Main windows are standalone windows; they are independent of all other windows. They provide the principal user interface for your applications, and can overlay other windows of the same type.
Define your independent windows as main windows. For example, suppose your application contains a calculator or scratch pad window that you want always to have available to the user. Make it a main window, which can be displayed at any time anywhere on the screen. As a main window, it can display on top of other windows on the screen.
