We are experimenting with comments and, for the moment, have implemented an unusual comments policy: comments are ephemeral. You can expect any comment that you post to be deleted sooner or later. Some will survive longer than others, at our discretion. If we especially like a comment, we may take it out of the comments section and archive it permanently, but, generally speaking, you should always keep a copy of any comment you post if you want to preserve it for posterity. As we continue to experiment, we may change this comments policy without notice.