Marks a VisualElement that hosts non-rectangular descendants using the "overflow: hidden;" style. Non-rectangular masks are implemented with the stencil. If applicable, the renderer breaks the batch to preemptively set the stencil state, before and after drawing the descendants, so that the descendants won't have to set them at the next masking level. When using this flag, consecutive stencil push/pop operations are cheap and don't require modifying the stencil reference. As a result, the batch doesn't need to be broken for each push/pop operation. Consecutive push/push or pop/pop operations are still expensive. Avoid cases that involve many subtrees, where each subtree uses 2 or more levels of masking, to avoid consecutive push/push or pop/pop operations.
This flag is implicitly set on the root VisualElement, making single-level masks non-batch-breaking by default.