> HN itself uses the terminology "comment" for top-level messages and "reply" for sub-level messages
Does it? I can't see any distinction in https://news.ycombinator.com/newsguidelines.html or https://news.ycombinator.com/newsfaq.html
Rereading your comment now with this in mind, I can make out the distinction, but I don't think you made it clearly.