what is the use of "v=747" at the end of /site_media/base.css?v=747"

Question

I have seen a web page source code containing the following css declaration at the header:

<link rel="stylesheet" href="/site_media/base.css?v=747" /> 

What is the use of "?v=747" at the end of this CSS declaration?

Answer 1

To bypass the caching mechanism of the browser. If the file is updated, the version (I guess that's what v stands for) will be incremented and the browser will not use the cache, but download the file, since it is a different URL.