Browser definition files contain definitions for individual browsers. At run time, ASP.NET uses the information in the request header to determine what type of browser has made the request. Then ASP.NET uses browser files to determine the capabilities of the browser, and how to render markup to that browser. This is useful to Web developers who want to create applications that can be viewed on mobile devices, making use of control adapters that adapt the behavior of an ASP.NET Web server control depending on the type of device.
Note: Browser definition files are new in the .NET Framework version 2.0. In earlier versions of the .NET Framework, the browserCaps element was used to define browser definitions in configuration files.