> I think the MDI was too complicated for most people. Simplicity wins. And wasn't it like an application had to implement it to use it, not part of the OS-GUI by itself?
It's true that MDI generally existed at a different level of abstraction (the "toolkit" that draws widgets rather than the "windowing system" that assigns screen regions to applications and lets them draw to those regions, while giving the user control over which application gives what region), but in contexts where the OS also provided a canonical platform GUI toolkit (such as Windows, see the documentation I linked above), the MDI implementation would naturally also come from the same vendor.
I'm aware that a common argument of the anti-MDI push was in fact that the OS window manager should be able to handle management of (sub)windows better and more natively than an application vendor's own low-resource proprietary implementation in the context of subwindows, but this superiority of platform window management never actually materialised and in 2022 I'm still occasionally finding myself trying to chase down all the different subwindows of multi-window applications that wound up on separate workspaces. Pre-single-window GIMP was a particularly egregious offender in this regard.
Juts to think about the difference a bit more, in MDI you could open new windows within the application-window, say multiple text-editor-windows within the MS Word application-window, if I recall.
What you could not do is open a new application-window from within the application window. And that would seem rather useless. But it would not be useless if the whole desktop worked that way, open new child-desktops from current one, recursively.
It's true that MDI generally existed at a different level of abstraction (the "toolkit" that draws widgets rather than the "windowing system" that assigns screen regions to applications and lets them draw to those regions, while giving the user control over which application gives what region), but in contexts where the OS also provided a canonical platform GUI toolkit (such as Windows, see the documentation I linked above), the MDI implementation would naturally also come from the same vendor.
I'm aware that a common argument of the anti-MDI push was in fact that the OS window manager should be able to handle management of (sub)windows better and more natively than an application vendor's own low-resource proprietary implementation in the context of subwindows, but this superiority of platform window management never actually materialised and in 2022 I'm still occasionally finding myself trying to chase down all the different subwindows of multi-window applications that wound up on separate workspaces. Pre-single-window GIMP was a particularly egregious offender in this regard.