Earlier quoted context omitted.
ummm, how? When I hit the green button for full screen, it takes over the screen like a Spaces screen. How are you able to have side by side full screen of 2 apps. That seems like you are breaking the definition of the word full. If 2 apps are "full" screen side by side, you either have "half" screen views or 2 monitors.
Press and hold the "full screen" button and you'll get the option to go full screen with 2 apps.
this was unknown to me. thanks for sharing