It's talking about the number's bits that it returns. So say if it's B001 You're looking at, if only that is happening then it will return 1. For B002 It would be 2 (10 in binary) and so on.

but isn't it supposed to return a number?

Yes it does. Say it returns 3. 3 in binary is 11. So that means that the sprite is being animated for b001 and b002 (unless it starts from 0).

What about magnification xy? I'm confused.

Because magnification XY is b05 (32), it would return 32.

huh. How do I get the amount of magnification from a sprite?