Abstract classes provide definitions for instance methods and class methods but are not intended to create instances. Abstract classes often define the message interfaces that subclasses should implement.
You create an abstract class like object or mixin classes. No extra messages or keywords on the ::CLASS directive are necessary. Rexx does not prevent users from creating instances of abstract classes. It is possible to create abstract methods on a class. An abstract method is a placeholder that subclasses are expected to override. Failing to provide a real method implementation will result in an error when the abstract version is called.