An NSNumber object that contains a value corresponding to one of the NSKeyValueChangeKindKey enumerations, indicating what sort of change has occurred.

A value of NSKeyValueChangeSetting indicates that the observed object has received a setValue:forKey: message, or that the key-value-coding-compliant set method for the key has been invoked, or that willChangeValueForKey:/didChangeValueForKey: has otherwise been invoked.

A value of NSKeyValueChangeInsertion, NSKeyValueChangeRemoval, or NSKeyValueChangeReplacement indicates that mutating messages have been sent to the array returned by a mutableArrayValueForKey: message sent to the object, or that one of the key-value-coding-compliant array mutation methods for the key has been invoked, or that willChange:valuesAtIndexes:forKey:/didChange:valuesAtIndexes:forKey: has otherwise been invoked.

You can use NSNumber's intValue method to retrieve the integer value of the change kind.

Available in Mac OS X v10.3 and later.