anchor.diff:  
   (defmethod (setf medium-clipping-region) :after (region (medium medium))
     (declare (ignore region))
  -  (let ((sheet (medium-sheet medium)))    
  +  (let ((sheet (medium-sheet medium)))
       (when sheet
         (%invalidate-cached-device-regions sheet))))
   
  
positive.code: 
  (defmethod merge-text-styles (s1 s2)
    (when (and (typep s1 'text-style)
               (typep s2 'text-style)
               (eq s1 s2))
      (return-from merge-text-styles s1))
    (setq s1 (parse-text-style s1))
    (setq s2 (parse-text-style s2))
    (if (and (not (device-font-text-style-p s1))
  	   (not (device-font-text-style-p s2)))
        (let* ((family (or (text-style-family s1) (text-style-family s2)))
               (face1 (text-style-face s1))
               (face2 (text-style-face s2))
               (face (if (subsetp '(:bold :italic) (list face1 face2))
                         '(:bold :italic)
                         (or face1 face2)))
               (size1 (text-style-size s1))
  
negative.code: ;;
  ;;
  ;;; And when you start to think about it, text-styles are not fonts. So
  ;;; we need two protocols: A text style protocol and a font protocol.
  ;;
  ;;; A text style is then something, which maps a sequence of characters
  ;;; into a couple of drawing commands, while probably using some font.
  