After discussing this with @bardiharborow, I think this is the best middle solution; if Java is available HTML validation will run, otherwise it will be skipped.
Also, this is a lot faster than the html-validator solution and we don't introduce another point of external failure (like with Sauce Labs).
TODO:
-
Fix ignores -
Fix multiple ignores -
Combine ignores to an array instead of manually doing this? -
Update jekyll-toc when they fix the HTML validation issues upstream -
Verify ignores
Fixes #23171 (closed)