diff --git a/source b/source
index 1df0a0cc4b4..06a1ef7b01e 100644
--- a/source
+++ b/source
@@ -3866,6 +3866,8 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
      <li><dfn data-x-href="https://drafts.csswg.org/selectors/#type-selector">type selector</dfn></li>
      <li><dfn data-x-href="https://drafts.csswg.org/selectors/#attribute-selector">attribute selector</dfn></li>
      <li><dfn data-x-href="https://drafts.csswg.org/selectors/#pseudo-class">pseudo-class</dfn></li>
+     <li><dfn data-x-href="https://drafts.csswg.org/selectors/#focus-visible-pseudo"
+     data-x="focus-visible-pseudo">:focus-visible</dfn></li>
     </ul>
 
     <p>The following features are defined in <cite>CSS Values and Units</cite>: <ref
@@ -68057,6 +68059,9 @@ interface <dfn>ElementInternals</dfn> {
   boolean <span data-x="dom-ElementInternals-reportValidity">reportValidity</span>();
 
   readonly attribute <span>NodeList</span> <span data-x="dom-ElementInternals-labels">labels</span>;
+
+  // Focus management
+  attribute DOMString <span data-x="dom-ElementInternals-focusBehavior">focusBehavior</span>;
 };
 
 dictionary <dfn>ValidityStateFlags</dfn> {
@@ -68145,6 +68150,19 @@ dictionary <dfn>ValidityStateFlags</dfn> {
    <var>internals</var>'s <span data-x="internals-target">target element</span> is associated with.
    </p></dd>
 
+   <dt><var>internals</var> . <code data-x="dom-ElementInternals-focusBehavior">focusBehavior</code>
+   [ = <var>value</var> ]</dt>
+   <dd>
+    <p>Returns the <span data-x="ce-focus-behavior">focus behavior</span> of the
+    <var>internals</var>'s <span data-x="internals-target">target element</span>. Possible values
+    are "<code data-x="ce-focusBehavior-default">default</code>", "<code
+    data-x="ce-focusBehavior-focusable">focusable</code>", and "<code
+    data-x="ce-focusBehavior-simple-control">simple-control</code>". If an unknown value was set,
+    this returns "<code data-x="ce-focusBehavior-focusable">focusable</code>".</p>
+
+    <p>Can be set, to change the <span data-x="ce-focus-behavior">focus behavior</span> to the new
+    value.</p>
+   </dd>
   </dl>
 
   <p>Each <code>ElementInternals</code> has a <dfn data-x="internals-target">target element</dfn>,
@@ -68352,6 +68370,60 @@ dictionary <dfn>ValidityStateFlags</dfn> {
    <span data-x="face-submission-value">submission value</span>.</p></li>
   </ol>
 
