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chromium/content/test/data/accessibility/html/optgroup.html 

<!--
@MAC-ALLOW:AXRoleDescription
@WIN-ALLOW:xml-roles*
@WIN-ALLOW:IA2_STATE_VERTICAL
@WIN-ALLOW:SELECTABLE
@UIA-WIN-ALLOW:Value.IsReadOnly*
@BLINK-ALLOW:setSize*
@BLINK-ALLOW:posInSet*
@AURALINUX-ALLOW:xml-roles*
@AURALINUX-ALLOW:posinset*
@AURALINUX-ALLOW:setsize*
@AURALINUX-ALLOW:enabled
-->
<!DOCTYPE html>
<html>
<body>

<select size="10" id="listbox">
<optgroup label="Enabled" id="listbox_optgroup_enabled">
    <option value="listbox_e1" id="listbox_option_enabled_one">One</option>
    <option value="listbox_e2">Two</option>
    <option value="listbox_e3">Three</option>
    <option value="listbox_e4">Four</option>
</optgroup>
<optgroup label="Disabled" disabled id="listbox_optgroup_disabled">
    <option value="listbox_d1" id="listbox_option_disabled_one">One</option>
    <option value="listbox_d2">Two</option>
    <option value="listbox_d3">Three</option>
    <option value="listbox_d4">Four</option>
</optgroup>
</select>

<select id="menulist">
  <option>Random Transformer</option>
  <optgroup label="group 1">
    <option>Optimus Prime</option>
    <option>Bumblebee</option>
    <option>Jazz</option>
  </optgroup>
  <optgroup label="group 2">
    <option>Megatron</option>
    <option>Starscream</option>
    <option>Brawl</option>
  </optgroup>
</select>

</body>
</html>