One of the main advantages to using a WPF control or a Silverlight control is that controls are "lookless" with a fully customizable user interface. Just as you design your own user interface (UI), or look and feel, for WPF or Silverlight applications, you can provide your own UI for data managed by DropDown for WPF and Silverlight. Extensible Application Markup Language (XAML), an XML-based declarative language, offers a simple approach to designing your UI without having to write code.