Extract subelement from obj, according to tokens.

        :param obj: the object source
        :param bypass_ref: disable JSON Reference errors

def extract(self, obj, bypass_ref=False):
        """
        Extract subelement from obj, according to tokens.

        :param obj: the object source
        :param bypass_ref: disable JSON Reference errors
        """
        for token in self.tokens:
            obj = token.extract(obj, bypass_ref)
        return obj