Split view
It is possible to open two views side-by-side, allowing working on two documents at once or referencing information in one doc while writing another.
Entering split view
In the desktop app simply cmd+`click` on a document to open in split. On web and elsewhere menus also include an “Open in split view” option.

Exiting split view
Simply click the close button that appears in the top right corner of either pane to close.