desc

    OpenVMS usage:char_string
    type:         character-coded text string
    access:       write only
    mechanism:    by descriptor
    Output record buffer. The desc argument is the address of a
    descriptor pointing to the buffer that receives the sorted or
    merged record.

 length

    OpenVMS usage:word_unsigned
    type:         word (unsigned)
    access:       write only
    mechanism:    by reference
    Length of the output record. The length argument is the address
    of a word receiving the length of the record returned from
    SORT/MERGE.

 context

    OpenVMS usage:context
    type:         longword (unsigned)
    access:       modify
    mechanism:    by reference
    Value that distinguishes between multiple, concurrent SORT/MERGE
    operations. The context argument is the address of a longword
    containing the context value. When your program makes its first
    call to a SORT/MERGE routine for a particular sort or merge
    operation, the context longword must equal zero. SORT/MERGE
    then stores a value in the longword to identify the operation
    just initiated. When you make subsequent routine calls for the
    same operation, you must pass the context value supplied by
    SORT/MERGE.