/LIBRARY=disk:[directory]filename.MSGHLP$DATA
    /LIBRARY=disk:[directory]
    /LIBRARY=logical-name

    Defines the messages database for the current command to be
    a particular .MSGHLP$DATA file, all the .MSGHLP$DATA files in
    a specified directory, or all the files in a search path defined
    by a logical name.

    For most operations, the default database is either
    SYS$HELP:MSGHLP$LIBRARY.MSGHLP$DATA or a search path
    of .MSGHLP$DATA files defined by logical name MSGHLP$LIBRARY.

    For /DELETE and /INSERT operations, the default database is
    either SYS$HELP:MSGHLP$LIBRARY.MSGHLP$DATA or the first
    file in a search path defined by logical name MSGHLP$LIBRARY.