It's not clear which metrics Twitter uses to determine which tweets get slotted into the "While you were away" recaps, but the microblogging service says the feature uses "engagement and other factors" to display "a few of the best Tweets you probably wouldn't have seen otherwise." The new feature, similar in concept to Facebook's "top stories," breaks up Twitter's otherwise chronological timelines. Its introduction comes as Twitter plans a raft of new features, including better direct messages, designed to entice the 500 million people who visit Twitter every month to actually sign in to the service.