Usually, I'm able to address a comment to someone by writing "@[whoever]" before the text; but in a comment to a recent question (Compact, densely ordered spaces) I wasn't able to do this: when I typed "@[whoever]," it just didn't appear in the comment at all. Am I doing something wrong?
$\begingroup$ Could you describe the precise situation? -- I think if the addressee would be notified anyway (i.e. you are commenting on their post), the @[whoever] is omitted, and if you cannot notify the addressee (they don't have a comment in the same comment thread), this happens as well. $\endgroup$– Stefan Kohl ModJun 23, 2014 at 20:29
1$\begingroup$ Oh, that would explain it - I tried addressing the answerer, and then the OP (who was not in the comment thread). I didn't know you there were limits to who one could address a comment to. $\endgroup$– Noah SchweberJun 23, 2014 at 20:30
$\begingroup$ Another limit is that you cannot notify with @ more than one person. $\endgroup$– Emil JeřábekJun 23, 2014 at 22:17
6$\begingroup$ And here are the gory details: meta.stackexchange.com/a/43020/226864 $\endgroup$– Emil JeřábekJun 23, 2014 at 22:25
4$\begingroup$ I retagged as this is not a bug. In view of the the uncertainty you expressed regarding tagging I add: if you are not very convinced it is a bug or the matter is not urgent to start with support is a good option. If it turn out to be an actual bug you can still retag then. Using the "bug" tag is mainly good for getting SE staff's attention more quickly. $\endgroup$– user9072Jun 23, 2014 at 22:26
$\begingroup$ The issue is that the software assumes that the only reason to mention someone's name is to "ping" them. Of course, there are several other reasons you might want to mention their name (e.g. to indicate to others that the comment is written to a specific person rather than a general comment on the question or answer). In that case, if you find the software mistakenly removes their name, you can always write something like "To John Smith: " at the beginning, instead of "@John Smith". $\endgroup$– Carl MummertJun 26, 2014 at 14:14
The way comment notification and related auto-completion works precisely is a little subtle. The details can be found in How do comment @replies work?
The main issue in the current case appears to be that since OP is always notified of a comment, an "@OP'sname" is removed upon submission of the comment (and it is not suggested in tab-completion) as long as there is noone else in the conversation. [If there is an additional commenter "@OP'sname" works, though it is irrelevant for the purpose of notification.]
Some further remarks that seem relevant in the context:
one can only comment-notify users involved in the post on which one comments (question and answers are seperate posts), where "involved" means have posted, have commented, have edited [no tab completetion for those], and have closed and are a moderator.
One can typically write "@something" for users other than the above but they are irrelevant for the purpose of notification (and thus are not suggested in tab completetion). The presence of more than one @user the presence of which as a consequence has a notification results in blocking the comment submission.
As said, this is not at all everything that is to be said, but it is meant to address roughly the key-issues in the current situation.
2$\begingroup$ The above does not really add much beyond the comments, but in the interest of having an answer I typed it up. $\endgroup$– user9072Jun 24, 2014 at 14:57
$\begingroup$ Thanks! I've accepted. $\endgroup$ Jun 24, 2014 at 15:29