anchor.diff:    (sheet-adopt-child pane (first contents))
     (with-slots (scroll-bar viewport vscrollbar hscrollbar) pane
       (setq viewport (first (sheet-children pane)))
  +    ;; make the background of the viewport match the background of the
  +    ;; things scrolled.
  +    (when (first (sheet-children viewport))
  +      (setf (slot-value pane 'background)  ;### hmm ...
  +            (pane-background (first (sheet-children viewport)))))
  +    ;;
       (when (member scroll-bar '(:vertical t))
         (setq vscrollbar
               (make-pane 'scroll-bar-pane
  
positive.code:       (when viewport
          (setf (sheet-transformation viewport)
                (make-translation-transformation
                     (if vscrollbar *scrollbar-thickness* 0) 0))
          (allocate-space viewport
                          viewport-width
                          viewport-height)))))
  
  ;;;; Initialization
  
  
negative.code:         (make-space-requirement))))
  
  (defmethod allocate-space ((pane scroller-pane) width height)
    (with-slots (viewport vscrollbar hscrollbar x-spacing y-spacing) pane
      (let ((viewport-width  (if vscrollbar (- width  *scrollbar-thickness*) width))
            (viewport-height (if hscrollbar (- height *scrollbar-thickness*) height)))
        
  