can GPL apply to more than source and object code?

[Nelson Rush]

Can the GPL apply to documentation, art, movies, models, game maps, etc.?
I'm the leader of the QuakeForge project and we've been arguing about
whether or not we should have a different license for each of these things.
I saw the FDL on the GNU website and thought that maybe we should use that
on our documentation and then write our own license for other media. What's
the deal? Thanks.