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:    (vscrollbar :initform nil)
     (hscrollbar :initform nil)
     (suggested-width  :initform 300 :initarg :suggested-width)
     (suggested-height :initform 300 :initarg :suggested-height))
    (:default-initargs
     :x-spacing 4
     :y-spacing 4))
  
  (defmacro scrolling ((&rest options) &body contents)
    `(let ((viewport (make-pane 'viewport-pane :contents (list ,@contents))))
  