This informal protocol provides a way for clients to access a class's instance variables (or other properties) without having to explicitly rely on accessor methods. NSKeyValueCoding provides indirect access to an object's instance variables through the use of strings or keys. The two most commonly used methods in the protocol are takeValue:forKey: and valueForKey:, which are used to set and get the value of an instance variable, respectively. This protocol, and the associated NSScriptKeyValueCoding protocol, both form the basis of scripting in Cocoa. Chapter 2 goes into more detail about this protocol.

@interface NSObject (NSKeyValueCoding)
// Class Methods
+ (BOOL)accessInstanceVariablesDirectly;
+ (BOOL)useStoredAccessor;
// Instance Methods
- (id)valueForKey:(NSString *)key;
- (void)takeValue:(id)value forKey:(NSString *)key;
- (id)storedValueForKey:(NSString *)key;
- (void)takeStoredValue:(id)value forKey:(NSString *)key;
- (id)valueForKeyPath:(NSString *)key;
- (void)takeValue:(id)value forKeyPath:(NSString *)key;
- (NSDictionary *)valuesForKeys:(NSArray *)keys;
- (void)takeValuesFromDictionary:(NSDictionary *)dictionary;
- (id)handleQueryWithUnboundKey:(NSString *)key;
- (void)handleTakeValue:(id)value forUnboundKey:(NSString *)key;
- (void)unableToSetNilForKey:(NSString *)key;
@end