anchor.diff:     (display-function :initform 'default-frame-top-level
   		     :initarg :display-function
   		     :accessor pane-display-function)
  -   ; pour le label, il derive peut-etre de label-pane
  +   ; Should inherit from label-pane for this one ??
      (label :type string :initform nil
   	  :initarg :label
   	  :reader pane-label)
  
positive.code: ;(defgeneric (setf window-viewport-position) (x y clim-stream-pane))
  
  
  ;; CLIM-STREAM-PANE
  
  (defclass clim-stream-pane (output-recording-stream sheet-leaf-mixin basic-pane)
    ((display-time :initform nil
  
negative.code: 
  (defmethod (setf medium-background) (ink (pane pane))
    (setf (medium-background (sheet-medium pane)) ink))
  
  (defmethod compose-space ((pane pane))
    (make-space-requirement :width 200
  