anchor.diff:    (when (typep sheet 'never-repaint-background-mixin)
       (return-from handle-repaint))
     (labels ((effective-repaint-region (mirrored-sheet sheet region)
  -	     (if (eq mirrored-sheet sheet)
  -		 (region-intersection (sheet-region mirrored-sheet) region)
  -		 (effective-repaint-region mirrored-sheet
  -					   (sheet-parent sheet)
  -					   (transform-region (sheet-transformation sheet)
  +             (if (eq mirrored-sheet sheet)
  +                 (region-intersection (sheet-region mirrored-sheet) region)
  +                 (effective-repaint-region mirrored-sheet
  +                                           (sheet-parent sheet)
  +                                           (transform-region (sheet-transformation sheet)
                                                                (region-intersection region
                                                                                     (sheet-region sheet)))))))
       (let* ((parent (sheet-mirrored-ancestor sheet))
              (native-sheet-region (effective-repaint-region parent sheet region)))
  -	  (with-sheet-medium (medium parent)
  -	    (with-drawing-options (medium :clipping-region native-sheet-region
  -					  :ink (pane-background sheet)
  -					  :transformation +identity-transformation+)
  -	      (with-bounding-rectangle* (left top right bottom)
  -		  native-sheet-region
  -		(medium-draw-rectangle* medium left top right bottom t)))))))
  +          (with-sheet-medium (medium parent)
  +            (with-drawing-options (medium :clipping-region native-sheet-region
  +                                          :ink (pane-background sheet)
  +                                          :transformation +identity-transformation+)
  +              (with-bounding-rectangle* (left top right bottom)
  +                  native-sheet-region
  +                (medium-draw-rectangle* medium left top right bottom t)))))))
  
positive.code: ;;; -*- Mode: Lisp; Package: CLIM-INTERNALS -*-
  
  ;;;  (c) copyright 1998,1999,2000 by Michael McDonald (mikemac@mikemac.com), 
  ;;;  (c) copyright 2000 by 
  ;;;           Iban Hatchondo (hatchond@emi.u-bordeaux.fr)
  ;;;           Julien Boninfante (boninfan@emi.u-bordeaux.fr)
  ;;;  (c) copyright 2000, 20014 by
  
negative.code:   (repaint-sheet sheet region))
  
  (defmethod handle-event ((sheet immediate-repainting-mixin)
                           (event window-repaint-event))
    (repaint-sheet sheet (window-event-region event)))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  