You can create a new document group when you have two or more documents in the same group. You can choose vertical or horizontal arrangement.
On the main menu:
Window New Horizontal Document Group to to create a new group split horizontally.Window New Vertical Document Group to to create a new group split horizontally.If you want a new document group on a different screen, float one of the documents to create a new dock-site and drag other documents on top of it.