Standardizing on IDNA 2003 in the URL Standard

Jiankang Yao yaojk at
Thu Jan 16 04:03:18 CET 2014

Aà.com has been registered. 

Your search for Aà.com returns the below results:


Whois Server Version 2.0

   Domain Name: AÀ.COM (XN--A-SFA.COM)
   Registrar: INTERNET.BS CORP.
   Whois Server:
   Referral URL:
   Status: clientTransferProhibited
   Updated Date: 12-sep-2013
   Creation Date: 22-feb-2009
   Expiration Date: 22-feb-2014

Jiankang Yao

From: Andrew Sullivan
Date: 2014-01-16 10:52
To: Jiankang Yao
CC: Anne van Kesteren; Mark Davis ?; PUBLIC-IRI at W3.ORG; uri at; John C Klensin; IDNA update work; Vint Cerf;
Subject: Re: Re: Standardizing on IDNA 2003 in the URL Standard
On Thu, Jan 16, 2014 at 10:07:36AM +0800, Jiankang Yao wrote:
>   In which section of rfc idnabis does say some meaning related to  that " "Aà.com" is not PVALID"?

Upper case characters are not PVALID.  This is because of B:
toNFKC(toCaseFold(toNFKC(cp))) != cp.  In appendix B.1 it's
illustrated in this entry:


> I check Aà.com in verisign conversion tool, it shows ""
> does it follow idna2003 instead of idnabis?

I have no idea.  Maybe it has a bug.  Or maybe it does case mapping
before it touches the string; that's what RFC 5895 suggests.  In that
case, of course, the Verisign conversion tool includes some things
that applications are supposed to do.


Andrew Sullivan
ajs at
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