diff --git a/source b/source
index aac8bb72e5f..99acc9a49d7 100644
--- a/source
+++ b/source
@@ -13775,8 +13775,10 @@ Transport Protocol">HTTP&lt;/abbr> today.&lt;/p></code></pre> <!-- DO NOT REWRAP
         <ol>
          <li><p><span>Assert</span>: <var>child</var> is an <code>Element</code> node.</p></li>
 
-         <li><p>Set <var>childDirection</var> to the <span>auto directionality</span> of
-         <var>child</var>.</p></li>
+         <li><p>Set <var>childDirection</var> to the <span>contained text auto directionality</span>
+         of <var>child</var> with <i><span
+         data-x="auto-directionality-can-exclude-root">canExcludeRoot</span></i> set to
+         true.</p></li>
         </ol>
        </li>
 
@@ -13789,6 +13791,16 @@ Transport Protocol">HTTP&lt;/abbr> today.&lt;/p></code></pre> <!-- DO NOT REWRAP
     </ol>
    </li>
 
+   <li><p>Return the <span>contained text auto directionality</span> of <var>element</var> with
+   <i><span data-x="auto-directionality-can-exclude-root">canExcludeRoot</span></i> set to
+   false.</p></li>
+  </ol>
+
+  <p>To compute the <dfn>contained text auto directionality</dfn> of an element
+  <var>element</var> with a boolean <dfn
+  data-x="auto-directionality-can-exclude-root"><var>canExcludeRoot</var></dfn>:</p>
+
+  <ol>
    <li>
     <p><span data-x="list iterate">For each</span> node <var>descendant</var> of
     <var>element</var>'s <span data-x="descendant">descendants</span>, in <span>tree
@@ -13796,8 +13808,15 @@ Transport Protocol">HTTP&lt;/abbr> today.&lt;/p></code></pre> <!-- DO NOT REWRAP
 
     <ol>
      <li>
-      <p>If <var>descendant</var>, or any of its ancestor elements that are descendants of
-      <var>element</var>, is one of</p>
+      <p>If any of</p>
+
+      <ul class="brief">
+       <li><var>descendant</var></li>
+       <li>any ancestor element of <var>descendant</var> that is a descendant of <var>element</var></li>
+       <li>if <var>canExcludeRoot</var> is true, <var>element</var></li>
+      </ul>
+
+      <p>is one of</p>
 
       <ul class="brief">
        <li>a <code>bdi</code> element</li>