There are a number of details hidden within the newly released Batman: Arkham Knight trailer that a few highly observant fans of the series managed to spot.
According to an r/games thread on reddit, there are codes hidden within the trailer–four of which have been identified thus far. Their meaning remains reclusive, but the codes appear to pertain to the Person of Interest fields on the game's official website. Entering the text in the site results in a message advising visitors to crack the code.
Fans, diligent as they are, have managed to crack at least one of the codes revealing an extended character biography for Poison Ivy, one of the game's main characters, using the password "botanical gardens".
It features new concept artwork and information on her appearance in the upcoming game from Rocksteady. To access it, you'll need to click the small arrow to the right of the first person of interest field to find Ivy's bio. I've screencapped it for your viewing, above.
Batman: Arkham Knight is slated for release later this year on the PC, Xbox One and PS4.