> GNOME decided that GTK+ must not support MDI (as in the UI paradigm where you have a container window with subwindows floating around inside it), and moreover

> GNOME decided that GTK+ must not support MDI (as in the UI paradigm where you have a container window with subwindows floating around inside it), and moreover the same kind of user interface should be implemented at the top level because a good window manager should be able of keeping an application's windows together. This is what macOS does, and does it well. Aqua/Quartz (is it still called that?) doesn't support (or at least doesn't encourage) MDI either, but unlike Windows it's app-centric instead of document-centric, which can annoy some Windows users when ALL of an app's windows come to front when they click on its icon in the dock.