I have a project that started on 2008 and had been updated yet. Now I want to implement size classes and I find myself without being able to create universal xibs. I looked at the project settings and I have two "Main Interface" windows, as you can see here:
As a comparison, here is the same portion of a new project created with Xcode 7 & iOS 9
How can I update the project so that I can create universal, size-classes-using XIB files?