anchor.diff:                  ((overlay-get overlay :display-left)
                    (when (and (point<= view-point start)
                               (point<= end view-end-point))
  -                   (let ((i (count-lines view-point start)))
  -                     (when (< i (length (screen-left-lines screen)))
  +                   (let ((i (calc-row start)))
  +                     (when (< i (screen-height screen))
                          (let ((str (overlay-get overlay :text)))
                            (setf left-width (max left-width (length str)))
                            (setf (aref (screen-left-lines screen) i)
  
positive.code: 	 (unless (line-offset point 1)
  	   (return-from disp-set-overlay))))))
  
  (defun disp-set-overlays (screen overlays view-point)
    (let ((view-end-point
           (with-point ((view-point view-point))
             (or (line-offset view-point (screen-height screen))
                 (buffer-end view-point))))
          (left-width 0))
      (loop :for overlay :in overlays
            :for start := (overlay-start overlay)
            :for end := (overlay-end overlay)
  
negative.code:                                         (length string))
                                      attribute)))))
  
  (defun disp-set-overlay (screen attribute screen-row start end)
    (let ()
      (disp-set-line screen attribute screen-row (point-charpos start) nil)
      (with-point ((point start))
        (line-offset point 1)
  