: {
 }
 ```
 
-The GHS feature distinguishes a couple of types of content that it treats a bit differently:
+The GHS feature distinguishes several content types that it treats a bit differently:
 
-* container elements (e.g. `<section>`, `<div>`),
+* Container elements (e.g. `<section>`, `<div>`),
 * inline elements (e.g. `<span>`, `<a>`),
 * and object elements (e.g. `<iframe>`, `<video>`).
 
-Enabled elements will not be available "anywhere" in the content, but still need to adhere to certain rules derived from HTML schema and common sense. Also, the behavior of specific type of elements in the editing area will be different. For instance, object elements will only be selectable as a whole, and inline elements will work as other formatting features supported by CKEditor 5 (e.g. bold, italic).
+Enabled elements will not be available "anywhere" in the content, as they still need to adhere to certain rules derived from the HTML schema and from common sense. Also, the behavior of specific types of elements in the editing area will be different. For instance, the object elements will only be selectable as a whole, and the inline elements will work same as other formatting features supported by CKEditor 5 (e.g. bold, italic).
 
 ## Extending specific editor features
 
-It is possible to add support for arbitrary styles, classed and other attributes to existing CKEditor 5 features (such as paragraphs, headings, list items, etc.).
+It is possible to add support for arbitrary styles, classes and other attributes to existing CKEditor 5 features (such as paragraphs, headings, list items, etc.).
 
 Most of the existing CKEditor 5 features can already be extended this way, however, some cannot yet. This includes:
 
@@ -203,7 +204,7 @@ Most of the existing CKEditor 5 features can already be extended this way, howev
 
 ## Related features
 
-There is other source-related CKEditor 5 feature you may want to check:
+There are other HTML editing related CKEditor 5 features you may want to check:
 
 * {@link features/source-editing Source editing} &ndash; Provides the ability for viewing and editing the source of the document.
 * {@link features/html-embed HTML embed} &ndash; Allows embedding an arbitrary HTML snippet in the editor. It is a more constrained and controllable approach to arbitrary HTML than GHS.

From 6e1238fd06c6dbb978c47d74e3ca0ce70b2bf31a Mon Sep 17 00:00:00 2001
From: godai78 <b.biedrzycki@cksource.com>
Date: Mon, 14 Jun 2021 11:38:53 +0200
Subject: [PATCH 180/217] Docs: grammar fix.

---
 .../ckeditor5-source-editing/docs/features/source-editing.md    | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-source-editing/docs/features/source-editing.md b/packages/ckeditor5-source-editing/docs/features/source-editing.md
index 79838b31c25..dda84173d1b 100644
--- a/packages/ckeditor5-source-editing/docs/features/source-editing.md
+++ b/packages/ckeditor5-source-editing/docs/features/source-editing.md
@@ -27,7 +27,7 @@ The source editing plugin also works well with the {@link features/markdown Mark
 
 ## Related features
 
-There is other source-related CKEditor 5 feature you may want to check:
+There are other source-related CKEditor 5 features you may want to check:
 
 * {@link features/general-html-support General HTML support} &ndash; Allows enabling a generic support for additional HTML features.
 * {@link features/html-embed HTML embed} &ndash; Allows embedding an arbitrary HTML snippet in the editor.

From ef6a9c186879b5a94e3e07b1abf5aba1d8c291bf Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 15 Jun 2021 10:18:48 +0200
Subject: [PATCH 181/217] Moved docs to package directory.

---
 .../docs}/_snippets/features/general-html-support.html            | 0
 .../docs}/_snippets/features/general-html-support.js              | 0
 .../ckeditor5-html-support/docs}/features/general-html-support.md | 0
 3 files changed, 0 insertions(+), 0 deletions(-)
 rename {docs => packages/ckeditor5-html-support/docs}/_snippets/features/general-html-support.html (100%)
 rename {docs => packages/ckeditor5-html-support/docs}/_snippets/features/general-html-support.js (100%)
 rename {docs => packages/ckeditor5-html-support/docs}/features/general-html-support.md (100%)

diff --git a/docs/_snippets/features/general-html-support.html b/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html
similarity index 100%
rename from docs/_snippets/features/general-html-support.html
rename to packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html
diff --git a/docs/_snippets/features/general-html-support.js b/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.js
similarity index 100%
rename from docs/_snippets/features/general-html-support.js
rename to packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.js
diff --git a/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
similarity index 100%
rename from docs/features/general-html-support.md
rename to packages/ckeditor5-html-support/docs/features/general-html-support.md

From 7ba990c3aa75c725111df4bf9b2b78768778a066 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 15 Jun 2021 15:40:47 +0200
Subject: [PATCH 182/217] Updated technical docs issues.

---
 .../features/general-html-support.html        |  2 +-
 .../features/general-html-support.js          |  6 ++---
 .../docs/features/general-html-support.md     | 26 +++++++++----------
 .../ckeditor5-html-support/src/dataschema.js  |  9 +++++++
 4 files changed, 25 insertions(+), 18 deletions(-)

diff --git a/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html b/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html
index 3648628f0d3..26e9df33855 100644
--- a/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html
+++ b/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html
@@ -1,7 +1,7 @@
 <div id="snippet-general-html-support">
 	<h2 data-i18n-context="title">General HTML support</h2>
 
-	<div styles="color: red; padding: 10px; text-align: center; border: solid 3px red">
+	<div style="color: red; padding: 10px; text-align: center; border: solid 3px red">
 		<p data-i18n-context="experimental-note">This is an experimental feature.</p>
 
 		<details data-i18n-context="experimental-note">
diff --git a/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.js b/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.js
index 2456c18133c..558b009de2a 100644
--- a/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.js
+++ b/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.js
@@ -15,7 +15,7 @@ import ImageUpload from '@ckeditor/ckeditor5-image/src/imageupload';
 import CloudServices from '@ckeditor/ckeditor5-cloud-services/src/cloudservices';
 
 import SourceEditing from '@ckeditor/ckeditor5-source-editing/src/sourceediting';
-import GeneralHtmlSupport from '@ckeditor/ckeditor5-content-compatibility/src/generalhtmlsupport';
+import GeneralHtmlSupport from '@ckeditor/ckeditor5-html-support/src/generalhtmlsupport';
 
 ClassicEditor
 	.create( document.querySelector( '#snippet-general-html-support' ), {
@@ -68,8 +68,8 @@ ClassicEditor
 		},
 		cloudServices: CS_CONFIG,
 
-		generalHtmlSupport: {
-			allowed: [
+		htmlSupport: {
+			allow: [
 				// Enables <div>, <details>, and <summary> elements with all kind of attributes.
 				{
 					name: /^(div|details|summary)$/,
diff --git a/packages/ckeditor5-html-support/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
index 3d48751c578..d6eba58d9dc 100644
--- a/packages/ckeditor5-html-support/docs/features/general-html-support.md
+++ b/packages/ckeditor5-html-support/docs/features/general-html-support.md
@@ -27,7 +27,7 @@ The enabled HTML features can be loaded (e.g. via `editor.setData()`), pasted, o
 
 ## Demo
 
-The general HTML support feature is configured via the `config.generalHtmlSupport` property in which you need to list the HTML features that should be handled by GHS.
+The general HTML support feature is configured via the `config.htmlSupport` property in which you need to list the HTML features that should be handled by GHS.
 
 The demo below uses the following configuration:
 
@@ -39,8 +39,8 @@ ClassicEditor
 	.create( document.querySelector( '#editor' ), {
 		plugins: [ SourceEditing, GeneralHtmlSupport, ... ],
 		toolbar: [ 'sourceEditing', ... ],
-		generalHtmlSupport: {
-			allowed: {
+		htmlSupport: {
+			allow: {
 				// Enables <div>, <details>, and <summary> elements with all kind of attributes.
 				{
 					name: /^(div|details|summary)$/,
@@ -96,20 +96,18 @@ Therefore, GHS's main use cases would be:
 
 ## Configuration
 
-By default, enabling the {@link module:content-compatibility/generalhtmlsupport~GeneralHtmlSupport} plugin does not enable support for any element. The elements the user wants to be supported, need to be configured via the {@link TODOmodule:core/editor/editorconfig~EditorConfig#generalHtmlSupport `config.generalHtmlSupport`} option:
+By default, enabling the {@link module:html-support/generalhtmlsupport~GeneralHtmlSupport} plugin does not enable support for any element. The elements the user wants to be supported, need to be configured via the {@link module:core/editor/editorconfig~EditorConfig#htmlSupport `config.htmlSupport`} option:
 
 ```js
 ClassicEditor.create( document.querySelector( '#editor' ), {
-	generalHtmlSupport: {
-		allowed: [ /* HTML features to allow */ ]
-		disallowed: [ /* HTML features to disallow */ ]
+	htmlSupport: {
+		allow: [ /* HTML features to allow */ ]
+		disallow: [ /* HTML features to disallow */ ]
 	}
 } )
 ```
 
-The notation of the `allowed` and `disallowed` rules looks as follows:
-
-<!-- TODO REVIEW THE BELOW. I WROTE IT FROM THE TOP OF MY HEAD. -->
+The notation of the `allow` and `disallow` rules looks as follows:
 
 ```js
 [
@@ -119,13 +117,13 @@ The notation of the `allowed` and `disallowed` rules looks as follows:
 		name: string|regexp,
 
 		// Styles to allow (by name, name and value or just all).
-		styles: object<string=>true|string|regexp>|array<string>|true,
+		styles: object<string=>true|string|regexp>|array<string|object>|true,
 
 		// Classes to allow (by name or just all).
 		classes: array<string|regexp>|true,
 
 		// Other attributes to allow (by name, name and value or just all).
-		attributes: object<string=>true|string|regexp>|array<string>|true,
+		attributes: object<string=>true|string|regexp>|array<string|object>|true,
 	}
 ]
 ```
@@ -133,8 +131,8 @@ The notation of the `allowed` and `disallowed` rules looks as follows:
 Several implementation examples:
 
 ```js
-generalHtmlSupport: {
-	allowed: [
+htmlSupport: {
+	allow: [
 		// Enables plain <div> elements.
 		{
 			name: 'div'
diff --git a/packages/ckeditor5-html-support/src/dataschema.js b/packages/ckeditor5-html-support/src/dataschema.js
index 17db7ac2edb..c6260e81ca6 100644
--- a/packages/ckeditor5-html-support/src/dataschema.js
+++ b/packages/ckeditor5-html-support/src/dataschema.js
@@ -148,6 +148,15 @@ export default class DataSchema extends Plugin {
 			}
 		} );
 
+		// TODO Remove it once we have proper support for div elements.
+		this.registerBlockElement( {
+			model: 'htmlDiv',
+			view: 'div',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		} );
+
 		this.registerBlockElement( {
 			view: 'article',
 			model: 'htmlArticle',

From 63d6d498aceb8edf4f2207b185828b0dbcdc1feb Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Tue, 15 Jun 2021 19:03:58 +0200
Subject: [PATCH 183/217] Reverted unnecessary change.

---
 .../docs/features/general-html-support.md                     | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-html-support/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
index d6eba58d9dc..0a74637dae9 100644
--- a/packages/ckeditor5-html-support/docs/features/general-html-support.md
+++ b/packages/ckeditor5-html-support/docs/features/general-html-support.md
@@ -117,13 +117,13 @@ The notation of the `allow` and `disallow` rules looks as follows:
 		name: string|regexp,
 
 		// Styles to allow (by name, name and value or just all).
-		styles: object<string=>true|string|regexp>|array<string|object>|true,
+		styles: object<string=>true|string|regexp>|array<string>|true,
 
 		// Classes to allow (by name or just all).
 		classes: array<string|regexp>|true,
 
 		// Other attributes to allow (by name, name and value or just all).
-		attributes: object<string=>true|string|regexp>|array<string|object>|true,
+		attributes: object<string=>true|string|regexp>|array<string>|true,
 	}
 ]
 ```

From f12c7f9550cbcfb1020b2a10da23e907eb2ecd2d Mon Sep 17 00:00:00 2001
From: godai78 <b.biedrzycki@cksource.com>
Date: Wed, 16 Jun 2021 08:25:44 +0200
Subject: [PATCH 184/217] Docs: further fixes to the docs.

---
 .../docs/features/general-html-support.md     | 36 +++++++++----------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/packages/ckeditor5-html-support/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
index 0a74637dae9..28b0cabfc4e 100644
--- a/packages/ckeditor5-html-support/docs/features/general-html-support.md
+++ b/packages/ckeditor5-html-support/docs/features/general-html-support.md
@@ -6,14 +6,14 @@ updated_at: 2021-06-14
 
 # General HTML support
 
-The general HTML support ("GHS") feature allows the user to easily enable HTML features that are not explicitly supported by any other dedicated CKEditor 5 features.
+The general HTML support ("GHS") feature allows the user to easily enable HTML features that are not explicitly supported by any other dedicated CKEditor 5 plugins.
 
-Some examples of HTML features that can be easily enabled thanks to GHS include:
+Some examples of HTML features that can be easily enabled using general HTML support include:
 
-* The `<section>`, `<article>`, and `<div>` elements,
-* the `<audio>`, `<video>`, and `<iframe>` elements,
-* the `<span>` and `<cite>` elements,
-* some of the attributes on existing dedicated CKEditor 5 features:
+* The `<section>`, `<article>`, and `<div>` elements.
+* The `<audio>`, `<video>`, and `<iframe>` elements.
+* The `<span>` and `<cite>` elements.
+* Some of the attributes on existing dedicated CKEditor 5 features:
 	* `data-*` and `id` attributes on e.g. `<p>` and `<h1-h6>`,
 	* `style` and `classes` on e.g. `<strong>` and `<a>`.
 
@@ -27,7 +27,7 @@ The enabled HTML features can be loaded (e.g. via `editor.setData()`), pasted, o
 
 ## Demo
 
-The general HTML support feature is configured via the `config.htmlSupport` property in which you need to list the HTML features that should be handled by GHS.
+The general HTML support feature is configured via the `config.htmlSupport` property. In it, you need to list the HTML features that should be handled by GHS.
 
 The demo below uses the following configuration:
 
@@ -79,11 +79,11 @@ ClassicEditor
 
 ## Level of support
 
-The difference between specific CKEditor 5 features such as {@link features/basic-styles basic styles} or {@link features/headings headings} and the HTML features enabled by GHS is that a plugin that support a specific HTML feature provides a complete user experience for that feature, whereas GHS ensures only that such a content is accepted by the editor.
+The difference between specific CKEditor 5 features such as {@link features/basic-styles basic styles} or {@link features/headings headings} and the HTML features enabled by GHS is that a plugin that supports a specific HTML feature provides a complete user experience for that feature, whereas GHS ensures only that such a content is accepted by the editor.
 
-For instance, the dedicated {@link module:basic-styles/bold~Bold} feature offers a toolbar button used to make the selected text bold. Together with the {@link features/autoformat autoformatting feature}, it also allows for applying bold style to content by typing a Markdown shortcode (`**foo**`). The {@link features/headings headings} feature offers a dropdown from which the user can choose a heading level and ensures that pressing <kbd>Enter</kbd> at the end of a heading creates a new paragraph (and not another heading).
+For instance, the dedicated {@link features/basic-styles#available-text-styles bold} feature offers a toolbar button used to make the selected text bold. Together with the {@link features/autoformat autoformatting feature}, it also allows for applying bold style to content by typing a Markdown shortcode (`**foo**`) in the editor. The {@link features/headings headings} feature offers a dropdown from which the user can choose a heading level and ensures that pressing <kbd>Enter</kbd> at the end of a heading creates a new paragraph (and not another heading).
 
-General HTML support does not offer any UI for the enabled features and takes only basic semantics of a given feature into account. If you enable support for `<div>`s via GHS, the user will not be able to create `<div>`s from the editor UI. The GHS will know that a `<div>` is a container element, so it can wrap other blocks (like paragraphs) but cannot be used inline (next to e.g. a `<strong>` element). But there is no more.
+The general HTML support does not offer any UI for the enabled features and takes only basic semantics of a given feature into account. If you enable support for `<div>`s via GHS, the user will not be able to create `<div>`s from the editor UI. The GHS will know that a `<div>` is a container element, so it can wrap other blocks (like paragraphs) but cannot be used inline (next to e.g. a `<strong>` element). There is no more, however.
 
 Therefore, GHS's main use cases would be:
 
@@ -96,7 +96,7 @@ Therefore, GHS's main use cases would be:
 
 ## Configuration
 
-By default, enabling the {@link module:html-support/generalhtmlsupport~GeneralHtmlSupport} plugin does not enable support for any element. The elements the user wants to be supported, need to be configured via the {@link module:core/editor/editorconfig~EditorConfig#htmlSupport `config.htmlSupport`} option:
+By default, enabling the {@link module:html-support/generalhtmlsupport~GeneralHtmlSupport} plugin does not enable support for any given element. The elements the user wants to be supported, need to be configured via the {@link module:core/editor/editorconfig~EditorConfig#htmlSupport `config.htmlSupport`} option:
 
 ```js
 ClassicEditor.create( document.querySelector( '#editor' ), {
@@ -156,7 +156,7 @@ htmlSupport: {
 		},
 
 		// Adds support for `foo` and `bar` classes to the already supported
-		// <p> elements (those are enabled by the specific Paragraph feature).
+		// <p> elements (those are enabled by the dedicated paragraph feature).
 		{
 			name: 'p',
 			classes: [ 'foo', 'bar' ]
@@ -172,7 +172,7 @@ htmlSupport: {
 			}
 		},
 
