Call SOR$SPEC_FILE to pass a specification file name or a buffer
    with specification text to a sort or merge operation. Through
    the use of a specification file, you can selectively omit or
    include particular records from the sort or merge operation and
    specify the reformatting of the output records. (See the Sort
    Utility in the OpenVMS User's Manual for a complete description
    of specification files.)

    If you call the SOR$SPEC_FILE routine, you must do so before you
    call any other routines. You must pass either the spec_file or
    spec_buffer argument, but not both.

    Some of the return condition values are used with different
    severities, depending on whether SORT/MERGE can recover. Thus,
    if you want to check for a specific status, you should use
    LIB$MATCH_COND.