What does the notation for supported frequencies mean? I read “2ghz-b-channels=2412:27,2417:27,2422:27,[…]”, “5ghz-turbo-channels=5210:17,5250:23, […]” etc.
What do the values after the colons mean?
max output power
In dBm, I suppose?
Do you read this information from the cards (my example was an AR5212)?
no, these are the limitations.
what you are seeing is the new regulatory system. in each country there are different allower outputs, so if you turn on regulatory domain and select your country - you will have these limits. its from some EU rules
Aaaah! I’ve been waiting for that… 
but this is AFAIR, so wait for a clear manual for that one
Yeah, I know - beta etc. But fine to see it