-		// Adds support for style="color: *" to already supported
+		// Adds support for style="color: *" to the already supported
 		// <p> and <h2-h4> elements.
 		{
 			name: /^(p|h[2-4])$/',
@@ -181,13 +181,13 @@ htmlSupport: {
 }
 ```
 
-The GHS feature distinguishes several content types that it treats a bit differently:
+The general HTML support feature distinguishes several content types that it treats a bit differently:
 
-* Container elements (e.g. `<section>`, `<div>`),
-* inline elements (e.g. `<span>`, `<a>`),
-* and object elements (e.g. `<iframe>`, `<video>`).
+* Container elements (e.g. `<section>`, `<div>`).
+* Inline elements (e.g. `<span>`, `<a>`).
+* Object elements (e.g. `<iframe>`, `<video>`).
 
-Enabled elements will not be available "anywhere" in the content, as they still need to adhere to certain rules derived from the HTML schema and from common sense. Also, the behavior of specific types of elements in the editing area will be different. For instance, the object elements will only be selectable as a whole, and the inline elements will work same as other formatting features supported by CKEditor 5 (e.g. bold, italic).
+The enabled elements will not just be available "anywhere" in the content, as they still need to adhere to certain rules derived from the HTML schema and from common sense. Also, the behavior of specific types of elements in the editing area will be different. For instance, the object elements will only be selectable as a whole, and the inline elements will work the same as other formatting features supported by CKEditor 5 (e.g. bold, italic) do.
 
 ## Extending specific editor features
 

From 6192504200eee8983d55f5ca45744e39191c1f34 Mon Sep 17 00:00:00 2001
From: godai78 <b.biedrzycki@cksource.com>
Date: Thu, 17 Jun 2021 12:48:29 +0200
Subject: [PATCH 185/217] Docs: renaming section.

---
 .../docs/features/general-html-support.md                     | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/packages/ckeditor5-html-support/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
index 28b0cabfc4e..ca8e8299c8d 100644
--- a/packages/ckeditor5-html-support/docs/features/general-html-support.md
+++ b/packages/ckeditor5-html-support/docs/features/general-html-support.md
@@ -189,7 +189,7 @@ The general HTML support feature distinguishes several content types that it tre
 
 The enabled elements will not just be available "anywhere" in the content, as they still need to adhere to certain rules derived from the HTML schema and from common sense. Also, the behavior of specific types of elements in the editing area will be different. For instance, the object elements will only be selectable as a whole, and the inline elements will work the same as other formatting features supported by CKEditor 5 (e.g. bold, italic) do.
 
-## Extending specific editor features
+## Known issues
 
 It is possible to add support for arbitrary styles, classes and other attributes to existing CKEditor 5 features (such as paragraphs, headings, list items, etc.).
 
@@ -207,8 +207,6 @@ There are other HTML editing related CKEditor 5 features you may want to check:
 * {@link features/source-editing Source editing} &ndash; Provides the ability for viewing and editing the source of the document.
 * {@link features/html-embed HTML embed} &ndash; Allows embedding an arbitrary HTML snippet in the editor. It is a more constrained and controllable approach to arbitrary HTML than GHS.
 
-<!-- TODO link to HTML comments features once it's ready. -->
-
 ## Contribute
 
 The source code of the feature is available on GitHub in https://github.com/ckeditor/ckeditor5/tree/master/packages/ckeditor5-media-embed.

From 8ac83d41f225fcc8faaedfb71b62300267bd5bae Mon Sep 17 00:00:00 2001
From: godai78 <b.biedrzycki@cksource.com>
Date: Thu, 17 Jun 2021 12:50:14 +0200
Subject: [PATCH 186/217] Docs: section rewording.

---
 .../docs/features/general-html-support.md                      | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-html-support/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
index ca8e8299c8d..86fafb9a540 100644
--- a/packages/ckeditor5-html-support/docs/features/general-html-support.md
+++ b/packages/ckeditor5-html-support/docs/features/general-html-support.md
@@ -195,7 +195,8 @@ It is possible to add support for arbitrary styles, classes and other attributes
 
 Most of the existing CKEditor 5 features can already be extended this way, however, some cannot yet. This includes:
 
-* Some of the table and image features' markup.
+* Some of the table markup.
+* Some of the image features' markup.
 * The `<ul>` and `<ol>` elements of the list feature.
 
 <!-- TODO link the above points to specific tickets on GH -->

From e0849a416b6c99d208aeb58d412129288a709431 Mon Sep 17 00:00:00 2001
From: Mgsy <kacpertomporowski@gmail.com>
Date: Thu, 17 Jun 2021 14:53:46 +0200
Subject: [PATCH 187/217] Docs: Updated package name in the GHS feature guide.

---
 .../docs/features/general-html-support.md                       | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-html-support/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
index 86fafb9a540..dfa20577d10 100644
--- a/packages/ckeditor5-html-support/docs/features/general-html-support.md
+++ b/packages/ckeditor5-html-support/docs/features/general-html-support.md
@@ -210,4 +210,4 @@ There are other HTML editing related CKEditor 5 features you may want to check:
 
 ## Contribute
 
-The source code of the feature is available on GitHub in https://github.com/ckeditor/ckeditor5/tree/master/packages/ckeditor5-media-embed.
+The source code of the feature is available on GitHub in https://github.com/ckeditor/ckeditor5/tree/master/packages/ckeditor5-html-support.

From ab2124e51ca70f8f94fd39eb836c0287950dbdb3 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 18 Jun 2021 14:05:52 +0200
Subject: [PATCH 188/217] Updated known issues section.

---
 .../docs/features/general-html-support.md                | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/packages/ckeditor5-html-support/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
index dfa20577d10..a76a8f732d2 100644
--- a/packages/ckeditor5-html-support/docs/features/general-html-support.md
+++ b/packages/ckeditor5-html-support/docs/features/general-html-support.md
@@ -195,11 +195,10 @@ It is possible to add support for arbitrary styles, classes and other attributes
 
 Most of the existing CKEditor 5 features can already be extended this way, however, some cannot yet. This includes:
 
-* Some of the table markup.
-* Some of the image features' markup.
-* The `<ul>` and `<ol>` elements of the list feature.
-
-<!-- TODO link the above points to specific tickets on GH -->
+* Some of the table markup [#9914](https://github.com/ckeditor/ckeditor5/issues/9914).
+* Some of the image features' markup [#9916](https://github.com/ckeditor/ckeditor5/issues/9916).
+* Some of the media embed features' markup [#9918](https://github.com/ckeditor/ckeditor5/issues/9918).
+* The `<ul>` and `<ol>` elements of the list feature [#9917](https://github.com/ckeditor/ckeditor5/issues/9917).
 
 ## Related features
 

From 66e080626f8207c172eb4625a35bc2941efdcbb0 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 21 Jun 2021 09:29:30 +0200
Subject: [PATCH 189/217] Added missing definitions for headings.

---
 packages/ckeditor5-html-support/src/dataschema.js | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/packages/ckeditor5-html-support/src/dataschema.js b/packages/ckeditor5-html-support/src/dataschema.js
index c6260e81ca6..96541daeeba 100644
--- a/packages/ckeditor5-html-support/src/dataschema.js
+++ b/packages/ckeditor5-html-support/src/dataschema.js
@@ -135,6 +135,21 @@ export default class DataSchema extends Plugin {
 			view: 'blockquote'
 		} );
 
+		this.registerBlockElement( {
+			model: 'heading1',
+			view: 'h2'
+		} );
+
+		this.registerBlockElement( {
+			model: 'heading2',
+			view: 'h3'
+		} );
+
+		this.registerBlockElement( {
+			model: 'heading3',
+			view: 'h4'
+		} );
+
 		this.registerBlockElement( {
 			model: 'listItem',
 			view: 'li'

From 4d7b3b3ce338d799e738110f83e035ed81533216 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 21 Jun 2021 09:31:53 +0200
Subject: [PATCH 190/217] Removed unused attributes in demo.

---
 .../docs/_snippets/features/general-html-support.html       | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html b/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html
index 26e9df33855..b22d1c35231 100644
--- a/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html
+++ b/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html
@@ -15,8 +15,8 @@ <h2 data-i18n-context="title">General HTML support</h2>
 	<p data-i18n-context="description">The <abbr title="General HTML Support">GHS</abbr> feature is enabled in this editor and configured to support the following content (in addition to content already support by other editor features):</p>
 
 	<ul>
-		<li data-i18n-context="description"><code>&lt;div></code>, <code>&lt;details></code>, and <code>&lt;summary></code> elements with all kind of attributes,</li>
-		<li data-i18n-context="description">paragraphs and headings with <code>data-*</code> attributes and all classes,</li>
-		<li data-i18n-context="description"><code>&lt;span></code> elements with all inline styles and <code>&lt;abbr></code> elements with `title` attributes.</li>
+		<li><code>&lt;div></code>, <code>&lt;details></code>, and <code>&lt;summary></code> elements with all kind of attributes,</li>
+		<li>paragraphs and headings with <code>data-*</code> attributes and all classes,</li>
+		<li><code>&lt;span></code> elements with all inline styles and <code>&lt;abbr></code> elements with `title` attributes.</li>
 	</ul>
 </div>

From 6b281c2e137d4daefebb73c058c6818e28064f2a Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 21 Jun 2021 09:32:56 +0200
Subject: [PATCH 191/217] Typo.

---
 .../docs/_snippets/features/general-html-support.html           | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html b/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html
index b22d1c35231..7ac8aa9749d 100644
--- a/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html
+++ b/packages/ckeditor5-html-support/docs/_snippets/features/general-html-support.html
@@ -12,7 +12,7 @@ <h2 data-i18n-context="title">General HTML support</h2>
 		</details>
 	</div>
 
-	<p data-i18n-context="description">The <abbr title="General HTML Support">GHS</abbr> feature is enabled in this editor and configured to support the following content (in addition to content already support by other editor features):</p>
+	<p data-i18n-context="description">The <abbr title="General HTML Support">GHS</abbr> feature is enabled in this editor and configured to support the following content (in addition to the content already support by other editor features):</p>
 
 	<ul>
 		<li><code>&lt;div></code>, <code>&lt;details></code>, and <code>&lt;summary></code> elements with all kind of attributes,</li>

From efb10967222fbaaa0f39635a0c25a2d49d4851cd Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 21 Jun 2021 09:43:54 +0200
Subject: [PATCH 192/217] Added missing abbrv definition.

---
 packages/ckeditor5-html-support/src/dataschema.js | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/packages/ckeditor5-html-support/src/dataschema.js b/packages/ckeditor5-html-support/src/dataschema.js
index 96541daeeba..ba5b50ef986 100644
--- a/packages/ckeditor5-html-support/src/dataschema.js
+++ b/packages/ckeditor5-html-support/src/dataschema.js
@@ -266,6 +266,11 @@ export default class DataSchema extends Plugin {
 			model: 'htmlCode'
 		} );
 
+		this.registerInlineElement( {
+			view: 'abbr',
+			model: 'htmlAbbr'
+		} );
+
 		this.registerInlineElement( {
 			view: 'a',
 			model: 'htmlA',

From 301f6f60ce099debf1eaa216ef578d536eb37bd6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jacek=20Bogda=C5=84ski?= <jacekbogd@gmail.com>
Date: Mon, 21 Jun 2021 09:51:44 +0200
Subject: [PATCH 193/217] Apply suggestions from code review

---
 .../docs/features/general-html-support.md              | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/packages/ckeditor5-html-support/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
index a76a8f732d2..508b4078da4 100644
--- a/packages/ckeditor5-html-support/docs/features/general-html-support.md
+++ b/packages/ckeditor5-html-support/docs/features/general-html-support.md
@@ -6,9 +6,9 @@ updated_at: 2021-06-14
 
 # General HTML support
 
-The general HTML support ("GHS") feature allows the user to easily enable HTML features that are not explicitly supported by any other dedicated CKEditor 5 plugins.
+The general HTML support ("GHS") feature allows developers to easily enable HTML features that are not explicitly supported by any other dedicated CKEditor 5 plugins.
 
-Some examples of HTML features that can be easily enabled using general HTML support include:
+Some examples of HTML features that can be easily enabled using General HTML Support include:
 
 * The `<section>`, `<article>`, and `<div>` elements.
 * The `<audio>`, `<video>`, and `<iframe>` elements.
@@ -27,7 +27,7 @@ The enabled HTML features can be loaded (e.g. via `editor.setData()`), pasted, o
 
 ## Demo
 
-The general HTML support feature is configured via the `config.htmlSupport` property. In it, you need to list the HTML features that should be handled by GHS.
+The General HTML Support feature is configured via the `config.htmlSupport` property. In it, you need to list the HTML features that should be handled by GHS.
 
 The demo below uses the following configuration:
 
@@ -83,7 +83,7 @@ The difference between specific CKEditor 5 features such as {@link features/basi
 
 For instance, the dedicated {@link features/basic-styles#available-text-styles bold} feature offers a toolbar button used to make the selected text bold. Together with the {@link features/autoformat autoformatting feature}, it also allows for applying bold style to content by typing a Markdown shortcode (`**foo**`) in the editor. The {@link features/headings headings} feature offers a dropdown from which the user can choose a heading level and ensures that pressing <kbd>Enter</kbd> at the end of a heading creates a new paragraph (and not another heading).
 
-The general HTML support does not offer any UI for the enabled features and takes only basic semantics of a given feature into account. If you enable support for `<div>`s via GHS, the user will not be able to create `<div>`s from the editor UI. The GHS will know that a `<div>` is a container element, so it can wrap other blocks (like paragraphs) but cannot be used inline (next to e.g. a `<strong>` element). There is no more, however.
+The General HTML Support does not offer any UI for the enabled features and takes only the basic semantics of a given feature into account. If you enable support for `<div>`s via GHS, the user will not be able to create `<div>`s from the editor UI. The GHS will know that a `<div>` is a container element, so it can wrap other blocks (like paragraphs) but cannot be used inline (next to e.g. a `<strong>` element). There is no more, however.
 
 Therefore, GHS's main use cases would be:
 
@@ -181,7 +181,7 @@ htmlSupport: {
 }
 ```
 
-The general HTML support feature distinguishes several content types that it treats a bit differently:
+The General HTML Support feature distinguishes several content types that it treats a bit differently:
 
 * Container elements (e.g. `<section>`, `<div>`).
 * Inline elements (e.g. `<span>`, `<a>`).

From bafe5f1c8b8262da0a5c117ea6ba9511fd998e69 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 21 Jun 2021 09:56:45 +0200
Subject: [PATCH 194/217] Unified package name in docs guide.

---
 .../docs/features/general-html-support.md                 | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/packages/ckeditor5-html-support/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
index 508b4078da4..ce4970fefdf 100644
--- a/packages/ckeditor5-html-support/docs/features/general-html-support.md
+++ b/packages/ckeditor5-html-support/docs/features/general-html-support.md
@@ -4,9 +4,9 @@ modified_at: 2021-06-13
 updated_at: 2021-06-14
 ---
 
-# General HTML support
+# General HTML Support
 
-The general HTML support ("GHS") feature allows developers to easily enable HTML features that are not explicitly supported by any other dedicated CKEditor 5 plugins.
+The General HTML Support ("GHS") feature allows developers to easily enable HTML features that are not explicitly supported by any other dedicated CKEditor 5 plugins.
 
 Some examples of HTML features that can be easily enabled using General HTML Support include:
 
@@ -20,9 +20,9 @@ Some examples of HTML features that can be easily enabled using General HTML Sup
 The enabled HTML features can be loaded (e.g. via `editor.setData()`), pasted, output (e.g. via `editor.getData()`), and are visible in the editing area. Such content can also be edited in the editor, although, to a limited extend. Read more about it in the [Level of support](#level-of-support) section.
 
 <info-box>
-	The General HTML support feature is **experimental and not yet production-ready**.
+	The General HTML Support feature is **experimental and not yet production-ready**.
 
-	Follow the ["Stabilize and release a production-ready General HTML support feature"](https://github.com/ckeditor/ckeditor5/issues/9856) issue for more updates and related issues.
+	Follow the ["Stabilize and release a production-ready General HTML Support feature"](https://github.com/ckeditor/ckeditor5/issues/9856) issue for more updates and related issues.
 </info-box>
 
 ## Demo

From 88e0b9335d5c4ab1c7341abc096378195286d7bd Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 17 Jun 2021 10:40:13 +0200
Subject: [PATCH 195/217] Complete schema definition with missing features.

---
 packages/ckeditor5-html-support/package.json  |   8 +
 .../ckeditor5-html-support/src/datafilter.js  |   5 +-
 .../ckeditor5-html-support/src/dataschema.js  | 313 +-----------------
 .../src/schemadefinitions.js                  | 160 +++++++++
 .../tests/manual/features.html                | 123 +++++++
 .../tests/manual/features.js                  |  85 +++++
 .../tests/manual/features.md                  |   3 +
 .../tests/manual/sample.jpg                   | Bin 0 -> 114298 bytes
 8 files changed, 398 insertions(+), 299 deletions(-)
 create mode 100644 packages/ckeditor5-html-support/src/schemadefinitions.js
 create mode 100644 packages/ckeditor5-html-support/tests/manual/features.html
 create mode 100644 packages/ckeditor5-html-support/tests/manual/features.js
 create mode 100644 packages/ckeditor5-html-support/tests/manual/features.md
 create mode 100644 packages/ckeditor5-html-support/tests/manual/sample.jpg

diff --git a/packages/ckeditor5-html-support/package.json b/packages/ckeditor5-html-support/package.json
index 2835d584301..7cc325874dd 100644
--- a/packages/ckeditor5-html-support/package.json
+++ b/packages/ckeditor5-html-support/package.json
@@ -19,17 +19,25 @@
     "lodash-es": "^4.17.15"
   },
   "devDependencies": {
+    "@ckeditor/ckeditor5-alignment": "^28.0.0",
     "@ckeditor/ckeditor5-basic-styles": "^28.0.0",
     "@ckeditor/ckeditor5-block-quote": "^28.0.0",
+    "@ckeditor/ckeditor5-cloud-services": "^28.0.0",
     "@ckeditor/ckeditor5-code-block": "^28.0.0",
     "@ckeditor/ckeditor5-core": "^28.0.0",
+    "@ckeditor/ckeditor5-easy-image": "^28.0.0",
     "@ckeditor/ckeditor5-editor-classic": "^28.0.0",
     "@ckeditor/ckeditor5-engine": "^28.0.0",
     "@ckeditor/ckeditor5-essentials": "^28.0.0",
     "@ckeditor/ckeditor5-font": "^28.0.0",
     "@ckeditor/ckeditor5-highlight": "^28.0.0",
+    "@ckeditor/ckeditor5-horizontal-line": "^28.0.0",
+    "@ckeditor/ckeditor5-html-embed": "^28.0.0",
+    "@ckeditor/ckeditor5-image": "^28.0.0",
+    "@ckeditor/ckeditor5-indent": "^28.0.0",
     "@ckeditor/ckeditor5-link": "^28.0.0",
     "@ckeditor/ckeditor5-list": "^28.0.0",
+    "@ckeditor/ckeditor5-page-break": "^28.0.0",
     "@ckeditor/ckeditor5-paragraph": "^28.0.0",
     "@ckeditor/ckeditor5-table": "^28.0.0",
     "@ckeditor/ckeditor5-utils": "^28.0.0",
diff --git a/packages/ckeditor5-html-support/src/datafilter.js b/packages/ckeditor5-html-support/src/datafilter.js
index d1e5bf2ccd2..1440489025c 100644
--- a/packages/ckeditor5-html-support/src/datafilter.js
+++ b/packages/ckeditor5-html-support/src/datafilter.js
@@ -556,7 +556,10 @@ function iterableToObject( iterable, getValue ) {
 	const attributesObject = {};
 
 	for ( const prop of iterable ) {
-		attributesObject[ prop ] = getValue( prop );
+		const value = getValue( prop );
+		if ( value !== undefined ) {
+			attributesObject[ prop ] = getValue( prop );
+		}
 	}
 
 	return attributesObject;
diff --git a/packages/ckeditor5-html-support/src/dataschema.js b/packages/ckeditor5-html-support/src/dataschema.js
index ba5b50ef986..3602813c7d3 100644
--- a/packages/ckeditor5-html-support/src/dataschema.js
+++ b/packages/ckeditor5-html-support/src/dataschema.js
@@ -9,6 +9,7 @@
 
 import { Plugin } from 'ckeditor5/src/core';
 import { toArray } from 'ckeditor5/src/utils';
+import defaultConfig from './schemadefinitions';
 
