diff --git a/source b/source
index d0d75d360ce..a7089d03d8b 100644
--- a/source
+++ b/source
@@ -61801,6 +61801,37 @@ interface <dfn interface>HTMLDialogElement</dfn> : <span>HTMLElement</span> {
    data-x="attr-hidden">hidden</code> attribute to hide it.</p>
   </div>
 
+  <p>The following <span data-x="concept-element-attributes-change-ext">attribute change
+  steps</span>, given <var>element</var>, <var>localName</var>, <var>oldValue</var>,
+  <var>value</var>, and <var>namespace</var> are used for <code>dialog</code> elements:</p>
+
+    <ol>
+     <li><p>If <var>namespace</var> is not null, then return.</p></li>
+
+     <li><p>If <var>localName</var> is not <code data-x="attr-dialog-open">open</code>, then
+     return.</p></li>
+
+     <li><p>If <var>value</var> is null:</p>
+
+      <ol>
+       <li><p><span data-x="list remove">Remove</span> <var>element</var> from <var>element</var>'s
+       <span>node document</span>'s <span>open dialogs list</span>.</p></li>
+
+       <li><p>If <var>element</var>'s <span data-x="dialog-close-watcher">close watcher</span> is
+       not null, then:</p>
+
+        <ol>
+         <li><p><span data-x="close-watcher-destroy">Destroy</span> <var>element</var>'s <span
+         data-x="dialog-close-watcher">close watcher</span>.</p></li>
+
+         <li><p>Set <var>element</var>'s <span data-x="dialog-close-watcher">close watcher</span> to
+         null.</p></li>
+        </ol>
+       </li>
+      </ol>
+     </li>
+    </ol>
+
   <p>The <code data-x="attr-tabindex">tabindex</code> attribute must not be specified on
   <code>dialog</code> elements.</p>
 
@@ -62051,6 +62082,9 @@ interface <dfn interface>HTMLDialogElement</dfn> : <span>HTMLElement</span> {
   element <var>dialog</var>:</p>
 
   <ol>
+   <li><p><span>Assert</span>: <span>dialog</span>'s <span data-x="dialog-close-watcher">close
+   watcher</span> is null.</p></li>
+
    <li>
     <p>Set <var>dialog</var>'s <span data-x="dialog-close-watcher">close watcher</span> to the
     result of <span data-x="establish a close watcher">establishing a close watcher</span> given