switch ( $type )  { 
            case  'dt' : 
                if ( preg_match ( '/^(\d\d\d\d)-(\d\d?)-(\d\d?)$/' ,  $value ,  $m ) )  { 
                    return  sprintf ( '%d-%02d-%02d' ,  $m [ 1 ] ,  $m [ 2 ] ,  $m [ 3 ] ) ; 
                }