 /**
  * Holds representation of the extended HTML document type definitions to be used by the
@@ -53,7 +54,7 @@ export default class DataSchema extends Plugin {
 		 */
 		this._definitions = new Map();
 
-		this._registerDefaultDefinitions();
+		editor.config.define( 'dataSchema', defaultConfig );
 	}
 
 	/**
@@ -63,6 +64,19 @@ export default class DataSchema extends Plugin {
 		return 'DataSchema';
 	}
 
+	/**
+	 * @inheritDoc
+	 */
+	init() {
+		for ( const definition of defaultConfig.block ) {
+			this.registerBlockElement( definition );
+		}
+
+		for ( const definition of defaultConfig.inline ) {
+			this.registerInlineElement( definition );
+		}
+	}
+
 	/**
 	 * Add new data schema definition describing block element.
 	 *
@@ -104,303 +118,6 @@ export default class DataSchema extends Plugin {
 		return definitions;
 	}
 
-	/**
-	 * Registers default data schema definitions.
-	 *
-	 * @private
-	*/
-	_registerDefaultDefinitions() {
-		// Block elements.
-		this.registerBlockElement( {
-			model: '$htmlBlock',
-			modelSchema: {
-				allowChildren: '$block',
-				allowIn: [ '$root', '$htmlBlock' ],
-				isBlock: true
-			}
-		} );
-
-		this.registerBlockElement( {
-			model: 'codeBlock',
-			view: 'pre'
-		} );
-
-		this.registerBlockElement( {
-			model: 'paragraph',
-			view: 'p'
-		} );
-
-		this.registerBlockElement( {
-			model: 'blockQuote',
-			view: 'blockquote'
-		} );
-
-		this.registerBlockElement( {
-			model: 'heading1',
-			view: 'h2'
-		} );
-
-		this.registerBlockElement( {
-			model: 'heading2',
-			view: 'h3'
-		} );
-
-		this.registerBlockElement( {
-			model: 'heading3',
-			view: 'h4'
-		} );
-
-		this.registerBlockElement( {
-			model: 'listItem',
-			view: 'li'
-		} );
-
-		this.registerBlockElement( {
-			model: 'htmlPre',
-			view: 'pre',
-			modelSchema: {
-				inheritAllFrom: '$block'
-			}
-		} );
-
-		// TODO Remove it once we have proper support for div elements.
-		this.registerBlockElement( {
-			model: 'htmlDiv',
-			view: 'div',
-			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
-			}
-		} );
-
-		this.registerBlockElement( {
-			view: 'article',
-			model: 'htmlArticle',
-			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
-			}
-		} );
-
-		this.registerBlockElement( {
-			view: 'section',
-			model: 'htmlSection',
-			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
-			}
-		} );
-
-		this.registerBlockElement( {
-			view: 'form',
-			model: 'htmlForm',
-			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
-			}
-		} );
-
-		// Add data list elements.
-		this.registerBlockElement( {
-			view: 'dl',
-			model: 'htmlDl',
-			modelSchema: {
-				allowIn: [ '$htmlBlock', '$root' ],
-				isBlock: true
-			}
-		} );
-
-		this.registerBlockElement( {
-			model: '$htmlDatalist',
-			modelSchema: {
-				allowChildren: '$block',
-				allowIn: 'htmlDl',
-				isBlock: true
-			}
-		} );
-
-		this.registerBlockElement( {
-			view: 'dt',
-			model: 'htmlDt',
-			modelSchema: {
-				inheritAllFrom: '$htmlDatalist'
-			}
-		} );
-
-		this.registerBlockElement( {
-			view: 'dd',
-			model: 'htmlDd',
-			modelSchema: {
-				inheritAllFrom: '$htmlDatalist'
-			}
-		} );
-
-		// Add details elements.
-		this.registerBlockElement( {
-			view: 'details',
-			model: 'htmlDetails',
-			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
-			}
-		} );
-
-		this.registerBlockElement( {
-			view: 'summary',
-			model: 'htmlSummary',
-			modelSchema: {
-				allowChildren: '$text',
-				allowIn: 'htmlDetails'
-			}
-		} );
-
-		// Block objects.
-		this.registerBlockElement( {
-			model: '$htmlObjectBlock',
-			isObject: true,
-			modelSchema: {
-				isObject: true,
-				isBlock: true,
-				allowWhere: '$block'
-			}
-		} );
-
-		// Inline elements.
-		this.registerInlineElement( {
-			view: 'code',
-			model: 'htmlCode'
-		} );
-
-		this.registerInlineElement( {
-			view: 'abbr',
-			model: 'htmlAbbr'
-		} );
-
-		this.registerInlineElement( {
-			view: 'a',
-			model: 'htmlA',
-			priority: 5
-		} );
-
-		this.registerInlineElement( {
-			view: 'strong',
-			model: 'htmlStrong'
-		} );
-
-		this.registerInlineElement( {
-			view: 'i',
-			model: 'htmlI'
-		} );
-
-		this.registerInlineElement( {
-			view: 's',
-			model: 'htmlS'
-		} );
-
-		this.registerInlineElement( {
-			view: 'span',
-			model: 'htmlSpan',
-			attributeProperties: {
-				copyOnEnter: true
-			}
-		} );
-
-		this.registerInlineElement( {
-			view: 'cite',
-			model: 'htmlCite',
-			attributeProperties: {
-				copyOnEnter: true
-			}
-		} );
-
-		this.registerInlineElement( {
-			view: 'label',
-			model: 'htmlLabel',
-			attributeProperties: {
-				copyOnEnter: true
-			}
-		} );
-
-		// Inline objects
-		this.registerInlineElement( {
-			model: '$htmlObjectInline',
-			isObject: true,
-			modelSchema: {
-				isObject: true,
-				isInline: true,
-				allowWhere: '$text',
-				allowAttributesOf: '$text'
-			}
-		} );
-
-		this.registerInlineElement( {
-			view: 'object',
-			model: 'htmlObject',
-			isObject: true,
-			modelSchema: {
-				inheritAllFrom: '$htmlObjectInline'
-			}
-		} );
-
-		this.registerInlineElement( {
-			view: 'iframe',
-			model: 'htmlIframe',
-			isObject: true,
-			modelSchema: {
-				inheritAllFrom: '$htmlObjectInline'
-			}
-		} );
-
-		this.registerInlineElement( {
-			view: 'input',
-			model: 'htmlInput',
-			isObject: true,
-			modelSchema: {
-				inheritAllFrom: '$htmlObjectInline'
-			}
-		} );
-
-		this.registerInlineElement( {
-			view: 'button',
-			model: 'htmlButton',
-			isObject: true,
-			modelSchema: {
-				inheritAllFrom: '$htmlObjectInline'
-			}
-		} );
-
-		this.registerInlineElement( {
-			view: 'textarea',
-			model: 'htmlTextarea',
-			isObject: true,
-			modelSchema: {
-				inheritAllFrom: '$htmlObjectInline'
-			}
-		} );
-
-		this.registerInlineElement( {
-			view: 'select',
-			model: 'htmlSelect',
-			isObject: true,
-			modelSchema: {
-				inheritAllFrom: '$htmlObjectInline'
-			}
-		} );
-
-		this.registerInlineElement( {
-			view: 'video',
-			model: 'htmlVideo',
-			isObject: true,
-			modelSchema: {
-				inheritAllFrom: '$htmlObjectInline'
-			}
-		} );
-
-		this.registerInlineElement( {
-			view: 'audio',
-			model: 'htmlAudio',
-			isObject: true,
-			modelSchema: {
-				inheritAllFrom: '$htmlObjectInline'
-			}
-		} );
-	}
-
 	/**
 	 * Returns definitions matching the given view name.
 	 *
diff --git a/packages/ckeditor5-html-support/src/schemadefinitions.js b/packages/ckeditor5-html-support/src/schemadefinitions.js
new file mode 100644
index 00000000000..164f1c9647e
--- /dev/null
+++ b/packages/ckeditor5-html-support/src/schemadefinitions.js
@@ -0,0 +1,160 @@
+export default {
+	block: [
+		// Existing features
+		{ model: 'heading1', view: 'h2' },
+		{ model: 'heading2', view: 'h3' },
+		{ model: 'heading3', view: 'h4' },
+		{ model: 'codeBlock', view: 'pre' },
+		{ model: 'paragraph', view: 'p' },
+		{ model: 'blockQuote', view: 'blockquote' },
+		{ model: 'listItem', view: 'li' },
+		// New features
+		{
+			model: '$htmlBlock',
+			modelSchema: {
+				allowChildren: '$block',
+				allowIn: [ '$root', '$htmlBlock' ],
+				isBlock: true
+			}
+		},
+		{ model: 'htmlPre', view: 'pre', modelSchema: { inheritAllFrom: '$block' } },
+		{ model: 'htmlArticle', view: 'article', modelSchema: { inheritAllFrom: '$htmlBlock' } },
+		{ model: 'htmlSection', view: 'section', modelSchema: { inheritAllFrom: '$htmlBlock' } },
+		{ model: 'htmlForm', view: 'form', modelSchema: { inheritAllFrom: '$htmlBlock' } },
+		{ model: 'htmlDetails', view: 'details', modelSchema: { inheritAllFrom: '$htmlBlock' } },
+		{
+			model: 'htmlSumary',
+			view: 'summary',
+			modelSchema: {
+				allowChildren: '$text',
+				allowIn: 'htmlDetails',
+				isBlock: true
+			}
+		},
+		{
+			model: 'htmlDl',
+			view: 'dl',
+			modelSchema: {
+				allowIn: [ '$htmlBlock', '$root' ],
+				allowChildren: [ 'htmlDt', 'htmlDl' ],
+				isBlock: true
+			}
+		},
+		{
+			model: 'htmlDt',
+			view: 'dt',
+			modelSchema: {
+				allowChildren: '$block',
+				isBlock: true
+			}
+		},
+		{
+			model: 'htmlDd',
+			view: 'dd',
+			modelSchema: {
+				allowChildren: '$block',
+				isBlock: true
+			}
+		},
+		// Objects
+		{
+			model: '$htmlObjectBlock',
+			isObject: true,
+			modelSchema: {
+				isObject: true,
+				isBlock: true,
+				allowWhere: '$block'
+			}
+		}
+	],
+	inline: [
+		{ model: 'htmlA', view: 'a', priority: 5 },
+		{ model: 'htmlStrong', view: 'strong' },
+		{ model: 'htmlI', view: 'i' },
+		{ model: 'htmlS', view: 's' },
+		{ model: 'htmlU', view: 'u' },
+		{ model: 'htmlSub', view: 'sub' },
+		{ model: 'htmlSup', view: 'sup' },
+		{ model: 'htmlCode', view: 'code' },
+		{ model: 'htmlMark', view: 'mark' },
+		{ model: 'htmlSpan', view: 'span', attributeProperties: { copyOnEnter: true } },
+		{ model: 'htmlCite', view: 'cite', attributeProperties: { copyOnEnter: true } },
+		{ model: 'htmlLabel', view: 'label', attributeProperties: { copyOnEnter: true } },
+
+		// Objects
+		{
+			model: '$htmlObjectInline',
+			isObject: true,
+			modelSchema: {
+				isObject: true,
+				isInline: true,
+				allowWhere: '$text',
+				allowAttributesOf: '$text'
+			}
+		},
+		{
+			view: 'object',
+			model: 'htmlObject',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		},
+		{
+			view: 'iframe',
+			model: 'htmlIframe',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		},
+		{
+			view: 'input',
+			model: 'htmlInput',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		},
+		{
+			view: 'button',
+			model: 'htmlButton',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		},
+		{
+			view: 'textarea',
+			model: 'htmlTextarea',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		},
+		{
+			view: 'select',
+			model: 'htmlSelect',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		},
+		{
+			view: 'video',
+			model: 'htmlVideo',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		},
+		{
+			view: 'audio',
+			model: 'htmlAudio',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		}
+	]
+};
diff --git a/packages/ckeditor5-html-support/tests/manual/features.html b/packages/ckeditor5-html-support/tests/manual/features.html
new file mode 100644
index 00000000000..7b5937fd179
--- /dev/null
+++ b/packages/ckeditor5-html-support/tests/manual/features.html
@@ -0,0 +1,123 @@
+<head>
+	<meta http-equiv="Content-Security-Policy" content="script-src 'self' https://ckeditor.com 'unsafe-inline' 'unsafe-eval'">
+	<style>
+		td {
+			padding: .4em;
+		}
+		a[name][id] {
+			color: blue;
+			text-decoration: underline;
+		}
+		mark[data-mark] {
+			font-weight: 600;
+			text-decoration: underline;
+		}
+		.text-italic {
+			font-style: italic;
+		}
+	</style>
+</head>
+<div style="display: flex">
+	<div style="width: 40%; margin-right: 20px">
+		<div id="editor">
+			<p style="color:blue;">Feature paragraph</p>
+
+			<h2 style="color:green">Feature heading1</h2>
+			<h3 style="color:green">Feature heading2</h3>
+			<h4 style="color:green">Feature heading3</h4>
+
+			<p><strong style="color:blue;">Feature bold</strong></p>
+			<p><i style="color:blue;">Feature italic</i></p>
+			<p><s style="color:blue;">Feature strike</s></p>
+			<p><u style="color:blue;">Feature underline</u></p>
+			<p><code style="color:blue;">Feature code</code></p>
+			<p><sub style="color:blue;">Feature subscript</sub></p>
+			<p><sup style="color:blue;">Feature superscript</sup></p>
+
+			<p><a style="color:green;" href="https://example.com">Link feature</a></p>
+			<p><a name="anchor" id="anchor">Anchor (name, ID only)</a></p>
+
+			<p><mark class="marker-yellow" data-mark>Mark feature</mark></p>
+
+			<p><span class="text-big text-italic" style="background-color:hsl(60, 75%, 60%);color:hsl(240, 75%, 60%);font-family:'Courier New', Courier, monospace;border:1px solid black">Font feature</span></p>
+
+			<ul style="background:blue;">
+				<li style="color:yellow;">Bulleted List feature</li>
+				<li style="color:yellow;">Bulleted List feature</li>
+				<li style="color:yellow;">Bulleted List feature</li>
+			</ul>
+
+			<ol style="background:blue;">
+				<li style="color:yellow;">Numbered List feature</li>
+				<li style="color:yellow;">Numbered List feature</li>
+				<li style="color:yellow;">Numbered List feature</li>
+			</ol>
+
+			<ul class="todo-list" style="background:blue;">
+				<li style="color:yellow;">
+					<label class="todo-list__label">
+						<input type="checkbox" disabled="disabled">
+						<span class="todo-list__label__description">Todo List feature</span>
+					</label>
+				</li>
+				<li style="color:yellow;">
+					<label class="todo-list__label">
+						<input type="checkbox" disabled="disabled">
+						<span class="todo-list__label__description">Todo List feature</span>
+					</label>
+				</li>
+				<li style="color:yellow;">
+					<label class="todo-list__label">
+						<input type="checkbox" disabled="disabled">
+						<span class="todo-list__label__description">Todo List feature</span>
+					</label>
+				</li>
+			</ul>
+
+			<blockquote style="color:blue;"><p>Blockquote Feature</p></blockquote>
+
+			<figure style="border: 1px solid blue;" class="image">
+				<img src="sample.jpg" style="border: 1px solid red;" alt="bar">
+				<figcaption style="background:yellow;">Caption</figcaption>
+			</figure>
+
+			<pre style="background:blue;"><code style="color:yellow;" class="language-plaintext">Code Block</code></pre>
+
+			<table style="background:blue;">
+				<thead style="background:green;">
+					<tr>
+						<th style="color:red;">h1</th>
+						<th style="color:red;">h2</th>
+						<th style="color:red;">h3</th>
+					</tr>
+				</thead>
+				<tbody style="background:violet;">
+					<tr>
+						<td style="color:yellow;">1.1</td>
+						<td style="color:yellow;">1.2</td>
+						<td style="color:yellow;">1.3</td>
+					</tr>
+					<tr style="color:yellow;">
+						<td>2.1</td>
+						<td>2.2</td>
+						<td>2.3</td>
+					</tr>
+				</tbody>
+			</table>
+
+			<figure class="media" data-foo><oembed data-bar url="https://www.youtube.com/watch?v=ZVv7UMQPEWk"></oembed></figure>
+
+			<div style="border: 1px solid blue" class="raw-html-embed">HTML snippet</div>
+
+			<div style="border: 1px solid blue" class="page-break" style="page-break-after:always;"><span style="display:none;">&nbsp;</span></div>
+		</div>
+	</div>
+
+	<div style="width: 40%">
+		<h1 style="margin:12px 0 0 0; padding:0 0 5px 0; font-size: 18px; border-bottom: solid 1px grey">Source content:</h1>
+		<div id="preview"></div>
+	</div>
+</div>
+<script>
+	document.getElementById( 'preview' ).innerHTML = document.getElementById( 'editor' ).innerHTML;
+</script>
diff --git a/packages/ckeditor5-html-support/tests/manual/features.js b/packages/ckeditor5-html-support/tests/manual/features.js
new file mode 100644
index 00000000000..607568b7cc6
--- /dev/null
+++ b/packages/ckeditor5-html-support/tests/manual/features.js
@@ -0,0 +1,85 @@
+/**
+ * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/* globals console:false, window, document */
+
+import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
+import Alignment from '@ckeditor/ckeditor5-alignment/src/alignment';
+import ArticlePluginSet from '@ckeditor/ckeditor5-core/tests/_utils/articlepluginset';
+import Code from '@ckeditor/ckeditor5-basic-styles/src/code';
+import CodeBlock from '@ckeditor/ckeditor5-code-block/src/codeblock';
+import EasyImage from '@ckeditor/ckeditor5-easy-image/src/easyimage';
+import FontBackgroundColor from '@ckeditor/ckeditor5-font/src/fontbackgroundcolor';
+import FontColor from '@ckeditor/ckeditor5-font/src/fontcolor';
+import FontFamily from '@ckeditor/ckeditor5-font/src/fontfamily';
+import FontSize from '@ckeditor/ckeditor5-font/src/fontsize';
+import Highlight from '@ckeditor/ckeditor5-highlight/src/highlight';
+import HorizontalLine from '@ckeditor/ckeditor5-horizontal-line/src/horizontalline';
+import HtmlEmbed from '@ckeditor/ckeditor5-html-embed/src/htmlembed';
+import ImageResize from '@ckeditor/ckeditor5-image/src/imageresize';
+import IndentBlock from '@ckeditor/ckeditor5-indent/src/indentblock';
+import LinkImage from '@ckeditor/ckeditor5-link/src/linkimage';
+import ListStyle from '@ckeditor/ckeditor5-list/src/liststyle';
+import PageBreak from '@ckeditor/ckeditor5-page-break/src/pagebreak';
+import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
+import Subscript from '@ckeditor/ckeditor5-basic-styles/src/subscript';
+import Superscript from '@ckeditor/ckeditor5-basic-styles/src/superscript';
+import TableCellProperties from '@ckeditor/ckeditor5-table/src/tablecellproperties';
+import TableProperties from '@ckeditor/ckeditor5-table/src/tableproperties';
+import TableCaption from '@ckeditor/ckeditor5-table/src/tablecaption';
+import TodoList from '@ckeditor/ckeditor5-list/src/todolist';
+import Underline from '@ckeditor/ckeditor5-basic-styles/src/underline';
+import CloudServices from '@ckeditor/ckeditor5-cloud-services/src/cloudservices';
+import ImageUpload from '@ckeditor/ckeditor5-image/src/imageupload';
+
+import GeneralHtmlSupport from '../../src/generalhtmlsupport';
+
+ClassicEditor
+	.create( document.querySelector( '#editor' ), {
+		plugins: [
+			ArticlePluginSet, Underline, Strikethrough, Superscript, Subscript, Code,
+			FontColor, FontBackgroundColor, FontFamily, FontSize, Highlight,
+			CodeBlock, TodoList, ListStyle, TableProperties, TableCellProperties, TableCaption,
+			EasyImage, ImageResize, LinkImage, HtmlEmbed,
+			Alignment, IndentBlock,
+			PageBreak, HorizontalLine,
+			ImageUpload, CloudServices,
+			GeneralHtmlSupport
+		],
+		toolbar: [
+			'heading',
+			'|',
+			'bold', 'italic', 'strikethrough', 'underline', 'code', 'subscript', 'superscript', 'link',
+			'|',
+			'highlight', 'fontSize', 'fontFamily', 'fontColor', 'fontBackgroundColor',
+			'|',
+			'bulletedList', 'numberedList', 'todoList',
+			'|',
+			'blockQuote', 'uploadImage', 'insertTable', 'mediaEmbed', 'codeBlock',
+			'|',
+			'htmlEmbed',
+			'|',
+			'alignment', 'outdent', 'indent',
+			'|',
+			'pageBreak', 'horizontalLine',
+			'|',
+			'undo', 'redo'
+		],
+		dataSchema: {
+		},
+		htmlSupport: {
+			allow: [
+				{ name: /^.*$/, styles: true },
+				{ name: 'a', attributes: [ 'name', 'id' ] },
+				{ name: 'span', classes: [ 'text-italic' ] }
+			]
+		}
+	} )
+	.then( editor => {
+		window.editor = editor;
+	} )
+	.catch( err => {
+		console.error( err.stack );
+	} );
diff --git a/packages/ckeditor5-html-support/tests/manual/features.md b/packages/ckeditor5-html-support/tests/manual/features.md
new file mode 100644
index 00000000000..bcbf0b4cf46
--- /dev/null
+++ b/packages/ckeditor5-html-support/tests/manual/features.md
@@ -0,0 +1,3 @@
+## GHS features coverage
+
+Compare editor HTML with the raw HTML on the right side to find out which features are covered by General HTML Support.
diff --git a/packages/ckeditor5-html-support/tests/manual/sample.jpg b/packages/ckeditor5-html-support/tests/manual/sample.jpg
new file mode 100644
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HcmV?d00001


