Source file written in the Restructured Extended Executor (Rexx) programming language, a scripting and macro language mainly used to generate reports and process data; contains source code, which includes functions, variables, and other statements that tell the program how to function.

REXX is the default file extension used by the Regina Rexx Interpreter. There are several other free Rexx interpreters available, including Reginald and BRexx, that support the REXX fie.