Currently, @mention works in:
- Comment under a "question"
- The body of an "answer"
- Comment under an "answer"
- The body of a "post"
- Comment under a "post"
- The body of a "discussion"
- Reply under a "discussion"
- The body of a "blog"
- Comment under a "blog"
The only content type that you cannot mention someone inside the body of the content, is "question" content type. For questions, you can use the @mention in the comment under the questions or simply use the request answer button.
How @mention works? Very simple, just like what you do on Instagram. If you see a content that might be interesting for another user, if you want to share an idea or a comment with someone else, if you want to reply to someone in a comment, … you can mention the person by typing @ followed by the username or the name of the person.