+  <hr>
+
+  <p>Each <span>autonomous custom element</span> has <dfn data-x="ce-focus-behavior">focus
+  behavior</dfn> string, initially "<code data-x="ce-focusBehavior-default">default</code>". It also
+  can be "<code data-x="ce-focusBehavior-focusable">focusable</code>" or "<code
+  data-x="ce-focusBehavior-simple-control">simple-control</code>". These values have the following
+  impacts:</p>
+
+  <dl>
+   <dt>"<dfn><code data-x="ce-focusBehavior-default">default</code></dfn>"</dt>
+   <dd>
+    <p>The element is not <span>focusable</span> by default. The element's focus-related behavior
+    is same as elements like <code>div</code>, which are not <span>focusable</span> by default.</p>
+
+    <p class="note">There are ways for authors to make an element with "<code
+    data-x="ce-focusBehavior-default">default</code>" <span data-x="ce-focus-behavior">focus
+    behavior</span> <span>focusable</span>, e.g., adding a <code
+    data-x="attr-tabindex">tabindex</code> or <code
+    data-x="attr-contenteditable">contenteditable</code> content attribute.</p>
+   </dd>
+
+   <dt>"<dfn><code data-x="ce-focusBehavior-focusable">focusable</code></dfn>"</dt>
+   <dd><p>The element is <span>focusable</span> by default. The element's focus-related behavior is
+   same as general <span>focusable</span> elements such as <span data-x="editing host">editing
+   hosts</span>.</p></dd>
+
+   <dt>"<dfn><code data-x="ce-focusBehavior-simple-control">simple-control</code></dfn>"</dt>
+   <dd>
+    <p>The element is <span>focusable</span> by default. The element's focus-related behavior is
+    same as simple controls like <code>button</code> elements.</p>
+
+    <p class="note">Behavior differences between "<code
+    data-x="ce-focusBehavior-focusable">focusable</code>" and "<code
+    data-x="ce-focusBehavior-simple-control">simple-control</code>" depend on the user agent. They
+    might affect <span data-x="sequentially focusable">sequential focusability</span>, <span
+    data-x="click focusable">click focusability</span>, or the <code
+    data-x="focus-visible-pseudo">:focus-visible</code> <span>pseudo-class</span>.</p>
+   </dd>
+  </dl>
+
+
+  <p>The <dfn><code data-x="dom-ElementInternals-focusBehavior">focusBehavior</code></dfn> IDL
+  attribute, on getting, must return the <span data-x="ce-focus-behavior">focus behavior</span> of
+  this <code>ElementInternals</code>'s <span data-x="internals-target">target element</span>. On
+  setting, if the new string is one of "<code data-x="ce-focusBehavior-default">default</code>",
+  "<code data-x="ce-focusBehavior-focusable">focusable</code>", or "<code
+  data-x="ce-focusBehavior-simple-control">simple-control</code>", then set the <span
+  data-x="ce-focus-behavior">focus behavior</span> of this <code>ElementInternals</code>'s <span
+  data-x="internals-target">target element</span> to the given value. Otherwise, set it to "<code
+  data-x="ce-focusBehavior-focusable">focusable</code>".</p>
+
+  <p class="note">Setting <code data-x="dom-ElementInternals-focusBehavior">focusBehavior</code> to
+  an unknown value does not throw because new values might be added in the future, and user agents
+  without support for the new value have to work somehow with documents using the new keyword.</p>
   </div>
 
   <h3 split-filename="semantics-other" id="common-idioms">Common idioms without dedicated elements</h3>
@@ -73466,8 +73538,13 @@ END:VCARD</pre>
      Elements that meet all the following criteria:
 
      <ul class="brief">
-      <li>the element's <span>tabindex value</span> is a non-negative integer, or the element is
-      determined by the user agent to be focusable;</li>
+      <li>
+       <p>the element's <span>tabindex value</span> is a non-negative integer, or the element is
+       determined by the user agent to be focusable;</p>
+
+       <p>See the description of <span data-x="null-tabindex">null tabindex value</span> for the
+       latter case.</p>
+      </li>
 
       <li>the element is either not a <span>shadow host</span>, or has a <span
       data-x="concept-element-shadow-root">shadow root</span> whose <span>delegates focus</span> is
@@ -73666,6 +73743,11 @@ END:VCARD</pre>
    </li>
   </ul>
 
+  <p>For <span data-x="focusable area">focusable areas</span> that are
+  <span data-x="autonomous custom element">autonomous custom elements</span>, user agents should
+  consider the element's <span data-x="ce-focus-behavior">focus behavior</span> in determining
+  whether the element is <span>click focusable</span> or <span>sequentially focusable</span>.</p>
+
   <p class="note">Elements which are not <span>focusable</span> are not <span data-x="focusable
   area">focusable areas</span>, and thus not <span>sequentially focusable</span> and not <span>click
   focusable</span>.</p>
@@ -73864,7 +73946,7 @@ END:VCARD</pre>
 
   <dl>
 
-   <dt>If the value is null</dt>
+   <dt><dfn data-x="null-tabindex">If the value is null</dfn></dt>
 
    <dd>
 
@@ -73911,6 +73993,10 @@ END:VCARD</pre>
      <li><span data-x="editing host">Editing hosts</span></li>
 
      <li><span data-x="browsing context container">Browsing context containers</span></li>
+
+     <li><span data-x="autonomous custom element">Autonomous custom elements</span> whose <span
+     data-x="ce-focus-behavior">focus behavior</span> is not "<code
+     data-x="ce-focusBehavior-default">default</code>".</li>
     </ul>
 
    </dd>