From 4137e836dec68ba7780c933ecd76cb2470bb3059 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 17 Jun 2021 16:35:40 +0200
Subject: [PATCH 196/217] Expanded data schema with missing elements.

---
 .../src/schemadefinitions.js                  | 664 +++++++++++++++++-
 .../tests/manual/generalhtmlsupport.html      |   2 +-
 2 files changed, 632 insertions(+), 34 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/schemadefinitions.js b/packages/ckeditor5-html-support/src/schemadefinitions.js
index 164f1c9647e..8dc62248ce2 100644
--- a/packages/ckeditor5-html-support/src/schemadefinitions.js
+++ b/packages/ckeditor5-html-support/src/schemadefinitions.js
@@ -1,14 +1,63 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module html-support/schemadefinitions
+ */
+
+// Skipped elements due to HTML deprecation:
+// * noframes (not sure if we should provide support for this element. CKE4 is not supporting frameset and frame,
+//   but it will unpack <frameset><noframes>foobar</noframes></frameset> to <noframes>foobar</noframes>, so there
+//   may be some content loss. Although using noframes as a standalone element seems invalid)
+// * keygen (this one is also empty)
+// * applet (support is limited mostly to old IE)
+// * basefont (this one is also empty)
+// * isindex (basically no support for modern browsers at all)
+// Skipped elements due to lack empty element support:
+// * hr
+// * area
+// * br
+// * command
+// * map
+// * wbr
+// Skipped elements due to complexity:
+// * datalist with option elements used as a data source for input[list] element
+
 export default {
 	block: [
 		// Existing features
-		{ model: 'heading1', view: 'h2' },
-		{ model: 'heading2', view: 'h3' },
-		{ model: 'heading3', view: 'h4' },
-		{ model: 'codeBlock', view: 'pre' },
-		{ model: 'paragraph', view: 'p' },
-		{ model: 'blockQuote', view: 'blockquote' },
-		{ model: 'listItem', view: 'li' },
-		// New features
+		{
+			model: 'heading1',
+			view: 'h2'
+		},
+		{
+			model: 'heading2',
+			view: 'h3'
+		},
+		{
+			model: 'heading3',
+			view: 'h4'
+		},
+		{
+			model: 'codeBlock',
+			view: 'pre'
+		},
+		{
+			model: 'paragraph',
+			view: 'p'
+		},
+		{
+			model: 'blockQuote',
+			view: 'blockquote'
+		},
+		{
+			model: 'listItem',
+			view: 'li'
+		},
+
+		// Compatibility features
 		{
 			model: '$htmlBlock',
 			modelSchema: {
@@ -17,11 +66,299 @@ export default {
 				isBlock: true
 			}
 		},
-		{ model: 'htmlPre', view: 'pre', modelSchema: { inheritAllFrom: '$block' } },
-		{ model: 'htmlArticle', view: 'article', modelSchema: { inheritAllFrom: '$htmlBlock' } },
-		{ model: 'htmlSection', view: 'section', modelSchema: { inheritAllFrom: '$htmlBlock' } },
-		{ model: 'htmlForm', view: 'form', modelSchema: { inheritAllFrom: '$htmlBlock' } },
-		{ model: 'htmlDetails', view: 'details', modelSchema: { inheritAllFrom: '$htmlBlock' } },
+		{
+			model: 'htmlParagraph',
+			view: 'p',
+			modelSchema: {
+				inheritAllFrom: '$block'
+			}
+		},
+		{
+			model: 'htmlBlockQuote',
+			view: 'blockquote',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
+		{
+			model: 'htmlTable',
+			view: 'table',
+			modelSchema: {
+				allowIn: [ '$htmlBlock', '$root' ],
+				isBlock: true
+			}
+		},
+		{
+			model: 'htmlTableBody',
+			view: 'tbody',
+			modelSchema: {
+				allowIn: 'htmlTable',
+				isBlock: true
+			}
+		},
+		{
+			model: 'htmlTableHead',
+			view: 'thead',
+			modelSchema: {
+				allowIn: 'htmlTable',
+				isBlock: true
+			}
+		},
+		{
+			model: 'htmlCaption',
+			view: 'caption',
+			modelSchema: {
+				allowIn: 'htmlTable',
+				allowChildren: '$text',
+				isBlock: true
+			}
+		},
+		{
+			model: 'htmlTableRow',
+			view: 'tr',
+			modelSchema: {
+				allowIn: [ 'htmlTable', 'htmlTableHead', 'htmlTableBody' ],
+				isBlock: true
+			}
+		},
+		// TODO can also include text.
+		{
+			model: 'htmlTableData',
+			view: 'td',
+			modelSchema: {
+				allowIn: 'tr',
+				allowChildren: [ '$block', '$htmlBlock' ],
+				isBlock: true
+			}
+		},
+		// TODO can also include text.
+		{
+			model: 'htmlTableHeader',
+			view: 'th',
+			modelSchema: {
+				allowIn: 'tr',
+				allowChildren: [ '$block', '$htmlBlock' ],
+				isBlock: true
+			}
+		},
+		// TODO can also include text.
+		{
+			model: 'htmlFigure',
+			view: 'figure',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock',
+				isBlock: true
+			}
+		},
+		// TODO can also include other block elements.
+		{
+			model: 'htmlFigcaption',
+			view: 'figcaption',
+			modelSchema: {
+				allowIn: 'htmlFigure',
+				allowChildren: '$text',
+				isBlock: true
+			}
+		},
+		// TODO can also include other block elements.
+		{
+			model: 'htmlAddress',
+			view: 'address',
+			modelSchema: {
+				inheritAllFrom: '$block'
+			}
+		},
+		// TODO can also include text.
+		{
+			model: 'htmlAside',
+			view: 'aside',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
+		// TODO can also include text.
+		{
+			model: 'htmlMain',
+			view: 'main',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
+		// TODO can also include text.
+		{
+			model: 'htmlDetails',
+			view: 'details',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
+		// TODO can also include text.
+		{
+			model: 'htmlDiv',
+			view: 'div',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
+		// TODO can also include text.
+		{
+			model: 'htmlFieldset',
+			view: 'fieldset',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
+		// TODO can also include text.
+		{
+			model: 'htmlHeader',
+			view: 'header',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
+		// TODO can also include text.
+		{
+			model: 'htmlFooter',
+			view: 'footer',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
+		// TODO can also include text.
+		{
+			model: 'htmlForm',
+			view: 'form',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
+		{
+			model: 'htmlHeadingGroup',
+			view: 'hgroup',
+			modelSchema: {
+				allowChildren: [
+					'htmlHeading1',
+					'htmlHeading2',
+					'htmlHeading3',
+					'htmlHeading4',
+					'htmlHeading5',
+					'htmlHeading6',
+					'heading1',
+					'heading2',
+					'heading3'
+				],
+				isBlock: true
+			}
+		},
+		{
+			model: 'htmlHeading1',
+			view: 'h1',
+			modelSchema: {
+				inheritAllFrom: '$block'
+			}
+		},
+		{
+			model: 'htmlHeading2',
+			view: 'h2',
+			modelSchema: {
+				inheritAllFrom: '$block'
+			}
+		},
+		{
+			model: 'htmlHeading3',
+			view: 'h3',
+			modelSchema: {
+				inheritAllFrom: '$block'
+			}
+		},
+		{
+			model: 'htmlHeading4',
+			view: 'h4',
+			modelSchema: {
+				inheritAllFrom: '$block'
+			}
+		},
+		{
+			model: 'htmlHeading5',
+			view: 'h5',
+			modelSchema: {
+				inheritAllFrom: '$block'
+			}
+		},
+		{
+			model: 'htmlHeading6',
+			view: 'h6',
+			modelSchema: {
+				inheritAllFrom: '$block'
+			}
+		},
+		{
+			model: '$htmlList',
+			modelSchema: {
+				allowIn: [ '$htmlBlock', 'htmlListItem' ],
+				allowChildren: 'htmlListItem',
+				isBlock: true
+			}
+		},
+		{
+			model: 'htmlDirectory',
+			view: 'dir',
+			modelSchema: {
+				inheritAllFrom: '$htmlList'
+			}
+		},
+		{
+			model: 'htmlMenu',
+			view: 'menu',
+			modelSchema: {
+				inheritAllFrom: '$htmlList'
+			}
+		},
+		{
+			model: 'htmlUnorderedList',
+			view: 'ul',
+			modelSchema: {
+				inheritAllFrom: '$htmlList'
+			}
+		},
+		{
+			model: 'htmlOrderedList',
+			view: 'ol',
+			modelSchema: {
+				inheritAllFrom: '$htmlList'
+			}
+		},
+		// TODO can also include other block elements.
+		{
+			model: 'htmlListItem',
+			view: 'li',
+			modelSchema: {
+				allowChildren: '$text',
+				allowIn: '$htmlList',
+				isBlock: true
+			}
+		},
+		{
+			model: 'htmlPre',
+			view: 'pre',
+			modelSchema: {
+				inheritAllFrom: '$block'
+			}
+		},
+		{
+			model: 'htmlArticle',
+			view: 'article',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
+		{
+			model: 'htmlSection',
+			view: 'section',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
 		{
 			model: 'htmlSumary',
 			view: 'summary',
@@ -68,18 +405,233 @@ export default {
 		}
 	],
 	inline: [
-		{ model: 'htmlA', view: 'a', priority: 5 },
-		{ model: 'htmlStrong', view: 'strong' },
-		{ model: 'htmlI', view: 'i' },
-		{ model: 'htmlS', view: 's' },
-		{ model: 'htmlU', view: 'u' },
-		{ model: 'htmlSub', view: 'sub' },
-		{ model: 'htmlSup', view: 'sup' },
-		{ model: 'htmlCode', view: 'code' },
-		{ model: 'htmlMark', view: 'mark' },
-		{ model: 'htmlSpan', view: 'span', attributeProperties: { copyOnEnter: true } },
-		{ model: 'htmlCite', view: 'cite', attributeProperties: { copyOnEnter: true } },
-		{ model: 'htmlLabel', view: 'label', attributeProperties: { copyOnEnter: true } },
+		{
+			model: 'htmlCenter',
+			view: 'center',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlAcronym',
+			view: 'acronym',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlTeletypeText',
+			view: 'tt',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlFont',
+			view: 'font',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlTime',
+			view: 'time',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlVar',
+			view: 'var',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlBig',
+			view: 'big',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlSmall',
+			view: 'small',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlSample',
+			view: 'samp',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlQuote',
+			view: 'q',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlOutput',
+			view: 'output',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlKeyboardInput',
+			view: 'kbd',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlBdi',
+			view: 'bdi',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlBdo',
+			view: 'bdo',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlAbbreviation',
+			view: 'abbr',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlLink',
+			view: 'a',
+			priority: 5,
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlStrong',
+			view: 'strong',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlBold',
+			view: 'b',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlItalic',
+			view: 'i',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlEmphasis',
+			view: 'em',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlStrike',
+			view: 's',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		// TODO According to HTML-spec can behave as div-like element, althouth CKE4 only handles it as an inline element.
+		{
+			model: 'htmlDeleted',
+			view: 'del',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		// TODO According to HTML-spec can behave as div-like element, althouth CKE4 only handles it as an inline element.
+		{
+			model: 'htmlInserted',
+			view: 'ins',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlUnderline',
+			view: 'u',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlSubscript',
+			view: 'sub',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlSuperscript',
+			view: 'sup',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlCode',
+			view: 'code',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlMark',
+			view: 'mark',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlSpan',
+			view: 'span',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlCite',
+			view: 'cite',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlLabel',
+			view: 'label',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
+		{
+			model: 'htmlDefinition',
+			view: 'dfn',
+			attributeProperties: {
+				copyOnEnter: true
+			}
+		},
 
 		// Objects
 		{
@@ -93,64 +645,110 @@ export default {
 			}
 		},
 		{
-			view: 'object',
 			model: 'htmlObject',
+			view: 'object',
 			isObject: true,
 			modelSchema: {
 				inheritAllFrom: '$htmlObjectInline'
 			}
 		},
 		{
-			view: 'iframe',
 			model: 'htmlIframe',
+			view: 'iframe',
 			isObject: true,
 			modelSchema: {
 				inheritAllFrom: '$htmlObjectInline'
 			}
 		},
 		{
-			view: 'input',
 			model: 'htmlInput',
+			view: 'input',
 			isObject: true,
 			modelSchema: {
 				inheritAllFrom: '$htmlObjectInline'
 			}
 		},
 		{
-			view: 'button',
 			model: 'htmlButton',
+			view: 'button',
 			isObject: true,
 			modelSchema: {
 				inheritAllFrom: '$htmlObjectInline'
 			}
 		},
 		{
-			view: 'textarea',
 			model: 'htmlTextarea',
+			view: 'textarea',
 			isObject: true,
 			modelSchema: {
 				inheritAllFrom: '$htmlObjectInline'
 			}
 		},
 		{
-			view: 'select',
 			model: 'htmlSelect',
+			view: 'select',
 			isObject: true,
 			modelSchema: {
 				inheritAllFrom: '$htmlObjectInline'
 			}
 		},
 		{
-			view: 'video',
 			model: 'htmlVideo',
+			view: 'video',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		},
+		{
+			model: 'htmlEmbed',
+			view: 'embed',
 			isObject: true,
 			modelSchema: {
 				inheritAllFrom: '$htmlObjectInline'
 			}
 		},
 		{
-			view: 'audio',
 			model: 'htmlAudio',
+			view: 'audio',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		},
+		// TODO Should image be an object?
+		{
+			model: 'htmlImage',
+			view: 'img',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		},
+		// TODO Should canvas be an object?
+		{
+			model: 'htmlCanvas',
+			view: 'canvas',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		},
+		// TODO it could be probably represented as non-object element, although it has grafical representation,
+		// so probably makes more sense to keep it as an object.
+		{
+			model: 'htmlMeter',
+			view: 'meter',
+			isObject: true,
+			modelSchema: {
+				inheritAllFrom: '$htmlObjectInline'
+			}
+		},
+		// TODO it could be probably represented as non-object element, although it has grafical representation,
+		// so probably makes more sense to keep it as an object.
+		{
+			model: 'htmlProgress',
+			view: 'progress',
 			isObject: true,
 			modelSchema: {
 				inheritAllFrom: '$htmlObjectInline'
diff --git a/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.html b/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.html
index 36c562b8946..c9e04007638 100644
--- a/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.html
+++ b/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.html
@@ -21,7 +21,7 @@
 
 			<details>
 				<summary>Summary</summary>
-				Hello world
+				<p>Hello, world</p>
 			</details>
 
 			<dl>

From 14e4235326b5ddf8b7ba16e30c39686783e67efe Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 17 Jun 2021 16:55:04 +0200
Subject: [PATCH 197/217] Updated definintions with another set of elements.

