Just as each Workplace Shell object is an instance of a class, the class itself is an instance of another class known as its metaclass. Just as an object has instance data and methods that pertain only to a specific instance of the class, so the metaclass has class data and methods that pertain to the entire class. Such methods are known as class methods, whereas methods that operate only for a particular instance of the class are known as instance methods.
Class methods and data are available to the programmer when creating new object classes. A programmer may introduce new class data and methods for an object class, as well as instance data and methods. Similarly, a new object class may override existing class methods to modify the processing performed by those methods.