If you wanted to include another .config file within your websites web.config you can reference it as a property of
Note that appconfig\custom\secretconfig.config is relative to the root of your website.
Including extra configuration files are useful for cases where you want to lock down production process ID’s and other secret settings. You can grant your production management team and IIS access to /appconfig which would conceal the settings from being read by say developers.
One thing to remember is if you change settings in this included file the IIS app pool will need to be refreshed for the changes to be picked up. web.config changes will induce an app pool refresh however included files will not automatically.