macOS IB inxcode3.1

The functionality that existed in 3.0 should also exist in 3.1. The only difference I am aware of is that in 3.1, XCode/IB default to creating XIBs targeting 10.5, so most warnings will get suppressed. You will want to bring up the file's info (in IB) to check/edit this.

If you have a single NIB/XIB that is getting complicated to the point where you need to figure out how to organize it... it is too big. There isn't anything like folders, but you can split it up into multiple NIBs/XIBs and load them programmatically.

An example would be: A XIB for the main program window, another for program preferences, a third for Get Info-like windows, etc.

This method of splitting up the XIB is also useful because a window in its own XIB that you load programmatically can be loaded multiple times and its window spawned multiple times. Something you can't do nearly as easily if the window lives in the same XIB as everything else.

Another salient point to mention is that when the NIB is loaded all of its objects are instantiated (loaded into memory, initialized, etc).

If you don't need everything at startup, then you should split out to separate NIBs (XIBs are just XML-based NIBs that get compiled into read-only NIBs on build).