Where to find online documentation for older versions of Swift? Is there an official online Apple source for documentation for Swift 3? (Preferably that can be accessed without signing in to a developer account.) Browser searches for "Swift 3" are finding links to documentation for Swift 4 at developer.apple.com, but I am interested in the older version.
If you're using a modern Apple Device, which you must be in order to develop with Swift 3, you can use iBooks' Swift 3.1 Guide. Once Xcode 9 and Swift 4 are finalized, this book may receive an update to Swift 4, but you should be able to decline the update.
Check out the book here: The Swift Programming Language (Swift 3.1)