anchor.diff:      (print-unreadable-object (space stream :type t :identity t)
         (format stream "width: ~S height: ~S" width height))))
   
  -(defun make-space-requirement (&key (width 1) (max-width 1) (min-width 1)
  -				    (height 1) (max-height 1) (min-height 1))
  +(defun make-space-requirement (&key (width 1) (height 1)
  +				    (min-width 0) (min-height 0)
  +				    (max-width +fill+) (max-height +fill+))
  +  (assert (<= 0 min-width width max-width) (min-width width max-width))
  +  (assert (<= 0 min-height height max-height) (min-height height max-height))
     (make-instance 'space-requirement
       :width width
       :max-width max-width
  
positive.code: 
  ;;; PANES
  
  (defconstant +fill+ :fill)
  
  (defclass space-requirement ()
    ((width :initform 1
  
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
  