Clipping and Masking are 2 different concepts and what JavaFX calls a clip on a node right now is really a mask.

Clip should mean -> Define the renderable bounds of a Node and don't render outside that, bounds are defined as a Rectangle2D object
Mask should mean -> Define a shape to display and a shape to mask against, the mask is then composited against the displayable shape to generate the final output.

Right now JavaFX is using the concept of masking as a "clip" and it is an inefficient way to provide general purpose clipping. The most common implementations of clipping will be on text fields and groups and will be bounds oriented rather then shape oriented.