There are two important super classes that you have to know because almost all other MUI classes are children of these two super classes: The first one is Notify class which handles MUI's event notification system. Notify class allows your MUI objects to listen to certain events and trigger notifications whenever these events occur. See Notify class for details.
The second important super class is Area class. Area class is the the super class for all MUI objects that have a visual representation in form of a gadget in a MUI window. Thus, you can use all of Area class' attributes on all of your MUI gadgets. For example, you can use the Area.Width and Area.Height attributes to find out the dimensions of a listview, texteditor, or string gadget because these are all subclasses of Area class. See Area class for details.