Meta: export "listener" and "event handler map"

Helps with w3c/ServiceWorker#1672.

source

@@ -102054,9 +102054,9 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
    handler</span>'s <span data-x="event handler value">value</span> must be set to
    null.</span></p></li>
 
-   <li><p>a <dfn data-x="event handler listener">listener</dfn>, which is either null or an
-   <span>event listener</span><span w-nodev> responsible for running <span>the event handler
-   processing algorithm</span></span>. <span w-nodev>Initially, an <span data-x="event
+   <li><p>a <dfn export for="event handler" data-x="event handler listener">listener</dfn>, which is
+   either null or an <span>event listener</span><span w-nodev> responsible for running <span>the
+   event handler processing algorithm</span></span>. <span w-nodev>Initially, an <span data-x="event
    handlers">event handler</span>'s <span data-x="event handler listener">listener</span> must be
    set to null.</span></p></li>
   </ul>
@@ -102127,9 +102127,9 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
   <hr>
 
   <p>Each <code>EventTarget</code> object that has one or more <span>event handlers</span> specified
-  has an associated <dfn>event handler map</dfn>, which is a <span data-x="ordered map">map</span>
-  of strings representing <span data-x="event handler name">names</span> of <span>event
-  handlers</span> to <span>event handlers</span>.</p>
+  has an associated <dfn export for="EventTarget">event handler map</dfn>, which is a <span
+  data-x="ordered map">map</span> of strings representing <span data-x="event handler
+  name">names</span> of <span>event handlers</span> to <span>event handlers</span>.</p>
 
   <p>When an <code>EventTarget</code> object that has one or more <span>event handlers</span>
   specified is created, its <span>event handler map</span> must be initialized such that it contains