Whether the child is hidden from the rest of the tree.
If true, the child is laid out as if it was in the tree, but without painting anything, without making the child available for hit testing, and without taking any room in the parent.
Offstage children are still active: they can receive focus and have keyboard input directed to them.
Animations continue to run in offstage children, and therefore use battery and CPU time, regardless of whether the animations end up being visible.
If false, the child is included in the tree as normal.
final bool offstage