How Does the VS 2010 web.config work?

I am j开发者_运维知识库ust wondering in VS2010 the web.config is broken up into

web.config
web.debug.config
web.release.config

So from what I gathered is the web.config is just like the master template. So I am guessing in my debug I could put things like my local database where in my release one I would put my server database.

Now how does it know when to use the release version or debug version?

I also here that you can have more than 2. How does that work?

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VS will use the debug version if you publish/run with the Debug configuration, and will use the Release version if you publish/run with the Release configuration. Also, if you add more build configurations, you can have web.config versions for each of those build configurations as well.