Perhaps this will be a "well of course you idiot" thing, but while reviewing https://github.com/wildfly/wildfly/pull/12381 I realized it's quite simple to manually test the docs output from a PR...

1) check out the PR branch locally

2) cd docs

3) mvn clean package

4) open target/generated-docs/index.html

Voila, you have the root page for the 'current' version of the docs open in your browser and you can maneuver around without problem to have a look at the proposed docs.