I've been looking for the detail of every rules at cloud armor WAF. I just found handbook (paid one) and some kind of code regex for every rules. I still didn't find any explainations detail for every rule. Is there any official documentation on this ?
There is an official documentation on WAF rules for Cloud Armomr here and how to use them in the optimal way.
Additionally you can have a look at the Cloud Armor documentation itself - it's a good starting point to get you head around it's concept (configuration, monitoring, troubleshooting and more).