frame-title-format

I'm trying to figure out how to give my different frames different names. In particular, I want to create a gnus-only frame and give it a title of "gnus". I want to keep my other frame titles as they are, which is roughly: "XEmacs＠zion [21.1] %b". First I was surprised that the frame title doesn't seem to be a frame property. Then I was surprised that I couldn't make frame-title-format a function. I seem to be thwarted; I could make frame-title-format buffer-local, but that's not what I want, either. Suggestions? TIA, vin