anchor.diff:  (defparameter slider-button-long-dim 30)
   (defparameter slider-button-short-dim 10)
   
  -(defclass slider-pane (slider-gadget activate/deactivate-repaint-mixin basic-pane)
  -  ((drag-callback  :initform nil
  -                   :initarg :drag-callback
  -                   :reader slider-drag-callback)
  -   (show-value-p   :type boolean
  -                   :initform nil
  -                   :initarg :show-value-p
  -                   :accessor gadget-show-value-p)
  -   (decimal-places :initform 0
  -                   :initarg :decimal-places
  -                   :reader slider-decimal-places)
  -   (number-of-quanta :initform nil
  -                     :initarg :number-of-quanta
  -                     :reader slider-number-of-quanta)))
  +(defclass slider-pane (slider
  +		       gadget-color-mixin
  +		       value-changed-repaint-mixin
  +		       activate/deactivate-repaint-mixin
  +		       basic-pane)
  +  ())
   
   (defmethod compose-space ((pane slider-pane) &key width height)
     (declare (ignore width height))
  
positive.code: 
  ;;; 30.4.5 The abstract slider Gadget
  
  (defclass slider-gadget (labelled-gadget-mixin
                           value-gadget
                           oriented-gadget-mixin
                           range-gadget-mixin
                           gadget-color-mixin
                           ;;
                           value-changed-repaint-mixin
                           )
    ()
    (:documentation "The value is a real number, and default value for orientation is :vertical,
  and must never be nil."))
  
  ;;; 30.4.6 The abstract radio-box and check-box Gadgets
  
  
negative.code:     :y-spacing 2))
  
  (defmethod compose-space ((gadget push-button-pane) &key width height)
    (space-requirement+* (space-requirement+* (compose-label-space gadget)
                                              :min-width (* 2 (pane-x-spacing gadget))
                                              :width (* 2 (pane-x-spacing gadget))
  