GRUB Legacy, as far as I know, doesn't support anything like that unless you're a real hungry coder
Don't know about GRUB 2's yet-unstable releases, haven't tried and probably won't before they're close to something I can rely on.
Read GRUB website rather than Wikipedia, if you want the facts about GRUB. If you want to know about what a skilled coder could do with GRUB sources, or something else, then read Wikipedia. Note that it's written by anyone, not necessarily a person who knows things well - some of the content, I understand, is completely based off hearsays.