In REXX there are three class types:
An object class (the default) can create instance objects in response to receiving a NEW or ENHANCED message. An abstract class serves mainly to organize other classes in the hierarchy and define their message interface, rather than create objects. A mixin class, through multiple inheritance, can be designated as an additional superclass to a class. The mixin class typically possesses methods useful to the class that inherits it, but these must be specifically added because they lie outside the class's normal line of inheritance.
The following sections explain these class types in more detail.