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chromium/chrome/test/data/extensions/api_test/executescript/destructive/xhtml_document.xhtml 

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <title>Some valid XHTML document</title>
</head>
<body>
  This is a XHTML document.
</body>
</html>