anchor.diff:                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))))
  +                              (gadget-value gadget))))))))
   
   (defgeneric generic-list-pane-item-strings (generic-list-pane))
   
  
positive.code: (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 compose-space ((pane generic-list-pane) &key width height)
    (declare (ignore width height))
  
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+))
  