@namespace a url(http://www.example.org/a);
@namespace b url(http://www.example.org/b);
@namespace html url(http://www.w3.org/1999/xhtml);
*|p, *|q, *|r, *|s { display : block ; margin-bottom : 1em }
*|p, *|r { background-color : red }
*|*[a|foo~="bar"], *|*[|class~="bar"] { background-color : lime }
*|*[html|class~="bar"] { background-color : red }

 <p class="t bar u">This paragraph should have a green background.</p>
 <q xmlns="http://www.example.org/a" a:foo="hgt bardot f">This paragraph should be unstyled.</q>
 <r xmlns="http://www.example.org/a" a:foo="hgt bar f">This paragraph should have a green background.</r>
 <s xmlns="http://www.example.org/b" b:foo="hgt bar f">This paragraph should be unstyled.</s>