Take a look at http://www.w3.org/TR/css3-ui/#pseudo-choices  :

"Similarly, a form element which represents a list of options may 
contain both a label for the list, and the list of choices itself. For 
such elements, the ::choices pseudo-element selects the representation 
of just the list of choices themselves, in order to style their appearance."

It seems that ::choices should also apply to nl elements.

-- 
Sjoerd Visscher
http://w3future.com/weblog/