Rearrangeable Listbox Example: Add note on APG vs. browser multiselec…

…t listbox keyboard pattern (pull #2476)


Co-authored-by: Matt King <[email protected]>

content/patterns/listbox/examples/listbox-rearrangeable.html

@@ -264,7 +264,14 @@ <h2 id="kbd_label">Keyboard Support</h2>
         </tr>
       </tbody>
     </table>
-    <h4 id="kbd_label_multiselect">Multiple selection keys supported in example 2</h4>
+    <h3 id="kbd_label_multiselect">Multiple selection keys supported in example 2</h3>
+    <p class="note">
+      The selection behavior demonstrated differs from the behavior provided by browsers for native HTML <code>&lt;select multiple&gt;</code> elements.
+      The HTML select element behavior is to alter selection with unmodified up/down arrow keys, requiring the use of modifier keys to select multiple options.
+      This example demonstrates  the multiple selection interaction model recommended in the
+      <a href="../listbox-pattern.html#keyboard_interaction">Keyboard Interaction section of the Listbox Pattern</a>,
+      which  does not require the use of modifier keys.
+    </p>
     <table aria-labelledby="kbd_label_multiselect" class="def">
       <thead>
         <tr>