http://y7egb5vi45k74makeixpfb7jnimfxm3gf233lb3ke2ldonozjk55nvad.onion/notes_on_dns.html
These caching servers will preform “recursive lookups”
for you - or in one shot taking an arbitarily deep and potentially
unseen hostname a.subdomain.domain.tld and preforming all lookups
necessary and using whatever is cached to return a result. This is
actually necessary, because the “resolvers” built into computer programs
that use DNS, usually through the c libraries gethostbyname() function,
cannot use a non-recursive server.