context

    OpenVMS usage:context
    type:         longword (unsigned)
    access:       write only
    mechanism:    by reference
    Value identifying the data stream that DCX$COMPRESS_INIT
    initializes. The context argument is the address of a longword
    containing this value. You should not modify the context value
    after DCX$COMPRESS_INIT initializes it. You can define multiple
    context arguments to identify multiple data streams that are
    processed simultaneously.

 map

    OpenVMS usage:address
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference
    The function created by DCX$MAKE_MAP. The map argument is the
    address of the compression/expansion function's virtual address.

    The map argument must remain at this address until data
    compression is completed and the context is deleted by means
    of a call to DCX$COMPRESS_DONE.