DC Protection circuit

[braintree]

Hi all,
Can anyone help me understand what's going on in this circuit? Here's a Falstad link https://tinyurl.com/2bds334y
It's supposed to do polarity correction, overvoltage & short circuit protection for a DC supply.
I can follow the polarity correction easily enough, it just looks like a MOSFET rectifier, but I'm struggling to understand what's happening with the overvoltage & short circuit protection. I've been playing with it for a while, and I'm really stuck