Up until Blend 3, UI designers had difficult time prototyping a real functional UI. The main problem was the lack of behaviors. Creating a UI prototype that deals with navigation, window creation on event, animation on data changes etc, usually ends up with source code development. And when it comes to coding, UI designers had to have kind of developer colleague. XAML Tools Over time, developers (like me :) created many XAML extensions using both XAML Markup Extensions and the powerful Attached Property...