Can't find yield namespace

Hello. I know I'm missing something simple, but I can not seem to find the namespace for yield. It's supposed to be in the System.Collections namespace (which is referenced and works because other classes are found), but I can not seem to get yield to show up. Am I missing something? API compatiblity is .Net 2.0 not .Net 2.0 subset (although, it doesn't make a difference either way). thanks![alt text][1] [1]: /storage/temp/69844-missingyield.png