anchor.diff:                              (return-from worker
                                 (values (x1 stroke-dimensions) (y1 stroke-dimensions)
                                         (dimensions-height line-dimensions)
  -                                      (- (if (= end-offset (1+ start-offset))
  -                                             (x2 stroke-dimensions)
  -                                             (offset-in-stroke-position pane view stroke (1+ offset)))
  -                                         (x1 stroke-dimensions)))))
  +                                      (if (= end-offset (1+ start-offset))
  +                                          (dimensions-width stroke-dimensions)
  +                                          (offset-in-stroke-position pane view stroke (1+ offset))))))
                              ((and (<= start-offset offset)
                                    (< offset end-offset))
                               (return-from worker
  
positive.code:                                                 (text-size stream stroke-string
                                                   :text-style (merge-text-styles
                                                                (face-style (drawing-options-face drawing-options))
                                                                (medium-default-text-style stream)))
                                                  (values (- x2 x1) (- y2 y1)))
            (clear-rectangle* stream cursor-x cursor-y
                              (+ cursor-x width) (+ cursor-y height
  
negative.code: buffer offset `start-offset', and will be drawn starting
  at (`cursor-x', `cursor-y')"
    (let* ((line (line-information view (displayed-lines-count view)))
           (old-line-height (dimensions-height (line-dimensions line)))
           (old-line-width (dimensions-width (line-dimensions line)))
           (orig-x-offset cursor-x))
      (setf (line-start-offset line) start-offset
            (line-stroke-count line) 0)
      (loop for index from 0
  