Comments allow users to discuss questions and answers without posting an actual answer. You can add comments to ask for clarification, suggest corrections, and provide additional information about posts.
You can also make comments more targeted by using the @name syntax anywhere in your comment to prompt the attention of a specific user.
All about comments
Comments are intentionally short (600 characters max), and allow only limited markup. URLs in comments automatically become hyperlinks. Users may post no more than one comment every 15 seconds.
By design, comments are temporary. Unlike posts, there's no revision history, and they can be deleted without warning by their authors, by moderators, and in response to flags.
Anyone can leave comments on any post, though site administrators can require users to have a certain amount of reputation first. Admins and moderators can leave comments on any post regardless of their reputation.
Any user can edit or delete their own comment, though only within five minutes of when the comment was posted. Admins and moderators have the ability to edit or delete the comments of other users at any time.
Since comments should contain information that is temporary in nature (for example: an edit suggestion for an answer), regular deletion of obsolete comments is a good way to keep content relevant and current. In the event that a comment should persist and be easily found, you can find the direct link to a comment by clicking the timestamp to its right.
Using @reply to notify users in comments
With the "@reply" feature, Stack Overflow allows you to notify users directly by typing the user's name preceded by the "@" symbol (for example: @rsmith). This will create a notification in that user's global inbox.
While entering or editing a comment, typing "@" will provide a list of users you can notify. Clicking a username from the list will automatically fill out the @reply so you don't have to enter it manually.
NOTE: The author of a post will receive a notification for any comment activity on their post, regardless of the use of @reply.
The @reply feature may seem similar to the Ask people button you can click when first posting a question, but the latter method is more effective in most cases. Ask people allows you to identify specific users or groups, and, unlike the @reply feature, the request is not attached to a temporary comment.
If you need further support or have questions, contact your site administrator.