Extensible Application Markup Language (XAML) is a markup language that maps XML markup to objects in the .NET Framework and WinFXT, enabling developers and designers to work together to create user experiences much the way HTML does. XAML is not Windows Presentation Foundation-specific, but it is designed to work with the type system of the .NET Framework's common language runtime.
Through the use of XAML you can even develop 3D animations !!! That means your 20 KB XAML file can play a 30 minutes animation movie !! Thats how Microsoft is creating future !