In the Moodle plugin code prechecks, Mustache lint seems to treat HTML validation info messages as warnings.

I have run into this recently, while checking my course format plugin. I guess there's been a recent change to the HTML validator that's caused it? A Mustache file failed validation because some included Moodle Mustache files closed HTML single tags with /> instead of just >. I got the "info" message "Trailing slash on void elements has no effect and interacts badly with unquoted attribute values." As far as I can tell, this message is only ever given when there is no actual problem, and if there is an actual problem with a trailing /, I think another, non-info message will likely be given.

I don't think it's necessary to treat "info" messages as warnings, and I suspect it will now cause most course format plugins to fail validation in a way that's beyond the author's control. (Not sure about other plugin types.)

(I've also reported essentially the same issue with the Moodle local CI plugin https://github.com/moodlehq/moodle-local_ci/pull/274 . I had thought the Moodle plugin code prechecks might have used this, but now I suspect not?)