setFormValue() returns silently for elements with submit behavior

Author: Ana Sollano Kim

source

@@ -79089,8 +79089,7 @@ dictionary <dfn dictionary>AttachInternalsOptions</dfn> {
    <span>"<code>NotSupportedError</code>"</span> <code>DOMException</code>.</p></li>
 
    <li><p>If <var>element</var> <span data-x="has-behavior">has a behavior</span> of type
-   <code>HTMLSubmitButtonBehavior</code>, then throw a
-   <span>"<code>NotSupportedError</code>"</span> <code>DOMException</code>.</p></li>
+   <code>HTMLSubmitButtonBehavior</code>, then return.</p></li>
 
    <li><p>Set <var>element</var>'s <span
    data-x="face-submission-value">submission value</span> to <var>value</var> if <var>value</var> is
@@ -79110,6 +79109,14 @@ dictionary <dfn dictionary>AttachInternalsOptions</dfn> {
   </ol>
   </div>
 
+  <p class="note">For elements with <code>HTMLSubmitButtonBehavior</code>, <code
+  data-x="dom-ElementInternals-setFormValue">setFormValue()</code> returns without modifying the
+  element's <span data-x="face-submission-value">submission value</span>. During form submission,
+  the <span data-x="constructing the entry list">construct the entry list</span> algorithm uses the
+  behavior's <span data-x="behavior-name">name</span> and <span
+  data-x="behavior-value">value</span> instead, mirroring how native submit buttons contribute their
+  name/value pair only when they are the submitter.</p>
+
   <hr>
 
   <p>Each <span>form-associated custom element</span> has validity flags named