What ClipPlaneAllocator.allocate hands back: the clip a node's subtree inherits, and the mask draw that makes it true.
Readonly
Accumulated bit planes of this clip and every enclosing one.
The record every item in the subtree carries.
The record the clip node's own mask draw carries.
What ClipPlaneAllocator.allocate hands back: the clip a node's subtree inherits, and the mask draw that makes it true.