I'm not the author (but I know him and he doesn't have an HN account--I've also contributed a chapter currently awaiting as a PR). PRs are certainly welcome.

Also, in Chapter 1 the completed regex is

    [0-9]{1,2} U\.S\.\C. § \d+(\w+)?( \([0-9]{4}\))?

Should be

    [0-9]{1,2} U\.S\.C\. § \d+(\w+)?( \([0-9]{4}\))?

Note the backslash location change in U.S.C.