pragma strict create List of Array of strings for class?

I'm declaring a class that holds animation frames, each frame is a list of rotations which are strings.

for example animation[0].frames[0]=a list of strings.
pragma strict
class animation{
var name:String;
var frames:?
}

how do I declare the frames class using lists? I'm writing this with < as t because this field erases my tags. My guesses so far are not working... frames:[List.tStringt,List.tStringt?]

Thanks,