“With this frequently requested feature, companies like Foursquare can implement user mentions that work like they do in posts on Facebook,” a Facebook representative said in a blog post announcing the addition.
“When people mention a friend in an Open Graph app, the story on Facebook links the person’s name to their timeline, and their friend will receive a notification. The story will also be added to the friend’s timeline or, if enabled, to timeline review. There are no privacy changes associated with this new feature.”
Different than Action Tagging (tagging someone you are physically with), Mention Tagging is designed to be used when someone wants to reference a person in a particular post. For instance, tag the friends in a photo or suggest that a friend check out a restaurant where you’re eating dinner.
Developers who want to implement mention tagging will have to provide users with a tokenizer or some other way that they can reference their friends. Developers are also not allowed to prefill messages. Everything in a message needs to be written by the user with the intention specifically of sharing that message on Facebook.
Developers will also need to resubmit their actions and requests approval to Facebook for user messages and tags.