https://blog.offline-net.com/2008/04/30/flash%e3%83%96%e3%83%a9%e3%82%b0%e3%82%a4%e3%83%b3%e3%81%ae%e3%83%90%e3%83%bc%e3%82%b8%e3%83%a7%e3%83%b3%e3%82%92%e7%9f%a5%e3%82%8b/