Clarify that UA should listen to focus change

index.html

@@ -424,8 +424,13 @@ <h2>
                     </p>
                   </li>
                   <li>
-                    <p>If the <a>current settings object</a>'s's [=relevant global object=]'s [=associated Document=]'s
-                      [=top-level browsing context=] is losing <a data-cite="!HTML/#gains-focus">focus</a>,
+                    <p>Let <var>topContext</var> be the <a>current settings object</a>'s's [=relevant global object=]'s
+                      [=associated Document=]'s [=top-level browsing context=].</p>
+                  </li>
+                  <li>
+                    <p>Start listening to <var>topContext</var>'s change of <a data-cite="!HTML/#gains-focus">focus</a>.
+                      Whenever <var>topContext</var> is losing <a data-cite="!HTML/#gains-focus">focus</a>, stop listening
+                      to <var>topContext</var>'s change of <a data-cite="!HTML/#gains-focus">focus</a> and
                       queue a global task on the <a data-cite="!HTML/#user-interaction-task-source">user interaction task source</a>
                       given <a>current settings object</a>'s [=relevant global object=] to run the following step:
                       <ol>
@@ -438,7 +443,7 @@ <h2>
                       This algorithm describes what to do for surface pickers implemented by the <a>user agent</a> but the same
                       requirement applies to surface pickers implemented outside of the <a>user agent</a>,
                       where the loss of capturing document focus is not necessarily the signal triggering setting
-                      {{CaptureController/[[FocusChangeDisabled]]}} to<code>true</code>.
+                      {{CaptureController/[[FocusChangeDisabled]]}} to <code>true</code>.
                     </p>
                   </li>
                   <li>