/home/set/maradns/maradns-0.9.35/doc/en/misc/private_rrs.html

MaraDNS' private RR space

The DNS specification allows 65534 different resource record types; after DNS being in use for nearly 20 years, only 53 different resource record types have been formally assigned; one more (256) is in limited use by BIND.

This in mind, I do not think it is unreasonable for MaraDNS to use the DNS space between 19712 (8859-1: M\0) and 19967 (8859-1: Mÿ) for experimental RRs.