anchor.diff:    (space-requirement+* (space-requirement+* (compose-label-space gadget)
                                               :min-width (* 2 (pane-x-spacing gadget))
                                               :width (* 2 (pane-x-spacing gadget))
  -                                            :max-width (* 2 (pane-x-spacing gadget))
  +                                            :max-width +fill+
                                               :min-height (* 2 (pane-y-spacing gadget))
                                               :height (* 2 (pane-y-spacing gadget))
  -                                            :max-height (* 2 (pane-y-spacing gadget)))
  +                                            :max-height +fill+
                          :min-width (* 2 *3d-border-thickness*)
                          :width (* 2 *3d-border-thickness*)
  -                       :max-width (* 2 *3d-border-thickness*)
                          :min-height (* 2 *3d-border-thickness*)
  -                       :height (* 2 *3d-border-thickness*)
  -                       :max-height (* 2 *3d-border-thickness*)))
  +                       :height (* 2 *3d-border-thickness*))))
   
   (defmethod handle-event ((pane push-button-pane) (event pointer-button-press-event))
     (with-slots (pressedp) pane
  
positive.code:                             :max-width +fill+
                              :min-height total-height
                              :height total-height
                              :max-height total-height)))
  
  (defgeneric generic-option-pane-draw-widget (pane))
  
  
negative.code:   (space-requirement+* (space-requirement+* (compose-label-space gadget)
                                              :min-width (* 2 (pane-x-spacing gadget))
                                              :width (* 2 (pane-x-spacing gadget))
                                              :max-width +fill+
                                              :min-height (* 2 (pane-y-spacing gadget))
                                              :height (* 2 (pane-y-spacing gadget))
                                              :max-height +fill+)
                         :min-width (* 2 *3d-border-thickness*)
                         :width (* 2 *3d-border-thickness*)
                         :min-height (* 2 *3d-border-thickness*)
                         :height (* 2 *3d-border-thickness*)))
  
  ;;; ------------------------------------------------------------------------------------------
  ;;;  30.4.4 The concrete scroll-bar Gadget
  