17.2. Understanding Templates
This look at the visual tree raises a few interesting questions. For example, how is a control translated from the logical tree into the expanded representation of the visual tree?
It turns out that every control has a built-in recipe that determines how it should be rendered (as a group of more fundamental elements). That recipe is called a control template, and it's defined using a block of XAML markup.
Every WPF control is designed to be lookless, which means that its visuals (the "look") can be completely redefined. What doesn't change is the control's behavior, which is hardwired into the control class (although it can often be fine-tuned using various properties). When you choose to use a control like ...