@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, *|t{ display : block ; margin-bottom : 1em }
*|p, *|r { background-color : red }
*|*[|title="si on chantait"] { background-color : lime }

<p title="si on chantait">This paragraph should have a green background</p>
<q xmlns="http://www.example.org/a" a:title="si on chantait">This paragraph should NOT
          have a green background</q>
<r xmlns="http://www.example.org/a" title="si on chantait">This paragraph should
          have a green background</r>
<s xmlns="http://www.example.org/b" b:title="si on chantait">This paragraph should NOT
          have a green background</s>
<t xmlns="http://www.example.org/b" title="si nous chantions">This paragraph should NOT
          have a green background</t>