Private API Is the Wrong Question
So, here we have a blob of common code that helps define the platform and I can’t get to it. This sounds like private API to me, even if it isn’t actually in the pile labelled “UIKit”. Instead of finishing this and making it available, the code is seemingly included directly in each of the iWork applications. The claim of iWork using 100% public API comes off a bit like a kid finishing cleaning their room by sweeping the last pile of junk under the bed.
