@tarunon https://developer.apple.com/documentation/objectivec/nsobjectprotocol
Class, and the place of its class in the inheritance hierarchy. Conformance to protocols. Ability to respond to a particular message. The Cocoa root class NSObject adopts this protocol, so all objects inheriting from NSObject have the features described by this protocol.
An object that conforms to this protocol can be considered a first-class object. Such an object can be asked about its: