JavaFX unnecessarily restricts interpolation in the following ways:
1. `Interpolatable` values often clamp intermediate values to the interpolation factor range [0,1].
2. `SplineInterpolator` doesn't accept values larger than 1 or less than 0 for the Y coordinate of its control points.

As a consequence, many types of animations can't be modeled in JavaFX. The solution is to relax the restrictions, as they are not required.