The user-written USER-FORMAT-ROUTINE performs format operations.
    The symbiont's control logic routine calls your format routine
    at one of two possible points within the symbiont's execution
    stream. You select this point by specifying one of two routine
    codes when you call the PSM$REPLACE routine.

    A user format routine can be an input filter routine (routine
    code PSM$K_INPUT_FILTER) or an output filter routine (routine
    code PSM$K_OUTPUT_FILTER). The main format routine (routine code
    PSM$K_MAIN_FORMAT) cannot be replaced.

    A user format routine must use the call interface described here.

    Format

      USER-FORMAT-ROUTINE  request_id ,work_area ,func ,func_desc_1

                           ,func_arg_1 ,func_desc_2 ,func_arg_2