/BACKUP=keyword(=value) This qualifier is used in combination
    with 3 possible keywords : BEFORE=date, SINCE=date or NONE. The
    backup date is used in for selecting files. Use SINCE and BEFORE
    or NONE, but not both. The NONE keyword returns files which don't
    have a backup date recorded. Examples :

    o  /BACKUP=BEFORE=date

    o  /BACKUP=(BEFORE=date,SINCE=anotherdate)

    o  /BACKUP=NONE