Add setHTMLUnsafe() and parseHTMLUnsafe()

These are modern HTML-parsing methods, replacing the innerHTML setter and (new DOMParser()).parseFromString(). See https://github.com/otherdaniel/purification/blob/explainer-examples/explainer.md#proposed-api for more background. The "unsafe" part of their names comes from the fact that safe versions, which sanitize by default, will be introduced in the future.

Notable differences from the older versions include support for declarative shadow roots (whatwg#5465) by default, no mode-switching between XML and HTML, and (for parseHTMLUnsafe()) no inheritance from the outer document.

Author: josepharhar

source

@@ -10609,6 +10609,8 @@ typedef (<span>HTMLScriptElement</span> or <span>SVGScriptElement</span>) <dfn t
 
 [<span>LegacyOverrideBuiltIns</span>]
 partial interface <dfn id="document" data-lt="">Document</dfn> {
+  static <code>Document</code> <span data-x="dom-parseHTMLUnsafe">parseHTMLUnsafe</span>(DOMString html);
+
   // <span>resource metadata management</span>
   [PutForwards=<span data-x="dom-location-href">href</span>, <span>LegacyUnforgeable</span>] readonly attribute <span>Location</span>? <span data-x="dom-document-location">location</span>;
   attribute USVString <span data-x="dom-document-domain">domain</span>;
@@ -109471,6 +109473,8 @@ document.body.appendChild(frame)</code></pre>
        also live here? -->
   <h3 id="dom-parsing-and-serialization">DOM parsing</h3>
 
+  <h4>The <code>DOMParser</code> interface</h4>
+
   <p>The <code>DOMParser</code> interface allows authors to create new <code>Document</code> objects
   by parsing strings, as either HTML or XML.</p>
 
@@ -109491,17 +109495,19 @@ document.body.appendChild(frame)</code></pre>
 
     <p>Note that <code>script</code> elements are not evaluated during parsing, and the resulting
     document's <span data-x="document's character encoding">encoding</span> will always be
-    <span>UTF-8</span>.</p>
+    <span>UTF-8</span>. The document's <span data-x="concept-document-url">URL</span> will be
+    inherited from <var>parser</var>'s <span>relevant global object</span>.</p>
 
     <p>Values other than the above for <var>type</var> will cause a <code>TypeError</code> exception
     to be thrown.</p>
    </dd>
   </dl>
 
   <p class="note">The design of <code>DOMParser</code>, as a class that needs to be constructed and
-  then have its <code data-x="dom-DOMParser-parseFromString">parseFromString()</code> method called,
-  is an unfortunate historical artifact. If we were designing this functionality today it would be a
-  standalone function.</p>
+  then have its <code data-x="dom-DOMParser-parseFromString">parseFromString()</code> method
+  called, is an unfortunate historical artifact. If we were designing this functionality today it
+  would be a standalone function. For parsing HTML, the modern alternative is <code
+  data-x="dom-parseHTMLUnsafe">Document.parseHTMLUnsafe()</code>.</p>
 
   <pre><code class="idl">[Exposed=Window]
 interface <dfn interface>DOMParser</dfn> {
@@ -109531,7 +109537,7 @@ enum <dfn enum>DOMParserSupportedType</dfn> {
    <li>
     <p>Let <var>document</var> be a new <code>Document</code>, whose <span
     data-x="concept-document-content-type">content type</span> is <var>type</var> and <span
-    data-x="concept-document-URL">url</span> is this's <span>relevant global object</span>'s <span
+    data-x="concept-document-URL">URL</span> is this's <span>relevant global object</span>'s <span
     data-x="concept-document-window">associated <code>Document</code></span>'s <span
     data-x="concept-document-URL">URL</span>.</p>
     <!-- When https://github.com/whatwg/html/issues/4792 gets fixed we need to investigate which of
@@ -109552,23 +109558,8 @@ enum <dfn enum>DOMParserSupportedType</dfn> {
      data-x="dom-DOMParserSupportedType-texthtml"><code>text/html</code>"</dfn></dt>
      <dd>
       <ol>
-       <li><p>Set <var>document</var>'s <span data-x="concept-document-type">type</span> to "<code
-       data-x="">html</code>".</p></li>
-
-       <li><p>Create an <span>HTML parser</span> <var>parser</var>, associated with
-       <var>document</var>.</p></li>
-
-       <li><p>Place <var>string</var> into the <span>input stream</span> for <var>parser</var>. The
-       encoding <span data-x="concept-encoding-confidence">confidence</span> is
-       <i>irrelevant</i>.</p></li>
-
-       <li>
-        <p>Start <var>parser</var> and let it run until it has consumed all the characters just
-        inserted into the input stream.</p>
-
-        <p class="note">This might mutate the document's <span
-        data-x="concept-document-mode">mode</span>.</p>
-       </li>
+       <li><p><span>Parse HTML from a string</span> given <var>document</var> and
+       <var>string</var>.</p></li>
       </ol>
 
       <p class="note">Since <var>document</var> does not have a <span
@@ -109610,6 +109601,135 @@ enum <dfn enum>DOMParserSupportedType</dfn> {
    <li><p>Return <var>document</var>.</p>
   </ol>
 
