anchor.diff:  (defmethod compose-space ((box vbox-pane))
     (let ((space (make-space-requirement)))
       (loop for child in (sheet-children box)
  -	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:    (enabledp :initform nil
  	     :initarg :enabledp
  	     :accessor pane-enabledp)
     (space-requirement :initarg :space-requirement
  		      :initform (make-space-requirement :width 300 :max-width 300
  							:height 300 :max-height 300)
  		      :accessor pane-space-requirement)
     )
    )
  
negative.code: 		   :initarg :output-history
  		   :accessor pane-output-history)))
  
  (defmethod compose-space ((pane clim-stream-pane))
    (make-space-requirement :width 300 :height 300
  			  :max-width 300 :max-height 300))
  
  (defmethod window-clear ((pane clim-stream-pane))
  ;  (setf (pane-output-history pane) (make-instance 'standard-tree-output-history))
  