Changing ASP.NET web.config inheritance when mixing versions of child applications

My blog and all the sites in and around it are a mix of .NET 2.0, 3.5 and 4. This blog engine is currently .NET 3.5 and runs at http://hanselman.com/blog, but the application at http://hanselman.com/ (the root) is .NET 4.

You can happily mix and match applications across .NET versions on a single IIS instance. You can see how mixed my system is in the screenshot at right there.

However, things got messy when I changed the parent / application to .NET 4, but kept the child /blog as .NET 3.5 (the 2.0 CLR). I got lots of errors like

• Unrecognized attribute ‘targetFramework’. Note that attribute names are case-sensitive. The targetFramework attribute was inherited from the root .NET 4 Web.config file in the Default Web Site root using ASP.NET configuration inheritance and confused the /blog .NET 2 application.

I didn't want to change the /blog applications' web.config. I just wanted to stop it from inheriting the settings from the parent application. Turns out you can wrap whole sections in a location tag, and then tell that scoped tag to prevent child applications from inheriting.

What you do is change the parent .NET 4 app's web.config to indicate its settings shouldn't flow down to the children, like the .NET 2/3.5 /blog app.

    ...your system.web stuff goes here

You can actually read about this in detail in the ASP.NET 4 "breaking changes" documentation. Of course YOU read those closely, don't you? ;)

I chose to change this settings for all of System.Web, but you could do it on a per-section basis if you preferred.

Hope this helps you!