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chromium/third_party/blink/web_tests/external/wpt/css/css-page/page-name-orthogonal-writing-001-print-ref.html 

<!DOCTYPE html>
<html style="writing-mode: vertical-rl">
  <body>
    <div style="writing-mode: horizontal-tb">
      <div>a</div>
      <div>b</div>
    </div>
  </body>
</html>