http://www.rfc-editor.org/rfc/rfc3491.txt
RFC 3491: Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN), P. Hoffman, M. Blanchet2003-03-01T23:00:00-00:00This document describes how to prepare internationalized domain name (IDN) labels in order to increase the likelihood that name input and name comparison work in ways that make sense for typical users throughout the world. This profile of the stringprep protocol is used as part of a suite of on-the-wire protocols for internationalizing the Domain Name System (DNS). [STANDARDS-TRACK]