Add logic for reflecting IDREF (single) attributes.

source

@@ -7309,8 +7309,62 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
   return a <code>DOMTokenList</code> object whose associated element is the element in question and
   whose associated attribute's local name is the name of the attribute in question.</p>
 
-  </div>
+  <p>If a reflecting IDL attribute has the type <code>HTMLElement</code>,
+  or an interface that descends from <code>HTMLElement</code>,
+  then it must be paired with another reflecting IDL attribute
+  that has the type <code data-x="idl-DOMString">DOMString</code>.
+  The relationship between these two attributes is as follows:</p>
+
+  <ol>
+    <li>The attribute which has the type <code>HTMLElement</code>
+      should be named <code data-x=""><var>attr</var>Element</code>,
+      where the paired <code data-x="idl-DOMString">DOMString</code> attribute is named
+      <code data-x=""><var>attr</var></code>.</li>
 
+    <li>On getting the <code data-x=""><var>attr</var></code> attribute,
+      the IDL attribute must return the value of the content attribute as normal.</li>
+
+    <li>On getting the <code data-x=""><var>attr</var>Element</code> attribute,
+      it must run the following algorithm
+      (stopping at the first point where a value is returned):</li>
+    <ol>
+      <li>If the content attribute corresponding to <code data-x=""><var>attr</var></code>
+        is absent, then the IDL attribute <code data-x=""><var>attr</var>Element</code> must return null.</li>
+
+      <li>Let <var>candidate</var> be the element that the
+        <code data-x="dom-Document-getElementById">document.getElementById()</code> method
+        would find when called on the content attribute's element's <span>node document</span>
+        if it were passed as its argument the current value
+        of the corresponding content attribute.</li>
+
+      <li>If <var>candidate</var> is null, or if it is not type-compatible with the IDL attribute,
+        then the IDL attribute must return null.</li>
+
+      <li>Otherwise, it must return <var>candidate</var>.</li>
+    </ol>
+    <li>On setting the <code data-x=""><var>attr</var></code> attribute,
+      the content attribute must be set to the specified value.</li>
+
+    <li>On setting the <code data-x=""><var>attr</var>Element</code> attribute,
+        it must run the following algorithm:</li>
+    <ol>
+      <li>Let <var>id</var> be the empty string.</li>
+      <li>If the given element has an <code data-x="attr-id">id</code> attribute,
+        and has the same <span>tree</span> as the element of the attribute being set,
+        and the given element is the first element in that <span>tree</span>
+        whose <span data-x="concept-ID">ID</span> is the value
+        of that <code data-x="attr-id">id</code> attribute,
+        then let <var>id</var> be the value of that <code data-x="attr-id">id</code> attribute.
+      <li>Set the <code data-x=""><var>attr</var></code> content attribute to <var>id</var>.
+    </ol>
+  </ol>
+
+  <p>If a reflecting IDL attribute has the type <code data-x="">sequence&lt;Element&gt;</code>,
+  or <code data-x="">sequence&lt;<var>T</var>&gt;</code> where T descends from <code>Element</code>...</p>
+
+  <p>TODO</p>
+
+  </div>
 
   <h4>Collections</h4>