public function addStripper($stripper)
    {
        if (is_string($stripper)) {
            if (!class_exists($stripper)) {
                $stripper = '\\' . __NAMESPACE__ . '\\Stripper\\' . $stripper;
                if (!class_exists($stripper)) {
                    throw new \InvalidArgumentException('Class ' . $stripper . ' can not be found');
                }
            }

            $stripper = new $stripper;
            if (!$stripper instanceof StripperInterface) {
                throw new InvalidArgumentException('Class "' . get_class($stripper) . '" must implement StripperInterface');
            }

        } elseif (!$stripper instanceof StripperInterface) {
            throw new InvalidArgumentException('Class "' . get_class($stripper) . '" must implement StripperInterface');
        }

        $this->_stippers[] = $stripper;
    }