WAP11 2.2 antenna selection, WHAT IS "AUTO SELECT" compared to diversity

So like everyone else, I want to run two antennas on my WAP11.

I see on the "hidden admin page" http://192.168.10.9/weca.htm
that I can choose "AUTO SELECT" for the Antenna Selection screen,
along with Left, Right, and Diversity.

So what's the difference between AUTO SELECT and diversity?

PS: Any other good solutions for two, non-overlapping antenna
requirements other than a second WAP?

Thanks!
-Brendan