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Versions: 00 01 02

Network Working Group                                         J. Klensin
Internet-Draft
Updates: 5892 (if approved)                                 P. Faltstrom
Intended status: Standards Track                                  Netnod
Expires: December 14, 2019                                 June 12, 2019


                  IDNA Review for New Unicode Versions
                 draft-klensin-idna-unicode-review-00

Abstract

   The standards for Internationalized Domain Names in Applications
   (IDNA) require a review of each new version of Unicode to determine
   whether incompatibilities with prior version or other issues exist
   and, where appropriate, to allow the IETF to decide on the trade-offs
   between compatibility with prior IDNA versions and compatibility with
   Unicode going forward.  That requirement, and its relationship to
   tables maintained by IANA, has caused significant confusion in the
   past.  This document makes adjustments to the review procedure based
   on experience and updates IDNA, specifically RFC 5892, to reflect
   those changes and clarify the various relationships involved.  It
   also makes other minor adjustments to align that document with
   experience.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 14, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Brief History of IDNA Versions, the Review Requirement, and
       RFC 5982  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  The Review Model  . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Review Model Part I: Algorithmic Comparison . . . . . . .   4
     3.2.  Review Model Part II: New Code Point Analysis . . . . . .   5
   4.  IDNA Assumptions and Current Practice . . . . . . . . . . . .   6
   5.  Derived Tables Published by IANA  . . . . . . . . . . . . . .   7
   6.  Editorial clarification to RFC 5892 . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Appendix A.  Summary of Changes to RFC 5892 . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   The standards for Internationalized Domain Names in Applications
   (IDNA) require a review of each new version of Unicode to determine
   whether incompatibilities with prior version or other issues exist
   and, where appropriate, to allow the IETF to decide on the trade-offs
   between compatibility with prior IDNA versions and compatibility with
   Unicode [Unicode] going forward.  That requirement, and its
   relationship to tables maintained by IANA, has caused significant
   confusion in the past.  This document makes adjustments to the review
   procedure based on nearly a decade of experience and updates IDNA,
   specifically the document that specifies the relationship between
   Unicode code points and IDNA derived properties [RFC5892], to reflect
   those changes and clarify the various relationships involved.

   Terminology note: In this document, "IDNA" refers to the current
   version as described in RFC 5890 [RFC5890] and subsequent documents
   and sometimes known as "IDNA2008".  Distinctions between it and the



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   earlier version are explicit only where that is necessary to
   understanding the relationships involved, e.g., in Section 2.

2.  Brief History of IDNA Versions, the Review Requirement, and RFC 5982

   The original, now-obsolete, version of IDNA, commonly known as
   "IDNA2003" [RFC3490] [RFC3491] was defined in terms of a profile of a
   collection of IETF-specific tables [RFC3454] that specified the
   usability of each Unicode code point with IDNA.  Because the tables
   themselves were normative, they were intrinsically tied to a
   particular version of Unicode.  As Unicode evolved, the standard
   would either have required a new version for each new version of
   Unicode or it would fall further and further behind.

   When that version of IDNA was superseded by the current one, known as
   IDNA2008 [RFC5890], a different strategy, one that was property-based
   rather than table-based, was adopted for a number of reasons of which
   the reliance on normative tables was not dominant [RFC4690].  In the
   IDNA2008 model, the use of normative tables was replaced by a set of
   procedures and rules that operated on Unicode properties
   [Unicode-properties] and a few internal definitions to determine the
   category and status, and hence an IDNA-specific "derived property",
   for any given code point.  Those rules are, in principle, independent
   of Unicode versions.  They can be applied to any version of Unicode,
   at least from approximately version 5.0 forward, to yield an
   appropriate set of derived properties.  However, the working group
   that defined IDNA2008 recognized that not all of the Unicode
   properties were completely stable and that, because the criteria for
   new code points and property assignment used by the Unicode
   Consortium might not precisely align with the needs of IDNA, there
   were possibilities of incompatible changes to the derived property
   value.  More specifically, there could be changes that would make
   previously-disallowed labels valid, previously-valid labels
   disallowed, or that would be disruptive to IDNA's defining rule
   structure.  Consequently, IDNA2008 provided for an expert review of
   each new version of Unicode with the possibility of providing
   exceptions to the rules for particular new code points, code points
   whose properties had changed, and newly-discovered issues with the
   IDNA2008 collection of rules.  When problems were identified, the
   reviewer was expected to notify the IESG.  The assumption was that
   the IETF would review the situation and modify IDNA2008 as needed,
   most likely by adding exceptions to preserve backward compatibility
   (see Section 3.1 below).

