Your best bet on "documentation" for GC is to take the Game Core course. It is actually pretty good and your tutor answers questions. You are given scripts and demos to work with and tear apart. They also give you game content you can use in your own games.

Every Wednesday you got video tutorials for that lesson and course material to work with. You had your own course download page and the forums where you could ask questions about that week's lesson. At the end of the course you ended up with a working game.

Game Core Course <-- I requested that they do a game course like this for A7. Maybe if there is enough interest he will do it. I would love to see a course like this for A7 as this was excellent.