anchor.diff:  (defmethod compose-space ((rack vrack-pane))
     (let ((space (make-space-requirement)))
       (loop for child in (sheet-children rack)
  -	for request = (compose-space child)
  +	for request = (compute-and-set-space child)
   	do (setf (space-requirement-width space)
   	     (max (space-requirement-width space)
   		  (space-requirement-width request)))
  
positive.code:   ()
    (:documentation "For the first pane in the architecture"))
  
  (defmethod allocate-space ((pane top-level-sheet-pane) width height)
    (allocate-space (car (sheet-children pane)) width height))
  
  (defmethod dispatch-event ((pane top-level-sheet-pane) event)
    (handle-event pane event))
  
negative.code: (defmethod compose-space ((box vbox-pane))
    (let ((space (make-space-requirement)))
      (loop for child in (sheet-children box)
  	for request = (compute-and-set-space child)
  	do (setf (space-requirement-width space)
  	     (max (space-requirement-width space)
  		  (space-requirement-width request)))
  