diff --git a/source b/source
index a92a00a0afb..8ab48035a46 100644
--- a/source
+++ b/source
@@ -86855,6 +86855,12 @@ new PaymentRequest(…); // Allowed to use
    object</span> given "<code data-x="">html</code>", <var>type</var>, and
    <var>navigationParams</var>.</p></li>
 
+   <li><p>Set <var>document</var>'s <span>parser cannot change the mode flag</span> to
+   true.</p></li>
+
+   <li><p>Set <var>document</var>'s <span data-x="concept-document-mode">mode</span>
+   to "<code data-x="">no-quirks</code>".</p></li>
+
    <li><p>Create an <span>HTML parser</span> and associate it with the <var>document</var>. Act as
    if the tokenizer had emitted a start tag token with the tag name "pre" followed by a single
    U+000A LINE FEED (LF) character<!-- to get eaten, so that a leading LF in the text/plain stream
@@ -86931,6 +86937,9 @@ new PaymentRequest(&hellip;); // Allowed to use
    object</span> given "<code data-x="">html</code>", <var>type</var>, and
    <var>navigationParams</var>.</p></li>
 
+   <li><p>Set <var>document</var>'s <span data-x="concept-document-mode">mode</span>
+   to "<code data-x="">no-quirks</code>".</p></li>
+
    <li><p>Append an <code>html</code> element to <var>document</var>.</p></li>
 
    <li><p>Append a <code>head</code> element to the <code>html</code> element.</p></li>
@@ -86992,6 +87001,9 @@ new PaymentRequest(&hellip;); // Allowed to use
    object</span> given "<code data-x="">html</code>", <var>type</var>, and
    <var>navigationParmas</var>.</p></li>
 
+   <li><p>Set <var>document</var>'s <span data-x="concept-document-mode">mode</span>
+   to "<code data-x="">no-quirks</code>".</p></li>
+
    <li><p>Mark <var>document</var> as being a <dfn>plugin document</dfn></p></li>
 
    <li><p>Append an <code>html</code> element to <var>document</var>.</p></li>
@@ -87061,6 +87073,9 @@ new PaymentRequest(&hellip;); // Allowed to use
    object</span> given "<code data-x="">html</code>", "<code data-x="">text/html</code>", and
    <var>navigationParams</var>.</p></li>
 
+   <li><p>Set <var>document</var>'s <span data-x="concept-document-mode">mode</span>
+   to "<code data-x="">no-quirks</code>".</p></li>
+
    <li><p>Either associate <var>document</var> with a custom rendering that is not rendered using
    the normal <code>Document</code> rendering rules, or mutate <var>document</var> until it
    represents the content the user agent wants to render.</p>
@@ -104216,7 +104231,8 @@ dictionary <dfn>StorageEventInit</dfn> : <span>EventInit</span> {
      than "<code data-x="">PUBLIC</code>" and "<code data-x="">SYSTEM</code>" keywords after a <span
      data-x="syntax-doctype">DOCTYPE</span> name. In such a case, the parser ignores any following
      public or system identifiers, and if the DOCTYPE is correctly placed as a document preamble,
-     sets the <code>Document</code> to <span>quirks mode</span>.</p>
+     and if the <span>parser cannot change the mode flag</span> is false, sets the <code>Document</code>
+     to <span>quirks mode</span>.</p>
 
     <tr>
      <td><dfn data-x="parse-error-invalid-first-character-of-tag-name">invalid-first-character-of-tag-name</dfn>
@@ -109109,6 +109125,9 @@ document.body.appendChild(text);
 
   <h6>The "<dfn data-x="insertion mode: initial">initial</dfn>" insertion mode</h6>
 
+  <p>A <code>Document</code> object has an associated <dfn>parser cannot change the mode flag</dfn>
+  (a boolean). It is initially false.</p>
+
   <p>When the user agent is to apply the rules for the "<span data-x="insertion mode:
   initial">initial</span>" <span>insertion mode</span>, the user agent must handle the token as
   follows:</p>
@@ -109145,9 +109164,9 @@ document.body.appendChild(text);
     <code>Document</code> object.</p>
 
     <p id="quirks-mode-doctypes">Then, if the document is <em>not</em> <span>an <code>iframe</code>
-    <code data-x="attr-iframe-srcdoc">srcdoc</code> document</span>, and the DOCTYPE token matches
-    one of the conditions in the following list, then set the <code>Document</code> to <span>quirks
-    mode</span>:</p>
+    <code data-x="attr-iframe-srcdoc">srcdoc</code> document</span>, and the <span>parser cannot
+    change the mode flag</span> is false, and the DOCTYPE token matches one of the conditions in the
+    following list, then set the <code>Document</code> to <span>quirks mode</span>:</p>
 
     <ul class="brief">
      <li> The <i data-x="force-quirks flag">force-quirks flag</i> is set to <i>on</i>. </li>
@@ -109216,9 +109235,9 @@ document.body.appendChild(text);
     </ul>
 
     <p>Otherwise, if the document is <em>not</em> <span>an <code>iframe</code> <code
-    data-x="attr-iframe-srcdoc">srcdoc</code> document</span>, and the DOCTYPE token matches one of
-    the conditions in the following list, then set the <code>Document</code> to <span>limited-quirks
-    mode</span>:</p>
+    data-x="attr-iframe-srcdoc">srcdoc</code> document</span>, and the <span>parser cannot change
+    the mode flag</span> is false, and the DOCTYPE token matches one of the conditions in the
+    following list, then then set the <code>Document</code> to <span>limited-quirks mode</span>:</p>
 
     <ul class="brief">
      <li> The public identifier starts with: "<code data-x="">-//W3C//DTD XHTML 1.0 Frameset//</code>" </li>
@@ -109240,7 +109259,8 @@ document.body.appendChild(text);
    <dd>
     <p>If the document is <em>not</em> <span>an <code>iframe</code> <code
     data-x="attr-iframe-srcdoc">srcdoc</code> document</span>, then this is a <span>parse
-    error</span>; set the <code>Document</code> to <span>quirks mode</span>.</p>
+    error</span>; if the <span>parser cannot change the mode flag</span> is false, set the
+    <code>Document</code> to <span>quirks mode</span>.</p>
 
     <p>In any case, switch the <span>insertion mode</span> to "<span data-x="insertion mode: before
     html">before html</span>", then reprocess the token.</p>