def __render_config_block(self, config_block):
        """Summary

        Args:
            config_block [config.Item, ...]: config lines

        Returns:
            str: config block str
        """
        config_block_str = ''
        for line in config_block:
            if isinstance(line, config.Option):
                line_str = self.__render_option(line)
            elif isinstance(line, config.Config):
                line_str = self.__render_config(line)
            elif isinstance(line, config.Server):
                line_str = self.__render_server(line)
            elif isinstance(line, config.Bind):
                line_str = self.__render_bind(line)
            elif isinstance(line, config.Acl):
                line_str = self.__render_acl(line)
            elif isinstance(line, config.UseBackend):
                line_str = self.__render_usebackend(line)
            elif isinstance(line, config.User):
                line_str = self.__render_user(line)
            elif isinstance(line, config.Group):
                line_str = self.__render_group(line)
            # append line str
            config_block_str = config_block_str + line_str

        return config_block_str