We just finished covering the principles of Swift's API Guidelines. In addition, I provided you with resources on how to find the Swift Evolution proposals that document the motivations for each change. We also covered new features to work with #selector and #keyPath expressions when working with Objective-C APIs in Swift. Finally, we explored working with C APIs and controlling how they are imported into Swift 3. In the next chapter, we will cover more language changes. Stay tuned as we still a have a lot of new things to cover!