spline animation

From spec:

*********
keySplines:
The values must all be in the range 0 to 1

********

I'm puzzled by this, if I understand correctly, This limits the possibility
to create smooth curves from one value to the next.

I agree that x1 and x2 should be limited to 0..1, but y1, y2 shouldn't have
that limitation.

Am I misunderstanding something?

thanks,

--
Sigurd Lerstad