Posfixed 能够让网页的导航或表头等固定在顶部或底部，让用户更方便的操作或查看信息，淘宝网、易迅网等电子商务网站常常用到这种效果。除了导航和表头，也可以固定其他内容，比如广告、返回顶部等等，同时 Posfixed 也可以作为 IE6 不支持 fixed 的一个解决方案。(Posfixed can enable Web pages to be fixed on the top or bottom of the web, such as navigation or headers, to make users more convenient to operate or view information. E-commerce websites such as Taobao et al. Often use this effect. Besides navigation and header, you can also fix other contents, such as advertisement, return to the top and so on. At the same time, Posfixed can also be a solution that IE6 does not support fixed.)