   For the convenience of the community, IDNA2008 also provided that
   IANA would maintain copies of calculated tables resulting from each
   review, showing the derived properties for each code point.  Those
   tables were expected to be helpful, especially to those without the



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   facilities to easily compute derived properties themselves.
   Experience with the community and those tables has shown that they
   have been confused with the normative tables of IDNA2003: the
   IDNA2008 tables published by IANA have never been normative and
   statements about IDNA2008 being out of date with regard to some
   Unicode version because the IANA tables have not been updated are
   incorrect or meaningless.

3.  The Review Model

   While the text has sometimes been interpreted differently, IDNA2008
   actually calls for two types of review when a new Unicode version is
   introduced.  One is an algorithmic comparison of the set of derived
   properties calculated from the new version of Unicode to the derived
   properties calculated from the previous one to determine whether
   incompatible changes have occurred.  The other is a review of newly-
   assigned code points to determine whether any of them require special
   treatment (e.g., assignment of what IDNA2008 calls contextual rules)
   and whether any of them violate any of the assumptions underlying the
   IDNA2008 derived property calculations.  Any of the cases of either
   review might require either per-code point exceptions or other
   adjustments to the rules for deriving properties that are part of RFC
   5892.  The subsections below provide a revised specification for the
   review procedure.

   Unless the IESG or the Designated Expert conclude that there are
   special problems or unusual circumstances, these reviews will be
   performed only for full Unicode versions (i.e., those numbered NN.0,
   e.g., 12.0) and not for minor updates (e.g., 12.1).

3.1.  Review Model Part I: Algorithmic Comparison

   Section 5.1 of RFC 5892 is the description of the process for
   creating the initial IANA tables.  It is noteworthy that, while it
   can be read as strongly implying new reviews and new tables for
   versions of Unicode after 5.2, it does not explicitly specify those
   reviews or, e.g., the timetable for completing them.  It also
   indicates that incompatibilities are to be "flagged for the IESG" but
   does not specify exactly what the IESG is to do about them and when.
   For reasons related to the other type of review and discussed below,
   only one review was completed, documented [RFC6452], and a set of
   corresponding new tables installed.  That review, for Unicode 6.0,
   found only three incompatibilities; the consensus was to ignore them
   (not create exceptions in IDNA2008) and remain consistent with
   computations based on current (Unicode 6.0) properties rather than
   preserving backward compatibility within IDNA.  The 2018 review (for
   Unicode 11.0 and versions in between it and 6.0) [IDNA-Unicode12]
   also concluded that maintain Unicode compatibility, rather than IDNA



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   backward compatibility, should be maintained.  That decision was
   partially driven by the long period between reviews and the concern
   that table calculations by others in the interim could result in
   unexpected incompatibilities if derived property definitions where
   then changed.  See Section 4 for further discussion of these
   preferences.

3.2.  Review Model Part II: New Code Point Analysis

   The second type of review is not clearly explained in RFC 5892, but
   is intended to identify cases in which newly-added code points, or
   perhaps even newly-discovered problematic older ones, violate design
   assumptions of IDNA, identify defects in those assumptions, or are
   inconsistent (from an IDNA perspective) with Unicode commitments
   about assignment, properties, and stability of newly-added code
   points.  The discovery after Unicode 7.0 was released that new code
   points were being added that were potentially visually equivalent, in
   the same script, to previously-available code point sequences was one
   example of the type of situation the review was expected to discover
   (and did so [IAB-Unicode7-2015] [IDNA-Unicode7]).

