YOu know, I've been pondering this since you posted your comment and I honestly can't decide where the line is between "outside source" and a crossover... I mean, in a way it seems like an easy answer -- if you're using two series extensively, or whatever, then it's probably a crossover. But if that's not the intention, if it's telling a story about the one character and there's a way to set up some kind of alternate text... arg! I could drive myself crazy. I guess I'll need to take it on a case by case basis.