VMS Help MMS, Description File, Action line prefixes  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    An action line prefix is a modifier that controls the processing of a
    single action line in a description file.  The action line prefixes
    are:

    Prefix           Function

    - (Ignore)       Causes MMS to ignore errors generated by the action
                     line on which the prefix appears.

    @ (Silent)       Suppresses the writing to the output file of the
                     action line  on which the prefix appears. (The output
                     file can be either SYS$OUTPUT or the file specified
                     by the /OUTPUT qualifier).

    ?name (Severity) Use named user-defined severity rule to convert the
                     status returned by the action line to the equivalent
                     VMS severity. Select 'Description_File' subtopic
                     'User_Defined_Severity' for more information.

    An action line prefix must appear as the first character on an action
    line.   The rest of the action line must be separated from the prefix
    by at least one space or tab.  To  use  more than  one prefix  on the
    same action line, type them next to each other with no intervening
    spaces; they must be separated from the rest of the action line with at
    least one space or tab.