Shadow: add shadow root

This is basically the introduction of ShadowRoot objects as a node in
the DOM Standard. The plan is to port over the features over time,
while trying to make sure the new features and terminology remain
consistent and coherent with the rest of the standard.

I’ll try to prefix ShadowRoot-object-related commits with “Shadow”.

dom.bs

@@ -83,9 +83,6 @@ urlPrefix: https://html.spec.whatwg.org/multipage/
             text: Unicode serialization of an origin; url: #unicode-serialisation-of-an-origin
         urlPrefix: infrastructure.html
             text: in parallel
-urlPrefix: https://w3c.github.io/webcomponents/spec/shadow/
-	type: dfn; urlPrefix: #dfn-
-		text: shadow root
 url: https://w3c.github.io/DOM-Parsing/#widl-Range-createContextualFragment-DocumentFragment-DOMString-fragment
     type: method; text: createContextualFragment(); for: Range;
 type: interface
@@ -95,8 +92,6 @@ type: interface
         text: UIEvent
     url: https://www.w3.org/TR/touch-events/#touchevent-interface
         text: TouchEvent
-    url: https://w3c.github.io/webcomponents/spec/shadow/#the-shadowroot-interface
-        text: ShadowRoot
 urlPrefix: https://slightlyoff.github.io/ServiceWorker/spec/service_worker/#
     type: interface; text: ServiceWorkerGlobalScope; url: service-worker-global-scope-interface
     type: dfn; urlPrefix: dfn-
@@ -1381,13 +1376,9 @@ can be used to explore this matter in more detail.
 
 <h3 id=node-trees>Node tree</h3>
 
-Objects implementing the {{Document}},
-{{DocumentFragment}}, {{DocumentType}},
-{{Element}}, {{Text}}, {{ProcessingInstruction}},
-or {{Comment}} interface (simply called
-<dfn export id=concept-node>nodes</dfn>)
-<a>participate</a> in a
-<a>tree</a>, simply named the
+<p>{{Document}}, {{DocumentType}}, {{DocumentFragment}}, {{ShadowRoot}}, {{Element}}, {{Text}},
+{{ProcessingInstruction}}, and {{Comment}} objects (simply called
+<dfn export id=concept-node>nodes</dfn>) <a>participate</a> in a <a>tree</a>, simply named the
 <dfn export id=concept-node-tree>node tree</dfn>.
 
 A <a>node tree</a> is constrained as
@@ -1409,6 +1400,7 @@ follows, expressed as a relationship between the type of
    {{ProcessingInstruction}} or {{Comment}}.
   </ol>
  <dt>{{DocumentFragment}}
+ <dt>{{ShadowRoot}}
  <dt>{{Element}}
  <dd>Zero or more nodes each of which is one of {{Element}},
  {{ProcessingInstruction}}, {{Comment}}, or
@@ -3005,9 +2997,9 @@ interface Node : EventTarget {
 };
 </pre>
 
-<p class="note no-backref">{{Node}} is an abstract interface and does not exist as
-<a>node</a>. It is used by all <a>nodes</a>
-({{Document}}, {{DocumentFragment}}, {{DocumentType}}, {{Element}}, {{Text}}, {{ProcessingInstruction}}, and {{Comment}}).
+<p class="note no-backref">{{Node}} is an abstract interface and does not exist as <a>node</a>. It
+is used by all <a>nodes</a> ({{Document}}, {{DocumentType}}, {{DocumentFragment}}, {{ShadowRoot}},
+{{Element}}, {{Text}}, {{ProcessingInstruction}}, and {{Comment}}).
 
 Each <a>node</a> has an associated
 <dfn export for=Node id=concept-node-document>node document</dfn>, set upon creation,
@@ -3052,8 +3044,7 @@ that is a <a>document</a>.
    <a>doctype</a>.
 
    <dt><code>{{Node}} . {{Node/DOCUMENT_FRAGMENT_NODE}}</code> (11)
-   <dd><var>node</var> is a {{DocumentFragment}}
-   <a>node</a>.
+   <dd><var>node</var> is a {{DocumentFragment}} or {{ShadowRoot}} <a>node</a>.
   </dl>
 
  <dt><code><var>node</var> . {{Node/nodeName}}</code>
@@ -3081,6 +3072,7 @@ that is a <a>document</a>.
    <dd>Its <a for=DocumentType>name</a>.
 
