Exactly. Any GUI element is a "window" and composed of other sub-areas, also windows. You could create windows in the "root window", then the WM would manage then and draw window decorations, but in theory you could also just render a window in a certain area within another window (e.g. a full application, or even just a single view or editor of an application).
I'm not too familiar with higher level frameworks like Qt or gtk, but I suspect since they just draw the whole thing, that they only use single X windows and don't compose them, so you wouldn't be able to render a subview of them inside a different context.
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Exactly. Any GUI element is a "window" and composed of other sub-areas, also windows. You could create windows in the "root window", then the WM would manage then and draw window decorations, but in theory you could also just render a window in a certain area within another window (e.g. a full application, or even just a single view or editor of an application).
I'm not too familiar with higher level frameworks like Qt or gtk, but I suspect since they just draw the whole thing, that they only use single X windows and don't compose them, so you wouldn't be able to render a subview of them inside a different context.