anchor.diff:                            (subseq (line-str line) start end)
                             (not (null end))))))
   
  -@export
   (defun points-to-string (start-point end-point)
     @lang(:jp "`start-point`から`end-point`までの範囲の文字列を返します。")
     (assert (eq (point-buffer start-point)
  
positive.code:         ((null line) (1+ offset))
        (incf offset (1+ (line-length line))))))
  
  @export
  (defun move-to-position (point position)
    @lang(:jp "`point`をバッファの先頭からの1始まりのオフセット`position`に移動してその位置を返します。
  `position`がバッファの範囲外なら`point`は移動せず、NILを返します。")
  
negative.code:     (let ((string (delete-char/point point n)))
        string)))
  
  (defun erase-buffer (&optional (buffer (current-buffer)))
    @lang(:jp "`buffer`のテキストをすべて削除します。")
    (buffer-start (buffer-point buffer))
  