anchor.diff:                                :reader scroll-bar-scroll-down-page-callback)
      (scroll-up-page-callback :initarg :scroll-up-page-callback
                               :initform nil
  -                            :reader scroll-bar-scroll-up-page-callback)))
  +                            :reader scroll-bar-scroll-up-page-callback)
  +   
  +   (thumb-size :initarg :thumb-size :initform 1/4
  +               :reader scroll-bar-thumb-size) ))
   
   (defmethod drag-callback ((pane scroll-bar) client gadget-id value)
     (declare (ignore client gadget-id))
  
positive.code: ;;;  (c) copyright 2001 by
  ;;; Lionel Salabartan (salabart@emi.u-bordeaux.fr)
  ;;;  (c) copyright 2001 by Michael McDonald (mikemac@mikemac.com)
  
  ;;; This library is free software; you can redistribute it and/or
  ;;; modify it under the terms of the GNU Library General Public
  
negative.code: 	  (draw-label pane (gadget-label pane) (round w 2) (round h 2)))))))
  
  
  ;;;;
  ;;;; SCROLL-BAR gadget
  ;;;;
  
  (defgeneric drag-callback (pane client gadget-id value))
  (defgeneric scroll-to-top-callback (scroll-bar client gadget-id))
  