Oh how many fun things have been skipped! For example, errors in message header are a nibble. There is compression of sorts, and labels referenced by an offset. There is an unique notation of emails in the SOA records; and some domains and nameservers are just plain magic. If you set out to implement a complete DNS resolver, you are IN for a fun, fun, fun time with printouts of quite a few RFCs dating back to 1987 IIRC. But the most fun part is reading these documents and seeing a story - of networks that never came to be, of dawn of the internet, of very much constrained computers and networking equipment and the genius of the thing that still is the root of the internet as we know it even some 30 years later.