static function createSubParser($name)
    {
        
        if(isset(self::$sub_parsers[$name]) === false) {
            throw new ParserException('Unknown subparser at '.$name);
        }
        
        if(is_object(self::$sub_parsers[$name]) === false) {
            self::$sub_parsers[$name] = new self::$sub_parsers[$name]();
        }
        
        return self::$sub_parsers[$name];
    }