anchor.diff:  
   (defclass push-button (action-gadget labelled-gadget-mixin) ())
     
  -(defclass push-button-pane  (push-button clim-stream-pane)
  +(defclass push-button-pane  (push-button)
     ((show-as-default-p :type (member '(t nil))
   		      :initform nil
   		      :initarg :show-as-default-p
  
positive.code: 	    x1 1
  	    y2 (- y2 y1 1)
  	    y1 1)
        (define-gadget-color pane x1 y1 x2 y2)
        (if (or (gadget-value pane) (eql armed ':button-press))
  	  (progn
  	    (draw-line* pane x1 y1 x2 y1 :ink +black+)
  	    (draw-line* pane x1 y1 x1 y2 :ink +black+)
  	    (draw-line* pane x1 y2 x2 y2 :ink +white+)
  	    (draw-line* pane x2 y1 x2 y2 :ink +white+))
  	  (progn
  	    (draw-line* pane x1 y1 x2 y1 :ink +white+)
  	    (draw-line* pane x1 y1 x1 y2 :ink +white+)
  	    (draw-line* pane x1 y2 x2 y2 :ink +black+)
  	    (draw-line* pane x2 y1 x2 y2 :ink +black+)))
        (draw-text* pane text
  		     (round (- x2 x1) 2)
  		     (round (- y2 y1) 2)
  
negative.code:       (if (gadget-value pane)
  	  (setf (gadget-current-color pane) (gadget-pushed-and-highlighted-color pane))
  	  (setf (gadget-current-color pane) (gadget-normal-color pane)))
        (disarmed-callback pane (gadget-client pane) (gadget-id pane)))))
  
  (defmethod handle-event ((pane toggle-button-pane) (event pointer-button-press-event))
    (with-slots (armed) pane
      (unless armed
        (armed-callback pane (gadget-client pane) (gadget-id pane)))
      (setf armed ':button-press
  	  (gadget-current-color pane) (gadget-pushed-and-highlighted-color pane))))
        
  (defmethod handle-event ((pane toggle-button-pane) (event pointer-button-release-event))
    (with-slots (armed) pane
      (when (eql armed ':button-press)
        (setf armed t
  	    (gadget-value pane :invoke-callback t) (not (gadget-value pane)))
        (unless (gadget-value pane)
  	(setf (gadget-current-color pane) (gadget-highlighted-color pane)))
        (disarmed-callback pane (gadget-client pane) (gadget-id pane)))))
  
  (defmethod handle-event ((pane toggle-button-pane) (event window-repaint-event))
  