NSUser protocol works with the
NSValidated protocol to allow the target of a user interface element such as a menu item or a toolbar item to decide whether or not the user interface element should be enabled.
- macOS 10.0+
Your custom classes should adopt this protocol if an instance may be the target of a user interface element and need to conditionally enable or disable the element based on the current state of the instance. For more details, read User Interface Validation.