old_contents: class AccessTokenNotFound(Exception):
      pass
  
  
  class RegistrationException(Exception):
      pass
  
new_contents: """
  Errors raised during the Twitcher flow.
  """
  
  
  class AccessTokenNotFound(Exception):
      """
      Error indicating that an access token could not be read from the
      storage backend by an instance of :class:`twitcher.store.AccessTokenStore`.
      """
      pass
  
  
  class RegistrationException(Exception):
      pass
  
subject: update comments