Lukas Mathis has written a good post about “MDIs on the Mac”.
“MDI” stands for “multiple-document interface”, a term Microsoft used for it’s way of having all of an application’s document windows inside a single application window. There was a steady trend away from MDI among Windows applications since...I dunno...at least 1985, I’d say.
Recently there has been a trend (on all systems) towards multiple documents in a single window. Most often with “tabs”.
The first important point is that the new wave of MDIOW (multiple documents in one window) applications are not bringing back many of the worst features of the old MDI. Secondly, the reason this is happening is because there are advantages to it.
As Mathis himself points out, there are way to mitigate the remaining disadvantages. One of the simplest ways is to allow both multiple windows and multiple documents per window. Then the application empowers the user to choose the mix that best suits themselves and the tasks at hand.
I’m particularly impressed by how Safari not only gives me multiple windows and multiple documents in each window, but how I can easily rearrange what documents are in what windows.
Since there is no history of MDI applications on the Mac, and since Apple doesn’t have anything similar to these applications, there are no established UI guidelines. Hence, MDI-based applications confuse users since they behave inconsistently with each other.
True. Even if Apple did have MDI guidelines, however, these new MDIOW applications shouldn’t use them because MDI was seriously flawed. We’re trying to do it better this time. It’s going to take time to figure out what the consistent guidelines should be. This is unfortunate but unavoidable.