anchor.diff:      (setf (pane-space-requirement bp) space)
       space))
   
  +;;; FIXME: I don't see how this one could possibly work
   (defmethod allocate-space ((bp border-pane) width height)
     (let ((h-percent (/ width (space-requirement-width (pane-space-requirement bp))))
   	(v-percent (/ height (space-requirement-height (pane-space-requirement bp))))
  
positive.code: 	for request = (pane-space-requirement child)
  	for new-width = (floor (* h-percent (space-requirement-width request)))
  	for new-height = (floor (* v-percent (space-requirement-height request)))
  	do (setf (sheet-region child)
  	     (make-bounding-rectangle 0 y new-width (+ y new-height)))
  	   (allocate-space child new-width new-height)
  	   (incf y new-height))))
  
  
  (defmacro changing-space-requirement (&body body &key resize-frame)
  
negative.code: 
  ;; TOP-LEVEL-SHEET
  
  (defclass top-level-sheet-pane (composite-pane)
    ()
    (:documentation "For the first pane in the architecture"))
  
  (defclass unmanaged-top-level-sheet-pane (top-level-sheet-pane)
    ()
    (:documentation "Top-level sheet without window manager intervention"))
  
  (defmethod dispatch-event ((pane top-level-sheet-pane) event)
    (handle-event pane event))
  
  (defmethod handle-event ((pane top-level-sheet-pane) (event window-configuration-event))
    (let ((x (window-configuration-event-x event))
  	(y (window-configuration-event-y event))
  	(width (window-configuration-event-width event))
          (height (window-configuration-event-height event)))
      ;; avoid goint into an infinite loop by not using (setf sheet-region)
      (setf (slot-value pane 'transformation)
  	  (make-translation-transformation x y))
      (setf (slot-value pane 'region)
  	  (make-bounding-rectangle 0 0 width height))
      (allocate-space pane width height)))
  
  ;; SHEET 
  