diff --git a/source b/source
index 809aeb97590..8a964867f11 100644
--- a/source
+++ b/source
@@ -100056,24 +100056,32 @@ location.href = '#foo';</code></pre>
     <ol>
      <li><p>Set <var>unloadPromptShown</var> to true.</p></li>
 
-     <li><p>Invoke <span>WebDriver BiDi user prompt opened</span> with <var>document</var>'s
-     <span>relevant global object</span>, "<code data-x="">beforeunload</code>", and "".</p></li>
+     <li><p>Let <var>userPromptHandler</var> be the result of <span>WebDriver BiDi user prompt
+     opened</span> with <var>document</var>'s <span>relevant global object</span>,
+     "<code data-x="">beforeunload</code>", and "".</p></li>
 
-     <li>
-      <p>Ask the user to confirm that they wish to unload the document, and <span>pause</span> while
-      waiting for the user's response.</p>
+     <li><p>If <var>userPromptHandler</var> is "<code data-x="">dismiss</code>", set
+     <var>unloadPromptCanceled</var> to true.
 
-      <p class="note">The message shown to the user is not customizable, but instead determined by
-      the user agent. In particular, the actual value of the <code
-      data-x="dom-BeforeUnloadEvent-returnValue">returnValue</code> attribute is ignored.</p>
-     </li>
+     <li><p>If <var>userPromptHandler</var> is "<code data-x="">none</code>":</p>
 
-     <li><p>If the user did not confirm the page navigation, set <var>unloadPromptCanceled</var> to
-     true.</p></li>
+      <ul>
+       <li>
+        <p>Ask the user to confirm that they wish to unload the document, and <span>pause</span> while
+        waiting for the user's response.</p>
+
+        <p class="note">The message shown to the user is not customizable, but instead determined by
+        the user agent. In particular, the actual value of the <code
+        data-x="dom-BeforeUnloadEvent-returnValue">returnValue</code> attribute is ignored.</p>
+       </li>
+
+       <li><p>If the user did not confirm the page navigation, set <var>unloadPromptCanceled</var> to
+       true.</p></li>
+     </ul>
 
      <li><p>Invoke <span>WebDriver BiDi user prompt closed</span> with <var>document</var>'s
-     <span>relevant global object</span> and true if <var>unloadPromptCanceled</var> is false or
-     false otherwise.</p></li>
+     <span>relevant global object</span>, "<code data-x="">beforeunload</code>", and true
+     if <var>unloadPromptCanceled</var> is false or false otherwise.</p></li>
     </ol>
    </li>
 
@@ -114034,16 +114042,20 @@ function sendData(data) {
    <li><p>Set <var>message</var> to the result of <span data-x="optionally truncate a simple dialog
    string">optionally truncating</span> <var>message</var>.</p></li>
 
-   <li><p>Show <var>message</var> to the user, treating U+000A LF as a line break.</p></li>
+   <li><p>Let <var>userPromptHandler</var> be <span>WebDriver BiDi user prompt opened</span> with
+   <span>this</span>, "<code data-x="">alert</code>", and <var>message</var>.</p></li>
 
-   <li><p>Invoke <span>WebDriver BiDi user prompt opened</span> with <span>this</span>,
-   "<code data-x="">alert</code>", and <var>message</var>.</p></li>
+   <li><p>If <var>userPromptHandler</var> is "<code data-x="">none</code>":</p>
+    <ol>
+     <li><p>Show <var>message</var> to the user, treating U+000A LF as a line break.</p></li>
 
-   <li><p>Optionally, <span>pause</span> while waiting for the user to acknowledge the
-   message.</p></li>
+     <li><p>Optionally, <span>pause</span> while waiting for the user to acknowledge the
+     message.</p></li>
+    </ol>
+   </li>
 
-   <li><p>Invoke <span>WebDriver BiDi user prompt closed</span> with <span>this</span>
-   and true.</p></li>
+   <li><p>Invoke <span>WebDriver BiDi user prompt closed</span> with <span>this</span>,
+   "<code data-x="">alert</code>", and true.</p></li>
   </ol>
 
