def matches(event):
    """Return a list of subscriptions that match the given event.

        :param event: a `NotificationEvent`
        :return: a list of tuples (class, distributor, sid, authenticated,
                 address, format, priority, adverb), where small `priority`
                 values override larger ones and `adverb` is either
                 'always' or 'never'.
        """
