So both addresses are unambiguous. For what reason now would I need a
FQDN? Why wouldn't a domain name suffice?
Typically, I see it that a domain refers to an entity, whereas a FQDN refers to a host or service within that entity. For your purposes the following sdhould be sufficient:
domain.tld is a FQDN if "tld" is a valid tld. a domain is fqdn if it
contains all labels until the top domain. same as for an absolute path
(aka /tld/domain). in dns terms, fqdn ends with a dot though.
now, I don't see why Stefan wants to do that...