[css3-images] missing nonterminal

http://dev.w3.org/csswg/css3-images/#image says:
  <image> = <url> | <image-list> | <element-reference> | <image-combination> | <gradient>

But <image-combination> doesn't occur anywhere else in the spec.
Should it?  Or should it be removed?

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                           http://www.mozilla.org/   𝄂