Editing Internationalized domain name (section)

== Guidelines for the Implementation of Internationalized Domain Names ==
A technical community working group to create the first IDN Guidelines was created<ref>Mohan, Dam, Karp, Kane & Hotta, [http://www.icann.org/general/idn-guidelines-20jun03.htm IDN Guidelines 1.0], ICANN, June 2003</ref> in August 2002, consisting of Ram Mohan (Afilias), Hiro Hotta (JPRS), Pat Kane (Verisign), Cary Karp (.museum) and Tina Dam (ICANN). Version 1.0 of these Guidelines was published<ref>{{Cite web |last=Mohan, Dam, Karp, Kane & Hotta |date=20 June 2023 |title=Guidelines for the Implementation of Internationalized Domain Names {{!}} Version 1.0 |url=https://www.icann.org/resources/pages/idn-guidelines-2003-06-20-en |url-status=live |website=ICANN}}</ref> on 20 June 2003, coinciding with the launch of deployment of IDNs under the IETF's Proposed Standard reflected in RFCs 3490, 3491, and 3492. After the publication of the Guidelines, it was possible to register [[.jp]] domains using this system in July 2003 and [[.info]]<ref>Mohan, Ram, [https://www.iana.org/domains/idn-tables/tables/info_de_1.0.html German IDN], [http://www.afilias.info/register/idn/DE-INFO_IDN_Language_Table-v1-1.pdf German Language Table] {{Webarchive|url=https://web.archive.org/web/20061218142725/http://www.afilias.info/register/idn/DE-INFO_IDN_Language_Table-v1-1.pdf |date=2006-12-18 }}, March 2003</ref> domains in March 2004. Several other top-level domain registries started accepting registrations in 2004 and 2005. These Guidelines have been updated<ref>Mohan, Dam, Karp, Kane, Hotta, El Bashir, [http://www.icann.org/general/idn-guidelines-14nov05.htm IDN Guidelines 2.0], ICANN, November 2005</ref> to respond to [[phishing]] concerns as well as to accommodate<ref>{{Cite web |last=ICANN |date=Sep 22, 2022 |title=IDN Guidelines v4.1 |url=https://www.icann.org/en/system/files/files/idn-guidelines-22sep22-en.pdf |url-status=live |website=ICANN}}</ref> IDN variants. An ICANN working group focused on country-code domain names at the top level was formed in November 2007<ref>{{cite news|author=Jesdanun, Anick (Associated Press) |url=https://abcnews.go.com/Technology/wireStory?id=3813334 |title=Group on Non-English Domains Formed |date=2 November 2007 |access-date=2 November 2007 |url-status=dead |archive-url=https://web.archive.org/web/20081220044332/https://abcnews.go.com/Technology/wireStory?id=3813334 |archive-date=December 20, 2008 }}</ref> and promoted jointly by the country code supporting organization and the Governmental Advisory Committee.

Additionally, ICANN supports the community-led [[Universal Acceptance]] Steering Group, founded by Ram Mohan in 2015, which seeks to promote the usability of IDNs and other new gTLDS in all applications, devices, and systems.<ref>{{cite web|url=https://www.icann.org/resources/pages/universal-acceptance-2012-02-25-en|title=ICANN – Universal Acceptance|date=February 25, 2012|website=ICANN}}</ref>

[[Mozilla Application Suite|Mozilla]] 1.4, [[Netscape Navigator|Netscape]] 7.1, and [[Opera (web browser)|Opera]] 7.11 were among the first applications to support IDNA. A browser plugin is available for Internet Explorer 6 to provide IDN support. Internet Explorer 7.0<ref name="auto">{{Cite web|url=https://learn.microsoft.com/en-us/previous-versions/windows/internet-explorer/ie-developer/|title=Internet Explorer for Developers|date=October 22, 2021|website=learn.microsoft.com}}</ref> and [[Windows Vista]]'s URL APIs provide native support for IDN.<ref>{{Cite web|url=https://learn.microsoft.com/en-us/windows/win32/intl/handling-internationalized-domain-names--idns|title=Handling Internationalized Domain Names (IDNs) - Win32 apps|date=January 7, 2021|website=learn.microsoft.com}}</ref>

===ToASCII and ToUnicode===
The conversions between ASCII and non-ASCII forms of a domain name are accomplished by a pair of algorithms called ToASCII and ToUnicode. These algorithms are not applied to the domain name as a whole, but rather to individual labels. For example, if the domain name is www.example.com, then the labels are ''www'', ''example'', and ''com''. ToASCII or ToUnicode is applied to each of these three separately.

The details of these two algorithms are complex. They are specified in RFC 3490. Following is an overview of their workings.

ToASCII leaves ASCII labels unchanged. It fails if the label is unsuitable for the Domain Name System.  For labels containing at least one non-ASCII character, ToASCII applies the [[Nameprep]] algorithm. This converts the label to lowercase and performs other normalization. ToASCII then translates the result to ASCII, using [[Punycode]].<ref name="rfc3492">RFC 3492, ''Punycode: A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA)'', A. Costello, The Internet Society (March 2003)</ref> Finally, it prepends the four-character string "<code>xn--</code>".<ref>{{cite web |url=http://www.atm.tut.fi/list-archive/ietf-announce/msg13572.html |title=Completion of IANA Selection of IDNA Prefix |author=Internet Assigned Numbers Authority |author-link=Internet Assigned Numbers Authority |website=www.atm.tut.fi |date=2003-02-14 |access-date=2017-09-22 |archive-url=https://web.archive.org/web/20100427154004/http://www.atm.tut.fi/list-archive/ietf-announce/msg13572.html |archive-date=2010-04-27 |url-status=dead }}</ref> This four-character string is called the ASCII Compatible Encoding (''ACE'') prefix.  It is used to distinguish labels encoded in Punycode from ordinary ASCII labels.  The ToASCII algorithm can fail in several ways.  For example, the final string could exceed the 63-character limit of a DNS label. A label for which ToASCII fails cannot be used in an internationalized domain name.

The function ToUnicode reverses the action of ToASCII, stripping off the ACE prefix and applying the Punycode decode algorithm. It does not reverse the Nameprep processing, since that is merely a normalization and is by nature irreversible. Unlike ToASCII, ToUnicode always succeeds, because it simply returns the original string if decoding fails. In particular, this means that ToUnicode does not affect a string that does not begin with the ACE prefix.

===Example of IDNA encoding===
IDNA encoding may be illustrated using the example domain <code>Bücher.example</code>. ({{langx|de|Bücher|lit=books}}.) This domain name has two labels, ''Bücher'' and ''example''. The second label is pure ASCII and is left unchanged. The first label is processed by Nameprep to give <code>bücher</code>, and then converted to [[Punycode]] to result in <code>bcher-kva</code>. It is then prefixed with <code>xn--</code> to produce <code>xn--bcher-kva</code>. The resulting name suitable for use in DNS records and queries is therefore <code>xn--bcher-kva.example</code>.