   Because multiple perspectives on Unicode and writing systems are
   required, this review will not be successful unless done by a team --
   a single, all-knowing, Designated Expert is not feasible or likely to
   produce an adequate analysis.  It should also be recognized that, if
   this review identifies a problem, that problem is likely to be
   complex and/or involve multiple trade-offs.  Actions to deal with it
   are likely to be disruptive (although perhaps not to large
   communities of users) or to leave either security risks
   (opportunities for attacks and inadvertent confusion as expected
   matches do not occur) or excessive reliance on registries
   understanding and taking responsibility for what they are registering
   [RFC5894] [RegRestr].  The latter, while a requirement of IDNA, has
   often not worked out well in the past.

   Because resolution of problems identified by this part of the review
   may take some time even if that resolution is to add additional
   contextual rules or disallow one or more code points, there will be
   cases in which it will be appropriate to publish the results of the
   algorithmic review and provide IANA with corresponding tables, with
   warnings about code points whose status is uncertain until there are
   IETF consensus conclusions about how to proceed.  The affected code
   points should be considered unsafe and identified as "under review"
   in the IANA tables until final derived properties are assigned.







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4.  IDNA Assumptions and Current Practice

   At the time the IDNA2008 documents were written, the assumption was
   that, if new versions of Unicode introduced incompatible changes, the
   Standard would be updated to preserve backward compatibility for
   users of IDNA.  For most purposes, this would be done by adding to
   the table of exceptions associated with Rule G (Section 2.7 of RFC
   5892).

   This has not been the practice in the reviews completed subsequent to
   Unicode 5.2, as discussed in Section 3.  Incompatibilities were
   identified in Unicode 6.0 [RFC6452], in the cumulative review leading
   to tables for Unicode 11.0 [ID.draft-faltstrom-unicode11] and the
   subsequent one for Unicode 12.0 [IDNA-Unicode12].  In all of those
   cases, the decision was made to maintain compatibility with Unicode
   properties rather than with prior versions of IDNA.

   Subsequent to the publication of this document, changes in Unicode
   detected by algorithmic reviews that would break compatibility with
   derived properties associated with prior versions of Unicode or that
   preserve such compatibility within IDNA at the price of departing
   from current Unicode specifications must be documented (in documents
   expected to be published as standards track RFCs), explained to, and
   reviewed by the IETF.

   The community has now made decisions and updated tables for Unicode
   6.0 [RFC6452], done catch-up work between it and Unicode 11.0
   [ID.draft-faltstrom-unicode11], and completed the review and tables
   for Unicode 12.0 [IDNA-Unicode12].  The decisions made in those cases
   were driven by preserving consistency with Unicode and Unicode
   property changes for reasons most clearly explained by the IAB
   [IAB-Unicode-2018].  Doing things that way is not only at variance
   with the language in RFC 5892 but is also inconsistent with the
   intent of commitments to the registry and user communities to ensure
   that IDN labels, once valid under IDNA2008, would remain valid and,
   excepting those that were invalid because they contained unassigned
   code points, those that were invalid remained invalid.

   This document restores and clarifies that original language and
   intent: absent extremely strong evidence on a per-code point basis
   that preserving the validity status of possible existing (or
   prohibited) labels would cause significant harm, Unicode changes that
   would affect IDNA derived properties are to be reflected in IDNA
   exceptions that preserves the status of those labels.  There is one
   partial exception to this principle.  If the new code point analysis
   (see Section 3.2) concludes that some code points or collections of
   code points should be further analyzed, those code points, and labels
   including them, should be considered unsafe and used only with



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   extreme caution because the conclusions of the analysis may change
   their derived property values and status.

