Aaargh, I've broken the site during attempt to upgrade to Antora 3.1 about er-playbook HOT 2 CLOSED

I'm still lost on how to complete the upgrade such that it will build successfully; but I have at least worked out how to restore the output site to its earlier state. To remind myself:

1. Switch to the er-playbook directory.
2. Stash any work in progress, if any (unusual for this repo).
3. Switch to branch github-pages-source.
4. Find the commit that corresponds to the last successful publish (5105484).
5. Run command to 'discard' commits back to the last successful publish: git reset --hard 5105484
6. Run command to force this onto the remote repo: git push origin HEAD --force
7. Now that the earlier site content is available again in /docs, GitHub will publish it again to GitHub Pages, and thus it is visible at epricremastered.com once again.

from er-playbook.

It's taken lots of educated guesses and trial and error, but it looks like I've cracked it... I've gotten the site to build and publish successfully with this upgrade, at last.
I'll leave this issue open for a while, until I've pushed more changes and I'm satisfied that it is stable/repeatable.

from er-playbook.