Also check out the tree.gui presentation in the demo/examples directory. It lets you browse this hierarchy interactively. You need to specify a mime-type in your browser to make the presentation appear by clicking on this link.
Widget ContainerWidget GroupWidget Presentation PageWidget PopupWidget Tip PopupMenu DropDownMenu GroupBoxWidget FolderWidget WindowWidget ScrollingContainerWidget TreeWidget TableWidget SparseTableWidget ListWidget ButtonWidget CommandButtonWidget MenuButtonWidget URLButtonWidget CheckboxWidget OptionWidget TextWidget TextBoxWidget StaticTextWidget DropDownTextBoxWidget RichTextBoxWidget ChoiceWidget ListBoxWidget ComboBoxWidget DropDownListBoxWidget DropDownComboBoxWidget ValueWidget ScrollbarWidget ProgressIndicatorWidget SpinBoxWidget SliderWidget AnimatedWidget AnimatedTextWidget AnimatedImageWidget ShapeWidget LineWidget RectangleWidget OvalWidget PolygonWidget ResourceWidget ImageWidget AudioWidget PresentationWidget AWTWidget ComponentWidget AppletWidget PopupMenuItemWidget ListItemWidget TreeNodeWidget ListBoxItemWidget