---
 .../src/schemadefinitions.js                  | 45 +++++++++++++++++++
 .../tests/manual/objects.js                   |  3 --
 2 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/schemadefinitions.js b/packages/ckeditor5-html-support/src/schemadefinitions.js
index 8dc62248ce2..80ea5643f7d 100644
--- a/packages/ckeditor5-html-support/src/schemadefinitions.js
+++ b/packages/ckeditor5-html-support/src/schemadefinitions.js
@@ -24,6 +24,19 @@
 // * wbr
 // Skipped elements due to complexity:
 // * datalist with option elements used as a data source for input[list] element
+// Skipped elements as they are handled as an object content:
+// TODO shouldn't we also filter attributes on these element and enable them separately?
+// * track
+// * source
+// * option
+// * param
+// * optgroup
+// Skipped full page HTML elements:
+// * body
+// * html
+// * title
+// * head
+// * etc...
 
 export default {
 	block: [
@@ -104,6 +117,22 @@ export default {
 				isBlock: true
 			}
 		},
+		{
+			model: 'htmlTableFoot',
+			view: 'tfoot',
+			modelSchema: {
+				allowIn: 'htmlTable',
+				isBlock: true
+			}
+		},
+		{
+			model: 'htmlColumnGroup',
+			view: 'colgroup',
+			modelSchema: {
+				allowIn: 'htmlTable',
+				isBlock: true
+			}
+		},
 		{
 			model: 'htmlCaption',
 			view: 'caption',
@@ -208,6 +237,14 @@ export default {
 				inheritAllFrom: '$htmlBlock'
 			}
 		},
+		// TODO can also include h1-h6.
+		{
+			model: 'htmlLegend',
+			view: 'legend',
+			modelSchema: {
+				inheritAllFrom: '$block'
+			}
+		},
 		// TODO can also include text.
 		{
 			model: 'htmlHeader',
@@ -359,6 +396,14 @@ export default {
 				inheritAllFrom: '$htmlBlock'
 			}
 		},
+		// TODO can also include text.
+		{
+			model: 'htmlNav',
+			view: 'nav',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
 		{
 			model: 'htmlSumary',
 			view: 'summary',
diff --git a/packages/ckeditor5-html-support/tests/manual/objects.js b/packages/ckeditor5-html-support/tests/manual/objects.js
index 76a6c9b97b4..ba52088ae66 100644
--- a/packages/ckeditor5-html-support/tests/manual/objects.js
+++ b/packages/ckeditor5-html-support/tests/manual/objects.js
@@ -46,17 +46,14 @@ class ExtendHTMLSupport extends Plugin {
 
 		const definitions = [
 			{ name: 'object', attributes: [ 'classid', 'codebase' ] },
-			{ name: 'param', attributes: [ 'name', 'value' ] },
 			{ name: 'embed', attributes: [ 'allowfullscreen', 'pluginspage', 'quality', 'src', 'type' ] },
 			{ name: 'iframe', attributes: [ 'frameborder', 'scrolling', 'src' ] },
 			{ name: 'form', attributes: [ 'action', 'method', 'name' ] },
 			{ name: 'input', attributes: [ 'name', 'type', 'value', 'alt', 'src' ] },
 			{ name: 'textarea', attributes: [ 'name' ] },
 			{ name: 'select', attributes: [ 'name' ] },
-			{ name: 'option', attributes: [ 'value', 'selected' ] },
 			{ name: 'video', attributes: [ 'height', 'width', 'controls' ] },
 			{ name: 'audio', attributes: [ 'controls' ] },
-			{ name: 'source', attributes: [ 'src', 'type' ] },
 			{ name: 'button' },
 			{ name: 'label' },
 			{ name: 'xyz', attributes: [ 'data-foo' ] }

From 3e066ab7568670922958f4c578c390165e2dc11a Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Thu, 17 Jun 2021 17:01:49 +0200
Subject: [PATCH 198/217] Updated description list, fixed unit test.

---
 packages/ckeditor5-html-support/src/schemadefinitions.js | 8 ++++----
 packages/ckeditor5-html-support/tests/datafilter.js      | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/schemadefinitions.js b/packages/ckeditor5-html-support/src/schemadefinitions.js
index 80ea5643f7d..d3d8a08fc63 100644
--- a/packages/ckeditor5-html-support/src/schemadefinitions.js
+++ b/packages/ckeditor5-html-support/src/schemadefinitions.js
@@ -414,16 +414,16 @@ export default {
 			}
 		},
 		{
-			model: 'htmlDl',
+			model: 'htmlDescriptionList',
 			view: 'dl',
 			modelSchema: {
 				allowIn: [ '$htmlBlock', '$root' ],
-				allowChildren: [ 'htmlDt', 'htmlDl' ],
+				allowChildren: [ 'htmlDescriptionTerm', 'htmlDescriptionDetails' ],
 				isBlock: true
 			}
 		},
 		{
-			model: 'htmlDt',
+			model: 'htmlDescriptionTerm',
 			view: 'dt',
 			modelSchema: {
 				allowChildren: '$block',
@@ -431,7 +431,7 @@ export default {
 			}
 		},
 		{
-			model: 'htmlDd',
+			model: 'htmlDescriptionDetails',
 			view: 'dd',
 			modelSchema: {
 				allowChildren: '$block',
diff --git a/packages/ckeditor5-html-support/tests/datafilter.js b/packages/ckeditor5-html-support/tests/datafilter.js
index 085079bfeeb..4a062906f51 100644
--- a/packages/ckeditor5-html-support/tests/datafilter.js
+++ b/packages/ckeditor5-html-support/tests/datafilter.js
@@ -1078,7 +1078,7 @@ describe( 'DataFilter', () => {
 			editor.setData( '<p><a href="example.com" data-foo="foo">link</a></p>' );
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph><$text htmlA="(1)" linkHref="example.com">link</$text></paragraph>',
+				data: '<paragraph><$text htmlLink="(1)" linkHref="example.com">link</$text></paragraph>',
 				attributes: {
 					1: {
 						attributes: {

From a4d2052a29c141ee771d24beeb610212f1a43013 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 18 Jun 2021 06:47:53 +0200
Subject: [PATCH 199/217] Model renaming, adding new definitions.

---
 .../src/schemadefinitions.js                  | 95 ++++++++++---------
 .../tests/datafilter.js                       |  2 +-
 2 files changed, 53 insertions(+), 44 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/schemadefinitions.js b/packages/ckeditor5-html-support/src/schemadefinitions.js
index d3d8a08fc63..f25b13b068b 100644
--- a/packages/ckeditor5-html-support/src/schemadefinitions.js
+++ b/packages/ckeditor5-html-support/src/schemadefinitions.js
@@ -15,6 +15,7 @@
 // * applet (support is limited mostly to old IE)
 // * basefont (this one is also empty)
 // * isindex (basically no support for modern browsers at all)
+//
 // Skipped elements due to lack empty element support:
 // * hr
 // * area
@@ -24,6 +25,7 @@
 // * wbr
 // Skipped elements due to complexity:
 // * datalist with option elements used as a data source for input[list] element
+//
 // Skipped elements as they are handled as an object content:
 // TODO shouldn't we also filter attributes on these element and enable them separately?
 // * track
@@ -31,12 +33,19 @@
 // * option
 // * param
 // * optgroup
+//
 // Skipped full page HTML elements:
 // * body
 // * html
 // * title
 // * head
+// * meta
+// * link
 // * etc...
+//
+// Skipped hidden elements:
+// noscript
+// script
 
 export default {
 	block: [
@@ -80,14 +89,14 @@ export default {
 			}
 		},
 		{
-			model: 'htmlParagraph',
+			model: 'htmlP',
 			view: 'p',
 			modelSchema: {
 				inheritAllFrom: '$block'
 			}
 		},
 		{
-			model: 'htmlBlockQuote',
+			model: 'htmlBlockquote',
 			view: 'blockquote',
 			modelSchema: {
 				inheritAllFrom: '$htmlBlock'
@@ -102,7 +111,7 @@ export default {
 			}
 		},
 		{
-			model: 'htmlTableBody',
+			model: 'htmlTbody',
 			view: 'tbody',
 			modelSchema: {
 				allowIn: 'htmlTable',
@@ -110,7 +119,7 @@ export default {
 			}
 		},
 		{
-			model: 'htmlTableHead',
+			model: 'htmlThead',
 			view: 'thead',
 			modelSchema: {
 				allowIn: 'htmlTable',
@@ -118,7 +127,7 @@ export default {
 			}
 		},
 		{
-			model: 'htmlTableFoot',
+			model: 'htmlTfoot',
 			view: 'tfoot',
 			modelSchema: {
 				allowIn: 'htmlTable',
@@ -126,7 +135,7 @@ export default {
 			}
 		},
 		{
-			model: 'htmlColumnGroup',
+			model: 'htmlColgroup',
 			view: 'colgroup',
 			modelSchema: {
 				allowIn: 'htmlTable',
@@ -143,7 +152,7 @@ export default {
 			}
 		},
 		{
-			model: 'htmlTableRow',
+			model: 'htmlTr',
 			view: 'tr',
 			modelSchema: {
 				allowIn: [ 'htmlTable', 'htmlTableHead', 'htmlTableBody' ],
@@ -152,7 +161,7 @@ export default {
 		},
 		// TODO can also include text.
 		{
-			model: 'htmlTableData',
+			model: 'htmlTd',
 			view: 'td',
 			modelSchema: {
 				allowIn: 'tr',
@@ -162,7 +171,7 @@ export default {
 		},
 		// TODO can also include text.
 		{
-			model: 'htmlTableHeader',
+			model: 'htmlTh',
 			view: 'th',
 			modelSchema: {
 				allowIn: 'tr',
@@ -270,7 +279,7 @@ export default {
 			}
 		},
 		{
-			model: 'htmlHeadingGroup',
+			model: 'htmlHgroup',
 			view: 'hgroup',
 			modelSchema: {
 				allowChildren: [
@@ -288,42 +297,42 @@ export default {
 			}
 		},
 		{
-			model: 'htmlHeading1',
+			model: 'htmlH1',
 			view: 'h1',
 			modelSchema: {
 				inheritAllFrom: '$block'
 			}
 		},
 		{
-			model: 'htmlHeading2',
+			model: 'htmlH2',
 			view: 'h2',
 			modelSchema: {
 				inheritAllFrom: '$block'
 			}
 		},
 		{
-			model: 'htmlHeading3',
+			model: 'htmlH3',
 			view: 'h3',
 			modelSchema: {
 				inheritAllFrom: '$block'
 			}
 		},
 		{
-			model: 'htmlHeading4',
+			model: 'htmlH4',
 			view: 'h4',
 			modelSchema: {
 				inheritAllFrom: '$block'
 			}
 		},
 		{
-			model: 'htmlHeading5',
+			model: 'htmlH5',
 			view: 'h5',
 			modelSchema: {
 				inheritAllFrom: '$block'
 			}
 		},
 		{
-			model: 'htmlHeading6',
+			model: 'htmlH6',
 			view: 'h6',
 			modelSchema: {
 				inheritAllFrom: '$block'
@@ -332,13 +341,13 @@ export default {
 		{
 			model: '$htmlList',
 			modelSchema: {
-				allowIn: [ '$htmlBlock', 'htmlListItem' ],
-				allowChildren: 'htmlListItem',
+				allowIn: [ '$htmlBlock', 'htmlLi' ],
+				allowChildren: 'htmlLi',
 				isBlock: true
 			}
 		},
 		{
-			model: 'htmlDirectory',
+			model: 'htmlDir',
 			view: 'dir',
 			modelSchema: {
 				inheritAllFrom: '$htmlList'
@@ -352,14 +361,14 @@ export default {
 			}
 		},
 		{
-			model: 'htmlUnorderedList',
+			model: 'htmlUl',
 			view: 'ul',
 			modelSchema: {
 				inheritAllFrom: '$htmlList'
 			}
 		},
 		{
-			model: 'htmlOrderedList',
+			model: 'htmlOl',
 			view: 'ol',
 			modelSchema: {
 				inheritAllFrom: '$htmlList'
@@ -367,7 +376,7 @@ export default {
 		},
 		// TODO can also include other block elements.
 		{
-			model: 'htmlListItem',
+			model: 'htmlLi',
 			view: 'li',
 			modelSchema: {
 				allowChildren: '$text',
@@ -414,16 +423,16 @@ export default {
 			}
 		},
 		{
-			model: 'htmlDescriptionList',
+			model: 'htmlDl',
 			view: 'dl',
 			modelSchema: {
 				allowIn: [ '$htmlBlock', '$root' ],
-				allowChildren: [ 'htmlDescriptionTerm', 'htmlDescriptionDetails' ],
+				allowChildren: [ 'htmlDt', 'htmlDd' ],
 				isBlock: true
 			}
 		},
 		{
-			model: 'htmlDescriptionTerm',
+			model: 'htmlDt',
 			view: 'dt',
 			modelSchema: {
 				allowChildren: '$block',
@@ -431,7 +440,7 @@ export default {
 			}
 		},
 		{
-			model: 'htmlDescriptionDetails',
+			model: 'htmlDd',
 			view: 'dd',
 			modelSchema: {
 				allowChildren: '$block',
@@ -465,7 +474,7 @@ export default {
 			}
 		},
 		{
-			model: 'htmlTeletypeText',
+			model: 'htmlTt',
 			view: 'tt',
 			attributeProperties: {
 				copyOnEnter: true
@@ -507,14 +516,14 @@ export default {
 			}
 		},
 		{
-			model: 'htmlSample',
+			model: 'htmlSamp',
 			view: 'samp',
 			attributeProperties: {
 				copyOnEnter: true
 			}
 		},
 		{
-			model: 'htmlQuote',
+			model: 'htmlQ',
 			view: 'q',
 			attributeProperties: {
 				copyOnEnter: true
@@ -528,7 +537,7 @@ export default {
 			}
 		},
 		{
-			model: 'htmlKeyboardInput',
+			model: 'htmlKbd',
 			view: 'kbd',
 			attributeProperties: {
 				copyOnEnter: true
@@ -549,14 +558,14 @@ export default {
 			}
 		},
 		{
-			model: 'htmlAbbreviation',
+			model: 'htmlAbbr',
 			view: 'abbr',
 			attributeProperties: {
 				copyOnEnter: true
 			}
 		},
 		{
-			model: 'htmlLink',
+			model: 'htmlA',
 			view: 'a',
 			priority: 5,
 			attributeProperties: {
@@ -571,28 +580,28 @@ export default {
 			}
 		},
 		{
-			model: 'htmlBold',
+			model: 'htmlB',
 			view: 'b',
 			attributeProperties: {
 				copyOnEnter: true
 			}
 		},
 		{
-			model: 'htmlItalic',
+			model: 'htmlI',
 			view: 'i',
 			attributeProperties: {
 				copyOnEnter: true
 			}
 		},
 		{
-			model: 'htmlEmphasis',
+			model: 'htmlEm',
 			view: 'em',
 			attributeProperties: {
 				copyOnEnter: true
 			}
 		},
 		{
-			model: 'htmlStrike',
+			model: 'htmlS',
 			view: 's',
 			attributeProperties: {
 				copyOnEnter: true
@@ -600,7 +609,7 @@ export default {
 		},
 		// TODO According to HTML-spec can behave as div-like element, althouth CKE4 only handles it as an inline element.
 		{
-			model: 'htmlDeleted',
+			model: 'htmlDel',
 			view: 'del',
 			attributeProperties: {
 				copyOnEnter: true
@@ -608,28 +617,28 @@ export default {
 		},
 		// TODO According to HTML-spec can behave as div-like element, althouth CKE4 only handles it as an inline element.
 		{
-			model: 'htmlInserted',
+			model: 'htmlIns',
 			view: 'ins',
 			attributeProperties: {
 				copyOnEnter: true
 			}
 		},
 		{
-			model: 'htmlUnderline',
+			model: 'htmlU',
 			view: 'u',
 			attributeProperties: {
 				copyOnEnter: true
 			}
 		},
 		{
-			model: 'htmlSubscript',
+			model: 'htmlSub',
 			view: 'sub',
 			attributeProperties: {
 				copyOnEnter: true
 			}
 		},
 		{
-			model: 'htmlSuperscript',
+			model: 'htmlSup',
 			view: 'sup',
 			attributeProperties: {
 				copyOnEnter: true
@@ -671,7 +680,7 @@ export default {
 			}
 		},
 		{
-			model: 'htmlDefinition',
+			model: 'htmlDfn',
 			view: 'dfn',
 			attributeProperties: {
 				copyOnEnter: true
@@ -763,7 +772,7 @@ export default {
 		},
 		// TODO Should image be an object?
 		{
-			model: 'htmlImage',
+			model: 'htmlImg',
 			view: 'img',
 			isObject: true,
 			modelSchema: {
diff --git a/packages/ckeditor5-html-support/tests/datafilter.js b/packages/ckeditor5-html-support/tests/datafilter.js
index 4a062906f51..085079bfeeb 100644
--- a/packages/ckeditor5-html-support/tests/datafilter.js
+++ b/packages/ckeditor5-html-support/tests/datafilter.js
@@ -1078,7 +1078,7 @@ describe( 'DataFilter', () => {
 			editor.setData( '<p><a href="example.com" data-foo="foo">link</a></p>' );
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph><$text htmlLink="(1)" linkHref="example.com">link</$text></paragraph>',
+				data: '<paragraph><$text htmlA="(1)" linkHref="example.com">link</$text></paragraph>',
 				attributes: {
 					1: {
 						attributes: {

From 834ad63a77c4e778204e27c3ead886eeeb6bd06a Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 18 Jun 2021 07:45:28 +0200
Subject: [PATCH 200/217] Set attributes on correct editing element.

---
 packages/ckeditor5-html-support/src/converters.js | 5 +++++
 packages/ckeditor5-html-support/src/datafilter.js | 4 +++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-html-support/src/converters.js b/packages/ckeditor5-html-support/src/converters.js
index ee1c87afd53..73394f3794b 100644
--- a/packages/ckeditor5-html-support/src/converters.js
+++ b/packages/ckeditor5-html-support/src/converters.js
@@ -70,6 +70,11 @@ export function toObjectWidgetConverter( editor, { view: viewName, isInline } )
 		const viewElement = createObjectView( viewName, modelElement, writer );
 		writer.addClass( 'html-object-embed__content', viewElement );
 
+		const viewAttributes = modelElement.getAttribute( 'htmlAttributes' );
+		if ( viewAttributes ) {
+			setViewAttributes( writer, viewAttributes, viewElement );
+		}
+
 		writer.insert( writer.createPositionAt( viewContainer, 0 ), viewElement );
 
 		return toWidget( viewContainer, writer, { widgetLabel } );
diff --git a/packages/ckeditor5-html-support/src/datafilter.js b/packages/ckeditor5-html-support/src/datafilter.js
index 1440489025c..b28ff994436 100644
--- a/packages/ckeditor5-html-support/src/datafilter.js
+++ b/packages/ckeditor5-html-support/src/datafilter.js
@@ -351,11 +351,13 @@ export default class DataFilter extends Plugin {
 				return createObjectView( viewName, modelElement, writer );
 			}
 		} );
+
 		conversion.for( 'editingDowncast' ).elementToElement( {
 			model: modelName,
 			view: toObjectWidgetConverter( editor, definition )
 		} );
-		conversion.for( 'downcast' ).add( modelToViewBlockAttributeConverter( definition ) );
+
+		conversion.for( 'dataDowncast' ).add( modelToViewBlockAttributeConverter( definition ) );
 	}
 
 	/**

From 330f785a6a623fef3d471089378aab481ca1eb94 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 18 Jun 2021 09:53:38 +0200
Subject: [PATCH 201/217] Corrected definitions, tests.

