Nullable types and attribute change steps

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@@ -7369,8 +7369,9 @@ 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>
 
-  <p>If a reflecting IDL attribute <var>attr</var> has the type <code>Element</code>,
-  or an interface that inherits from <code>Element</code>, then:
+  <p>If a reflecting IDL attribute <var>attr</var> has the type <code
+  data-x=""><code>Element</code>?</code>, or an interface that inherits from <code
+  data-x=""><code>Element</code>?</code>, then:
   <ul>
    <li><p>This attribute defines an internal slot, [[<var>attr</var>AssociatedElement]], on the
    attribute's element. The initial value for this slot is null.</p></li>
@@ -7425,13 +7426,20 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
     </ol>
    </li>
 
-   <li><p>If the content attribute is set directly (such as via <code
-   data-x="">Element.setAttribute()</code>), the value for the IDL attribute is reset to null.</p></li>
+   <li>
+    <p>The following <span data-x="concept-element-attributes-change-ext">attribute change
+    step</span> is used to synchronize between the content attribute and the IDL attribute:</p>
+    <ol>
+     <li><p>If <var>localName</var> is associated attribute’s local name, and <var>namespace</var>
+     is null, reset [[<var>attr</var>AssociatedElement]] to null.</p></li>
+    </ol>
+   </li>
   </ul>
 
   <p>If a reflecting IDL attribute <var>attr</var> has the type <code
-  data-x="">sequence&lt;<code>Element</code>&gt;</code>, or <code data-x="">sequence&lt;<var>T</var>&gt;</code> where
-  <var>T</var> inherits from <code>Element</code>, then:</p>
+  data-x="">sequence&lt;<code>Element</code>&gt;?</code>, or <code
+  data-x="">sequence&lt;<var>T</var>&gt;?</code> where <var>T</var> inherits from
+  <code>Element</code>, then:</p>
 
   <ul>
    <li><p>This attribute defines an internal slot, [[<var>attr</var>AssociatedElements]], on the
@@ -7447,10 +7455,11 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
 
      <li><p>Otherwise, let <var>elements</var> be an empty list.</p></li>
 
-     <li>
-      <p><span data-x="list iterate">For each</span> <var>id</var> in the <span>set of space-separated
-      tokens</span>:</p>
+     <li><p>Let <var>tokens</var> be the content attribute's value, <span data-x="split a string on
+     ASCII whitespace">split on ASCII whitespace</span>.</p></li>
 
+     <li>
+      <p><span data-x="list iterate">For each</span> <var>id</var> in <var>tokens</var>:</p>
       <ul>
        <li><p>Let <var>candidate</var> be the first element within the content attribute's elements
        <span>node document</span>'s descendants whose <span data-x="concept-ID">ID</span> is
@@ -7527,8 +7536,14 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
     </ol>
    </li>
 
-   <li><p>If the content attribute is set directly (such as via <code
-   data-x="">Element.setAttribute()</code>), the value for the IDL attribute is reset to null.</p></li>
+   <li>
+    <p>The following <span data-x="concept-element-attributes-change-ext">attribute change
+    step</span> is used to synchronize between the content attribute and the IDL attribute:</p>
+    <ol>
+     <li><p>If <var>localName</var> is associated attribute’s local name, and <var>namespace</var>
+     is null, reset [[<var>attr</var>AssociatedElements]] to null.</p></li>
+    </ol>
+   </li>
   </ul>
 
   </div>