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chromium/content/test/data/accessibility/aria/aria-labelledby-heading.html 

<!--
@BLINK-ALLOW:hierarchicalLevel*
@MAC-ALLOW:AXTitleUIElement
-->
<!DOCTYPE html>
<html>
<body>
  <input aria-labelledby="h2">
  <h2 id="h2">h2</h1>
</body>
</html>