anchor.diff:  
   ;;; BORDER-PANE
   
  -(defclass border-pane (spacer-pane)
  +(defclass border-pane (spacing-pane)
     ((border-width :initarg :border-width :initform 1 :reader border-pane-width)
      )
     (:documentation ""))
  
positive.code: 			    (make-translation-transformation (- x x1) (- y y1))))
  		    (allocate-space child (round new-width) (round new-height)))))
  
  ;;; SPACER PANE
  
  (defclass spacer-pane (composite-pane)
    ((margin-width :initform nil :initarg :width)
     (margin-height :initform nil :initarg :height)
     (margin-max-width :initform nil :initarg :max-width)
     (margin-max-height :initform nil :initarg :max-height)
     (margin-min-width :initform nil :initarg :min-width)
     (margin-min-height :initform nil :initarg :min-height))
    (:documentation "The spacer pane will create a margin for his child.
  The margin sizes (w h) are given with the :width and :height initargs.
  During realization the child of the spacer will have as cordinates
   x = w/2 , y = h/2."))
  
  (defmethod initialize-instance :after ((spacer spacer-pane) &rest ignore)
    (declare (ignore ignore))
    (with-slots (margin-width margin-height
  	       margin-max-width margin-max-height
  	       margin-min-width margin-min-height) spacer
      (setf margin-width (or margin-width 0)
  	  margin-height (or margin-height 0)
  	  margin-max-width (or margin-max-width margin-width)
  
negative.code: 	  margin-min-width (or margin-min-width margin-width)
  	  margin-min-height (or margin-min-height margin-height))))
  
  (defun spacing-p (pane)
    (typep pane 'spacing-pane))
  
  (defmacro spacing ((&rest options) &body contents)
    `(make-pane 'spacing-pane ,@options :contents (list ,@contents)))
  
  (defmethod compose-space ((spacing spacing-pane))
    (compose-space (first (sheet-children spacing))))
  
  (defmethod allocate-space ((spacing spacing-pane) width height)
    (set-width-and-height spacing width height)
    (let* ((child (first (sheet-children spacing)))
  	 (margin-width (- (get-width spacing) (get-width child)))
  	 (margin-height (- (get-height spacing) (get-height child))))
      (setf margin-width
  	  (do-in (round (/ (* width margin-width) (get-size spacing)))
  		 (slot-value spacing 'margin-min-width)
  		 (slot-value spacing 'margin-max-width))
  	  margin-height
  	  (do-in (round (/ (* height margin-height) (get-size spacing nil)))
  		 (slot-value spacing 'margin-min-height)
  		 (slot-value spacing 'margin-max-height))
  	  (sheet-transformation child)
  	  (make-translation-transformation (/ margin-width 2)
  					   (/ margin-height 2)))
  