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chromium/content/test/data/accessibility/event/live-region-change-on-freshly-unignored-node.html 

<!DOCTYPE html>
<html>
<body>
<div id="live" aria-live="polite" style="display: none;">Before</div>
<script>
  function go() {
    let live = document.getElementById('live');
    live.setAttribute("style", "");
    live.firstChild.data = 'After';
  }
</script>
</body>
</html>