def extra(self, value, extra_name, default=None):
        """
        Get the additional enumeration value for ``extra_name``.

        :param unicode value: Enumeration value.
        :param str extra_name: Extra name.
        :param default: Default value in the case ``extra_name`` doesn't exist.
        """
        try:
            return self.get(value).get(extra_name, default)
        except InvalidEnumItem:
            return default
Get the additional enumeration value for ``extra_name``.

        :param unicode value: Enumeration value.
        :param str extra_name: Extra name.
        :param default: Default value in the case ``extra_name`` doesn't exist.