According to Apple's Document Revision History, the updated guide covers iOS 12 features like Siri Suggestions, Siri Shortcuts, the Shortcuts app, Screen Time, Password AutoFill Student ID cards, and more.
On Siri Suggestions, for example, Apple explains that suggestions for apps and shortcuts are generated using on-device machine learning, with no data going to Apple except info that can't be used to identify the user.
One interesting bit in the document relates to the new feature that lets a second appearance be added to Face ID in iOS 12. Adding a secondary appearance, says Apple, will decrease the probability that a random person can unlock the iPhone from 1 in 1,000,000 to 1 in 500,000.
The probability that a random person in the population could unlock your iPhone is 1 in 50,000 with Touch ID or 1 in 1,000,000 with Face ID. This probability increases with multiple enrolled fingerprints (up to 1 in 10,000 with five fingerprints) or appearances (up to 1 in 500,000 with two appearances).Apple's security document explains in detail how each and every iOS 12 feature works and how it's protected. The guide is filled with many small but significant details on iOS 12 features, and for anyone interested in the security of the iPhone and the iPad, the full document is worth checking out.