"Anything that is created or implemented in XAML can be expressed using a more traditional .net language, such as C# or Visual Basic .NET. However, a key aspect of the XAML technology is the more simple approach required for tools because it is simply XML. Consequently, a variety of products are emerging, particularly in the WPF space, to create XAML files. Being XML-based, XAML allows analysts, designers and developers to share artifacts more realistically and to enable these artifacts to be re-edited by any of these roles without requiring additional re-integration work by the others."
http://en.wikipedia.org/wiki/Extensible_Application_Markup_Language