With the September release we introduce more collaboration for documents by making it possible to mention other users and groups in the comments. Just type @ and it will bring up a list of the groups and users that are possible to notify. An email notification will be sent to the users and they can also see on the start page when they log in the you have mentioned them. Use it to tell people about your document update or that the delivery has been completed. Or just to make sure that someone know that you read and liked their revision.