What is Realtime and G-Mode?

Edited mistake: Real Time (Ctrl-R hotkey) is a settings of the viewport, can be found under small arrow in the corner. G-Mode is Game mode (G hotkey while in editor).

In UE4 AA Method documentation (here: 1.14 - AA Method | Unreal Engine Documentation)

It says for various AA methods, Realtime and G-Mode must be enabled.

There’s no links to the doc about this and I can’t seem to find references to them. What are Realtime and G-Mode and how do I enable them?