anchor.diff:                             (setf offset-hour 0
                                    offset-minute 0))
                            (if (= count 1)
  -                             (passert allow-missing-timezone-part-p)
  +                             (passert allow-missing-timezone-part)
                                (let* ((entry (second parts))
                                       (start (car entry))
                                       (end (cdr entry)))
  
positive.code:                      (cond ((= count 2)
                              (if (first parts)
                                  (full-date (first parts))
                                  (passert allow-missing-date-part-p))
                              (if (second parts)
                                  (full-time (second parts))
                                  (passert allow-missing-time-part-p))
                              (done))
                             ((and (= count 1)
                                   allow-missing-date-part-p
                                   (find time-separator time-string
                                         :start (car (first parts))
                                         :end (cdr (first parts))))
                              (full-time (first parts))
                              (done))
                             ((and (= count 1)
                                   allow-missing-time-part-p
                                   (find date-separator time-string
                                         :start (car (first parts))
                                         :end (cdr (first parts))))
  
negative.code:     (coerce result 'simple-base-string)))
  
  (defun format-rfc3339-timestring (destination timestamp &key
                                    omit-date-part
                                    omit-time-part
                                    omit-timezone-part
                                    (use-zulu t)
                                    (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))))))
      (format-timestring destination timestamp :format rfc3339-format :timezone timezone)))
  
  (defun %read-timestring (stream char)
    (declare (ignore char))
  