I've been a (curious, reasonably well-read, exposed to all sorts of non-mainstream topics) sysadmin for ~=25 years, but I was today years old when I learned why #DNS resource records require you to say "IN" all the time.
It's to specify the record is related to the INternet! Isn't that helpful?
Apparently we have to waste untold bytes of disk and network traffic on this because there used to be something called Chaosnet: https://twobithistory.org/2018/09/30/chaosnet.html
(and also Hesiod, I guess. Sure. Fine.)
