说明：  php实现的ajax三级直连菜单，使用了jquery插件，但是压缩包内同样也存在prototype.js文件，看来两个伟大的Ajax库都用上了，有朋友就迷惑了，实现一个三级级联菜单，难道就这么小题大作么？其实这样用有它的理由，熟悉代码的朋友一看就会明白哦。
(php ajax to achieve three straight with the menu, use the jquery plugin, but it also exists within the compressed prototype.js file, it appears the two great use both Ajax library, and a friend to get lost, and the realization of a three-tier cascading menu, What does it mean that such a fuss? In fact, such use has its reasons, a friend familiar with the code will understand Oh, look.)