Nice idea, I guess you should use "url:()" instead of "use:()" to make it resemble css rules more (like used in 'background-image')
hm… I'm not sure. Yes, :url() would be more common but it couldn't be clear enough what's menat here. use came into my mind as it's similar to some css3 selectors. But maybe there are more thoughts on it?
changed code to a better and backwards compatible solution.