# Notifying users in comments

I am a little bit confused by the @username syntax in comments. It says that both @peter and @PeterSmith will work, which in my opinion should be changed to something more clear.

Does this mean I can call user Peter Smith by @peter or do I have to address him with his full username including spaces?

• My understanding is that going up to the first space in the username works, e.g. @Peter will work on Peter Smith but not on PeterSmith. – Qiaochu Yuan Feb 23 '11 at 13:30
• @Qiaochu That would make sense. Nonetheless, I think you will agree with me that the explanation provided is confusing. – Milosz Wielondek Feb 23 '11 at 14:00
• Even @Mil is supposed to work. – Aryabhata Feb 23 '11 at 15:32
• I would say that ambiguity depends on context.If we had comments by a Peter Smith and by a Peter Jones, a reply starting @Peter would leave the adressee not well defined (!), but if only Peter Smith cared to post a comment, where is the problem? – Andrea Mori Feb 26 '11 at 9:12
• @Andrea Mori it's not about ambiguity as you understood it. It's about the automized notification system. – Milosz Wielondek Feb 26 '11 at 17:47

## 2 Answers

The authorative source with possibly more than you want to know is on meta.SO: How do comment @replies work?

My understanding is that at least the first three letters are needed, or enough to make a unique match, and that it's only matching against the limited set of users involved somehow in the post being commented on, such as the original poster, the person asking the question, and any previous commenters.