gecko-dev/testing/web-platform/tests/css/selectors

The format is:

   <csstest xmlns="http://www.example.org/css3tests"
      def="<put the title of the test here>"
      module="W3C Selectors"
      modulename="css3-modsel"
      number="<put your initials here>-<give each test a unique number>"
      rev="1.0"
      date="1-january-1979 <edit the date keeping the format>">
    <author><!-- Put your name here --></author>
    <cssrules>
     /* put the rules here */
    </cssrules>
    <code>
     <p xmlns="http://www.w3.org/1999/xhtml"> Put the test here. </p>
    </code>
   </csstest>


You can also use a special <restrict> element in elements in the <code>
element, as in:

  <test:restrict xmlns:test="http://www.example.org/css3tests" for="xml xhtml">
   ...
  </test:restrict>

See test -d2 for an example.