anchor.diff:  
   You can see examples in +ISO-8601-FORMAT+, +ASCTIME-FORMAT+, and +RFC-1123-FORMAT+."
     (declare (type (or boolean stream) destination))
  -  (let ((result (%construct-timestring timestamp format timezone)))
  +  (let ((result (%construct-timestring timestamp (if (stringp format) (parse-string-format format) format) timezone)))
       (when destination
         (write-string result (if (eq t destination) *standard-output* destination)))
       result))
  +
  +(define-compiler-macro format-timestring (destination timestamp &key
  +                                                 (format +iso-8601-format+ format-supplied-p)
  +                                                 (timezone '*default-timezone*))
  +  (let ((destination (if (eq t destination) '*standard-output* destination))
  +        (format (if (stringp format)
  +                    `(quote ,(parse-string-format format))
  +                    (if format-supplied-p
  +                        format
  +                        `(quote ,format)))))
  +    (if destination
  +        `(write-string (%construct-timestring ,timestamp ,format ,timezone) ,destination)
  +        `(%construct-timestring ,timestamp ,format ,timezone))))
   
   (defun format-rfc1123-timestring (destination timestamp &key
                                     (timezone *default-timezone*))
  
positive.code:   :MSEC              *milliseconds
    :USEC              *microseconds
    :NSEC              *nanoseconds
    :ISO-WEEK-YEAR     *year for ISO week date (can be different from regular calendar year)
    :ISO-WEEK-NUMBER   *ISO week number (i.e. 1 through 53)
    :ISO-WEEK-DAY      *ISO compatible weekday number (monday=1, sunday=7)
  
negative.code: 
  ;;; Declaims
  
  (declaim (inline now %get-current-time
                   format-rfc3339-timestring to-rfc3339-timestring
                   format-rfc1123-timestring to-rfc1123-timestring)
           (ftype (function (&rest t) simple-base-string) format-rfc3339-timestring)
  