I can see how combinations can be computed by watching keydown/keyup combinations and their order, but it seems very complicated to get right and kind of makes my head hurt 
Especially trying to figure this out on Mac where long key presses perform different operations than long key presses on Windows.
I don’t actually see where Visual Studio is doing combinations. It looks like they are using a key+modifier sequence. It doesn’t allow for creating key combinations like L+K