I got no upvote and a downvote with no explanatory comment.
I believe there is something wrong with my answer, but I'm unable to see what.
After the downvote, I added an edit to ask for explanations, but I got none.
I don't know if a meta question is appropriate, but I don't see what else to do.
Let me insist: I know I often make mistakes. I'd just like to know which mistakes I made in this post. This would be useful for me of course, but also for the user who asked the question, and for the people who read the thread.
Thank you very much in advance for your help.