diff --git a/source b/source
index 37c6d758c60..ac7f492cc0a 100644
--- a/source
+++ b/source
@@ -6988,6 +6988,8 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
    <span>tree order</span>.</p></li>
   </ol>
 
+  <hr>
+
   <p>A <span>URL</span> <dfn>matches <code>about:blank</code></dfn> if its <span
   data-x="concept-url-scheme">scheme</span> is "<code data-x="">about</code>", its <span
   data-x="concept-url-path">path</span> contains a single string "<code data-x="">blank</code>", its
@@ -7000,6 +7002,25 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
   record</span> created by <span data-x="URL parser">parsing</span> "<code
   data-x="">about:blank?foo#bar</code>" <span>matches <code>about:blank</code></span>.</p>
 
+  <p>A <span>URL</span> <dfn>matches <code>about:srcdoc</code></dfn> if its <span
+  data-x="concept-url-scheme">scheme</span> is "<code data-x="">about</code>", its <span
+  data-x="concept-url-path">path</span> contains a single string "<code data-x="">srcdoc</code>",
+  its <span data-x="concept-url-query">query</span> is null, its <span
+  data-x="concept-url-username">username</span> and <span
+  data-x="concept-url-password">password</span> are the empty string, and its <span
+  data-x="concept-url-host">host</span> is null.</p>
+
+  <p class="note">The reason that <span>matches <code>about:srcdoc</code></span> ensures that the
+  <span>URL</span>'s <span data-x="concept-url-query">query</span> is null is because it is not
+  possible to create <span data-x="an iframe srcdoc document">an <code>iframe</code> <code
+  data-x="attr-iframe-srcdoc">srcdoc</code> document</span> whose <span
+  data-x="concept-document-url">URL</span> has a non-null <span
+  data-x="concept-url-query">query</span>, unlike <code>Document</code>s whose <span
+  data-x="concept-document-url">URL</span> <span>matches <code>about:blank</code></span>. In other
+  words, the set of all <span>URL</span>s that <span data-x="matches about:srcdoc">match
+  <code>about:srcdoc</code></span> only vary in their <span
+  data-x="concept-url-fragment">fragment</span>.</p>
+
 
   <div w-nodev>
 
@@ -32541,8 +32562,10 @@ interface <dfn interface>HTMLIFrameElement</dfn> : <span>HTMLElement</span> {
 
   <p>The <dfn for="iframe" element-attr><code data-x="attr-iframe-srcdoc">srcdoc</code></dfn>
   attribute gives the content of the page that the element's <span>content navigable</span> is to
-  contain. The value of the attribute is the source of <dfn export>an <code>iframe</code> <code
-  data-x="attr-iframe-srcdoc">srcdoc</code> document</dfn>.</p>
+  contain. The value of the attribute is used to <span data-x="create navigation params from a
+  srcdoc resource">construct</span> <dfn export>an <code>iframe</code> <code
+  data-x="attr-iframe-srcdoc">srcdoc</code> document</dfn>, which is a <code>Document</code> whose
+  <span data-x="concept-document-url">URL</span> <span>matches <code>about:srcdoc</code></span>.</p>
 
   <p>The <code data-x="attr-iframe-srcdoc">srcdoc</code> attribute, if present, must have a value
   using <span>the HTML syntax</span> that consists of the following syntactic components, in the