5.  Derived Tables Published by IANA

   As discussed above, RFC 5892 specified that derived property tables
   be provided via an IANA registry.  Perhaps because most IANA
   registries are considered normative and authoritative, that registry
   has been the source of considerable confusion, including the
   incorrect assumption that the absence of published tables for
   versions of Unicode later than 6.0 meant that IDNA could not be used
   with later versions.  That position was raised in multiple ways, not
   all of them consistent, especially in the ICANN context
   [ICANN-LGR-SLA].

   If the changes specified in this document are not successful in
   significantly mitigating the confusion about the status of the tables
   published by IANA, serious consideration should be given to
   eliminating those tables entirely.

6.  Editorial clarification to RFC 5892

   In order to avoid this document going forward with remaining known
   errors or omissions in RFC 5892, this section updates that document
   to provide fixes to known applicable errata.  In particular, verified
   RFC Editor Erratum 3312 [RFC5892Erratum] provides a clarification to
   Appendix A and Section A.1 of RFC 5892, which is resolved below.

   1.  In Appendix A, add a new paragraph after the paragraph that
       begins "The code point...".  The new paragraph should read:

       "For the rule to be evaluated to True for the label, it MUST be
       evaluated separately for every occurrence of the Code point in
       the label; each of those evaluations must result in True."

   2.  In Appendix A, Section A.1, replace the "Rule Set" by

      Rule Set:
        False;
        If Canonical_Combining_Class(Before(cp)) .eq.  Virama Then True;
        If cp .eq. \u200C And
               RegExpMatch((Joining_Type:{L,D})(Joining_Type:T)*cp
          (Joining_Type:T)*(Joining_Type:{R,D})) Then True;








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7.  Acknowledgements

   This document was inspired by extensive discussions within the I18N
   Directorate of the IETF Applications and Real Time (ART) area in the
   first quarter of 2019 about sorting out the reviews for Unicode 11.0
   and 12.0.

8.  IANA Considerations

   For the algorithmic review described in Section 3.1, the IESG is to
   appoint a Designated Expert [RFC8126] with appropriate expertise to
   conduct the review and supply derived property tables to IANA.  For
   the code point review, the expertise will be supplied by an IESG-
   designated expert team as discussed in Section 3.2.  In both cases,
   the experts should draw on the expertise of other members of the
   community as needed.  In particular, and especially if there is no
   overlap in the people holding the various roles, coordination with
   the IAB-appointed liaison to the Unicode Consortium will be essential
   to mitigate possible errors due to confusion.

   As discussed in Section 5, and if they have not already done so, IANA
   is requested to modify the IDNA tables collection [IANA-IDNA-Tables]
   to identify them clearly as non-normative and in a way that drops the
   idea of a "current" or "correct" version of those tables, pointing to
   this document for an explanation.  That includes publishing and
   retaining tables, as supplied by the IETF's Designated Expert, for
   each new version of Unicode after this document is published, keeping
   all older versions available.  IANA is also also requested to change
   the current title of that registry from "IDNA Parameters", which is
   misleading, to "IDNA Rules and Derived Property Values".

   The "Note" in that registry should also be revised to be consistent
   with the above, perhaps to say:

      "IDNA does not require that applications and libraries, either for
      registration/storage or lookup, support any particular version of
      Unicode.  Instead, they are required to use derived property
      values based on calculations associated with whatever version of
      Unicode they are using elsewhere in the application or library.
      For the convenience of application and library developers and
      others, the IETF has supplied, and IANA maintains, derived
      property tables for several version of Unicode as listed below.
      It should be stressed that these are not normative that, in
      principle, an application can do its own calculations and these
      tables can change as IETF understanding evolves.  By contrast, the
      list of code points requiring contextual rules and the associated
      rules are normative and should be treated as updates to the list
      in RFC 5892."



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   As long as the intent is preserved, the specific text is at IANA's
   discretion.

   IANA's attention is called to the introduction, in Section 3.2, of a
   temporary "under review" category to the PVALID, DISALLOWED, etc.,
   entries in the tables.

