So I see this topic, and it would appear that they are saying it's already implemented but I can't see how.

I've tried 

- Dragging the whole tab out from the top

- Dragging from the corner of a panel

- Right clicking anywhere in the window (no split view option?)

Wait I found it! 

Right click -> Show aside.

But you can only have 1. Ok I see.

The location for the option is unusual but mirrors how GMS2 IDE works

You can either edit show-aside.js (which generally exists to demonstrate how to instantiate additional code editors) or use Peek Aside if you need a third pane