anchor.diff:                                 :name name
                                  :filename filename
                                  :read-only-p read-only-p
  -                               :enable-undo-p enable-undo-p
  +                               :%enable-undo-p enable-undo-p
                                  :major-mode 'fundamental-mode)))
       (buffer-reset buffer)
       (setf (buffer-undo-size buffer) 0)
  
positive.code:   filename
    modified-p
    read-only-p
    enable-undo-p
    major-mode
    minor-modes
    head-line
  
negative.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)
  