Summary

Expressions
Function or subroutine invocation
Built-in functions
Instructions:
   NOP
   SAY, SAYN (local)
   Assignment
   DROP
   NUMERIC
   EXIT
   DO
   LEAVE
   ITERATE
   IF
   SELECT
   PARSE
   QUEUE, PUSH
   CALL (and function calls)
   RETURN
   PROCEDURE
   INTERPRET
   SIGNAL
   SIGNAL ON
   TRACE
   OPTIONS
   ADDRESS
Commands to the environment
The REXX I/O model
The stack
Error messages