Returns value of a direct sub-record or None.

        Works as :py:meth:`sub_tag` but returns value of a sub-record
        instead of sub-record itself.

        :param str path: tag names separated by slashes.
        :param boolean follow: If True then resolve pointers.
        :return: String or `None` if sub-record with a given
            tag does not exist.

def sub_tag_value(self, path, follow=True):
        """Returns value of a direct sub-record or None.

        Works as :py:meth:`sub_tag` but returns value of a sub-record
        instead of sub-record itself.

        :param str path: tag names separated by slashes.
        :param boolean follow: If True then resolve pointers.
        :return: String or `None` if sub-record with a given
            tag does not exist.
        """
        rec = self.sub_tag(path, follow)
        if rec:
            return rec.value
        return None