diff --git a/dom.bs b/dom.bs
index b4c0abd3..f393b95d 100644
--- a/dom.bs
+++ b/dom.bs
@@ -908,9 +908,14 @@ for historical reasons.
 <h3 id=interface-eventtarget>Interface {{EventTarget}}</h3>
 
 <pre class=idl>
+[Exposed=*]
+interface EventTargetInternals {
+  attribute EventTarget parent;
+}
+
 [Exposed=*]
 interface EventTarget {
-  constructor();
+  constructor(optional EventTargetCallback cb);
 
   undefined addEventListener(DOMString type, EventListener? callback, optional (AddEventListenerOptions or boolean) options = {});
   undefined removeEventListener(DOMString type, EventListener? callback, optional (EventListenerOptions or boolean) options = {});
@@ -930,6 +935,8 @@ dictionary AddEventListenerOptions : EventListenerOptions {
   boolean once = false;
   AbortSignal signal;
 };
+
+callback EventTargetCallback = undefined (EventTargetInternals internals);
 </pre>
 
 <p>An {{EventTarget}} object represents a target to which an <a>event</a> can be <a>dispatched</a>
@@ -939,6 +946,26 @@ when something has occurred.
 <a for=/>list</a> of zero or more <a>event listeners</a>). It is initially the empty list.
 <!-- Intentionally not exported. -->
 
+<p>Each {{EventTarget}} object has an associated <dfn for=EventTarget>attached internals</dfn> (null
+or an {{EventTargetInternals}} object), initially null.
+
+<p>The <dfn export for=Event id=concept-eventtarget-constructor>new EventTarget(cb)</dfn> constructor steps are:
+
+<ol>
+ <li><p>If <var>cb</var> is not null then:
+
+  <ol>
+   <li><p>Let <var>eventTargetInternals</var> a new {{EventTargetInternals}} instance.
+
+   <li><a for=/invoke-a-callback-function>invoke</a> <var>cb</var> with «
+   <var>eventTargetInternals</var> » and with <var>eventTarget</var> as the <a>callback this
+   value</a>.
+
+   <li><p>Set <var>this</var>'s {{Eventtarget/attached internals}} to
+   <var>eventTargetInternals</var>.
+  </ol>
+</ol>
+
 <p>An <dfn export id=concept-event-listener>event listener</dfn> can be used to observe a specific
 <a>event</a> and consists of:
 
@@ -956,8 +983,9 @@ when something has occurred.
 object, an <a>event listener</a> is a broader concept as can be seen above.
 
 <p>Each {{EventTarget}} object also has an associated <dfn export>get the parent</dfn> algorithm,
-which takes an <a>event</a> <var>event</var>, and returns an {{EventTarget}} object. Unless
-specified otherwise it returns null.
+which takes an <a>event</a> <var>event</var>, and returns an {{EventTarget}}. Unless otherwise
+specified otherwise it returns the associated <a for=EventTarget>attached internals</a><a
+for=EventTargetInternals">parent</a> attribute.
 
 <p class=note><a for=/>Nodes</a>, <a for=/>shadow roots</a>, and <a>documents</a>
 override the <a>get the parent</a> algorithm.
@@ -1322,6 +1350,9 @@ property of the event being dispatched.
     <p>While <var>parent</var> is non-null:</p>
 
     <ol>
+     <li>If the <var>event</var>'s <a for=Event>path</a> <a for=/>contains</a> <var>parent</var> then <a>throw</a> a
+     "{{HierarchyRequestError!!exception}}" {{DOMException}}.
+
      <li>
       <p>If <var>slottable</var> is non-null: