This is SO's css path http://sstatic.net/so/all.css?v=6184" what is this ?v=6184"?

This is SO's css path http://sstatic.net/so/all.css?v=6184" what is this ?v=6184"?

What it does? if it useful then how to use this? can i use this on any site PHP, ASp.net 开发者_如何学Goetc

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It's a way to control caching. When the value of the "v" parameter changes, the browser will consider it a different URL and ask for a new copy of the file instead of using its cached copy. This technique is often used to "version" static files by providing something like a timestamp in the query string that marks when the file was last changed.

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It's a query string. It can be parsed by server-side processes for allowing variable parts of the stylesheet, or it can be used to disable caching by browsers or proxies.