public static function addInstance($className, $instance) {
		self::checkInstanceClassName($className, $instance);

		if ($instance instanceof t3lib_Singleton) {
			throw new InvalidArgumentException(
				'$instance must not be an instance of t3lib_Singleton. ' .
					'For setting singletons, please use setSingletonInstance.',
				1288969325
			);
		}

		if (!isset(self::$nonSingletonInstances[$className])) {
			self::$nonSingletonInstances[$className] = array();
		}
		self::$nonSingletonInstances[$className][] = $instance;
	}