synchronized.

Cocoa's design is a fairly, but not absolutely strict application of MVC principles. Under OpenStep, most of the classes provided were either high-level View classes (in AppKit) or one of a number of relatively low-level model classes like NSString. Compared to similar MVC systems, OpenStep lacked a strong model layer. No stock class represented a "document," for instance. During the transition to Cocoa, the model layer was expanded greatly, introducing a number of pre-rolled classes to provide functionality common to desktop