Gesture to split Safari screen?

[kat.hayes]

i accidentally swiped on my screen while using Safari and it split the screen between a bunch of tabs and one open window on the left and one different tab on the right.

1. How is this done?
2. How do you in-do it?

Thanks.

 

[adamfozzy]

Drag the tab to the side to create split view and drag it back to undo it.