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chromium/content/test/data/accessibility/event/tabindex-removed-on-aria-hidden.html 

<!DOCTYPE html>
<html>
<body>
<div id="d" tabindex="0" aria-hidden="true"></div>
<script>
  function go() {
    document.querySelector('#d').removeAttribute('tabindex');
  }
</script>
</body>
</html>