Custom interface control objects may adopt this protocol to partake in the Application Kit's automated validation mechanism. User interface validation works by having user interface items, such as buttons or text fields, query the targets of their action about whether or not they should be enabled. This protocol is closely related to the NSUserInterfaceItemValidations protocol, which declares the method validateUserInterfaceItem: for target objects to implement.

@protocol NSValidatedUserInterfaceItem
// Instance Methods
- (SEL)action;
- (int)tag;
@end