While reviewing the new content about NGINX phases, bihu@redhat.com (Terry) made this comment: 

Can we introduce more about the two kinds of policy chains? Eg. Do all policies in the upstream policy chain have their corresponding ones in the global policy chain? Because it looks like I don’t see any documents to describe how to set up the global 3scale policy chain via the environment variable way. It might need  a separate section to discuss the two kinds of policy chain in a bit detail. (differences between the two, how to set up, overriding the same policy, supported policies in the global policy chain, etc)

Dani Marin pointed to the following example, which is at the end of the upstream doc for the Logging policy, and also said: "The environment code loads the desired policies (so you can add any of the existing policies). This is done before loading the policies from the configuration, so they will be placed before the configured policies."

https://github.com/3scale/APIcast/tree/master/gateway/src/apicast/policy/logging 

We need a separate new section to introduce the global policies officially, with some examples and step-by-step procedures to follow in case customers want to configure the global policy chain on their own.

We need to update Administering the API Gateway, Chapter 4, "APIcast policies", section 4.2 "Policy chaings from standard 3scale policies". We need to add a concept module about global policy chains.