    <dt>{{DocumentFragment}}
+   <dt>{{ShadowRoot}}
    <dd>"<code>#document-fragment</code>".
   </dl>
 </dl>
@@ -3117,6 +3109,7 @@ the first matching statement, switching on the <a>context object</a>:
  <dd><dfn const for=Node>DOCUMENT_TYPE_NODE</dfn> (10);
 
  <dt>{{DocumentFragment}}
+ <dt>{{ShadowRoot}}
  <dd><dfn const for=Node>DOCUMENT_FRAGMENT_NODE</dfn> (11).
 </dl>
 
@@ -3177,6 +3170,7 @@ the first matching statement, switching on the <a>context object</a>:
  <dd>Its <a for=DocumentType>name</a>.
 
  <dt>{{DocumentFragment}}
+ <dt>{{ShadowRoot}}
  <dd>"<code>#document-fragment</code>".
 </dl>
 
@@ -3285,8 +3279,8 @@ must return the following, depending on the <a>context object</a>:
 <dl class=switch>
  <!--AttrExodus <dt>{{Attr}} -->
  <dt>{{Text}}
- <dt>{{Comment}}
  <dt>{{ProcessingInstruction}}
+ <dt>{{Comment}}
  <dd>The <a>context object</a>'s
  <a>data</a>.
 
@@ -3301,8 +3295,8 @@ instead, and then do as described below, depending on the <a>context object</a>:
 <dl class=switch>
  <!--AttrExodus <dt>{{Attr}} -->
  <dt>{{Text}}
- <dt>{{Comment}}
  <dt>{{ProcessingInstruction}}
+ <dt>{{Comment}}
  <dd><a>Replace data</a> with node
  <a>context object</a>, offset 0, count
  {{CharacterData/length}} attribute value, and
@@ -3312,12 +3306,12 @@ instead, and then do as described below, depending on the <a>context object</a>:
  <dd>Do nothing.
 </dl>
 
-The <dfn attribute for=Node>textContent</dfn>
-attribute must return the following, depending on the
-<a>context object</a>:
+<p>The <dfn attribute for=Node><code>textContent</code></dfn> attribute's getter must return the
+following, switching on <a>context object</a>:
 
 <dl class=switch>
  <dt>{{DocumentFragment}}
+ <dt>{{ShadowRoot}}
  <dt>{{Element}}
  <!--AttrExodus <dt>{{Attr}} -->
  <dd>The concatenation of <a>data</a> of all
@@ -3336,12 +3330,12 @@ attribute must return the following, depending on the
  <dd>Null.
 </dl>
 
-The {{Node/textContent}} attribute must,
-on setting, if the new value is null, act as if it was the empty string
-instead, and then do as described below, depending on the <a>context object</a>:
+<p>The {{Node/textContent}} attribute's setter must, if the new value is null, act as if it was the
+empty string instead, and then do as described below, switching on <a>context object</a>:
 
 <dl class=switch>
  <dt>{{DocumentFragment}}
+ <dt>{{ShadowRoot}}
  <dt>{{Element}}
  <!--AttrExodus <dt>{{Attr}} -->
  <dd>
@@ -3847,6 +3841,7 @@ To <dfn export>locate a namespace</dfn> for a <var>node</var> using
 
  <dt>{{DocumentType}}
  <dt>{{DocumentFragment}}
+ <dt>{{ShadowRoot}}
  <dd>Return null.
 
  <dt>Any other node
@@ -3884,6 +3879,7 @@ method must run these steps:
 
    <dt>{{DocumentType}}
    <dt>{{DocumentFragment}}
+   <dt>{{ShadowRoot}}
    <dd>Return null.
 
    <dt>Any other node
@@ -4979,6 +4975,26 @@ invoked, must return a new {{DocumentFragment}} <a>node</a> whose <a>node docume
 global object's associated <a>document</a>.
 
