anchor.diff:  
   ;;; 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
  -                         )
  -  ()
  +(defclass slider (labelled-gadget-mixin
  +		  value-gadget
  +		  oriented-gadget-mixin
  +		  range-gadget-mixin)
  +  ((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))
     (:documentation "The value is a real number, and default value for orientation is :vertical,
  -and must never be nil."))
  +and must never be nil.")
  +  (:default-initargs :orientation :vertical))
  +
  +(defmethod drag-callback ((pane slider) client gadget-id value)
  +  (declare (ignore client gadget-id))
  +  (when (slider-drag-callback pane)
  +    (funcall (slider-drag-callback pane) pane value)))
   
   ;;; 30.4.6 The abstract radio-box and check-box Gadgets
   
  
positive.code:     :y-spacing 2))
  
  (defmethod compose-space ((gadget push-button-pane) &key width height)
    (declare (ignore width height))
    (space-requirement+* (space-requirement+* (compose-label-space gadget)
                                              :min-width (* 2 (pane-x-spacing gadget))
                                              :width (* 2 (pane-x-spacing gadget))
  
negative.code:                               :min-height major :height major)
      (make-space-requirement :min-width  major :width  major
                              :min-height minor :height minor))))
  
  (defmethod handle-event ((pane slider-pane) (event pointer-enter-event))
    (with-slots (armed) pane
  