Generate the information required to create an ISBN-10 or
        ISBN-13.

def _body(self):
        """ Generate the information required to create an ISBN-10 or
        ISBN-13.
        """
        ean = self.random_element(RULES.keys())
        reg_group = self.random_element(RULES[ean].keys())

        # Given the chosen ean/group, decide how long the
        #   registrant/publication string may be.
        # We must allocate for the calculated check digit, so
        #   subtract 1
        reg_pub_len = ISBN.MAX_LENGTH - len(ean) - len(reg_group) - 1

        # Generate a registrant/publication combination
        reg_pub = self.numerify('#' * reg_pub_len)

        # Use rules to separate the registrant from the publication
        rules = RULES[ean][reg_group]
        registrant, publication = self._registrant_publication(reg_pub, rules)
        return [ean, reg_group, registrant, publication]