Variants in Second-Level Names Registered in Top-Level Domains
John R. Levine, P. Hoffman · 2013
Internationalized Domain Names for Applications (IDNA) provides a method to map a subset of names written in Unicode into the DNS. Because of Unicode decisions, appearance, language and writing system conventions, and historical reasons, it often has been asserted that there is more than one way to write what competent readers and writers think of as the same host name; these different ways of writing are often called variants. (The authors note that there are many conflicting definitions for the term variant in the IDNA community.) This document surveys the approaches that top-level domains have taken to the registration and provisioning of domain names that have variants. This document is not a product of the IETF, does not propose any method to make variants work correctly, and is not an introduction to internationalization or IDNA.