   <p class="note">This method is defined using two overloads, instead of using an
@@ -114068,16 +114080,27 @@ function sendData(data) {
    <li><p>Show <var>message</var> to the user, treating U+000A LF as a line break, and ask the user
    to respond with a positive or negative response.</p></li>
 
-   <li><p>Invoke <span>WebDriver BiDi user prompt opened</span> with <span>this</span>,
-   "<code data-x="">confirm</code>", and <var>message</var>.</p></li>
+   <li><p>Let <var>userPromptHandler</var> be <span>WebDriver BiDi user prompt opened</span> with
+   <span>this</span>, "<code data-x="">confirm</code>", and <var>message</var>.</p></li>
 
-   <li><p><span>Pause</span> until the user responds either positively or negatively.</p></li>
+   <li><p>Let <var>accepted</var> be false.</p></li>
+
+   <li><p>If <var>userPromptHandler</var> is "<code data-x="">none</code>":</p>
+
+    <ol>
+     <li><p><span>Pause</span> until the user responds either positively or negatively.</p></li>
+
+     <li><p>If the user responded positively set <var>accepted</var> to true</p></li>
+    </ol>
+   </li>
+
+   <li><p>If <var>userPromptHandler</var> is "<code data-x="">accept</code>" set <var>accepted</var> to
+   true.</p></li>
 
    <li><p>Invoke <span>WebDriver BiDi user prompt closed</span> with <span>this</span>,
-   and true if the user responded positively or false otherwise.</p></li>
+   "<code data-x="">confirm</code>", and <var>accepted</var>.</p></li>
 
-   <li><p>If the user responded positively, return true; otherwise, the user responded negatively:
-   return false.</p></li>
+   <li><p>Return <var>accepted</var>.</p></li>
   </ol>
 
   <p>The <dfn method for="Window"><code data-x="dom-prompt">prompt(<var>message</var>,
@@ -114100,18 +114123,29 @@ function sendData(data) {
    to either respond with a string value or abort. The response must be defaulted to the value given
    by <var>default</var>.</p></li>
 
-   <li><p>Invoke <span>WebDriver BiDi user prompt opened</span> with <span>this</span>,
-   "<code data-x="">prompt</code>", <var>message</var>, and <var>default</var>.</p></li>
+   <li><p>Let <var>userPromptHandler</var> be <span>WebDriver BiDi user prompt opened</span> with
+   <span>this</span>, "<code data-x="">prompt</code>" and <var>message</var>.</p></li>
 
-   <li><p><span>Pause</span> while waiting for the user's response.</p></li>
+   <li><p>Let <var>result</var> be null.</p></li>
 
-   <li><p>Let <var>result</var> be null if the user aborts, or otherwise the string that the user
-   responded with.</p></li>
+   <li><p>If <var>userPromptHandler</var> is "<code data-x="">none</code>":</p>
+
+    <ol>
+     <li><p><span>Pause</span> while waiting for the user's response.</p></li>
+
+     <li><p>If the user did not abort, set <var>result</var> to the string that the user
+     responded with.</p></li>
+    </ol>
+   </li>
+
+   <li><p>Otherwise if <var>userPromptHandler</var> is "<code data-x="">accept</code>", set <var>result</var>
+   to the emtpy string.</p></li>
 
    <li><p>Invoke <span>WebDriver BiDi user prompt closed</span> with <span>this</span>,
-   false if <var>result</var> is null or true otherwise, and <var>result</var>.</p></li>
+   "<code data-x="">prompt</code>", false if <var>result</var> is null or true otherwise,
+   and <var>result</var>.</p></li>
 
-   <li><p>Return <var>result</var>.</li>
+   <li><p>Return <var>result</var>.</p></li>
   </ol>
 
   <p>To <dfn>optionally truncate a simple dialog string</dfn> <var>s</var>, return either