anchor.diff:      (let ((res +nowhere+))
         (loop for (r) in erase-overlapping do (setf res (region-union res r)))
         (loop for (r) in move-overlapping do (setf res (region-union res r)))
  -      (replay history stream res)) ))
  +      (replay history stream res))))
   
   (defclass updating-stream-state (complete-medium-state)
     ((cursor-x :accessor cursor-x :initarg :cursor-x :initform 0)
  
positive.code:     ((record standard-updating-output-record) stream displayer)
    (multiple-value-bind (x y)
        (output-record-position record)
      (when (sub-record record)
        (delete-output-record (sub-record record) record))
      ;; Don't add this record repeatedly to a parent updating-output-record.
      (unless (eq (output-record-parent record)
  		(stream-current-output-record stream))
  
negative.code:   (with-output-recording-options (stream :record t :draw nil)
      (map-over-updating-output
       #'(lambda (r)
           (let ((sub-record (sub-record r)))
             (setf (old-children r) sub-record)
             (setf (output-record-dirty r) :updating)
             (setf (rectangle-edges* (old-bounds r))
                   (rectangle-edges* sub-record))))
       record
       nil)
      (finish-output stream)
  