anchor.diff:  
   (defmethod fully-redisplay-pane ((drei-pane drei-pane)
                                    (view point-mark-view))
  -  (reposition-pane drei-pane)
  -  (setf (full-redisplay-p view) nil))
  +  (reposition-pane drei-pane))
   
   (defmethod fully-redisplay-pane :after ((drei-pane drei-pane)
                                           (view drei-buffer-view))
  
positive.code:       (invalidate-all-strokes view :modified t))))
  
  (defun adjust-pane (drei-pane)
    "Adjust the bottom and top marks of the pane to be correct, and
  reposition the pane if point is outside the visible area."
    (with-accessors ((buffer buffer) (top top) (bot bot)
                     (point point)) (view drei-pane)
      (beginning-of-line top)
      (when (or (mark< point top)
                (mark> point bot))
        (reposition-pane drei-pane))))
  
  (defun page-down (view)
    (with-accessors ((top top) (bot bot)) view
  
negative.code: (defun display-drei-pane (frame drei-pane)
    "Display `pane'. If `pane' has focus, `current-p' should be
  non-NIL."
    (let ((view (view drei-pane)))
      (with-accessors ((buffer buffer)) view
        (when (typep view 'point-mark-view)
          (when (full-redisplay-p view)
            (fully-redisplay-pane drei-pane view)))
        (setf (stream-cursor-position drei-pane) (values 0 0))
        (display-drei-view-contents drei-pane view)
        (if (adjust-pane drei-pane)
            (display-drei-pane frame drei-pane)
            ;; Point must be on top of all other cursors.
            (progn
              (dolist (cursor (cursors drei-pane))
                (display-drei-view-cursor drei-pane view cursor))
              (fix-pane-viewport drei-pane (view drei-pane)))))))
  
  (defgeneric full-redisplay (pane)
    (:documentation "Queue a full redisplay for `pane'."))
  