anchor.diff:  
   ;;; PANES
   
  -(defconstant +fill+ :fill)
  +(defconstant +fill+ most-positive-fixnum)
   
   (defclass space-requirement ()
     ((width :initform 1
  
positive.code: (defclass bboard-pane (composite-pane) ())
  
  (defmethod compose-space ((bboard bboard-pane))
    (make-space-requirement :width 300 :max-width 300 :min-width 300
  			  :height 300 :max-height 300 :min-height 300))
  
  ;;; VIEWPORT
  
  
negative.code: 
  (defmethod compose-space ((pane pane))
    (make-space-requirement :width 200
  			  :height 200))
  
  (defmethod compose-space :around ((pane pane))
    (with-slots (sr-width sr-height sr-max-width
  