Letter to Unicode Technical Committee on IDNA2008

Lisa Moore lisam at us.ibm.com
Mon Nov 30 04:20:19 CET 2009

Dear Vint,

Thank you for the communication.  We will certainly give this our full 
attention and respond as soon as possible. We appreciate the consideration 
of the IETF and hope to further our joint consensus.

Best regards,

Lisa Moore
Chair, Unicode Technical Committee

Vint Cerf <vint at google.com> wrote on 11/28/2009 01:57:17 PM:

> [image removed] 
> Letter to Unicode Technical Committee on IDNA2008
> Vint Cerf 
> to:
> Lisa Moore
> 11/28/2009 01:57 PM
> Cc:
> emuller, markdavis, idna-update, lisa Dusseault
> Note to the IDNABIS Working Group: 
> During processing of the Last Call responses, the Area Director 
> expressed discomfort with the state of consensus on the use of Latin
> Small Letter Sharp S and  Greek Small Letter Final Sigma. To gain 
> additional input on whether these should remain PVALID, I am sending
> the letter below to the Unicode Technical Committee for its opinion. 
> vint cerf
> ------------------
> Ms. Lisa Moore
> Chairman, Unicode Technical Committee
> via email: lisam at us.ibm.com
> CC: 
> Eric Muller
> Vice Chairman, Unicode Technical Committee
> via email: emuller at adobe.com
> Mark Davis
> President, Unicode Consortium
> via email: markdavis at googlle.com
> 28 November 2010
> Dear Ms. Moore:
> I am writing to you in my role as chairman of the IDNABIS working 
> group, addressing this request to you as president of the Unicode 
> Consortium. As you know, treatment of the two characters, Greek 
> Small Letter Final Sigma (U+03C2) and Latin Small Letter Sharp S (U
> +00DF) have been the source of considerable discussion during the 
> IDNABIS Working Group effort on specifying the  IDNA2008 proposed 
> replacement of the IDNA2003 standard for the use of Unicode in 
> Internationalized Domain Names. Latin Capital Letter Sharp S (U
> +1E9E) was added in Unicode version 5.1.0 but recommended rules for 
> its use were provided as shown below:
> Begin quote from Unicode Version 5.1.0
> Tailored Casing Operations
> The Unicode Standard provides default casing operations. There are 
> circumstances in which the default operations need to be tailored 
> for specific locales or environments. Some of these tailorings have 
> data that is in the standard, in the SpecialCasing.txt file, notable
> for the Turkish dotted capital I and dotless small i. In other 
> cases, more specialized tailored casing operations may be 
> appropriate. These include:
> Titlecasing of IJ at the start of words in Dutch
> Removal of accents when uppercasing letters in Greek
> Uppercasing U+00DF ( ß ) LATIN SMALL LETTER SHARP S to the new U
> However, these tailorings may or may not be desired, depending on 
> the implementation in question.
> In particular, capital sharp s is intended for typographical 
> representations of signage and uppercase titles, and other 
> environments where users require the sharp s to be preserved in 
> uppercase. Overall, such usage is rare. In contrast, standard German
> orthography uses the string "SS" as uppercase mapping for small sharp s
> . Thus, with the default Unicode casing operations, capital sharp s 
> will lowercase to small sharp s, but not the reverse: small sharp s 
> uppercases to "SS". In those instances where the reverse casing 
> operation is needed, a tailored operation would be required. 
> End quote from Unicode Version 5.1.0
> In IDNA2003, Sharp S was mapped to "ss" by means of a casing 
> operation that mapped lower case Sharp S to uppercase "SS" and then 
> down to lowercase "ss". Registrations and lookups using the IDNA2003
> rules applied this mechanism. 
> During the discussions in the IDNABIS Working Group on IDNA2008, a 
> strong consensus developed around not mapping for example for 
> registration purposes and also for preserving the property that the 
> IDNA2008-defined A-Label and U-Label forms be fully symmetric (i.e.,
> convertible into one another without change or loss). 
> During these same discussions, a consensus seemed to develop to 
> permit (ie. make "PVALID" in IDNA2008 parlance) Latin Small Letter 
> Sharp S (U+00DF) and Greek Small Letter Final Sigma (U+03C2). The 
> recommended casing actions of Unicode (i.e. toCaseFold) on Sharp S 
> and Final Sigma produce "ss" in the case of Sharp S and Greek Small 
> Letter Sigma (U+03C3) in the case of Final Sigma.
> To make the lowercase forms PVALID using the functional rules of 
> IDNA2008, exceptions were required to overcome the recommended 
> casing mechanics of Unicode (i.e. application of CaseFolding). 
> Note that IDNA2008 explicitly permits mapping for User Interface 
> a) draft-ietf-idnabis-protocol-17#section-5.2 
> c) draft-ietf-idnabis-rationale-14#section-4.4
> d) draft-ietf-idnabis-rationale-14#section-6
> e) draft-ietf-idnabis-rationale-14#section-7.3
> f) draft-ietf-idnabis-mappings-05 
> If Small Letter Sharp S and Small Letter Final Sigma were to be made
> DISALLOWED, these mapping provisions would permit these characters 
> to be handled as a User Interface matter prior to lookup. 
> Because the practices of IDNA2003 are in conflict with the proposed 
> practices of IDNA2008, and because the Last Call discussions have 
> surfaced controversy over the incorporation of the two lowercase 
> forms in question, I request an organizational recommendation from 
> UTC as to the treatment of these characters. Taking into account the
> prohibition of mapping on registration, which I take to be firm, and
> the requirement that A-Label and U-Label forms must be unambiguously
> convertible into each other, would the UTC recommend to exclude the 
> use of Small Letter Sharp  S and Small Letter Final Sigma in 
> IDNA2008 by removing their exceptions and making each DISALLOWED?
> A prompt response would be much appreciated considering we have 
> delayed reporting the results of the IETF LAST CALL to the Internet 
> Engineering Steering Group while this matter is debated.
> Sincerely,
> Vinton Cerf
> Chairman, IDNABIS Working Group of the Internet Engineering Task Force

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