private function registerDefaultServices($userSettings)
    {
        $defaultSettings = $this->defaultSettings;

        /**
         * This service MUST return an array or an
         * instance of ArrayAccess.
         *
         * @return array|ArrayAccess
         */
        $this['settings'] = function () use ($userSettings, $defaultSettings) {
            return new Collection(array_merge($defaultSettings, $userSettings));
        };

        $defaultProvider = new DefaultServicesProvider();
        $defaultProvider->register($this);
    }