When you’re making apps intended for modern touch hardware, it’s important that your UI feels alive, fluid, and in motion. Some of Microsoft’s XAML controls will give you this motion for free, like Panorama in Windows Phone and the FlipView in WinRT, but other than that it was very difficult to duplicate the built-in animations and transitions of those respective platforms. The WinRT platform introduces the Transition API that applies to Controls and Containers that can apply a built in animation in a response to a predetermined trigger. Transitions are applied to individual controls using the Transitions property, and to Panels using the ChildrenTransitions property. For example, adding an EntranceThemeTransition to the ChildrenTransitions collection of a Grid will cause all children of the Grid to automatically slide in from the right when they first appear.