anchor.diff:                                                      (point-charpos end)))
                       ((and (point<= view-point start)
                             (point< end view-end-point))
  -                     (disp-attribute-to-screen-region screen
  +                     (draw-attribute-to-screen-region screen
                                                         (overlay-attribute overlay)
                                                         (calc-row start)
                                                         start
  
positive.code:                                          (or end-charpos (length string))
                                           attribute)))))
  
  (defun disp-attribute-to-screen-region (screen attribute screen-row start end)
    (flet ((draw-line (row start-charpos &optional end-charpos)
             (draw-attribute-to-screen-line screen attribute row start-charpos end-charpos)))
      (with-point ((point start))
  
negative.code:                     ((and (point<= start view-point)
                            (point<= view-point end)
                            (point<= end view-end-point))
                       (draw-attribute-to-screen-region screen
                                                        (overlay-attribute overlay)
                                                        0
                                                        view-point
                                                        end))
                      ((point<= view-point start)
                       (draw-attribute-to-screen-region screen
                                                        (overlay-attribute overlay)
                                                        (calc-row start)
                                                        start
  