Use empty string for reflection of Element(s) IDL attributes

Using the ID of the element led to surprising results in a number of edge cases.

Tests: web-platform-tests/wpt#36253.

Fixes #8306

source

@@ -7831,23 +7831,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
       </ol>
      </li>
 
-     <li><p>Let <var>id</var> be the empty string.</p></li>
-
-     <li>
-      <p>If the given value:</p>
-
-      <ul class="brief">
-       <li>has the same <span>root</span> as <span>this</span>, and</li>
-       <li>has an <code data-x="attr-id">id</code> attribute, and</li>
-       <li>is the first element in <span>this</span>'s <span>node tree</span> whose <span
-       data-x="concept-ID">ID</span> is the value of that <code data-x="attr-id">id</code>
-       attribute,</li>
-      </ul>
-
-      <p>then set <var>id</var> to the given value's <span data-x="concept-ID">ID</span>.</p>
-     </li>
-
-     <li><p>Set the content attribute's value for <span>this</span> to <var>id</var>.</p></li>
+     <li><p>Set the content attribute's value for <span>this</span> to the empty string.</p></li>
 
      <li><p>Set <span>this</span>'s <span>explicitly set <var>attr</var>-element</span> to a weak
      reference to the given value.</p></li>
@@ -7994,52 +7978,19 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
       </ol>
      </li>
 
-     <li><p>Let <var>value</var> be an empty string.</p></li>
+     <li><p>Set the content attribute's value for <span>this</span> to the empty string.</p></li>
+
+     <li><p>Let <var>elements</var> be an empty <span>list</span>.</p></li>
 
      <li>
       <p><span data-x="list iterate">For each</span> <var>element</var> in the given value:</p>
 
       <ol>
-       <li>
-        <p>If <var>value</var> is empty and <var>elements</var> is non-empty, then:</p>
-
-        <ol>
-         <li><p><span data-x="list append">Append</span> a weak reference to <var>element</var>
-         to <var>elements</var>.</p></li>
-
-         <li><p><span>Continue</span>.</p></li>
-        </ol>
-       </li>
-
        <li><p><span data-x="list append">Append</span> a weak reference to <var>element</var> to
        <var>elements</var>.</p></li>
-
-       <li>
-        <p>If <var>element</var>:</p>
-
-        <ul class="brief">
-         <li>does not have the same <span>root</span> as <span>this</span>, or</li>
-         <li>has no <code data-x="attr-id">id</code> attribute, or</li>
-         <li>is not the first element in <span>this</span>'s <span>node tree</span> whose <span
-         data-x="concept-ID">ID</span> is the value of that <code data-x="attr-id">id</code>
-         attribute,</li>
-        </ul>
-
-        <p>then set <var>value</var> to the empty string, and <span>continue</span>.</p>
-       </li>
-
-       <li><p>Let <var>id</var> be <var>element</var>'s <span
-       data-x="concept-ID">ID</span>.</p></li>
-
-       <li><p>If <var>value</var> is not the empty string, then append U+0020 SPACE to
-       <var>value</var>.</p></li>
-
-       <li><p>Append <var>id</var> to <var>value</var>.</p></li>
       </ol>
      </li>
 
-     <li><p>Set the content attribute's value for <span>this</span> to <var>value</var>.</p></li>
-
      <li><p>Set <span>this</span>'s <span>explicitly set <var>attr</var>-elements</span> to
      <var>elements</var>.</p></li>
     </ol>