DNS Esoterica – Why you can't dig Switzerland
The DNS "master file"/"zone file" format is a bloody disaster for the same reason, and practically unparseable. Every implementation  parses them differently when it comes to parenthesis.From the grammar in RFC 1035:     []

     []

     contents take one of the following forms:

        [] []  

        [] []  

All the columns being optional creates the ambiguity between the  and  columns in the TTL missing/2nd form. In the real world  is always "IN". It's even worse since the set of 's is unbounded and the  grammar depends on I believe this is one reason why tinydns has its own format https://cr.yp.to/djbdns/tinydns-data.html