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.