invo_handle_in

    OpenVMS usage:invo_handle
    type:         quadword
    access:       read only
    mechanism:    by reference

    The address of an invocation handle that represents a target
    invocation context.

 invo_handle_out

    OpenVMS usage:invo_handle
    type:         quadword
    access:       write only
    mechanism:    by reference

    Address of the location into which the invocation context handle
    of the previous context is to be written. If the call fails, the
    value of the previous invocation context handle is LIB$K_INVO_
    HANDLE_NULL.