Where to find these "magic" configuration keys?

Hi,

I was using the ShooterGame example game provided from the documentation and there are several keys in the configuration files that are confusing. I searched for them in the source code but found no information about them.

    [/Script/Engine.Engine]
        GameEngine=/Script/ShooterGame.ShooterEngine
        NearClipPlane=3.0 
        bEnableColorClear=true

For example, the GameEngine key is supposed to be a member decorated with UPROPERTY in UEngine class but I ran a search and there was no result that matches.

Would anybody provide some help with how to find the information about these configuration keys?