23.7. Levels of Windows
Very many of the rectangular areas on your screen are officially windows, more of them than you realize. A toolbar is a window, a button on the toolbar is a window, a scrollbar is a window, your main view is a window, and so on. When one window always lives inside some other window, we speak of them as a child window and a parent window. Thus a toolbar button is a child window of the parent toolbar window, and the toolbar is in turn a child window of the parent window running the application. When a parent window has the form of a frame around the child window, we often speak of the child window as the client of the parent frame.
One possible source of confusion here is that we also use the words ‘parent’ and ‘child’ ...
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