---
 .../src/schemadefinitions.js                  |  48 ++-
 .../tests/manual/no-features.html             | 337 ++++++++++++++++++
 .../tests/manual/no-features.js               |  39 ++
 .../tests/manual/no-features.md               |   5 +
 4 files changed, 401 insertions(+), 28 deletions(-)
 create mode 100644 packages/ckeditor5-html-support/tests/manual/no-features.html
 create mode 100644 packages/ckeditor5-html-support/tests/manual/no-features.js
 create mode 100644 packages/ckeditor5-html-support/tests/manual/no-features.md

diff --git a/packages/ckeditor5-html-support/src/schemadefinitions.js b/packages/ckeditor5-html-support/src/schemadefinitions.js
index f25b13b068b..d068177a879 100644
--- a/packages/ckeditor5-html-support/src/schemadefinitions.js
+++ b/packages/ckeditor5-html-support/src/schemadefinitions.js
@@ -23,6 +23,7 @@
 // * command
 // * map
 // * wbr
+// * colgroup -> col
 // Skipped elements due to complexity:
 // * datalist with option elements used as a data source for input[list] element
 //
@@ -134,14 +135,6 @@ export default {
 				isBlock: true
 			}
 		},
-		{
-			model: 'htmlColgroup',
-			view: 'colgroup',
-			modelSchema: {
-				allowIn: 'htmlTable',
-				isBlock: true
-			}
-		},
 		{
 			model: 'htmlCaption',
 			view: 'caption',
@@ -155,7 +148,7 @@ export default {
 			model: 'htmlTr',
 			view: 'tr',
 			modelSchema: {
-				allowIn: [ 'htmlTable', 'htmlTableHead', 'htmlTableBody' ],
+				allowIn: [ 'htmlTable', 'htmlThead', 'htmlTbody' ],
 				isBlock: true
 			}
 		},
@@ -164,7 +157,7 @@ export default {
 			model: 'htmlTd',
 			view: 'td',
 			modelSchema: {
-				allowIn: 'tr',
+				allowIn: 'htmlTr',
 				allowChildren: [ '$block', '$htmlBlock' ],
 				isBlock: true
 			}
@@ -174,7 +167,7 @@ export default {
 			model: 'htmlTh',
 			view: 'th',
 			modelSchema: {
-				allowIn: 'tr',
+				allowIn: 'htmlTr',
 				allowChildren: [ '$block', '$htmlBlock' ],
 				isBlock: true
 			}
@@ -198,12 +191,12 @@ export default {
 				isBlock: true
 			}
 		},
-		// TODO can also include other block elements.
+		// TODO can also include text.
 		{
 			model: 'htmlAddress',
 			view: 'address',
 			modelSchema: {
-				inheritAllFrom: '$block'
+				inheritAllFrom: '$htmlBlock'
 			}
 		},
 		// TODO can also include text.
@@ -230,6 +223,15 @@ export default {
 				inheritAllFrom: '$htmlBlock'
 			}
 		},
+		{
+			model: 'htmlSumary',
+			view: 'summary',
+			modelSchema: {
+				allowChildren: '$text',
+				allowIn: 'htmlDetails',
+				isBlock: true
+			}
+		},
 		// TODO can also include text.
 		{
 			model: 'htmlDiv',
@@ -251,7 +253,8 @@ export default {
 			model: 'htmlLegend',
 			view: 'legend',
 			modelSchema: {
-				inheritAllFrom: '$block'
+				allowIn: 'htmlFieldset',
+				allowChildren: '$text'
 			}
 		},
 		// TODO can also include text.
@@ -341,8 +344,8 @@ export default {
 		{
 			model: '$htmlList',
 			modelSchema: {
-				allowIn: [ '$htmlBlock', 'htmlLi' ],
-				allowChildren: 'htmlLi',
+				allowWhere: '$htmlBlock',
+				allowChildren: [ '$htmlList', 'htmlLi' ],
 				isBlock: true
 			}
 		},
@@ -379,8 +382,8 @@ export default {
 			model: 'htmlLi',
 			view: 'li',
 			modelSchema: {
-				allowChildren: '$text',
 				allowIn: '$htmlList',
+				allowChildren: '$text',
 				isBlock: true
 			}
 		},
@@ -413,15 +416,6 @@ export default {
 				inheritAllFrom: '$htmlBlock'
 			}
 		},
-		{
-			model: 'htmlSumary',
-			view: 'summary',
-			modelSchema: {
-				allowChildren: '$text',
-				allowIn: 'htmlDetails',
-				isBlock: true
-			}
-		},
 		{
 			model: 'htmlDl',
 			view: 'dl',
@@ -770,7 +764,6 @@ export default {
 				inheritAllFrom: '$htmlObjectInline'
 			}
 		},
-		// TODO Should image be an object?
 		{
 			model: 'htmlImg',
 			view: 'img',
@@ -779,7 +772,6 @@ export default {
 				inheritAllFrom: '$htmlObjectInline'
 			}
 		},
-		// TODO Should canvas be an object?
 		{
 			model: 'htmlCanvas',
 			view: 'canvas',
diff --git a/packages/ckeditor5-html-support/tests/manual/no-features.html b/packages/ckeditor5-html-support/tests/manual/no-features.html
new file mode 100644
index 00000000000..db54c7e089d
--- /dev/null
+++ b/packages/ckeditor5-html-support/tests/manual/no-features.html
@@ -0,0 +1,337 @@
+<head>
+	<meta http-equiv="Content-Security-Policy" content="script-src 'self' https://ckeditor.com 'unsafe-inline' 'unsafe-eval'">
+	<!-- Let's add some default styling for better readability -->
+	<style>
+		table {
+			border-collapse: collapse;
+		}
+		td, th {
+			border: 1px solid black;
+			padding: .5em;
+		}
+	</style>
+	<style>
+		[contenteditable="true"] :not([data-validation-allow]):not(.html-object-embed) {
+			border: 1px solid red !important;
+		}
+	</style>
+</head>
+<div style="display: flex">
+	<div style="width: 40%; margin-right: 20px">
+		<div id="editor">
+			<p><acronym>Acronym inline element</acronym></p>
+
+			<p><tt>Tt inline element</tt></p>
+			 
+			<p><font>Font inline element</font></p>
+			 
+			<p><var>Var inline element</var></p>
+			 
+			<p><big>Big inline element</big></p>
+
+			<p><small>Small inline element</small></p>
+			 
+			<p><samp>Samp inline element</samp></p>
+
+			<p><q>Q inline element</q></p>
+			 
+			<p><output>Output inline element</output></p>
+
+			<p><kbd>Kbd inline element</kbd></p>
+			 
+			<p><bdi>Bdi inline element</bdi></p>
+			 
+			<p><bdo>Bdo inline element</bdo></p>
+			 
+			<p><abbr>Abbr inline element</abbr></p>
+
+			<p><a href="#">A inline element</a></p>
+			 
+			<p><strong>Strong inline element</strong></p>
+
+			<p><b>B inline element</b></p>
+			 
+			<p><i>I inline element</i></p>
+
+			<p><em>Em inline element</em></p>
+			 
+			<p><s>S inline element</s></p>
+
+			<p><del>Del inline element</del></p>
+			 
+			<p><ins>Ins inline element</ins></p>
+
+			<p><u>U inline element</u></p>
+
+			<p><sub>Sub inline element</sub></p>
+			 
+			<p><sup>Sup inline element</sup></p>
+
+			<p><code>Code inline element</code></p>
+
+			<p><mark>Mark inline element</mark></p>
+
+			<p><span>Span inline element</span></p>
+
+			<p><cite>Cite inline element</cite></p>
+
+			<p><label>Label inline element</label></p>
+
+			<p><dfn>Dfn inline element</dfn></p>
+
+			<!-- Block elements -->
+			<header>
+				<p>Header</p>
+				<h1>h1</h1>
+			</header>
+
+			<hgroup>
+				<h1>h2</h1>
+				<h1>h3</h1>
+				<h1>h4</h1>
+				<h1>h5</h1>
+				<h1>h6</h1>
+			</hgroup>
+
+			<ol>
+				<li>ol - li</li>
+				<li>ol - li</li>
+				<li>ol - li</li>
+				<ol>
+					<li>ol - li - ol - li</li>
+					<li>ol - li - ol - li</li>
+					<li>ol - li - ol - li</li>
+				</ol>
+			</ol>
+
+			<ul>
+				<li>ul - li</li>
+				<li>ul - li</li>
+				<li>ul - li</li>
+				<ul>
+					<li>ul - li - ul - li</li>
+					<li>ul - li - ul - li</li>
+					<li>ul - li - ul - li</li>
+				</ul>
+			</ul>
+
+			<dir>
+				<li>dir - li</li>
+				<li>dir - li</li>
+				<li>dir - li</li>
+				<dir>
+					<li>dir - li - dir - li</li>
+					<li>dir - li - dir - li</li>
+					<li>dir - li - dir - li</li>
+				</dir>
+			</dir>
+
+			<menu>
+				<li>menu - li</li>
+				<li>menu - li</li>
+				<li>menu - li</li>
+				<menu>
+					<li>menu - li - menu - li</li>
+					<li>menu - li - menu - li</li>
+					<li>menu - li - menu - li</li>
+				</menu>
+			</menu>
+
+			<blockquote>
+				<p>Blockquote</p>
+				<blockquote>
+					<p>Nested Blockquote</p>
+				</blockquote>
+			</blockquote>
+
+			<table>
+				<caption>Caption</caption>
+				<thead>
+					<th><p>TH</p></th>
+					<th><p>TH</p></th>
+					<td><p>TD</p></td>
+					<td><p>TD</p></td>
+				</thead>
+				<tbody>
+					<tr>
+						<td><p>1</p></td>
+						<td><p>2</p></td>
+						<td><p>3</p></td>
+						<td><p>4</p></td>
+					</tr>
+					<tr>
+						<td><p>1</p></td>
+						<td><p>2</p></td>
+						<td><p>3</p></td>
+						<td><p>4</p></td>
+					</tr>
+					<tr>
+						<td><div><div><p>Nested</p></div></div></td>
+						<td><div><div><p>Nested</p></div></div></td>
+						<td><div><div><p>Nested</p></div></div></td>
+						<td><div><div><p>Nested</p></div></div></td>
+					</tr>
+				</tbody>
+				<tfoot>
+					<tr>
+						<th><div><div><p>Nested</p></div></div></th>
+						<th><div><div><p>Nested</p></div></div></th>
+						<td><p>TH</p></td>
+						<td><p>TH</p></td>
+					</tr>
+				</tfoot>
+			</table>
+
+			<figure>
+				<table>
+					<tr>
+						<td><p>1</p></td>
+						<td><p>2</p></td>
+						<td><p>3</p></td>
+						<td><p>4</p></td>
+					</tr>
+					<tr>
+						<td><p>1</p></td>
+						<td><p>2</p></td>
+						<td><p>3</p></td>
+						<td><p>4</p></td>
+					</tr>
+					<tr>
+						<td><div><div><p>Nested</p></div></div></td>
+						<td><div><div><p>Nested</p></div></div></td>
+						<td><div><div><p>Nested</p></div></div></td>
+						<td><div><div><p>Nested</p></div></div></td>
+					</tr>
+				</table>
+				<figcaption>Figcaption</figcaption>
+			</figure>
+
+			<p>
+				<img width="300" height="200" src="sample.jpg" />
+			</p>
+
+			<figure>
+				<img width="300" height="200" src="sample.jpg" />
+				<figcaption>Figcaption</figcaption>
+			</figure>
+
+			<address>
+				<p>Address</p>
+				<div><div><p>Nested</p></div></div>
+			</address>
+
+			<aside>
+				<p>Aside</p>
+				<div><div><p>Nested</p></div></div>
+			</aside>
+
+			<main>
+				<p>Main</p>
+				<div><div><p>Nested</p></div></div>
+			</main>
+
+			<details>
+				<summary>Details</summary>
+				<p>Details</p>
+				<div><div><p>Nested</p></div></div>
+			</details>
+
+			<pre>Pre</pre>
+
+			<div>
+				<p>Div</p>
+				<div><div><p>Nested</p></div></div>
+			</div>
+
+			<article>
+				<p>Article</p>
+				<div><div><p>Nested</p></div></div>
+			</article>
+
+			<section>
+				<p>Section</p>
+				<div><div><p>Nested</p></div></div>
+			</section>
+
+			<nav>
+				<p>Nav</p>
+				<div><div><p>Nested</p></div></div>
+			</nav>
+
+			<dl>
+				<dt><p>dt1</p></dt>
+				<dt><p>dt2</p></dt>
+				<dd><p>dd1</p></dd>
+				<dd><p>dd2</p></dd>
+			</dl>
+
+			<fieldset>
+				<legend>Legend</legend>
+				<p>Fieldset</p>
+				<div><div><p>Nested</p></div></div>
+			</fieldset>
+
+			<footer>
+				<p>Footer</p>
+				<div><div><p>Nested</p></div></div>
+			</footer>
+
+			<!-- Object elements -->
+			<form>
+				<p>Form</p>
+				<div><div><p>Nested</p></div></div>
+				<p><input name="checkbox" type="checkbox" value="10" /></p>
+
+				<p><input name="radio" type="radio" value="10" /></p>
+
+				<p><input name="text field" type="text" value="10" /></p>
+
+				<p><textarea name="textarea">10</textarea></p>
+
+				<p><select name="selection field"><option value="1">a1</option><option selected="selected" value="2">a2</option><option value="3">a3</option></select></p>
+
+				<p><input name="button" type="button" value="click me" /></p>
+
+				<p><button>Click me!</button></p>
+
+				<p><input alt="" src="https://via.placeholder.com/100" type="image" /></p>
+
+				<p><video controls="" height="240" width="320"><source src="http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/ElephantsDream.mp4" type="video/mp4" /> Your browser does not support the video tag.</video></p>
+
+				<p><embed type="image/jpg" src="sample.jpg" width="300" height="200"></p>
+
+				<p><audio controls=""><source src="https://www.soundhelix.com/examples/mp3/SoundHelix-Song-1.mp3" type="audio/mpeg" /> Your browser does not support the audio element.</audio></p>
+
+				<p>
+					<label for="canvas">Canvas:</label>
+					<canvas id="canvas" width="200" height="100"></canvas>
+				</p>
+
+				<p>
+					<label for="meter">Meter:</label>
+					<meter id="meter" min="0" max="100" low="33" high="66" optimum="80" value="50">
+						at 50/100
+					</meter>
+				</p>
+
+				<p>
+					<label for="progress">Progress:</label>
+					<progress id="progress" max="100" value="70"> 70% </progress>
+				</p>
+			</form>
+		</div>
+	</div>
+
+
+	<div style="width: 40%">
+		<h1 style="padding:0 0 5px 0; font-size: 16px; border-bottom: solid 1px grey">Source content:</h1>
+		<div id="preview"></div>
+	</div>
+</div>
+<script>
+	document.querySelectorAll( '#editor *' ).forEach( node => {
+		node.setAttribute( 'data-validation-allow', true );
+	} );
+
+	document.getElementById( 'preview' ).innerHTML = document.getElementById( 'editor' ).innerHTML;
+</script>
diff --git a/packages/ckeditor5-html-support/tests/manual/no-features.js b/packages/ckeditor5-html-support/tests/manual/no-features.js
new file mode 100644
index 00000000000..afd3c434972
--- /dev/null
+++ b/packages/ckeditor5-html-support/tests/manual/no-features.js
@@ -0,0 +1,39 @@
+/**
+ * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/* globals console:false, window, document */
+
+import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
+import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
+import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials';
+
+import GeneralHtmlSupport from '../../src/generalhtmlsupport';
+
+ClassicEditor
+	.create( document.querySelector( '#editor' ), {
+		plugins: [
+			Essentials,
+			GeneralHtmlSupport,
+			Paragraph
+		],
+		toolbar: [
+		],
+		dataSchema: {
+		},
+		htmlSupport: {
+			allow: [
+				{
+					name: /^.*$/,
+					attributes: true
+				}
+			]
+		}
+	} )
+	.then( editor => {
+		window.editor = editor;
+	} )
+	.catch( err => {
+		console.error( err.stack );
+	} );
diff --git a/packages/ckeditor5-html-support/tests/manual/no-features.md b/packages/ckeditor5-html-support/tests/manual/no-features.md
new file mode 100644
index 00000000000..937c06d3809
--- /dev/null
+++ b/packages/ckeditor5-html-support/tests/manual/no-features.md
@@ -0,0 +1,5 @@
+## Compatibility support when no features enabled
+
+* Verify if the editor's content looks similar to the source content on the right side of the editor.
+* Verify if editor's content supports all elements available in the source content.
+* If an element is not supporting allowed attributes filtering, it will be visible as a red border around this element.

From c7e419d9ae66c80df70c4d0864f55efac1c07a61 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 18 Jun 2021 10:15:29 +0200
Subject: [PATCH 202/217] Schema definitions test.

---
 .../tests/schemadefinitions.js                    | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
 create mode 100644 packages/ckeditor5-html-support/tests/schemadefinitions.js

diff --git a/packages/ckeditor5-html-support/tests/schemadefinitions.js b/packages/ckeditor5-html-support/tests/schemadefinitions.js
new file mode 100644
index 00000000000..f2b50f75353
--- /dev/null
+++ b/packages/ckeditor5-html-support/tests/schemadefinitions.js
@@ -0,0 +1,15 @@
+/**
+ * @license Copyright (c) 2003-2021, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+import schemaDefinitions from '../src/schemadefinitions';
+
+describe( 'schemadefinitions', () => {
+	it( 'should be an object', () => {
+		// Sanity check if object exists. We will add test coverage later.
+		expect( schemaDefinitions ).to.be.an( 'object' );
+		expect( schemaDefinitions.block ).to.be.an( 'array' );
+		expect( schemaDefinitions.inline ).to.be.an( 'array' );
+	} );
+} );

From 8326de37befde3856a240da3904dc1603a9e0fa9 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 18 Jun 2021 12:20:15 +0200
Subject: [PATCH 203/217] Refactoring, test coverage.

