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chromium/content/test/data/accessibility/event/aria-spinbutton-value-change.html 

<!DOCTYPE html>
<!--
@WIN-DENY:*
@WIN-ALLOW:EVENT_OBJECT_VALUECHANGE*
-->
<html>
<body>
<div id="spinbutton" role="spinbutton" aria-valuenow="1">
</div>
<script>
  function go() {
    document.getElementById('spinbutton').setAttribute('aria-valuenow', '2');
  }
</script>
</body>
</html>