This is taken from the OSX iCloud Storage reference document:
If you’re writing a shoebox app, on the other hand, you should not use
NSDocument. So if you’re doing a shoebox app, you must implement your
own file presenter and deal with version conflicts through that API.
What is a shoebox app?
A single-window or library style app. See the Mac App Programming Guide, specifically The App Style Determines the Core Architecture section.