anchor.diff:                                    (timezone *default-timezone*))
     "Formats a timestring in the RFC 3339 format, a restricted form of the ISO-8601 timestring specification for Internet timestamps."
     (let ((rfc3339-format
  -         (append
  -          (unless omit-date-part
  -            '((:year 4) #\-
  -              (:month 2) #\-
  -              (:day 2)))
  -          (unless (or omit-date-part
  -                      omit-time-part)
  -            '(#\T))
  -          (unless omit-time-part
  -            '((:hour 2) #\:
  -              (:min 2) #\:
  -              (:sec 2) #\.
  -              (:usec 6)))
  -          (unless omit-timezone-part
  -            (if use-zulu
  -                '(:gmt-offset-or-z)
  -                '(:gmt-offset))))))
  +         (if (and use-zulu
  +                  (not omit-date-part)
  +                  (not omit-time-part)
  +                  (not omit-timezone-part))
  +             +rfc3339-format+ ; micro optimization
  +             (append
  +              (unless omit-date-part
  +                '((:year 4) #\-
  +                  (:month 2) #\-
  +                  (:day 2)))
  +              (unless (or omit-date-part
  +                          omit-time-part)
  +                '(#\T))
  +              (unless omit-time-part
  +                '((:hour 2) #\:
  +                  (:min 2) #\:
  +                  (:sec 2) #\.
  +                  (:usec 6)))
  +              (unless omit-timezone-part
  +                (if use-zulu
  +                    '(:gmt-offset-or-z)
  +                    '(:gmt-offset)))))))
       (format-timestring destination timestamp :format rfc3339-format :timezone timezone)))
   
   (defun %read-timestring (stream char)
  
positive.code:            #:+hours-per-day+
             #:+days-per-week+
             #:+iso-8601-format+
             #:+asctime-format+
             #:+rfc-1123-format+
             #:astronomical-julian-date
  
negative.code:   '((:year 4) #\- (:month 2) #\- (:day 2) #\T
      (:hour 2) #\: (:min 2) #\: (:sec 2) #\.
      (:usec 6) :gmt-offset-or-z))
  (defparameter +rfc3339-format+
    '((:year 4) #\- (:month 2) #\- (:day 2) #\T
      (:hour 2) #\: (:min 2) #\: (:sec 2) #\.
      (:usec 6) :gmt-offset-or-z))
  (defparameter +rfc3339-format/date-only+
    '((:year 4) #\- (:month 2) #\- (:day 2)))
  (defparameter +asctime-format+
    '(:short-weekday #\space :short-month #\space (:day 2 #\space) #\space
      (:hour 2) #\: (:min 2) #\: (:sec 2) #\space
  