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: (defmethod compose-space ((rack vrack-pane))
    (mapc #'compose-space (sheet-children rack))
    (loop with space = (make-space-requirement 
  		      :max-width (get-max-width (car (sheet-children rack))))
  	for child in (sheet-children rack)
  	for request = (pane-space-requirement child)
  	sum (get-size child nil) into sum-height
  	do (setf (space-requirement-width space)
  		 (max (space-requirement-width space)
  		      (space-requirement-width request)))
  
negative.code:                               :width width :min-width min-width :max-width max-width
                                :height height :min-height min-height :max-height max-height))
    
  ;; Macros for quick access to space-requirement slots.
  (defmacro sr-width (pane)
    `(space-requirement-width (pane-space-requirement ,pane)))
  (defmacro sr-height (pane)
    `(space-requirement-height (pane-space-requirement ,pane)))
  (defmacro sr-max-width (pane)
    `(space-requirement-max-width (pane-space-requirement ,pane)))
  (defmacro sr-max-height (pane)
    `(space-requirement-max-height (pane-space-requirement ,pane)))
  (defmacro sr-min-width (pane)
    `(space-requirement-min-width (pane-space-requirement ,pane)))
  (defmacro sr-min-height (pane)
    `(space-requirement-min-height (pane-space-requirement ,pane)))
  
  (defclass pane (standard-sheet-input-mixin
  		temporary-medium-sheet-output-mixin
  