---
 packages/ckeditor5-html-support/src/datafilter.js   | 11 +++++------
 packages/ckeditor5-html-support/tests/datafilter.js | 12 ++++++++++++
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/datafilter.js b/packages/ckeditor5-html-support/src/datafilter.js
index b28ff994436..b3f84bba4c9 100644
--- a/packages/ckeditor5-html-support/src/datafilter.js
+++ b/packages/ckeditor5-html-support/src/datafilter.js
@@ -345,18 +345,17 @@ export default class DataFilter extends Plugin {
 		} );
 		conversion.for( 'upcast' ).add( viewToModelBlockAttributeConverter( definition, this ) );
 
+		conversion.for( 'editingDowncast' ).elementToElement( {
+			model: modelName,
+			view: toObjectWidgetConverter( editor, definition )
+		} );
+
 		conversion.for( 'dataDowncast' ).elementToElement( {
 			model: modelName,
 			view: ( modelElement, { writer } ) => {
 				return createObjectView( viewName, modelElement, writer );
 			}
 		} );
-
-		conversion.for( 'editingDowncast' ).elementToElement( {
-			model: modelName,
-			view: toObjectWidgetConverter( editor, definition )
-		} );
-
 		conversion.for( 'dataDowncast' ).add( modelToViewBlockAttributeConverter( definition ) );
 	}
 
diff --git a/packages/ckeditor5-html-support/tests/datafilter.js b/packages/ckeditor5-html-support/tests/datafilter.js
index 085079bfeeb..8f3285b7e9f 100644
--- a/packages/ckeditor5-html-support/tests/datafilter.js
+++ b/packages/ckeditor5-html-support/tests/datafilter.js
@@ -13,6 +13,7 @@ import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import { expectToThrowCKEditorError } from '@ckeditor/ckeditor5-utils/tests/_utils/utils';
 import { getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
 import { getModelDataWithAttributes } from './_utils/utils';
+import { addBackgroundRules } from '@ckeditor/ckeditor5-engine/src/view/styles/background';
 
 import GeneralHtmlSupport from '../src/generalhtmlsupport';
 
@@ -1276,6 +1277,17 @@ describe( 'DataFilter', () => {
 		}, /data-filter-invalid-definition/, null, definition );
 	} );
 
+	it( 'should handle expanded styles by matcher', () => {
+		editor.data.addStyleProcessorRules( addBackgroundRules );
+
+		dataFilter.allowElement( 'p' );
+		dataFilter.allowAttributes( { name: 'p', styles: true } );
+
+		editor.setData( '<p style="background:red;">foobar</p>' );
+
+		expect( editor.getData() ).to.equal( '<p style="background-color:red;">foobar</p>' );
+	} );
+
 	describe( 'loadAllowedConfig', () => {
 		it( 'should allow match all elements by ommiting pattern name', () => {
 			dataSchema.registerBlockElement( {

From 90e60a4c1971512c127d0e587c4e86d31300f512 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 18 Jun 2021 12:33:06 +0200
Subject: [PATCH 204/217] Cleanup.

---
 packages/ckeditor5-html-support/tests/manual/features.js    | 2 --
 packages/ckeditor5-html-support/tests/manual/no-features.js | 4 ----
 2 files changed, 6 deletions(-)

diff --git a/packages/ckeditor5-html-support/tests/manual/features.js b/packages/ckeditor5-html-support/tests/manual/features.js
index 607568b7cc6..307018ea3f5 100644
--- a/packages/ckeditor5-html-support/tests/manual/features.js
+++ b/packages/ckeditor5-html-support/tests/manual/features.js
@@ -67,8 +67,6 @@ ClassicEditor
 			'|',
 			'undo', 'redo'
 		],
-		dataSchema: {
-		},
 		htmlSupport: {
 			allow: [
 				{ name: /^.*$/, styles: true },
diff --git a/packages/ckeditor5-html-support/tests/manual/no-features.js b/packages/ckeditor5-html-support/tests/manual/no-features.js
index afd3c434972..2018f00b1a3 100644
--- a/packages/ckeditor5-html-support/tests/manual/no-features.js
+++ b/packages/ckeditor5-html-support/tests/manual/no-features.js
@@ -18,10 +18,6 @@ ClassicEditor
 			GeneralHtmlSupport,
 			Paragraph
 		],
-		toolbar: [
-		],
-		dataSchema: {
-		},
 		htmlSupport: {
 			allow: [
 				{

From 0a492a19b2b8e21b4e78d03e51fb98256ede8d74 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 18 Jun 2021 13:16:17 +0200
Subject: [PATCH 205/217] Fixed center element.

---
 .../src/schemadefinitions.js                     | 16 ++++++++--------
 .../tests/manual/no-features.html                |  2 ++
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/schemadefinitions.js b/packages/ckeditor5-html-support/src/schemadefinitions.js
index d068177a879..19cd0c6ffc6 100644
--- a/packages/ckeditor5-html-support/src/schemadefinitions.js
+++ b/packages/ckeditor5-html-support/src/schemadefinitions.js
@@ -441,6 +441,13 @@ export default {
 				isBlock: true
 			}
 		},
+		{
+			model: 'htmlCenter',
+			view: 'center',
+			modelSchema: {
+				inheritAllFrom: '$htmlBlock'
+			}
+		},
 		// Objects
 		{
 			model: '$htmlObjectBlock',
@@ -453,13 +460,6 @@ export default {
 		}
 	],
 	inline: [
-		{
-			model: 'htmlCenter',
-			view: 'center',
-			attributeProperties: {
-				copyOnEnter: true
-			}
-		},
 		{
 			model: 'htmlAcronym',
 			view: 'acronym',
@@ -780,7 +780,7 @@ export default {
 				inheritAllFrom: '$htmlObjectInline'
 			}
 		},
-		// TODO it could be probably represented as non-object element, although it has grafical representation,
+		// TODO it could be probably represented as non-object element, although it has graphical representation,
 		// so probably makes more sense to keep it as an object.
 		{
 			model: 'htmlMeter',
diff --git a/packages/ckeditor5-html-support/tests/manual/no-features.html b/packages/ckeditor5-html-support/tests/manual/no-features.html
index db54c7e089d..9b6452fd017 100644
--- a/packages/ckeditor5-html-support/tests/manual/no-features.html
+++ b/packages/ckeditor5-html-support/tests/manual/no-features.html
@@ -93,6 +93,8 @@ <h1>h5</h1>
 				<h1>h6</h1>
 			</hgroup>
 
+			<center><p>Center</p></center>
+
 			<ol>
 				<li>ol - li</li>
 				<li>ol - li</li>

From cf043a15d8f50a1479ba9b0d54adf80fd0022335 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 21 Jun 2021 11:34:02 +0200
Subject: [PATCH 206/217] Renaming  to .

---
 .../src/schemadefinitions.js                  | 44 +++++++++----------
 .../tests/datafilter.js                       |  2 +-
 .../tests/manual/generalhtmlsupport.js        |  2 +-
 3 files changed, 24 insertions(+), 24 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/schemadefinitions.js b/packages/ckeditor5-html-support/src/schemadefinitions.js
index 19cd0c6ffc6..bb37cbf9e2f 100644
--- a/packages/ckeditor5-html-support/src/schemadefinitions.js
+++ b/packages/ckeditor5-html-support/src/schemadefinitions.js
@@ -82,10 +82,10 @@ export default {
 
 		// Compatibility features
 		{
-			model: '$htmlBlock',
+			model: '$htmlSection',
 			modelSchema: {
 				allowChildren: '$block',
-				allowIn: [ '$root', '$htmlBlock' ],
+				allowIn: [ '$root', '$htmlSection' ],
 				isBlock: true
 			}
 		},
@@ -100,14 +100,14 @@ export default {
 			model: 'htmlBlockquote',
 			view: 'blockquote',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		{
 			model: 'htmlTable',
 			view: 'table',
 			modelSchema: {
-				allowIn: [ '$htmlBlock', '$root' ],
+				allowIn: [ '$htmlSection', '$root' ],
 				isBlock: true
 			}
 		},
@@ -158,7 +158,7 @@ export default {
 			view: 'td',
 			modelSchema: {
 				allowIn: 'htmlTr',
-				allowChildren: [ '$block', '$htmlBlock' ],
+				allowChildren: [ '$block', '$htmlSection' ],
 				isBlock: true
 			}
 		},
@@ -168,7 +168,7 @@ export default {
 			view: 'th',
 			modelSchema: {
 				allowIn: 'htmlTr',
-				allowChildren: [ '$block', '$htmlBlock' ],
+				allowChildren: [ '$block', '$htmlSection' ],
 				isBlock: true
 			}
 		},
@@ -177,7 +177,7 @@ export default {
 			model: 'htmlFigure',
 			view: 'figure',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock',
+				inheritAllFrom: '$htmlSection',
 				isBlock: true
 			}
 		},
@@ -196,7 +196,7 @@ export default {
 			model: 'htmlAddress',
 			view: 'address',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		// TODO can also include text.
@@ -204,7 +204,7 @@ export default {
 			model: 'htmlAside',
 			view: 'aside',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		// TODO can also include text.
@@ -212,7 +212,7 @@ export default {
 			model: 'htmlMain',
 			view: 'main',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		// TODO can also include text.
@@ -220,7 +220,7 @@ export default {
 			model: 'htmlDetails',
 			view: 'details',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		{
@@ -237,7 +237,7 @@ export default {
 			model: 'htmlDiv',
 			view: 'div',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		// TODO can also include text.
@@ -245,7 +245,7 @@ export default {
 			model: 'htmlFieldset',
 			view: 'fieldset',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		// TODO can also include h1-h6.
@@ -262,7 +262,7 @@ export default {
 			model: 'htmlHeader',
 			view: 'header',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		// TODO can also include text.
@@ -270,7 +270,7 @@ export default {
 			model: 'htmlFooter',
 			view: 'footer',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		// TODO can also include text.
@@ -278,7 +278,7 @@ export default {
 			model: 'htmlForm',
 			view: 'form',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		{
@@ -344,7 +344,7 @@ export default {
 		{
 			model: '$htmlList',
 			modelSchema: {
-				allowWhere: '$htmlBlock',
+				allowWhere: '$htmlSection',
 				allowChildren: [ '$htmlList', 'htmlLi' ],
 				isBlock: true
 			}
@@ -398,14 +398,14 @@ export default {
 			model: 'htmlArticle',
 			view: 'article',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		{
 			model: 'htmlSection',
 			view: 'section',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		// TODO can also include text.
@@ -413,14 +413,14 @@ export default {
 			model: 'htmlNav',
 			view: 'nav',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		{
 			model: 'htmlDl',
 			view: 'dl',
 			modelSchema: {
-				allowIn: [ '$htmlBlock', '$root' ],
+				allowIn: [ '$htmlSection', '$root' ],
 				allowChildren: [ 'htmlDt', 'htmlDd' ],
 				isBlock: true
 			}
@@ -445,7 +445,7 @@ export default {
 			model: 'htmlCenter',
 			view: 'center',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		},
 		// Objects
diff --git a/packages/ckeditor5-html-support/tests/datafilter.js b/packages/ckeditor5-html-support/tests/datafilter.js
index 8f3285b7e9f..9dba3d0ead6 100644
--- a/packages/ckeditor5-html-support/tests/datafilter.js
+++ b/packages/ckeditor5-html-support/tests/datafilter.js
@@ -612,7 +612,7 @@ describe( 'DataFilter', () => {
 				model: 'htmlXyz',
 				allowChildren: 'not-exists',
 				schema: {
-					inheritAllFrom: '$htmlBlock'
+					inheritAllFrom: '$htmlSection'
 				}
 			} );
 
diff --git a/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.js b/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.js
index 81a1f326591..0f41032407c 100644
--- a/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.js
+++ b/packages/ckeditor5-html-support/tests/manual/generalhtmlsupport.js
@@ -35,7 +35,7 @@ class ExtendHTMLSupport extends Plugin {
 			view: 'xyz',
 			model: 'htmlXyz',
 			modelSchema: {
-				inheritAllFrom: '$htmlBlock'
+				inheritAllFrom: '$htmlSection'
 			}
 		} );
 

From 71499fccf10500f34ea04c3f71b8eb513afc5efc Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 21 Jun 2021 12:20:07 +0200
Subject: [PATCH 207/217] Updated existing features.

---
 .../ckeditor5-html-support/src/schemadefinitions.js   | 11 +++++++++--
 .../ckeditor5-html-support/tests/manual/features.html |  4 ++--
 .../ckeditor5-html-support/tests/manual/features.js   |  9 ++++++---
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/schemadefinitions.js b/packages/ckeditor5-html-support/src/schemadefinitions.js
index bb37cbf9e2f..872d8e09cb3 100644
--- a/packages/ckeditor5-html-support/src/schemadefinitions.js
+++ b/packages/ckeditor5-html-support/src/schemadefinitions.js
@@ -41,8 +41,7 @@
 // * title
 // * head
 // * meta
-// * link
-// * etc...
+// * link * etc...
 //
 // Skipped hidden elements:
 // noscript
@@ -79,6 +78,14 @@ export default {
 			model: 'listItem',
 			view: 'li'
 		},
+		{
+			model: 'pageBreak',
+			view: 'div'
+		},
+		{
+			model: 'rawHtml',
+			view: 'div'
+		},
 
 		// Compatibility features
 		{
diff --git a/packages/ckeditor5-html-support/tests/manual/features.html b/packages/ckeditor5-html-support/tests/manual/features.html
index 7b5937fd179..7a51e72fa6f 100644
--- a/packages/ckeditor5-html-support/tests/manual/features.html
+++ b/packages/ckeditor5-html-support/tests/manual/features.html
@@ -105,11 +105,11 @@ <h4 style="color:green">Feature heading3</h4>
 				</tbody>
 			</table>
 
-			<figure class="media" data-foo><oembed data-bar url="https://www.youtube.com/watch?v=ZVv7UMQPEWk"></oembed></figure>
+			<oembed data-bar url="https://www.youtube.com/watch?v=ZVv7UMQPEWk"></oembed>
 
 			<div style="border: 1px solid blue" class="raw-html-embed">HTML snippet</div>
 
-			<div style="border: 1px solid blue" class="page-break" style="page-break-after:always;"><span style="display:none;">&nbsp;</span></div>
+			<div data-foo class="page-break" style="page-break-after:always;"><span style="display:none;">&nbsp;</span></div>
 		</div>
 	</div>
 
diff --git a/packages/ckeditor5-html-support/tests/manual/features.js b/packages/ckeditor5-html-support/tests/manual/features.js
index 307018ea3f5..7bfbdf66dc5 100644
--- a/packages/ckeditor5-html-support/tests/manual/features.js
+++ b/packages/ckeditor5-html-support/tests/manual/features.js
@@ -69,9 +69,12 @@ ClassicEditor
 		],
 		htmlSupport: {
 			allow: [
-				{ name: /^.*$/, styles: true },
-				{ name: 'a', attributes: [ 'name', 'id' ] },
-				{ name: 'span', classes: [ 'text-italic' ] }
+				{
+					name: /^.*$/,
+					styles: true,
+					attributes: true,
+					classes: true
+				}
 			]
 		}
 	} )

From daf203d2944730f673c81c89175ec99ef6a48356 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 25 Jun 2021 09:32:05 +0200
Subject: [PATCH 208/217] Removed unused config.

---
 packages/ckeditor5-html-support/src/dataschema.js | 2 --
 1 file changed, 2 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/dataschema.js b/packages/ckeditor5-html-support/src/dataschema.js
index 3602813c7d3..19ef1bf5466 100644
--- a/packages/ckeditor5-html-support/src/dataschema.js
+++ b/packages/ckeditor5-html-support/src/dataschema.js
@@ -53,8 +53,6 @@ export default class DataSchema extends Plugin {
 		 * @member {Map.<String, module:html-support/dataschema~DataSchemaDefinition>} #_definitions
 		 */
 		this._definitions = new Map();
-
-		editor.config.define( 'dataSchema', defaultConfig );
 	}
 
 	/**

From c4f74c4663036270fd56a4effcce192536101196 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 25 Jun 2021 13:13:14 +0200
Subject: [PATCH 209/217] Ensure that attribute is consumed.

---
 .../ckeditor5-html-support/src/converters.js  |  4 +--
 .../tests/datafilter.js                       | 28 +++++++++++++++++++
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/converters.js b/packages/ckeditor5-html-support/src/converters.js
index 73394f3794b..197a742b6c8 100644
--- a/packages/ckeditor5-html-support/src/converters.js
+++ b/packages/ckeditor5-html-support/src/converters.js
@@ -55,7 +55,7 @@ export function viewToModelObjectConverter( { model: modelName } ) {
 export function toObjectWidgetConverter( editor, { view: viewName, isInline } ) {
 	const t = editor.t;
 
-	return ( modelElement, { writer } ) => {
+	return ( modelElement, { writer, consumable } ) => {
 		const widgetLabel = t( 'HTML object' );
 
 		// Widget cannot be a raw element because the widget system would not be able
@@ -71,7 +71,7 @@ export function toObjectWidgetConverter( editor, { view: viewName, isInline } )
 		writer.addClass( 'html-object-embed__content', viewElement );
 
 		const viewAttributes = modelElement.getAttribute( 'htmlAttributes' );
-		if ( viewAttributes ) {
+		if ( viewAttributes && consumable.consume( modelElement, `attribute:htmlAttributes:${ modelElement.name }` ) ) {
 			setViewAttributes( writer, viewAttributes, viewElement );
 		}
 
diff --git a/packages/ckeditor5-html-support/tests/datafilter.js b/packages/ckeditor5-html-support/tests/datafilter.js
index 9dba3d0ead6..5d29be5943d 100644
--- a/packages/ckeditor5-html-support/tests/datafilter.js
+++ b/packages/ckeditor5-html-support/tests/datafilter.js
@@ -317,6 +317,34 @@ describe( 'DataFilter', () => {
 			expect( editor.getData() ).to.equal( '<p><input><input></p>' );
 		} );
 
+		it( 'should apply attributes to correct editing element', () => {
+			dataFilter.allowElement( 'input' );
+			dataFilter.allowAttributes( { name: 'input', attributes: 'type' } );
+
+			editor.setData( '<p><input type="number"/></p>' );
+
+			const input = editor.editing.view.document.getRoot()
+				.getChild( 0 ) // <p>
+				.getChild( 0 ) // <span>
+				.getChild( 0 ); // <input>
+
+			expect( input.getAttribute( 'type' ) ).to.equal( 'number' );
+		} );
+
+		it( 'should consume htmlAttributes attribute (editing downcast)', () => {
+			editor.conversion.for( 'editingDowncast' ).add( dispatcher => {
+				dispatcher.on( 'attribute:htmlAttributes:htmlInput', ( evt, data, conversionApi ) => {
+					conversionApi.consumable.consume( data.item, evt.name );
+					expect( conversionApi.consumable.test( data.item, evt.name ) ).to.be.true;
+				} );
+			} );
+
+			dataFilter.allowElement( 'input' );
+			dataFilter.allowAttributes( { name: 'input', attributes: 'type' } );
+
+			editor.setData( '<p><input type="number"/></p>' );
+		} );
+
 		function getObjectModelDataWithAttributes( model, options ) {
 			options.excludeAttributes = [ 'htmlContent' ];
 			return getModelDataWithAttributes( model, options );

From 3e6a1d3a515048fe68c7a738a8a9ca36c5fee009 Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 25 Jun 2021 14:22:51 +0200
Subject: [PATCH 210/217] Corrected invalid test.

