Do not apply default namespace if it was declared in an ancestor

package.json

@@ -27,7 +27,7 @@
   "types": "./lib/index.d.ts",
   "dependencies": {
     "@oozcitak/util": "8.3.3",
-    "@oozcitak/dom": "1.15.4",
+    "@oozcitak/dom": "1.15.5",
     "@oozcitak/infra": "1.0.5"
   },
   "devDependencies": {

src/callback/XMLBuilderCBImpl.ts

@@ -384,7 +384,10 @@ export class XMLBuilderCBImpl extends EventEmitter implements XMLBuilderCB {
       this._push(this._writer.openTagBegin(qualifiedName))
     } else {
       let prefix = node.prefix
-      let candidatePrefix = map.get(prefix, ns)
+      let candidatePrefix: string | null = null
+      if (prefix !== null || ns !== localDefaultNamespace) {
+        candidatePrefix = map.get(prefix, ns)
+      }
       if (prefix === "xmlns") {
         if (this._options.wellFormed) {
           this.emit("error", new Error("An element cannot have the 'xmlns' prefix (well-formed required)."))

src/writers/BaseWriter.ts

@@ -392,7 +392,16 @@ export abstract class BaseWriter<T extends BaseWriterOptions, U extends XMLSeria
        * null if no namespace key ns exists in map.
        */
       let prefix = node.prefix
-      let candidatePrefix = map.get(prefix, ns)
+      /**
+       * We don't need to run "retrieving a preferred prefix string" algorithm if
+       * the element has no prefix and its namespace matches to the default
+       * namespace.
+       * See: https://github.com/web-platform-tests/wpt/pull/16703
+       */
+      let candidatePrefix: string | null = null
+      if (prefix !== null || ns !== localDefaultNamespace) {
+        candidatePrefix = map.get(prefix, ns)
+      }
       /** 
        * 12.3. If the value of prefix matches "xmlns", then run the following 
        * steps: 

test/basic/namespace.test.ts

@@ -143,4 +143,16 @@ describe('namespaces', () => {
     expect(() => doc.ele({ 'root@@ns1': {} })).toThrow()
   })
 
+  test('default namespace does not apply if was declared in an ancestor', () => {
+    const doc = $$.create()
+      .ele('root').att('http://www.w3.org/2000/xmlns/', 'xmlns:x', 'uri1')
+        .ele('uri1', 'table').att('http://www.w3.org/2000/xmlns/', 'xmlns', 'uri1')
+      .doc().node as any
+    expect($$.serialize(doc)).toBe(
+      '<root xmlns:x="uri1">' +
+      '<table xmlns="uri1"/>' +
+      '</root>'
+    )
+  })
+
 })