anchor.diff:      (add-buffer buffer)
       buffer))
   
  +(defun buffer-enable-undo-p (&optional (buffer (current-buffer)))
  +  (buffer-%enable-undo-p buffer))
  +
   (defun buffer-reset (buffer)
     (let ((line (make-line nil nil "")))
       (setf (buffer-head-line buffer) line)
  
positive.code:   (delete-marker (buffer-point-marker buffer)))
  
  (defun buffer-enable-undo (buffer)
    (setf (buffer-enable-undo-p buffer) t)
    nil)
  
  (defun buffer-disable-undo (buffer)
    (setf (buffer-enable-undo-p buffer) nil)
    (setf (buffer-undo-size buffer) 0)
    (setf (buffer-undo-stack buffer) nil)
    (setf (buffer-redo-stack buffer) nil)
  
negative.code:                                :name name
                                 :filename filename
                                 :read-only-p read-only-p
                                 :%enable-undo-p enable-undo-p
                                 :major-mode 'fundamental-mode)))
      (buffer-reset buffer)
      (setf (buffer-undo-size buffer) 0)
  