anchor.diff:  (defconstant +pixie-slider-thumb-half-height+ 17)
   (defconstant +pixie-slider-thumb-height+      34)
   (defconstant +pixie-slider-thumb-half-width+   8)
  -
   
   (defclass pixie-slider-pane (pixie-gadget draggable-arming-mixin slider-pane)
     ((dragging
  
positive.code:     (setf (values left-margin right-margin)
            (if (or (typep (slot-value pane 'client) 'menu-bar)
                    (not vertical))
                (values *pixie-menubar-item-left-margin* *pixie-menubar-item-right-margin*)
                (values *pixie-menu-button-left-margin* *pixie-menu-button-right-margin*)))))
  
  (defmethod compose-space ((gadget pixie-menu-button-pane) &key width height)
    (declare (ignore width height))
  
negative.code: (defclass pixie-menu-button-pane (pixie-gadget menu-button-pane)
    ((left-margin :reader left-margin)
     (right-margin :reader right-margin))                
    (:default-initargs :align-x :left
  		     :align-y :center))
  
  (defparameter *pixie-menu-button-left-margin*  26)
  (defparameter *pixie-menu-button-right-margin* 26)
  