question about REUSE_ALV_LIST_DISPLAY .

Hi all,

Please tell me about the interface parameter I_CALLBACK_PROGRAM. The documentation says:

"Program which calls the function module and contains the exit routines. It must be a Report, Function group, Module pool or Form routine pool (not an Include).

Note: Never pass SY-REPID directly in the interface. If the desired program name is in SY-REPID, it must be assigned to an intermediate variable which is then passed to the interface."

Mu questions:

1) What is meant by contains the exit routines.

2) How can Function group call this FM?

3) Why should we not use sy-repid directly?

4) What if we don't use this parameter (as this is an optional parameter)?

Thanks,

Charles.