chromium/content/test/data/accessibility/event/menulist-with-optgroup-next.html

<!--
@DEFAULT-ACTION-ON:Fruit
-->
<!DOCTYPE html>
<html>
<body>
<select aria-label="Fruit" autofocus>
  <optgroup label="Citrus">
    <option selected>Lemon</option>
    <option>Orange</option>
  </optgroup>
  <optgroup label="Other">
    <option>Apple</option>
    <option>Banana</option>
  </optgroup>
</select>
<script>
function go() {
  document.querySelector('select').selectedIndex = 1;
}
</script>
</body>
</html>