Restore rules in autolabel mapping

Please correct me if I'm wrong. I assume that autolabel is asign torrent to label algorithm. There is some default magic algorithms like Default document rule or Default music rule. What these algorithms are based on? Can I look how they are constructed?

I have deleted some default autolabel rules. I need to restore them back. But how to tell system to use Default document rule?

I'm writing documents in Label field, but what must be written to Contains?