Surround Slider In Stereo Expander

Can someone explain how does the surround slider in the stereo expander effect work?

I mean, I know the output it generates, but I was wondering - on a more technical level - how does it work, or in more general terms, how does a surround feeling achieved on a stereo mix.

Surround sound is being produced by inverting the left or right channel bitwise in simple terms said regarding stereo samples. There is a lot more to it but i’m not that technical with samples.