diff --git a/source b/source
index e28b1716481..f17c3694ad9 100644
--- a/source
+++ b/source
@@ -48214,8 +48214,8 @@ interface <dfn interface>HTMLInputElement</dfn> : <span>HTMLElement</span> {
    <li><p>Run <var>element</var>'s <dfn>input activation behavior</dfn>, if any, and do nothing
    otherwise.</p></li>
 
-   <li><p>Run the <span>popover target attribute activation behavior</span> on
-   <var>element</var>.</p></li>
+   <li><p>Run the <span>popover target attribute activation behavior</span> given <var>element</var>
+   and <var>event</var>'s <span data-x="concept-event-target">target</span>.</p></li>
   </ol>
 
   <p class="note">Recall that an element's <span>activation behavior</span> runs for both
@@ -53512,8 +53512,8 @@ interface <dfn interface>HTMLButtonElement</dfn> : <span>HTMLElement</span> {
     </dl>
    </li>
 
-   <li><p>Run the <span>popover target attribute activation behavior</span> given
-   <var>element</var>.</p></li>
+   <li><p>Run the <span>popover target attribute activation behavior</span> given <var>element</var>
+   and <var>event</var>'s <span data-x="concept-event-target">target</span>.</p></li>
   </ol>
 
   </div>
@@ -86382,13 +86382,18 @@ dictionary <dfn dictionary>DragEventInit</dfn> : <span>MouseEventInit</span> {
   attribute, <span>limited to only known values</span>.</p>
 
   <p>To run the <dfn>popover target attribute activation behavior</dfn> given a <code>Node</code>
-  <var>node</var>:</p>
+  <var>node</var> and a <code>Node</code> <var>eventTarget</var>:</p>
 
   <ol>
    <li><p>Let <var>popover</var> be <var>node</var>'s <span>popover target element</span>.</p></li>
 
    <li><p>If <var>popover</var> is null, then return.</p></li>
 
+   <li><p>If <var>eventTarget</var> is a <span>shadow-including inclusive descendant</span> of
+   <var>popover</var> and <var>popover</var> is a
+   <span data-x="shadow-including descendant">shadow-including descendant</span> of <var>node</var>,
+   then return.</p></li>
+
    <li><p>If <var>node</var>'s <code data-x="attr-popovertargetaction">popovertargetaction</code>
    attribute is in the <span data-x="attr-popovertargetaction-show">show</span> state and
    <var>popover</var>'s <span>popover visibility state</span> is <span