post method in css?

I don't understand what Twitter is doing or how it's making Twitter adapt to browsers via CSS, but I saw this link in the source: http://a2.twimg.com/a/1297446951/stylesheets/newtwitter.css?1297453395 What 开发者_开发知识库does the 1297453395 do? Does it have anything to do with how Twitter adapts to browsers? I noticed that Twitter only uses -moz- on Firefox and only uses -webkit- on Chrome. I'm very interested in this.

All it does is cause a browser to retrieve the file without bothering about caching. The query string at the end makes a browser think it's a brand new file that it has to request. It has nothing to do with CSS or browser adaptation, and everything to do with HTTP.

Specifically, the 1297453395 represents a UNIX timestamp.

A HTTP request from a browser usually contains some information about that browser (User-Agent header). It’s not reliable information since it can easily be spoofed but it’s enough to deliver browser-specific CSS.

The query parameter is completely unnecessary (and indeed useless) to determine the client browser.

Actually the css file is not a real css file. it's a HTTP handler that returns of type "text/css".