Here it is. There is no visualization of the stack, which apparently Stackline in the other comment supports, but I don't tend to need that. Just being able to move between the windows is good enough for me.

https://github.com/koekeishiya/yabai/issues/203#issuecomment...

They may be referring to stackline https://github.com/AdamWagner/stackline

I've used it in the past, it was very aesthetically pleasing but did not work consistently enough for me to use day to day.