There is an article. It contains a typo. Someone mentions it in a comment. The comment is upvoted as helpful. Author fixes the typo. Now there is a no-longer-useful comment in the discussion, sometimes with replies (the author saying "thanks, fixed", etc.). Sometimes it sits at the top of the discussion, if it was sufficiently upvoted.
If I try to avoid this, I send the author a private message. This does not clutter the discussion, but the disadvantage is that other people don't see me doing this -- so they are likely to also send private messages to the author, and maybe someone will make a comment anyway.
Downvoting the comment gets it out of the way, but it's not fair to the person who made it. We should encourage reporting typos, definitely not punish it.
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My proposal is to make a new functionality that approximately means "this comment was useful at the moment it was made, but it has outlived is usefulness". Available in the three-dots menu in the upper-right corner of the comment.
A comment can be marked like this by the person who made it, or by the author of the article. (Or by the moderators, of course.) A comment marked like this will be moved to the bottom, regardless of the sorting mode, and will by default appear collapsed. (Maybe also displayed using a different color.)
Unlike retraction, this has no impact on voting, etc. (I am not 100% sure how retraction works.) You can still read the comment, even upvote it if you wish. It just doesn't get in the way. Also, semantically, there is a difference between "I no longer support this" and "this is no longer relevant, but it was when I wrote it".
Yeah. I was considering something like "the 'outdated' flag can be set by comment author, article authors, or the moderators... but if someone else has set it, the comment author will be notified and can remove the flag, in which case no one other than the comment author will be able to set it again" -- but this seems needlessly complicated.
From my perspective, in the case of abuse, the comment is not removed, only collapsed and moved to the bottom, so there remains a clear evidence of abuse that can be called out; which in my opinion is a sufficient protection against abuse. (I guess there should be a small print mentioning who specifically has set the "outdated" flag for given comment.)
Maybe the wording should be specific enough, like "This comment reported a typo which has been fixed", to make it more obvious what constitutes an abuse of the button.