anchor.diff:        (write-string result (if (eq t destination) *standard-output* destination)))
       result))
   
  -(defun format-rfc1123-timestring (destination timestamp)
  +(defun format-rfc1123-timestring (destination timestamp &key
  +                                  (timezone *default-timezone*))
     (format-timestring destination timestamp
                        :format +rfc-1123-format+
  -                     :timezone +gmt-zone+))
  +                     :timezone timezone))
   
   (defun to-rfc1123-timestring (timestamp)
     (format-rfc1123-timestring nil timestamp))
  
positive.code: (defparameter +rfc-1123-format+
    ;; Sun, 06 Nov 1994 08:49:37 GMT
    '(:short-weekday ", " (:day 2) #\space :short-month #\space (:year 4) #\space
      (:hour 2) #\: (:min 2) #\: (:sec 2) #\space :timezone)
    "Please note that you should use the +GMT-ZONE+ timezone to format a proper RFC 1123 timestring. See the RFC for the details about the possible values of the timezone field.")
  
  (defparameter +iso-week-date-format+
    ;; 2009-W53-5
  
negative.code:         (with-output-to-string (result nil :element-type 'base-char)
            (dolist (fmt format)
              (cond
                ((member fmt '(:gmt-offset :gmt-offset-or-z :gmt-offset-hhmm))
                 (multiple-value-bind (offset-hours offset-secs)
                     (floor offset +seconds-per-hour+)
                   (declare (fixnum offset-hours offset-secs))
                   (if (and (eql fmt :gmt-offset-or-z) (zerop offset))
                       (princ #\Z result)
                       (format result "~c~2,'0d~:[:~;~]~2,'0d"
                               (if (minusp offset-hours) #\- #\+)
                               (abs offset-hours)
                               (eql fmt :gmt-offset-hhmm)
                               (truncate (abs offset-secs)
                                         +seconds-per-minute+)))))
                ((eql fmt :short-year)
  