anchor.diff:     (user-min-height :accessor %pane-user-min-height)
      (user-max-height :accessor %pane-user-max-height)
      ;; size required by the stream
  -   (stream-width :initform 0 :accessor stream-width)
  -   (stream-height :initform 0 :accessor stream-height))
  +   (stream-width :initform 100 :accessor stream-width)
  +   (stream-height :initform 100 :accessor stream-height))
     (:documentation
      "This class implements a pane that supports the CLIM graphics,
       extended input and output, and output recording protocols."))
  
positive.code:   (dolist (child (alexandria:ensure-list contents))
      (sheet-adopt-child sheet child)))
  
  (defmethod compose-space ((bboard bboard-pane) &key width height)
    (declare (ignore width height))
    (make-space-requirement :width 300 :height 300))
  
  ;;; VIEWPORT
  
  
negative.code: (defmethod (setf medium-background) (ink (pane pane))
    (setf (medium-background (sheet-medium pane)) ink))
  
  (defmethod compose-space ((pane pane) &key (width 100) (height 100))
    (make-space-requirement :width width :height height))
  
  (defmethod allocate-space ((pane pane) width height)
    (declare (ignorable pane width height))
  