Add note with examples for ignoring eligibility/shared-autofill

source

@@ -55618,7 +55618,7 @@ form.method === input; // => true</code></pre>
    <span data-x="concept-document-origin">origin</span>.</p></li>
   </ul>
 
-  <div class="example">
+  <div class="example" id="sharedAutofillExample">
    <p>Consider the following page <code data-x="">https://pizza.example.com/</code>:</p>
 
    <pre><code class="html">&lt;form method=post>
@@ -55648,6 +55648,26 @@ form.method === input; // => true</code></pre>
    feature; this prevents leaking information to the ad server.</p>
   </div>
 
+  <div class="note">
+  <p>The user agent does not have to fill in all eligible form controls, and it can fill
+  in form controls that are not eligible. In particular, it can ignore
+  <code data-x="shared-autofill-feature">shared-autofill</code> depending on the type of data
+  to be filled and the relationships of the controls' <span>node navigable</span>s. For example:</p>
+
+  <ul>
+   <li><p>The user agent can ignore <code data-x="shared-autofill-feature">shared-autofill</code>
+   when filling in usernames and passwords which are associated to a specific
+   <span data-x="concept-document-origin">origin</span>.</p></li>
+   <li><p>The user agent can ignore <code data-x="shared-autofill-feature">shared-autofill</code>
+   in <code>Document</code>s whose <span>navigable</span> is not a <span>descendant</span>
+   of the <span>fully active descendant of a top-level traversible with user attention</span>
+   because payment form controls are frequently hosted in cross-origin <code>iframe</code>s
+   like in the <a href="#sharedAutofillExample">example above</a>.
+   <li><p>The user agent can fill in cross-origin form controls because the user
+   consented.</p></li>
+  </ul>
+  </div>
+
 
   <h6>The <code data-x="attr-fe-autocomplete">autocomplete</code> attribute</h6>