Fig 1-12 is the Wrong Image
For some reason, there are a couple of places that images got mixed up in the final pressing. One of the most glaring examples of this is on page 19. Figure 1-12 should be a picture of a Git repository with 4 commits. Instead, it's a picture of a DOM tree.
The actual picture for Figure 1-12 is here.
Thanks to Matthew Brockway for reporting this!