<p>Comments in reply to a specific previous comment can include @UserName to direct the comment to that User Name.</p>

<ul>
<li>Basics are explained in <a href="http://mathoverflow.net/editing-help#comment-reply">Editing help</a></li>
<li>More details can be found here: <a href="http://meta.stackexchange.com/questions/43019/how-do-comment-replies-work">How do comment @replies work?</a></li>
</ul>