invo_handle

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

    Handle for the desired invocation. Returned by LIB$GET_INVO_
    HANDLE.

 invo_context

    OpenVMS usage:invo_context_blk
    type:         structure
    access:       write only
    mechanism:    by reference

    Address of an invocation context block into which the procedure
    context of the frame specified by invo_handle will be written.