Whenever an application issues the STACK macro to add either a terminal element or an input file name to the input stack, the STACK service routine protects the previous contents of the REXX data stack by placing a terminal element, MARKTERM, on the REXX data stack. Similarly, when the terminal element or input file name is being removed from the input stack, the STACK service routine removes the MARKTERM terminal element from the REXX data stack.

However, when you create an alternate input stack, the STACK service routine will protect the REXX data stack through MARKTERM, but you must remove the MARKTERM element from the REXX data stack when you have completed using the alternate input stack. You can create an alternate input stack by clearing the ECTIOWA field in the ECT and then invoking the STACK macro to add a terminal element or an input file name. When you have completed using this alternate input stack, invoke the REXX stack routine, IRXSTK, with a function call of DROPTERM to remove the MARKTERM terminal element from the REXX data stack. By issuing DROPTERM when the input stack is no longer in use, you will keep the REXX data stack in synchronization with the input stack.