VMS Help RTL Routines, LIB$, LIB$GET_INVO_HANDLE, Returns  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    OpenVMS usage:invo_handle
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

    Invocation handle of the invocation context that was passed.
    If the returned value is LIB$K_INVO_HANDLE_NULL, the invocation
    context that was passed was invalid.