Make the focus fixup rule more explicit

* Split it into two variants: one which runs synchronously on HTML element removal, and one which runs during "update the rendering". Closes #8225.

* Be clear that the fixup does not cause any of the normal focus algorithms to run, and thus blur and change events do not fire. Also, delete the confusing "somehow unfocused without another element being explicitly focused" sentence. Fixes #3847. Fixes #6729.

source

@@ -1805,6 +1805,17 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
   <var>removedNode</var> and optionally <var>oldParent</var>, are defined as the following:</p>
 
   <ol>
+   <li id="node-remove-focus-fixup">
+    <p>If <var>removedNode</var>'s <span>node document</span>'s <span data-x="focused area of the
+    document">focused area</span> is <var>removedNode</var>, then set <var>removedNode</var>'s
+    <span>node document</span>'s <span data-x="focused area of the document">focused area</span> to
+    <var>removedNode</var>'s <span>node document</span>'s <span>viewport</span>.</p>
+
+    <p class="note">This does <em>not</em> perform the <span>unfocusing steps</span>,
+    <span>focusing steps</span>, or <span>focus update steps</span>, and thus no <code
+    data-x="event-blur">blur</code> event is fired.</p>
+   </li>
+
    <li><p>If <var>removedNode</var> is an element whose <span
    data-x="concept-element-namespace">namespace</span> is the <span>HTML namespace</span>, and this
    standard defines <span data-x="html element removing steps">HTML element removing steps</span>
@@ -59311,9 +59322,9 @@ interface <dfn interface>HTMLDialogElement</dfn> : <span>HTMLElement</span> {
 
     <p class="note" id="note-dialog-plus-focus-fixup">This will cause the <span>focused area of the
     document</span> to become <span>inert</span> (unless that currently focused area is a
-    <span>shadow-including descendant</span> of <var>subject</var>). In such cases, the <span>focus
-    fixup rule</span> will kick in and reset the <span>focused area of the document</span> to the
-    <span>viewport</span> for now. In a couple steps we will attempt to find a better candidate to
+    <span>shadow-including descendant</span> of <var>subject</var>). In such cases, the
+    <span>focused area of the document</span> will soon be <a href="#focus-fixup-rule">reset</a> to
+    the <span>viewport</span>. In a couple steps we will attempt to find a better candidate to
     focus.</p>
    </li>
 
@@ -77008,10 +77019,6 @@ partial interface <span id="NavigatorUserActivation-partial">Navigator</span> {
    </li>
   </ol>
 
-  <p>When the <span>currently focused area of a top-level browsing context</span> is somehow
-  unfocused without another element being explicitly focused in its stead, the user agent must
-  <span>immediately</span> run the <span>unfocusing steps</span> for that object.</p>
-
   <p class="note">The <span>unfocusing steps</span> do not always result in the focus changing, even
   when applied to the <span>currently focused area of a top-level browsing context</span>. For
   example, if the <span>currently focused area of a top-level browsing context</span> is a
@@ -77020,27 +77027,6 @@ partial interface <span id="NavigatorUserActivation-partial">Navigator</span> {
 
   <hr>
 
-  <p><dfn>Focus fixup rule</dfn>: When the designated <span data-x="focused area of the
-  document">focused area of the document</span> is removed from that <code>Document</code> in some
-  way (e.g. it stops being a <span>focusable area</span>, it is removed from the DOM, it becomes
-  <span>inert</span>, etc.), designate the <code>Document</code>'s <span>viewport</span> to be the
-  new <span>focused area of the document</span>.</p>
-
-  <p class="example">For example, this might happen because an element is removed from its
-  <code>Document</code>, or has a <code data-x="attr-hidden">hidden</code> attribute added. It might
-  also happen to an <code>input</code> element when the element gets <span
-  data-x="concept-fe-disabled">disabled</span>.</p>
-
-  <p class="example">In a <code>Document</code> whose <span data-x="focused area of the
-  document">focused area</span> is a <code>button</code> element, removing, disabling, or hiding
-  that button would cause the page's new <span data-x="focused area of the document">focused
-  area</span> to be the <span>viewport</span> of the <code>Document</code>. This would, in turn,
-  be reflected through the <code
-  data-x="dom-documentorshadowroot-activeElement">activeElement</code> API as <span>the body
-  element</span>.</p>
-
-  <hr>
-
   <p>The <dfn>focus update steps</dfn>, given an <var>old chain</var>, a <var>new chain</var>, and a <var>new focus target</var> respectively, are as
   follows:</p>
 
@@ -96741,6 +96727,26 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
      the animation frame callbacks</span> for that <code>Document</code>, passing in <var>now</var>
      as the timestamp.</p></li>
 
+     <li id="focus-fixup-rule">
+      <p>For each <span>fully active</span> <code>Document</code> in <var>docs</var>, if the <span
+      data-x="focused area of the document">focused area</span> of that <code>Document</code> is no
+      longer a <span>focusable area</span>, then set that <code>Document</code>'s <span
+      data-x="focused area of the document">focused area</span> to its <span>viewport</span>.</p>
+
+      <p class="example">For example, this might happen because an element has the <code
+      data-x="attr-hidden">hidden</code> attribute added, causing it to stop <span>being
+      rendered</span>. It might also happen to an <code>input</code> element when the element gets
+      <span data-x="concept-fe-disabled">disabled</span>.</p>
+
+      <p class="note">This does <em>not</em> perform the <span>unfocusing steps</span>,
+      <span>focusing steps</span>, or <span>focus update steps</span>, and thus no <code
+      data-x="event-blur">blur</code> event is fired.</p>
+
+      <p class="note">In addition to this asynchronous fixup, if the <span>focused area of the
+      document</span> is removed, there is a <a href="#node-remove-focus-fixup">synchronous
+      fixup</a>.</p>
+     </li>
+
      <li>
       <p>For each <span>fully active</span> <code>Document</code> <var>doc</var> in
       <var>docs</var>:</p>