VMS Help SCA, SCA Topics, Callable Routines, SCA$PUT_OUTPUT, Arguments  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 string
    type:       character string
    access:     read only
    mechanism:  by descriptor

    String to be written to SYS$OUTPUT. You can concatenate one or
    more additional character strings with the primary string to form
    a single output record. You can specify a maximum of 20 strings.
    The maximum resulting record length is 255 characters.

 user_argument
    type:       _UNSPECIFIED
    access:     read only
    mechanism:  by reference

    User-specified value that was passed to the routine that called
    this action routine.