public function registerDecorator($configKey, $className)
    {
        if (isset($this->decorators[$configKey])) {
            throw new \RuntimeException('Decorator key already in use: ' . $configKey);
        }
        if (in_array($className, $this->decorators)) {
            throw new \RuntimeException('Decorator class already registered: ' . $className);
        }
        $this->decorators[$configKey] = $className;
    }