Object REXX includes features typical of an object-oriented language--features like subclassing, polymorphism, and data encapsulation. As we said at the outset, Object REXX is an extension of the traditional REXX language, which has been expanded to include classes, objects, and methods. These extensions do not replace traditional REXX functions, or preclude the development or running of traditional REXX programs. You can program as before, program with objects, or intermix objects with regular REXX instructions. You decide when to use REXX's object-oriented features. The REXX programming concepts that support these features are the subject of this section.