chromium/third_party/blink/web_tests/css3/selectors3/xml/css3-modsel-166.xml

<?xml-stylesheet href="css3-modsel-166.css" type="text/css"?>
<test>
   <p xmlns="http://www.w3.org/1999/xhtml">The first letter of this paragraph should have a green background.</p>
</test>