Add config to an :py:class:`argparse.ArgumentParser` object.

        The parser’s :py:meth:`~argparse.ArgumentParser.add_argument`
        method is called for each config item. The argument name is
        constructed from the parent and item names, with a dot
        separator.

        :param argparse.ArgumentParser parser: The argument parser object.

        :keyword str prefix: The parent node name.

def parser_add(self, parser, prefix=''):
        """Add config to an :py:class:`argparse.ArgumentParser` object.

        The parser’s :py:meth:`~argparse.ArgumentParser.add_argument`
        method is called for each config item. The argument name is
        constructed from the parent and item names, with a dot
        separator.

        :param argparse.ArgumentParser parser: The argument parser object.

        :keyword str prefix: The parent node name.

        """
        if prefix:
            prefix += '.'
        for key, value in self.items():
            value.parser_add(parser, prefix + key)