@mkrawczuk - Yeah it looks like that was stripped out in this commit (ansible/ansible@445ff39) from Feb 2019. Good catch! I'll have this updated in version 1.23, coming soon!
At this point, I'm still keeping the source manuscript repo private because there's a lot of other stuff in it for the full book build, including many proprietary assets that I'm not sure I could put under an open source or CC license.
But at some point it's an option I'm considering exploring. Thanks again for posting these issues!