Elements are used to define a user interface. Each element can include a corresponding user interface widget and/or arrangement information for the user interface. The elements and/or corresponding widgets are hierarchically related. Each element implements a set of application programming interfaces that enable the rendering of both design-time views (e.g., design view and preview view) of the user interface as well as a runtime view of the user interface. As a result, a designer is able to view exactly what will be generated during runtime, and a widget developer will not need to develop additional software to support the design environment.