You can use @name syntax anywhere in your comment to reply to a specific user. This will notify that user in their global inbox. There can also be notification through email if you click the "email settings" link at the lower left of your global inbox.
Some more detail:
- The first author of the question or answer will always be notified of any new comment.
- You can explicitly notify one (1) other user if they have a current (non-deleted) comment on the post or their name appears anywhere in the revision history (only those who have commented will show up in the auto-complete dialog though). Also note that users who have closed or reopened a question without a binding close vote (i.e. without a gold tag badge or a moderator vote) cannot be notified, even though their usernames will appear in the revision history.
- Use @name, where name is the username with all spaces removed.
- Single trailing punctuation such as a dot, comma, or colon is ignored, e.g. @name, yes
- Multiple trailing dots work as well, e.g. @name... yes
- Things like @op, @downvoter or @all have no special meaning.
- If a user comments on their own post and there is only one person who has previously commented, then that person is also notified if @name is forgotten.
- Tab name completion can be used, and that knows when @name is unnecessary and will then not automatically complete names. It also does not work for editors.
And all details that make this work:
The question and answers are all considered independently. For example, if Alice was the author of, commented on, or edited the question or her answer, then you cannot notify her by commenting on Bob's answer (unless Alice also participated in that answer), and vice versa.
You must include @name, where name is a reasonable match to a user's current display name. Users who have not set a display name in their profile are not notified.
If the first word in the display name is at least three characters long, then there must be a starts-with, case-insensitive match of at least three characters in the display name. This means @a and @ab will never match anyone, unless a user uses a first word that is only two characters. Like: @Jo will notify Jo Miller, but not John, and @B. will notify B. Gates, but not B.Gates. If there are more than three characters in @name, then all given characters must match (neither @alix nor @aliceinwonderland will match user Alice).
Matching is performed in reverse chronological order, so if five people named John are participating, @john will match the most recent John. (Use the next rule to differentiate.)
Spaces are removed from the display names for matching purposes. So to match Peter Smith you may use @pet, @peter, @peters, or @petersmith. The last two are useful if Peter Jones is also participating, who can then be distinguished using @peterj. However, no spaces are allowed in the @name itself. Like to notify P Smith, one must use @psm or @psmith. (Here @P Smith would be handled as just @P, which is too short.) Single quotes, dots, dashes and underscores should not be removed.
Special characters are replaced with their simple equivalent. To reply to Piëre you can use both @piëre and @piere. And to reply to Jörg you could use @jorg, but not @joerg.
Comments containing more than one @name are blocked unless they contain a backtick
In the latter case, only the first name mentioned using the @name syntax will be notified. For example, @alice @bob Hi!` will notify Alice (if she has participated in that post), but not Bob.
An exception is the case when the first @name either matched nobody, or matched the post's author (and thus isn't necessary); in this case, the next @name will be checked.
When editing a comment within its limited editing period, if you change or add @name, the notification may or may not reach the new recipient depending on timing.
The first author of the question or answer will always be notified of any new comment. There is no need to use @name to notify them. (You may still use it for clarity, if needed; however if only you and the author have been commenting on the post so far, the @name will be automatically removed from the beginning of the comment, as it adds no value.)
The notification must begin with a space or be at the start of the comment. For example, you cannot use markup such as italics.
Single trailing punctuation such as a dot, comma or colon is ignored. Like @name, yes works,
but @name... no does not. (Though a dot is valid in a username, the last dot is removed for matching, so @St will notify St. although only two characters are used.) Hyphen can also be part of users display name, hence not ignored so @name- ... will not work.
The notification only works for the username that is current at the time the comment is submitted, not any previous username(s) the target may have had.
The exact matching rules are not documented, but extensive tests performed on 30 August 2011 indicate that the following algorithm is used:
- Take the first word immediately following the
@, where the word boundary is determined by a space, a character not valid in user names (such as
: , / ! ?) or the end of the comment.
- Remove one trailing dot
. from the resulting string if applicable (and if the string has more than two characters).
- If the remaining string ends in
's, remove that piece from the string.
- The resulting string will be matched against the user name with spaces removed.
Example: The comment ends with
@O'Conner's.). The word immediately following the
. are valid in user names. Then the trailing dot is removed, and finally the
's is removed, resulting in
Some examples of supported notifications:
@name some text
@name: some text
@name. Some text
@name, some text
some text, @name
some text, @name, more text
Some text, @name.
This is mentioned in @name's comment.
@P. for both P. Smith and P. Jones (whoever commented most recently), but not P.Smith nor P.Jones. Likewise,
@P. Smith is handled as
@P., so also matches P. Smith or P. Jones.
@psmith for P Smith
@peterj for Peter Smith or Peter Jones respectively
@name... now works.
Examples that will not trigger notifications: