A class that abstracts and manages validity relationships in a directed acyclic graph. If an object is invalid, its parent, grandparent (etc.), and downstream objects in that graph are also seen to be invalid.
Implemented by any object that has a state of validity that is managed by a ValidationService.
A callback that is expected to be invoked when something's state of validity changes.
Specifies whether, from the perspective of a Validity service, something is valid.