anchor.diff:      (let ((rules (read stream)))
         (mapcar #'(lambda (rule)
                     (let ((rule (append '(:test) rule)))
  -                    (setf (getf rule :included) (mapcar #'mode-invocation (getf rule :included))
  -                          (getf rule :excluded) (mapcar #'mode-invocation (getf rule :excluded)))
  +                    (setf (getf rule :included) (mode-invocations (getf rule :included))
  +                          (getf rule :excluded) (mode-invocations (getf rule :excluded)))
                       (when (stringp (getf rule :test))
                         (setf (getf rule :test) `(match-url ,(getf rule :test))))
                       (apply #'make-instance 'auto-mode-rule rule)))
  
positive.code: 
  (defun save-last-active-modes (auto-mode url)
    (when (can-save-last-active-modes auto-mode url)
      (setf (last-active-modes auto-mode) (mapcar #'mode-invocation (modes (buffer auto-mode)))
            (last-active-modes-url auto-mode) url)))
  
  (defun reapply-last-active-modes (auto-mode)
    (disable-modes
     (mapcar #'name
             (set-difference (mapcar #'mode-invocation (modes (buffer auto-mode)))
                             (last-active-modes auto-mode)
                             :test #'equals))
     (buffer auto-mode))
    (enable-modes
     (mapcar #'name
             (set-difference (last-active-modes auto-mode)
                             (mapcar #'mode-invocation (modes (buffer auto-mode)))
                             :test #'equals))
     (buffer auto-mode)))
  
  
negative.code:       (setf url (url url)))
      (add-modes-to-auto-mode-rules
       (url-infer-match url)
       :include (set-difference (mode-invocations (modes (current-buffer)))
                                (mode-invocations (default-modes (current-buffer)))
                                :test #'equals)
       :exclude (set-difference (mode-invocations (default-modes (current-buffer)))
                                (mode-invocations (modes (current-buffer)))
                                :test #'equals))))
  
  (define-command save-exact-modes-for-future-visits ()
  