A Tix mega-widget is composed of one or more component widgets. The main part of a mega-widget is called the root widget, which is usually a frame widget that encompasses all other component widgets. The other component widgets are called subwidgets.
The root widget has the same name as the the mega-widget itself. In the above example, we have a mega-widget called .up. It has a root widget which is a frame widget and is also called .up. Inside .up we have a button subwidget called .up.button.
Similar to variables and methods, component widgets are also classified into public and private component widgets. Only public widgets may be accessed by the application programmer, via the subwidget method (see section 1.3.1) of each widget instance.