---
 packages/ckeditor5-html-support/tests/datafilter.js | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/packages/ckeditor5-html-support/tests/datafilter.js b/packages/ckeditor5-html-support/tests/datafilter.js
index 5d29be5943d..6922643d4b9 100644
--- a/packages/ckeditor5-html-support/tests/datafilter.js
+++ b/packages/ckeditor5-html-support/tests/datafilter.js
@@ -332,17 +332,18 @@ describe( 'DataFilter', () => {
 		} );
 
 		it( 'should consume htmlAttributes attribute (editing downcast)', () => {
+			const spy = sinon.spy();
+
 			editor.conversion.for( 'editingDowncast' ).add( dispatcher => {
-				dispatcher.on( 'attribute:htmlAttributes:htmlInput', ( evt, data, conversionApi ) => {
-					conversionApi.consumable.consume( data.item, evt.name );
-					expect( conversionApi.consumable.test( data.item, evt.name ) ).to.be.true;
-				} );
+				dispatcher.on( 'attribute:htmlAttributes:htmlInput', spy );
 			} );
 
 			dataFilter.allowElement( 'input' );
 			dataFilter.allowAttributes( { name: 'input', attributes: 'type' } );
 
 			editor.setData( '<p><input type="number"/></p>' );
+
+			expect( spy.called ).to.be.false;
 		} );
 
 		function getObjectModelDataWithAttributes( model, options ) {

From a85bbf7b27f87a94035b976f4462fb6cf1719a7e Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Fri, 25 Jun 2021 14:29:09 +0200
Subject: [PATCH 211/217] Corrected comment.

---
 packages/ckeditor5-html-support/src/schemadefinitions.js | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/schemadefinitions.js b/packages/ckeditor5-html-support/src/schemadefinitions.js
index 872d8e09cb3..89d224b067a 100644
--- a/packages/ckeditor5-html-support/src/schemadefinitions.js
+++ b/packages/ckeditor5-html-support/src/schemadefinitions.js
@@ -24,11 +24,11 @@
 // * map
 // * wbr
 // * colgroup -> col
+//
 // Skipped elements due to complexity:
 // * datalist with option elements used as a data source for input[list] element
 //
 // Skipped elements as they are handled as an object content:
-// TODO shouldn't we also filter attributes on these element and enable them separately?
 // * track
 // * source
 // * option
@@ -41,7 +41,8 @@
 // * title
 // * head
 // * meta
-// * link * etc...
+// * link
+// * etc...
 //
 // Skipped hidden elements:
 // noscript

From 834bc1d42fbdd9491200b687b7afbbb4eff5d68f Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 28 Jun 2021 12:02:31 +0200
Subject: [PATCH 212/217] Remove already consumed attributes from data filter.

---
 .../ckeditor5-html-support/src/datafilter.js  | 26 +++++++-
 .../tests/datafilter.js                       | 66 +++++++++++++++----
 2 files changed, 78 insertions(+), 14 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/datafilter.js b/packages/ckeditor5-html-support/src/datafilter.js
index b3f84bba4c9..72e276a6f7f 100644
--- a/packages/ckeditor5-html-support/src/datafilter.js
+++ b/packages/ckeditor5-html-support/src/datafilter.js
@@ -26,7 +26,7 @@ import {
 	viewToModelBlockAttributeConverter,
 	modelToViewBlockAttributeConverter
 } from './converters';
-import { isPlainObject } from 'lodash-es';
+import { isPlainObject, pull as removeItemFromArray } from 'lodash-es';
 
 import '../theme/datafilter.css';
 
@@ -510,6 +510,8 @@ function consumeAttributeMatches( viewElement, { consumable }, matcher ) {
 	const consumedMatches = [];
 
 	for ( const match of matches ) {
+		removeConsumedAttributes( consumable, viewElement, match );
+
 		// We only want to consume attributes, so element can be still processed by other converters.
 		delete match.match.name;
 
@@ -521,6 +523,28 @@ function consumeAttributeMatches( viewElement, { consumable }, matcher ) {
 	return consumedMatches;
 }
 
+// Removes attributes from the given match that where already consumed by other converters.
+//
+// @private
+// @param {module:engine/view/element~Element} viewElement
+// @param {module:engine/conversion/modelconsumable~ModelConsumable} consumable
+// @param {Object} match
+function removeConsumedAttributes( consumable, viewElement, match ) {
+	for ( const key of [ 'attributes', 'classes', 'styles' ] ) {
+		const attributes = match.match[ key ];
+
+		if ( !attributes ) {
+			continue;
+		}
+
+		for ( const value of attributes ) {
+			if ( !consumable.test( viewElement, ( { [ key ]: [ value ] } ) ) ) {
+				removeItemFromArray( attributes, value );
+			}
+		}
+	}
+}
+
 // Merges the result of {@link module:engine/view/matcher~Matcher#matchAll} method.
 //
 // @private
diff --git a/packages/ckeditor5-html-support/tests/datafilter.js b/packages/ckeditor5-html-support/tests/datafilter.js
index 6922643d4b9..184269d9505 100644
--- a/packages/ckeditor5-html-support/tests/datafilter.js
+++ b/packages/ckeditor5-html-support/tests/datafilter.js
@@ -308,13 +308,17 @@ describe( 'DataFilter', () => {
 
 			expect( getObjectModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
 				data: '<paragraph>' +
-				'<htmlInput htmlContent=""></htmlInput>' +
+				'<htmlInput htmlAttributes="(1)" htmlContent=""></htmlInput>' +
 				'<htmlInput htmlContent=""></htmlInput>' +
 				'</paragraph>',
-				attributes: {}
+				attributes: {
+					1: {
+						classes: [ 'foo' ]
+					}
+				}
 			} );
 
-			expect( editor.getData() ).to.equal( '<p><input><input></p>' );
+			expect( editor.getData() ).to.equal( '<p><input class="foo"><input></p>' );
 		} );
 
 		it( 'should apply attributes to correct editing element', () => {
@@ -624,13 +628,17 @@ describe( 'DataFilter', () => {
 			);
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<htmlSection><paragraph>foo</paragraph></htmlSection>' +
+				data: '<htmlSection htmlAttributes="(1)"><paragraph>foo</paragraph></htmlSection>' +
 					'<htmlSection><paragraph>bar</paragraph></htmlSection>',
-				attributes: {}
+				attributes: {
+					1: {
+						classes: [ 'foo' ]
+					}
+				}
 			} );
 
 			expect( editor.getData() ).to.equal(
-				'<section><p>foo</p></section>' +
+				'<section class="foo"><p>foo</p></section>' +
 				'<section><p>bar</p></section>'
 			);
 		} );
@@ -962,14 +970,16 @@ describe( 'DataFilter', () => {
 			);
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph><$text htmlCite="(1)">foobar</$text></paragraph>',
+				data: '<paragraph><$text htmlCite="(1)">foo</$text><$text htmlCite="(2)">bar</$text></paragraph>',
 				attributes: {
-					1: {},
+					1: {
+						classes: [ 'foo' ]
+					},
 					2: {}
 				}
 			} );
 
-			expect( editor.getData() ).to.equal( '<p><cite>foobar</cite></p>' );
+			expect( editor.getData() ).to.equal( '<p><cite class="foo">foo</cite><cite>bar</cite></p>' );
 		} );
 
 		it( 'should not consume attribute already consumed (upcast)', () => {
@@ -1265,11 +1275,41 @@ describe( 'DataFilter', () => {
 			editor.setData( '<p class="foo bar">foo</p><p class="bar">bar</p>' );
 
 			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
-				data: '<paragraph>foo</paragraph><paragraph>bar</paragraph>',
-				attributes: {}
+				data: '<paragraph htmlAttributes="(1)">foo</paragraph><paragraph>bar</paragraph>',
+				attributes: {
+					1: {
+						classes: [ 'foo' ]
+					}
+				}
 			} );
 
-			expect( editor.getData() ).to.equal( '<p>foo</p><p>bar</p>' );
+			expect( editor.getData() ).to.equal( '<p class="foo">foo</p><p>bar</p>' );
+		} );
+
+		it( 'should preserve partially consumed attributes by other features', () => {
+			editor.conversion.for( 'upcast' ).add( dispatcher => {
+				dispatcher.on( 'element:span', ( evt, data, conversionApi ) => {
+					conversionApi.consumable.consume( data.viewItem, { attributes: [ 'data-foo' ] } );
+				} );
+			} );
+
+			dataFilter.allowElement( 'span' );
+			dataFilter.allowAttributes( { name: 'span', attributes: true } );
+
+			editor.setData( '<p><span data-foo data-bar>foobar</span></p>' );
+
+			expect( getModelDataWithAttributes( model, { withoutSelection: true } ) ).to.deep.equal( {
+				data: '<paragraph><$text htmlSpan="(1)">foobar</$text></paragraph>',
+				attributes: {
+					1: {
+						attributes: {
+							'data-bar': ''
+						}
+					}
+				}
+			} );
+
+			expect( editor.getData() ).to.equal( '<p><span data-bar="">foobar</span></p>' );
 		} );
 	} );
 
@@ -1886,7 +1926,7 @@ describe( 'DataFilter', () => {
 			const allowedConfig = [
 				{
 					name: 'span',
-					attributes: true,
+					attributes: /^data-.*$/,
 					// Allow it to really verify that the disallowing works.
 					classes: [ 'foo', 'bar', 'test' ]
 				}

From ef7156b645bb696632114c1f66a09591c3eac52f Mon Sep 17 00:00:00 2001
From: Jacek Bogdanski <jacekbogd@gmail.com>
Date: Mon, 28 Jun 2021 12:20:39 +0200
Subject: [PATCH 213/217] Args renaming.

---
 .../src/conversionutils.js                       | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/packages/ckeditor5-html-support/src/conversionutils.js b/packages/ckeditor5-html-support/src/conversionutils.js
index b844a2e613e..53245972e42 100644
--- a/packages/ckeditor5-html-support/src/conversionutils.js
+++ b/packages/ckeditor5-html-support/src/conversionutils.js
@@ -35,22 +35,22 @@ export function setViewAttributes( writer, viewAttributes, viewElement ) {
 /**
 * Merges view element attribute objects.
 *
-* @param {Object} oldValue
-* @param {Object} newValue
+* @param {Object} target
+* @param {Object} source
 * @returns {Object}
 */
-export function mergeViewElementAttributes( oldValue, newValue ) {
-	const result = cloneDeep( oldValue );
+export function mergeViewElementAttributes( target, source ) {
+	const result = cloneDeep( target );
 
-	for ( const key in newValue ) {
+	for ( const key in source ) {
 		// Merge classes.
-		if ( Array.isArray( newValue[ key ] ) ) {
-			result[ key ] = Array.from( new Set( [ ...oldValue[ key ], ...newValue[ key ] ] ) );
+		if ( Array.isArray( source[ key ] ) ) {
+			result[ key ] = Array.from( new Set( [ ...target[ key ], ...source[ key ] ] ) );
 		}
 
 		// Merge attributes or styles.
 		else {
-			result[ key ] = { ...oldValue[ key ], ...newValue[ key ] };
+			result[ key ] = { ...target[ key ], ...source[ key ] };
 		}
 	}
 

From f1d1ded18b3cc480a521770c5be0caadc851a310 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jacek=20Bogda=C5=84ski?= <jacekbogd@gmail.com>
Date: Mon, 28 Jun 2021 12:24:41 +0200
Subject: [PATCH 214/217] Apply suggestions from code review
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Maksymilian Barnaś <maxbarnas@users.noreply.github.com>
---
 .../docs/features/general-html-support.md                     | 2 +-
 packages/ckeditor5-html-support/src/datafilter.js             | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-html-support/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
index ce4970fefdf..f2937177496 100644
--- a/packages/ckeditor5-html-support/docs/features/general-html-support.md
+++ b/packages/ckeditor5-html-support/docs/features/general-html-support.md
@@ -17,7 +17,7 @@ Some examples of HTML features that can be easily enabled using General HTML Sup
 	* `data-*` and `id` attributes on e.g. `<p>` and `<h1-h6>`,
 	* `style` and `classes` on e.g. `<strong>` and `<a>`.
 
-The enabled HTML features can be loaded (e.g. via `editor.setData()`), pasted, output (e.g. via `editor.getData()`), and are visible in the editing area. Such content can also be edited in the editor, although, to a limited extend. Read more about it in the [Level of support](#level-of-support) section.
+The enabled HTML features can be loaded (e.g. via `editor.setData()`), pasted, output (e.g. via `editor.getData()`), and are visible in the editing area. Such content can also be edited in the editor, although, to a limited extent. Read more about it in the [Level of support](#level-of-support) section.
 
 <info-box>
 	The General HTML Support feature is **experimental and not yet production-ready**.
diff --git a/packages/ckeditor5-html-support/src/datafilter.js b/packages/ckeditor5-html-support/src/datafilter.js
index b3f84bba4c9..90dc2d5fc01 100644
--- a/packages/ckeditor5-html-support/src/datafilter.js
+++ b/packages/ckeditor5-html-support/src/datafilter.js
@@ -199,7 +199,7 @@ export default class DataFilter extends Plugin {
 	 */
 	_loadConfig( config, handleAttributes ) {
 		for ( const pattern of config ) {
-			// MatcherPattern allows omitting `name` to not narrow searches to specific elements.
+			// MatcherPattern allows omitting `name` to widen the search of elements.
 			// Let's keep it consistent and match every element if a `name` has not been provided.
 			const elementName = pattern.name || /[\s\S]+/;
 
@@ -566,7 +566,7 @@ function iterableToObject( iterable, getValue ) {
 	return attributesObject;
 }
 
-// Matcher by default has to match **all** patterns to count it as an actual match. By splitting the pattern
+// Matcher by default has to match **all** patterns to count it as an actual match. Splitting the pattern
 // into separate patterns means that any matched pattern will be count as a match.
 //
 // @private

From 8cfeafea852fcfdbf1be4f69fb40c5bc15226fbd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jacek=20Bogda=C5=84ski?= <jacekbogd@gmail.com>
Date: Mon, 28 Jun 2021 12:26:03 +0200
Subject: [PATCH 215/217] Updated docs.
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Maksymilian Barnaś <maxbarnas@users.noreply.github.com>
---
 .../docs/features/general-html-support.md                       | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-html-support/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
index f2937177496..bb2169502e0 100644
--- a/packages/ckeditor5-html-support/docs/features/general-html-support.md
+++ b/packages/ckeditor5-html-support/docs/features/general-html-support.md
@@ -181,7 +181,7 @@ htmlSupport: {
 }
 ```
 
-The General HTML Support feature distinguishes several content types that it treats a bit differently:
+The General HTML Support feature distinguishes several content types, each treated a bit differently:
 
 * Container elements (e.g. `<section>`, `<div>`).
 * Inline elements (e.g. `<span>`, `<a>`).

From eb0283fb61b0d10784dddd00949c0a441f60f740 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maksymilian=20Barna=C5=9B?=
 <maxbarnas@users.noreply.github.com>
Date: Mon, 28 Jun 2021 12:57:01 +0200
Subject: [PATCH 216/217] Update
 packages/ckeditor5-html-support/src/datafilter.js

---
 packages/ckeditor5-html-support/src/datafilter.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-html-support/src/datafilter.js b/packages/ckeditor5-html-support/src/datafilter.js
index 72e276a6f7f..df7a178f6ac 100644
--- a/packages/ckeditor5-html-support/src/datafilter.js
+++ b/packages/ckeditor5-html-support/src/datafilter.js
@@ -523,7 +523,7 @@ function consumeAttributeMatches( viewElement, { consumable }, matcher ) {
 	return consumedMatches;
 }
 
-// Removes attributes from the given match that where already consumed by other converters.
+// Removes attributes from the given match that were already consumed by other converters.
 //
 // @private
 // @param {module:engine/view/element~Element} viewElement

From 5932b3c428ec45766df09c910de52c37f27d5293 Mon Sep 17 00:00:00 2001
From: Mgsy <kacpertomporowski@gmail.com>
Date: Mon, 28 Jun 2021 13:11:31 +0200
Subject: [PATCH 217/217] Docs: Updated GHS feature guide.

---
 .../docs/features/general-html-support.md     | 29 ++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-html-support/docs/features/general-html-support.md b/packages/ckeditor5-html-support/docs/features/general-html-support.md
index bb2169502e0..a3a30e0c48a 100644
--- a/packages/ckeditor5-html-support/docs/features/general-html-support.md
+++ b/packages/ckeditor5-html-support/docs/features/general-html-support.md
@@ -83,7 +83,7 @@ The difference between specific CKEditor 5 features such as {@link features/basi
 
 For instance, the dedicated {@link features/basic-styles#available-text-styles bold} feature offers a toolbar button used to make the selected text bold. Together with the {@link features/autoformat autoformatting feature}, it also allows for applying bold style to content by typing a Markdown shortcode (`**foo**`) in the editor. The {@link features/headings headings} feature offers a dropdown from which the user can choose a heading level and ensures that pressing <kbd>Enter</kbd> at the end of a heading creates a new paragraph (and not another heading).
 
-The General HTML Support does not offer any UI for the enabled features and takes only the basic semantics of a given feature into account. If you enable support for `<div>`s via GHS, the user will not be able to create `<div>`s from the editor UI. The GHS will know that a `<div>` is a container element, so it can wrap other blocks (like paragraphs) but cannot be used inline (next to e.g. a `<strong>` element). There is no more, however.
+The General HTML Support does not offer any UI for the enabled features and takes only the basic semantics of a given feature into account. If you enable support for `<div>`s via GHS, the user will not be able to create `<div>`s from the editor UI. The GHS will know that a `<div>` is a container element, so it can wrap other blocks (like paragraphs) but cannot be used inline (next to e.g. a `<strong>` element).
 
 Therefore, GHS's main use cases would be:
 
@@ -94,6 +94,31 @@ Therefore, GHS's main use cases would be:
 	Taken the nature of GHS, you may consider installing the {@link features/source-editing source editing} feature alongside with it.
 </info-box>
 
+## Installation
+
+To add this feature to your rich-text editor, install the [`@ckeditor/ckeditor5-html-support`](https://www.npmjs.com/package/@ckeditor/ckeditor5-html-support) package:
+
+```plaintext
+npm install --save @ckeditor/ckeditor5-html-support
+```
+
+And add it to your plugin list configuration:
+
+```js
+import GeneralHtmlSupport from '@ckeditor/ckeditor5-html-support/src/generalhtmlsupport';
+
+ClassicEditor
+	.create( document.querySelector( '#editor' ), {
+		plugins: [ GeneralHtmlSupport, ... ],
+	} )
+	.then( ... )
+	.catch( ... );
+```
+
+<info-box info>
+	Read more about {@link builds/guides/integration/installing-plugins installing plugins}.
+</info-box>
+
 ## Configuration
 
 By default, enabling the {@link module:html-support/generalhtmlsupport~GeneralHtmlSupport} plugin does not enable support for any given element. The elements the user wants to be supported, need to be configured via the {@link module:core/editor/editorconfig~EditorConfig#htmlSupport `config.htmlSupport`} option:
@@ -200,6 +225,8 @@ Most of the existing CKEditor 5 features can already be extended this way, howev
 * Some of the media embed features' markup [#9918](https://github.com/ckeditor/ckeditor5/issues/9918).
 * The `<ul>` and `<ol>` elements of the list feature [#9917](https://github.com/ckeditor/ckeditor5/issues/9917).
 
+We're open for feedback, so if you find any issue, feel free to report it in the [main CKEditor 5 repository](https://github.com/ckeditor/ckeditor5/issues/).
+
 ## Related features
 
 There are other HTML editing related CKEditor 5 features you may want to check: