anchor.diff:  (defmethod generic-list-pane-item-height ((pane generic-list-pane))
     (+ (text-style-ascent  (pane-text-style pane) pane)
        (text-style-descent (pane-text-style pane) pane)))
  +
  +(defmethod visible-items ((pane generic-list-pane))
  +  (if (slot-boundp pane 'visible-items)
  +      (visible-items pane)
  +      (generic-list-pane-items-length pane)))
  +
  +(defmethod (setf visible-items) (new-value (pane generic-list-pane))
  +  (check-type new-value fixnum)
  +  (setf (slot-value pane 'visible-items) new-value))
   
   (defmethod compose-space ((pane generic-list-pane) &key width height)
     (declare (ignore width height))
  
positive.code:               last-index
                (reduce #'max
                        (mapcar #'(lambda (item) (position item (generic-list-pane-item-values gadget) :test test))
                                (gadget-value gadget)))))))
    (unless (slot-boundp gadget 'visible-items)
      (setf (visible-items gadget) (generic-list-pane-items-length gadget))))
  
  (defgeneric generic-list-pane-item-strings (generic-list-pane))
  
  
negative.code:      :documentation "Index of the first item to be rendered. This changes in
  response to scroll wheel events.")
     (visible-items :initarg :visible-items ; Clim 2.0 compatibility
                    :documentation "Maximum number of visible items in list"))
    (:default-initargs :text-style (make-text-style :sans-serif :roman :normal)
                       :background +white+ :foreground +black+))
  