HN is a plain-text site so we basically don't allow those. Software strips some of them out sometimes, but it's not the sort of thing we'd go for a 100% technical solution to. I edited them out of the posts in this thread. Interestingly, I don't think the meaning of any of the comments was affected by doing so.

(We detached this subthread from https://news.ycombinator.com/item?id=20776138.)