Config from an external source
Say you want your connectionStrings to be pulled in from an external file, you can do that like this:
<connectionStrings configSource="ConnectionStringsProduction.xml" />
That way, for example, your
application.config (for some other apps) and your
linqpad.config can all use the exact same file for connectionStrings (even though the rest of their config is very unique.
Or if you have 3 different web applications that all want the same config for just part of their config file, you can use this trick.