The SOR$BEGIN_SORT routine initializes the sort process by
    setting up sort work areas and provides key specification and
    sort options.

    Specify the key information with the key_buffer argument, with
    the user_compare argument, or in a specification file. If no key
    information is specified, the default (character for the entire
    record) is used.

    You must use the SOR$BEGIN_SORT routine to initialize the sort
    process for the file, record, and mixed interfaces. For record
    interface on input, you must use the lrl (longest record length)
    argument.

    Some of the following 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.