VMS Help CLI Routines, CLI$DISPATCH, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 userarg

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    Data to be passed to the action routine. The userarg argument
    is a longword that contains the data to be passed to the action
    routine. This data can be used in any way you want.