 
+<h3 id=interface-shadowroot>Interface {{ShadowRoot}}</h3>
+
+<pre class=idl>
+[Exposed=Window]
+interface ShadowRoot : DocumentFragment {
+  readonly attribute Element host;
+};
+</pre>
+
+<p>{{ShadowRoot}} <a>nodes</a> are simply known as
+<dfn export id=concept-shadow-root>shadow roots</dfn>.
+
+<p>The <dfn attribute for=ShadowRoot><code>host</code></dfn> attribute's getter must return the
+<a>context object</a>'s <a for=DocumentFragment>host</a>.
+
+<p class="XXX">For now you can find more information about this object in
+<a href="https://w3c.github.io/webcomponents/spec/shadow/">Shadow DOM</a>. The DOM Standard will be
+updated over time to cover more details.
+
+
 <h3 id='interface-element'>Interface {{Element}}</h3>
 
 <pre class=idl>
@@ -5926,10 +5942,8 @@ interface CharacterData : Node {
 };
 </pre>
 
-<p class="note">{{CharacterData}} is an abstract interface and does
-not exist as <a>node</a>. It is used by
-{{Text}}, {{Comment}}, and
-{{ProcessingInstruction}} <a>nodes</a>.
+<p class="note no-backref">{{CharacterData}} is an abstract interface and does not exist as
+<a>node</a>. It is used by {{Text}}, {{ProcessingInstruction}}, and {{Comment}} <a>nodes</a>.
 
 Each <a>node</a> inheriting from the
 {{CharacterData}} interface has an associated mutable string
@@ -9057,13 +9071,15 @@ making this standard what it is today.
 With that, many thanks to
 Adam Klein,
 Adrian Bateman,
+Alex Komoroske,
 Alex Russell,
 Anthony Ramine,
 Arkadiusz Michalski,
 Arnaud Le Hors,
 Arun Ranganathan,
 Björn Höhrmann,
 Boris Zbarsky,
+Brandon Payton,
 Brandon Slade,
 Brandon Wallace,
 Brian Kardell,
@@ -9072,24 +9088,33 @@ Chris Dumez,
 Chris Paris,
 Chris Rebert,
 Daniel Glazman,
+Darin Fisher,
 David Bruant,
 David Flanagan,
 David Håsäther,
+David Hyatt,
+Deepak Sherveghar,
 Dethe Elza,
 Dimitri Glazkov,
 Domenic Denicola,
 Dominic Cooney,
 Dominique Hazaël-Massieux,
 Don Jordan,
 Doug Schepers,
+Edward O'Connor,
+Elisée Maurer
 Elliott Sprehn,
+Eric Bidelman,
 Erik Arvidsson,
 Gavin Nicol,
 Geoffrey Sneddon,
 Giorgio Liscio,
 Glen Huang,
+Glenn Adams,
 Glenn Maynard,
+Hajime Morrita,
 Harald Alvestrand,
+Hayato Ito,
 Henri Sivonen,
 Hunan Rostomyan,
 Ian Hickson,
@@ -9112,8 +9137,10 @@ Jungkee Song,
 Justin Summerlin,
 呂康豪 (Kang-Hao Lu),
 Kevin Sweeney,
+Koji Ishii,
 Lachlan Hunt,
 Lauren Wood,
+Malte Ubl,
 Manish Goregaokar,
 Manish Tripathi,
 Marcos Caceres,
@@ -9124,26 +9151,34 @@ Michael™ Smith,
 Mike Champion,
 Mike Taylor,
 Ojan Vafai,
+Oliver Nightingale,
 Olli Pettay,
 Ondřej Žára,
 Peter Sharpe,
 Philip Jägenstedt,
 Philippe Le Hégaret,
 Rafael Weinstein,
+Richard Bradshaw,
 Rick Byers,
 Rick Waldron,
 Robbert Broersma,
 Robin Berjon,
+Roland Steiner,
 Rune <span title=Fabulous>F.</span> Halvorsen,
+Ruud Steltenpool,
 Ryosuke Niwa,
+Sam Dutton,
 Samuel Giles,
 Sebastian Mayr,
 Seo Sanghyeon,
+Sergey G. Grekhov,
 Shiki Okasaka,
+Shinya Kawanaka,
 Simon Pieters,
 Steve Byrne,
 Stig Halvorsen,
 Tab Atkins,
+Takashi Sakamoto,
 <i>timeless</i>,
 Timo Tijhof,
 Tobie Langel,
@@ -9154,7 +9189,8 @@ Vidur Apparao,
 Warren He,
 Yehuda Katz,
 Yoav Weiss,
-Yoichi Osato, and
+Yoichi Osato,
+Yoshinori Sano, and
 Zack Weinberg
 for being awesome!