public static function instance($instance = null)
	{
		if ($instance === true)
		{
			return static::$_instances;
		}
		elseif ($instance !== null)
		{
			if ( ! array_key_exists($instance, static::$_instances))
			{
				return false;
			}

			return static::$_instances[$instance];
		}

		return static::$_instance;
	}