[HOpenGL] fullscreen mode

I don't know if I'm missing out on something, but the 'fullscreen' function doesn't seem to work when i try to use it; I just get a "Not in scope: `fullscreen' " error. Am I missing out on something? It's a function that features in several tutorials...it's mentioned in the old documentation, but I seem not to be able to find anything about it in the new one :/