content/test/data/accessibility/event/add-alert.html

<!--
@WIN-DENY:*
@WIN-ALLOW:EVENT_SYSTEM_ALERT*
@UIA-WIN-DENY:*
@UIA-WIN-ALLOW:SystemAlert*
@UIA-WIN-ALLOW:LiveRegionChanged*
-->
<!DOCTYPE html>
<html>
<body>
<div id="a" aria-label="a" role="alert" style="display:none">This is alert #1</div>
<div id="b" aria-label="b" role="alertdialog" aria-live="polite" style="display:none">This is an alert dialog</div>
<div id="c" aria-label="c" role="alert" aria-hidden="true">This is alert #2</div>
<div id="d" aria-label="d" role="alert" aria-hidden="true">This alert shouldn't fire an event</div>
<script>
  const go_passes = [
    () => {
      document.getElementById('a').style.display = "block";
    },
    () => {
      document.getElementById('b').style.display = "block";
    },
    () => {
      document.getElementById('c').setAttribute('aria-hidden', 'false');
    }
  ];

  let current_pass = 0;
  function go() {
    go_passes[current_pass++].call();
    return current_pass < go_passes.length;
  }

</script>
</body>
</html>