VMS Help BACKUP_API, BACKUP$START, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 argument-buffer

    OpenVMS usage:user-defined array
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference
    Arguments that specify the BACKUP operation to be performed.
    The argument-buffer argument is the address of a variable-length
    array of one or more Backup API option structures that define
    the attributes of the requested BACKUP operation. The variable-
    length array is terminated by an option structure of 16 bytes
    that contains all zeros.

                                   NOTE

       The length of the terminating option structure is 2
       longwords (16 bytes). The first longword identifies the
       option structure and has a value of 0. It is recommended
       that the second longword contain a value of 0.

    For more information on the Backup API option structures, refer
    to the OpenVMS Utility Routines Manual.