Yet more fixes to focus delegation

Fixes #8156. Fixes #8157.

See also previous work in #7361, #7284, and #7079.

source

@@ -76857,51 +76857,59 @@ partial interface <span id="NavigatorUserActivation-partial">Navigator</span> {
    <dd><p>Return null.</p></dd>
   </dl>
 
-  <p>The <dfn>focus delegate</dfn> for a <var>focus target</var>, given an optional string
-  <var>focus trigger</var> (default "<code data-x="">other</code>"), is given by the following
+  <p>The <dfn>focus delegate</dfn> for a <var>focusTarget</var>, given an optional string
+  <var>focusTrigger</var> (default "<code data-x="">other</code>"), is given by the following
   steps:</p>
 
   <ol>
-   <li><p>Let <var>autofocus delegate</var> be the <span>autofocus delegate</span> for <var>focus
-   target</var> given <var>focus trigger</var>.</p></li>
-
-   <li><p>If <var>autofocus delegate</var> is not null, then return <var>autofocus
-   delegate</var>.</p></li>
-
-   <li><p>If <var>focus target</var> is a <span>shadow host</span> and its <span
+   <li><p>If <var>focusTarget</var> is a <span>shadow host</span> and its <span
    data-x="concept-element-shadow-root">shadow root</span>'s <span>delegates focus</span> is false,
    then return null.</p></li>
 
-   <li><p>Let <var>parent</var> be <var>focus target</var>.</p></li>
+   <li><p>Let <var>whereToLook</var> be <var>focusTarget</var>.</p></li>
+
+   <li><p>If <var>whereToLook</var> is a <span>shadow host</span>, then set <var>whereToLook</var>
+   to <var>whereToLook</var>'s <span data-x="concept-element-shadow-root">shadow
+   root</span>.</p></li>
+
+   <li><p>Let <var>autofocusDelegate</var> be the <span>autofocus delegate</span> for
+   <var>whereToLook</var> given <var>focusTrigger</var>.</p></li>
 
-   <li><p>If <var>parent</var> is a <span>shadow host</span>, then set <var>parent</var> to
-   <var>parent</var>'s <span data-x="concept-element-shadow-root">shadow root</span>.</p></li>
+   <li><p>If <var>autofocusDelegate</var> is not null, then return
+   <var>autofocusDelegate</var>.</p></li>
 
    <li>
-    <p><span data-x="list iterate">For each</span> <var>child</var> of <var>parent</var>'s <span
-    data-x="concept-tree-child">children</span>:</p>
+    <p><span data-x="list iterate">For each</span> <var>descendant</var> of
+    <var>whereToLook</var>'s <span data-x="descendant">descendants</span>, in <span>tree
+    order</span>:</p>
 
     <ol>
+     <li><p>If <var>descendant</var> is a <span>focusable area</span>, then return
+     <var>descendant</var>.</p></li>
+
      <li>
-      <p>Let <var>focusable area</var> be <var>child</var>, if <var>child</var> is a
-      <span>focusable area</span>; otherwise let <var>focusable area</var> be the result of <span
-      data-x="get the focusable area">getting the focusable area</span> for <var>child</var> given
-      <var>focus trigger</var>.</p>
+      <p>Let <var>focusableArea</var> be the result of <span data-x="get the focusable
+      area">getting the focusable area</span> for <var>descendant</var> given
+      <var>focusTrigger</var>.</p>
 
       <p class="note">This step can end up recursing, i.e., the <span>get the focusable area</span>
-      steps might return the <span>focus delegate</span> of <var>child</var>.</p>
+      steps might return the <span>focus delegate</span> of <var>descendant</var>.</p>
      </li>
 
-     <li><p>If <var>focusable area</var> is not null, then return <var>focusable
-     area</var>.</p></li>
+     <li><p>If <var>focusableArea</var> is not null, then return <var>focusableArea</var>.</p></li>
     </ol>
+
+    <p class="note">It's important that we are <em>not</em> looking at the <span
+    data-x="shadow-including descendant">shadow-including descendants</span> here, but instead only
+    at the <span data-x="descendant">descendants</span>. <span data-x="shadow host">Shadow
+    hosts</span> are instead handled by the recursive case mentioned above.</p>
    </li>
 
    <li><p>Return null.</p></li>
   </ol>
 
   <p class="note">The above algorithm essentially returns the first suitable <span>focusable
-  area</span> where the path between its <span>DOM anchor</span> and <var>focus target</var>
+  area</span> where the path between its <span>DOM anchor</span> and <var>focusTarget</var>
   delegates focus at any shadow tree boundaries.</p>
 
   <p>The <dfn>autofocus delegate</dfn> for a <var>focus target</var> given a <var>focus