def _regex_strings(self):
        """
        A property to link into IntentEngine's _regex_strings.

        Warning: this is only for backwards compatiblility and should not be used if you
            intend on using domains.

        Returns: the domains _regex_strings from its IntentEngine
        """
        domain = 0
        if domain not in self.domains:
            self.register_domain(domain=domain)
        return self.domains[domain]._regex_strings
A property to link into IntentEngine's _regex_strings.

        Warning: this is only for backwards compatiblility and should not be used if you
            intend on using domains.

        Returns: the domains _regex_strings from its IntentEngine