def nest(self, verb):
        """
        Add a TwiML doc. Unlike `append()`, this returns the created verb.

        :param verb: TwiML Document

        :returns: the TwiML verb
        """
        if not isinstance(verb, TwiML) and not isinstance(verb, str):
            raise TwiMLException('Only nesting of TwiML and strings are allowed')

        self.verbs.append(verb)
        return verb
Add a TwiML doc. Unlike `append()`, this returns the created verb.

        :param verb: TwiML Document

        :returns: the TwiML verb