Anybody happen to know (*cough*@Krinkle*cough*) whether / what comment syntax MediaWiki:Gadgets-definition supports? For things like site-wide styles or gadgets (default|hidden), things meant to be loaded by other gadgets, etc. it'd be very useful to drop a comment in the definition to help other admins out when trying to figure out what something does or why it is the way it is. Not that I've spent waaay too much time cleaning up inherited code here or anything… :)
Topic on Extension talk:Gadgets
Hello. <!--HTML comments--> worked for me.
HTML comments are removed before any processing. However, spaces around them aren’t, which has caused issues in the past (phab:T354385), so you should look out for spacing-related issues if you use comments.