Set empty string for reflection of IDREF attributes

To avoid issues with wrong IDs in IDREF attributes
we set the content attribute's value to the empty string
in the setter steps for Element and FrozenArray<Element>.

Fixes whatwg#8306

source

@@ -7789,23 +7789,7 @@ 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>
@@ -7952,51 +7936,7 @@ 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><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 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>-elements</span> to
      <var>elements</var>.</p></li>