Facebook announced a new Open Graph feature today, which lets users mention-tag friends in messages within apps.

“With this frequently requested feature, companies like foursquare can implement user mentions that work like they do in posts on Facebook,” explains Facebook’s Cindy Li, on the company’s Developer Blog. “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.”

In fact, Foursquare is talking up the feature itself.

“Want to let a friend know that you’re trying the dish they recommended, invite them to join you at the bar, or let the world know you’re hanging out with them? You can mention them in your foursquare check-in, and automatically tag them on Facebook and Twitter too!” says Foursquare’s Talisa Chang.

Facebook points out that mention tagging works differently than action tagging. The former can be used when users want to reference friends in their messages, and the latter, when people are performing actions together (such as running together or going to a restaurant together).

Here’s the difference in how they appear on Facebook:

Developers looking to implement mention tagging can find the documentation here.