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

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

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

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

        Returns: the domains regular_expression_entities from its IntentEngine