+  <p>To <dfn>parse HTML from a string</dfn>, given a <var>document</var> <code>Document</code> and a
+  <span>string</span> <var>html</var>:</p>
+
+  <ol>
+   <li><p>Set <var>document</var>'s <span data-x="concept-document-type">type</span> to "<code
+   data-x="">html</code>".</p></li>
+
+   <li><p>Create an <span>HTML parser</span> <var>parser</var>, associated with
+   <var>document</var>.</p></li>
+
+   <li><p>Place <var>html</var> into the <span>input stream</span> for <var>parser</var>. The
+   encoding <span data-x="concept-encoding-confidence">confidence</span> is
+   <i>irrelevant</i>.</p></li>
+
+   <li>
+    <p>Start <var>parser</var> and let it run until it has consumed all the characters just
+    inserted into the input stream.</p>
+
+    <p class="note">This might mutate the document's <span
+    data-x="concept-document-mode">mode</span>.</p>
+   </li>
+  </ol>
+
+  </div>
+
+  <h4>Unsafe HTML parsing methods</h4>
+
+  <dl class="domintro">
+   <dt><code data-x=""><var>element</var>.<span subdfn
+   data-x="dom-Element-setHTMLUnsafe">setHTMLUnsafe</span>(<var>html</var>)</code></dt>
+
+   <dd>
+    <p>Parses <var>html</var> using the HTML parser, and replaces the children of <var>element</var>
+    with the result. <var>element</var> provides context for the HTML parser.</p>
+   </dd>
+
+   <dt><code data-x=""><var>shadowRoot</var>.<span subdfn
+   data-x="dom-ShadowRoot-setHTMLUnsafe">setHTMLUnsafe</span>(<var>html</var>)</code></dt>
+
+   <dd>
+    <p>Parses <var>html</var> using the HTML parser, and replaces the children of
+    <var>shadowRoot</var> with the result. <var>shadowRoot</var>'s <span
+    data-x="concept-DocumentFragment-host">host</span> provides context for the HTML parser.</p>
+   </dd>
+
+   <dt><code data-x=""><var>doc</var> = Document.<span
+   data-x="dom-parseHTMLUnsafe">parseHTMLUnsafe</span>(<var>html</var>)</code></dt>
+
+   <dd>
+    <p>Parses <var>html</var> using the HTML parser, and returns the resulting
+    <code>Document</code>.</p>
+
+    <p>Note that <code>script</code> elements are not evaluated during parsing, and the resulting
+    document's <span data-x="document's character encoding">encoding</span> will always be
+    <span>UTF-8</span>. The document's <span data-x="concept-document-url">URL</span> will be
+    <code>about:blank</code>.</p>
+   </dd>
+  </dl>
+
+  <p class="warning">These methods perform no sanitization to remove potentially-dangerous elements
+  and attributes like <code>script</code> or <span>event handler content attributes</span>.</p>
+
+  <pre><code class="idl">partial interface <span id="Element-partial">Element</span> {
+  undefined <span data-x="dom-Element-setHTMLUnsafe">setHTMLUnsafe</span>(DOMString html);
+};
+
+partial interface <span id="ShadowRoot-partial">ShadowRoot</span> {
+  undefined <span data-x="dom-ShadowRoot-setHTMLUnsafe">setHTMLUnsafe</span>(DOMString html);
+};</code></pre>
+
+  <div w-nodev>
+
+  <p><code>Element</code>'s <dfn method for="Element"><code
+  data-x="dom-Element-setHTMLUnsafe">setHTMLUnsafe(<var>html</var>)</code></dfn> method steps
+  are:</p>
+
+  <ol>
+   <li><p>Let <var>target</var> be <span>this</span>'s <span>template contents</span> if
+   <span>this</span> is a <code>template</code> element; otherwise <span>this</span>.</p></li>
+
+   <li><p><span>Unsafely set HTML</span> given <var>target</var>, <span>this</span>, and
+   <var>html</var>.</p></li>
+  </ol>
+
+  <p><code>ShadowRoot</code>'s <dfn method for="ShadowRoot"><code
+  data-x="dom-ShadowRoot-setHTMLUnsafe">setHTMLUnsafe(<var>html</var>)</code></dfn> method steps
+  are to <span>unsafely set HTML</span> given <span>this</span>, <span>this</span>'s <span
+  data-x="concept-DocumentFragment-host">shadow host</span>, and <var>html</var>.</p>
+
+  <p>To <dfn>unsafely set HTML</dfn>, given an <code>Element</code> or <code>DocumentFragment</code>
+  <var>target</var>, an <code>Element</code> <var>contextElement</var>, and a <span>string</span>
+  <var>html</var>:</p>
+
+  <ol>
+   <li><p>Let <var>newChildren</var> be the result of the <span>HTML fragment parsing algorithm</span>
+   given <var>contextElement</var> and <var>html</var>.</p></li>
+
+   <li><p>Let <var>fragment</var> be a new <code>DocumentFragment</code> whose <span>node
+   document</span> is <var>contextElement</var>'s <span>node document</span>.</p></li>
+
+   <li><p>For each <var>node</var> in <var>newChildren</var>, <span
+   data-x="concept-node-append">append</span> <var>node</var> to <var>fragment</var>.</p></li>
+
+   <li><p><span data-x="concept-node-replace-all">Replace all</span> with <var>fragment</var> within
+   <var>target</var>.</p></li>
+  </ol>
+
+  <hr>
+
+  <p>The static <dfn method for="Document"><code
+  data-x="dom-parseHTMLUnsafe">parseHTMLUnsafe(<var>html</var>)</code></dfn> method steps are:</p>
+
+  <ol>
+   <li>
+    <p>Let <var>document</var> be a new <code>Document</code>, whose <span
+    data-x="concept-document-content-type">content type</span> is "<code
+    data-x="">text/html</code>".</p>
+
+    <p class="note">Since <var>document</var> does not have a <span
+    data-x="concept-document-bc">browsing context</span>, <span data-x="concept-n-script">scripting
+    is disabled</span>.</p>
+   </li>
+
+   <li><p><span>Parse HTML from a string</span> given <var>document</var> and
+   <var>html</var>.</p></li>
+
+   <li><p>Return <var>document</var>.</p></li>
+  </ol>
+
   </div>