anchor.diff:  (defmethod compose-space ((rack hrack-pane))
     (mapc #'compose-space (sheet-children rack))
     (loop with space = (make-space-requirement
  -		      :max-height (get-max-height (car (sheet-children rack))))
  +		      :max-height (sr-max-height (car (sheet-children rack))))
   	for child in (sheet-children rack)
   	for request = (pane-space-requirement child)
  -	sum (get-size child) into sum-width
  +	sum (get-pane-width child) into sum-width
   	do (incf (space-requirement-width space)
   		 (space-requirement-width request))
   	   (incf (space-requirement-max-width space)
  
positive.code: 		  (return space))))
  	   
  (defmethod compute-extremum ((box vbox-pane))
    (make-extremums-children-ratio box (sheet-children box) :width nil))
  
  (defmethod allocate-space ((box vbox-pane) width height)
    (resize-sheet box width height)
    (allocate-space-internal box height nil)
    (loop for child in (sheet-children box)
  	  for nh = (slot-value child 'new-height)
  	  and y = 0 then (+ y nh)
  	  and nw = (/ (* width (get-size child)) (get-size box))
  	  do (move-sheet child 0 y)
  	     (setf nw (do-in nw (get-min-width child) (get-max-width child)))
  	     (allocate-space child (round nw) nh)))
    
  ;;; HRACK-PANE
  
negative.code: 		  (return space))))
  
  (defmethod compute-extremum ((rack vrack-pane))
    (make-extremums-children-ratio-height rack (sheet-children rack)))
    
  (defmethod allocate-space ((rack vrack-pane) width height)
    (resize-sheet rack width height)
    (allocate-space-internal-height rack height)
    (loop for child in (sheet-children rack)
  	for nh = (slot-value child 'new-height)
  	and y = 0 then (+ y nh)
  