Is there an Apple document listing the differences between each version of the iOS SDK? (e.g. differences between iOS 3 and iOS 4)

Is there an Apple document listing the differences between each version of the iOS SDK? (e.g. differences between iOS 3 and iOS 4).

If not, how do oth开发者_Go百科er iOS developers keep up to date with the latest features without having to search through lots of documentation.

For each new release of the SDK, Apple publishes three documents:

1. What's New in iOS x.x, giving a high-level overview of the new features.
2. iOS SDK x.x Release Notes, mentioning known issues and bugs.
3. iOS x.x API Diffs, listing every single (documented) change in the APIs.