The RFC lays out the core principles of IANA's delegation of domains to registries. It identifies the key criteria to be considered when reviewing a request for delegation. It also states the maxim that the IANA is "not in the business of deciding what is and what is not a country." Postel adopted the ISO-3166-1 list of two-letter country codes as the canonical reference for what is considered a country, "with the knowledge that ISO has a procedure for determining which entities should be and should not be on that list."
The decision to utilize the ISO-3166 list has stood the test of time to the present day, although not without some controversy. The proliferation of open use ccTLDs caused some to rethink the system of two letter country codes. For example, in RFC 3071, written in 2001, John Klensin suggested a reclassification of TLDs as either "true generic," "purpose specific," or "country domains," the last category consisting of ISO-3166 country codes that are "operated according to the original underlying assumptions of [RFC] 1591."