9.  Security Considerations

   Application of the procedures described in this document and
   understanding of the clarifications it provides should reduce
   confusion about IDNA requirements.  Because past confusion has
   provided opportunities for bad behavior, the effect of these changes
   should improve Internet security to at least some small extent.

   Because of the preference to keep the derived property value stable
   (as specified in RFC 5892 and discussed in Section 4), the algorithm
   used to calculate those derived properties does change as explained
   in Section 3.  If these changes are not taken into account, the
   derived property value will change and the implications might have
   negative consequences, in some cases with security implications.  For
   example, changes in the calculated derived property value for a code
   point from either DISALLOWED to PVALID or from PVALID to DISALLOWED
   can cause changes in label interpretation that would be visible and
   confusing to end users and might enable attacks.

10.  References

10.1.  Normative References

   [IANA-IDNA-Tables]
              Internet Assigned Numbers Authority (IDNA), "IDNA
              Parameters", March 2019,
              <https://www.iana.org/assignments/idna-tables-11.0.0/
              idna-tables-11.0.0.xhtml>.

              This documents make changes to this registry and a way
              that could change the title, the URL, or both.  This
              citation is to be version published on 2019-03-31.  It may
              be appropriate to supply a citation to the finished
              version when this document is published.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.





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   [RFC5892]  Faltstrom, P., Ed., "The Unicode Code Points and
              Internationalized Domain Names for Applications (IDNA)",
              RFC 5892, DOI 10.17487/RFC5892, August 2010,
              <https://www.rfc-editor.org/info/rfc5892>.

   [RFC5892Erratum]
              "RFC5892, "The Unicode Code Points and Internationalized
              Domain Names for Applications (IDNA)", August 2010, Errata
              ID: 3312", Errata ID 3312, August 2012,
              <http://www.rfc-editor.org/errata_search.php?rfc=5892>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [Unicode]  The Unicode Consortium, "The Unicode Standard (Current
              Version)", 2019,
              <http://www.unicode.org/versions/latest/>.

              The link given will always access the current version of
              the Unicode Standard, independent of its version number or
              date.

   [Unicode-properties]
              The Unicode Consortium, "The Unicode Standard Version
              11.0", 2018,
              <https://www.unicode.org/versions/Unicode11.0.0/>.

              Section 3.5.

10.2.  Informative References

   [IAB-Unicode-2018]
              Internet Architecture Board (IAB), "IAB Statement on
              Identifiers and Unicode", March 2018,
              <https://www.iab.org/documents/
              correspondence-reports-documents/2018-2/
              iab-statement-on-identifiers-and-unicode/>.

   [IAB-Unicode7-2015]
              Internet Architecture Board (IAB), "IAB Statement on
              Identifiers and Unicode 7.0.0", February 2015,
              <https://www.iab.org/documents/
              correspondence-reports-documents/2015-2/
              iab-statement-on-identifiers-and-unicode-7-0-0/>.





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   [ICANN-LGR-SLA]
              Internet Corporation for Assigned Names and Numbers
              (ICANN), "Proposed IANA SLAs for Publishing LGRs/IDN
              Tables", June 2019, <https://www.icann.org/public-
              comments/proposed-iana-sla-lgr-idn-tables-2019-06-10-en>.

              Captured 2019-06-12.  In public comment until 2019-07-26.

   [ID.draft-faltstrom-unicode11]
              Faltstrom, P., "IDNA2008 and Unicode 11.0.0", March 2019,
              <https://datatracker.ietf.org/doc/
              draft-faltstrom-unicode11/>.

   [IDNA-Unicode12]
              Faltstrom, P., "IDNA2008 and Unicode 12.0.0", March 2019,
              <https://datatracker.ietf.org/doc/
              draft-faltstrom-unicode12/>.

              This document is in the RFC Editor queue at of 2019-06-09.
              Update to RFC reference if/when appropriate.

