anchor.diff:                            (or (third fmt) #\0)
                             val)))))))))))
   
  -
   (defun format-timestring (destination timestamp &key
                             (format +iso-8601-format+)
                             (timezone *default-timezone*))
  
positive.code:            #:timestamp-year
             #:parse-timestring
             #:format-timestring
             #:format-rfc3339-timestring
             #:encode-timestamp
             #:parse-rfc3339-timestring
  
negative.code: (defun modified-julian-date (timestamp)
    "Returns the modified julian date referred to by the timestamp."
    (- (day-of timestamp) +modified-julian-date-offset+))
  
  (declaim (notinline format-timestring))
  