An object that provides one or more of the following options: - beforeShown: a function that is called after boundary behavior ...

An object that provides one or more of the following options:
- beforeShown: a function that is called after boundary behavior has been applied but before the screen is shown.
+ Signature: beforeShown(screen)
- afterClosed: a function that is called after boundary behavior has been applied and the screen has been closed.
+ Signature: afterClosed(screen, action : msls.NavigateBackAction)