Important The XAML syntax for all properties that use a TransitionCollection value is unusual in that you must declare an explicit TransitionCollection object element as the value, and then provide object elements as child elements of TransitionCollection for each of the transition animations you want to use. For most other XAML collection properties you could omit the collection object element because it can be implicit, but properties that use TransitionCollection don't support the implicit collection usage. For more info on implicit collections and XAML, see Basic XAML syntax guide.
Transition animations play a particular role in UI design of your app. The basic idea is that when there is a change or transition, the animation draws the attention of the user to the change.