Well, so that's what doesn't make sense. Other documentation also indicates a 'hot_standby' setting and I'm looking to see if it can do 'warm_standby' as well. I was hoping for a complete list because it seems scattered right now.
The documentation is version specific. All of the values allowed for the specified version are listed on that page. There is not and never was a "warm_standby" value. The valid values for wal_level do not fully restrict how one can setup their standby configuration but rather define the minimum possible configuration (which is basically either cold or warn standby depending on whether you decide to run an independent standby server full time). The settings at https://www.postgresql.org/docs/current/static/runtime-config-replication.html are use if you wish to convert the warm standby into a hot standby. In either case the relevant wal_level needs to be "replica". It was deemed unnecessary to distinguish between "archive (cold/warn) and hot_standby" in 9.6 - in terms of what information was recorded in the WAL.
