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chromium/content/test/data/accessibility/aria/aria-grid-aria-selected.html 

<html>
<body>
  <div role="grid" aria-label="my_grid">
    <div role="row">
      <span role="columnheader">Browser</span>
      <span role="columnheader">Rendering Engine</span>
    </div>
    <div role="row">
      <span aria-selected="true" role="gridcell">Chrome</span>
      <span role="gridcell">Blink</span>
    </div>
  </div>
</body>
</html>