Add shadowRoot to ElementInternals

Closes WICG/webcomponents#871.

Author: mfreed7

source

@@ -2917,7 +2917,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
      <li><dfn data-x-href="https://dom.spec.whatwg.org/#concept-node-document">node document</dfn> concept</li>
      <li><dfn data-x="concept-document-type" data-x-href="https://dom.spec.whatwg.org/#concept-document-type">document type</dfn> concept</li>
      <li><dfn data-x="concept-DocumentFragment-host" data-x-href="https://dom.spec.whatwg.org/#concept-documentfragment-host">host</dfn> concept</li>
-     <li>The <dfn data-x-href="https://dom.spec.whatwg.org/#concept-shadow-root">shadow root</dfn> concept, and its <dfn data-x-href="https://dom.spec.whatwg.org/#shadowroot-delegates-focus">delegates focus</dfn></li>
+     <li>The <dfn data-x-href="https://dom.spec.whatwg.org/#concept-shadow-root">shadow root</dfn> concept, and its <dfn data-x-href="https://dom.spec.whatwg.org/#shadowroot-delegates-focus">delegates focus</dfn> and <dfn data-x-href="https://dom.spec.whatwg.org/#shadowroot-available-to-element-internals">available to element internals</dfn>.</li>
      <li>The <dfn data-x-href="https://dom.spec.whatwg.org/#element-shadow-host">shadow host</dfn> concept</li>
      <li><dfn data-x-href="https://dom.spec.whatwg.org/#interface-htmlcollection"><code>HTMLCollection</code></dfn> interface, its
          <dfn data-x="dom-HTMLCollection-length" data-x-href="https://dom.spec.whatwg.org/#dom-htmlcollection-length"><code>length</code></dfn> attribute, and its
@@ -67310,6 +67310,8 @@ interface <dfn>ElementInternals</dfn> {
   boolean <span data-x="dom-ElementInternals-reportValidity">reportValidity</span>();
 
   readonly attribute <span>NodeList</span> <span data-x="dom-ElementInternals-labels">labels</span>;
+
+  readonly attribute <code>ShadowRoot</code>? <span data-x="dom-ElementInternals-shadowRoot">shadowRoot</span>;
 };
 
 ElementInternals includes <span>ARIAMixin</span>;
@@ -67409,6 +67411,12 @@ dictionary <dfn>ValidityStateFlags</dfn> {
    <var>internals</var>'s <span data-x="internals-target">target element</span>, which will be used
    unless the page author overrides them using the <code data-x="attr-aria-*">aria-*</code>
    attributes.</p></dd>
+
+   <dt><var>internals</var> . <code data-x="dom-ElementInternals-shadowRoot">shadowRoot</code></dt>
+   <dd><p>Returns the <code>ShadowRoot</code> for <var>internals</var>'s
+   <span data-x="internals-target">target element</span>, if the
+   <span data-x="internals-target">target element</span> is a <span>shadow host</span>, or null
+   otherwise.</p></dd>
   </dl>
 
   <p>Each <code>ElementInternals</code> has a <dfn data-x="internals-target">target element</dfn>,
@@ -67453,6 +67461,23 @@ dictionary <dfn>ValidityStateFlags</dfn> {
    <span data-x="internals-target">targeting</span> <var>element</var>, and return it.</p></li>
   </ol>
 
+  <p>The <dfn><code data-x="dom-ElementInternals-shadowRoot">shadowRoot</code></dfn> getter steps are:
+
+  <ol>
+   <li><p>Let <var>target</var> be <code>ElementInternals</code>'s <span
+   data-x="internals-target">target element</span>.</p></li>
+
+   <li><p>If <var>target</var> is not a <span>shadow host</span>, then return null.</p></li>
+
+   <li><p>Let <var>shadow</var> be <var>target</var>'s
+   <span data-x="concept-element-shadow-root">shadow root</span>.</p></li>
+
+   <li><p>If <var>shadow</var>'s <span>available to element internals</span> is false, then return
+   null.</p></li>
+
+   <li><p>Return <var>shadow</var>.</p></li>
+  </ol>
+
   <hr>
 
   <p>Each <span>form-associated custom element</span> has <dfn