diff --git a/source b/source
index 139e2870c0b..6ce86be5abf 100644
--- a/source
+++ b/source
@@ -3292,6 +3292,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
      <li><dfn data-x-href="https://dom.spec.whatwg.org/#dictdef-eventinit"><code>EventInit</code></dfn> dictionary type</li>
      <li><dfn data-x="dom-Event-type" data-x-href="https://dom.spec.whatwg.org/#dom-event-type"><code>type</code></dfn> attribute</li>
      <li>An event's <dfn data-x="concept-event-target" data-x-href="https://dom.spec.whatwg.org/#concept-event-target">target</dfn></li>
+     <li>An event's <dfn data-x="concept-event-source" data-x-href="https://dom.spec.whatwg.org/#concept-event-source">source</dfn></li>
      <li><dfn data-x="dom-Event-currentTarget" data-x-href="https://dom.spec.whatwg.org/#dom-event-currenttarget"><code>currentTarget</code></dfn> attribute</li>
      <li><dfn data-x="dom-Event-bubbles" data-x-href="https://dom.spec.whatwg.org/#dom-event-bubbles"><code>bubbles</code></dfn> attribute</li>
      <li><dfn data-x="dom-Event-cancelable" data-x-href="https://dom.spec.whatwg.org/#dom-event-cancelable"><code>cancelable</code></dfn> attribute</li>
@@ -61172,6 +61173,9 @@ dictionary <dfn dictionary>SubmitEventInit</dfn> : <span>EventInit</span> {
   data-x="dom-SubmitEvent-submitter">submitter</code></dfn> attribute must return the value it was
   initialized to.</p>
 
+  <p>The <code data-x="dom-SubmitEvent-submitter">submitter</code> attribute defines the <span
+  data-x="concept-event-source">source</span> for a <code>SubmitEvent</code>.</p>
+
   </div>
 
   <h5>The <code>FormDataEvent</code> interface</h5>
@@ -80615,6 +80619,9 @@ dictionary <dfn dictionary>ToggleEventInit</dfn> : <span>EventInit</span> {
   Currently an event attribute initialized to a value cannot also have a getter, and so an internal
   slot (or map of additional fields) is required to properly specify this.</p>
 
+  <p>The <code data-x="dom-ToggleEvent-source">source</code> attribute defines the <span
+  data-x="concept-event-source">source</span> for a <code>ToggleEvent</code>.</p>
+
   <p>A <dfn>toggle task tracker</dfn> is a <span>struct</span> which has:</p>
 
   <dl>