   [IDNA-Unicode7]
              Klensin, J. and P. Falstrom, "IDNA Update for Unicode
              7.0.0", January 2015, <https://datatracker.ietf.org/doc/
              draft-klensin-idna-5892upd-unicode70/03/>.

              Note that this is an historical reference to a superseded
              document.  There is nothing "in progress" about it.

   [RegRestr]
              Klensin, J. and A. Freytag, "Internationalized Domain
              Names in Applications (IDNA): Registry Restrictions and
              Recommendations", September 2017,
              <https://datatracker.ietf.org/doc/
              draft-klensin-idna-rfc5891bis/>.

   [RFC3454]  Hoffman, P. and M. Blanchet, "Preparation of
              Internationalized Strings ("stringprep")", RFC 3454,
              DOI 10.17487/RFC3454, December 2002,
              <https://www.rfc-editor.org/info/rfc3454>.

   [RFC3490]  Faltstrom, P., Hoffman, P., and A. Costello,
              "Internationalizing Domain Names in Applications (IDNA)",
              RFC 3490, DOI 10.17487/RFC3490, March 2003,
              <https://www.rfc-editor.org/info/rfc3490>.






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   [RFC3491]  Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
              Profile for Internationalized Domain Names (IDN)",
              RFC 3491, DOI 10.17487/RFC3491, March 2003,
              <https://www.rfc-editor.org/info/rfc3491>.

   [RFC4690]  Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and
              Recommendations for Internationalized Domain Names
              (IDNs)", RFC 4690, DOI 10.17487/RFC4690, September 2006,
              <https://www.rfc-editor.org/info/rfc4690>.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, DOI 10.17487/RFC5890, August 2010,
              <https://www.rfc-editor.org/info/rfc5890>.

   [RFC5894]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Background, Explanation, and
              Rationale", RFC 5894, DOI 10.17487/RFC5894, August 2010,
              <https://www.rfc-editor.org/info/rfc5894>.

   [RFC6452]  Faltstrom, P., Ed. and P. Hoffman, Ed., "The Unicode Code
              Points and Internationalized Domain Names for Applications
              (IDNA) - Unicode 6.0", RFC 6452, DOI 10.17487/RFC6452,
              November 2011, <https://www.rfc-editor.org/info/rfc6452>.

Appendix A.  Summary of Changes to RFC 5892

   Other than the editorial correction specified in Section 6 all of the
   changes in this document are concerned with the reviews for new
   versions of Unicode and with the IANA Considerations in Section 5,
   particularly Section 5.1, of RFC 5982.  Whether the changes are
   substantive or merely clarifications may be somewhat in the eye of
   the beholder so the list below should not be assumed to be
   comprehensive.  At a very high level, this document clarifies that
   two types of review were intended and separates them for clarity and
   restores the original (but so far unobserved) default for actions
   when code point derived properties change.  For this reason, this
   document effectively provides a replacement for Section 5.1 of RFC
   5892 and adds or changes some material needed to have the replacement
   be clear or make better sense.

   Changes or clarifications that may be considered important include:

   o  Separated the new Unicode version review into two explicit parts
      and provided for different review methods and, potentially,
      asynchronous outcomes.





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   o  Specified a review team, not a single expert, for the code point
      review.

   o  Eliminated the de facto requirement for the (formerly single)
      Designated Expert to be the same person as the IAB's Liaison to
      the Unicode Consortium but called out the importance of
      coordination.

   o  Created an explicit provision for an "under review" entry in the
      IANA tables so that, if there is ever again a need to tell the
      community to wait until the IETF sorts things out, that will be
      about selected potentially problematic code points and not whole
      Unicode versions.

   o  In part because Unicode is now on a regular one-year cycle rather
      than producing major and minor versions as needed, to avoid
      overloading the IETF's i18n resources, and to avoid generating and
      storing IANA tables for trivial changes (e.g., the single new code
      point in Unicode 12.1), the review procedure is applied only to
      major versions of Unicode unless exceptional circumstances arise
      and are identified.

Authors' Addresses

   John C Klensin
   1770 Massachusetts Ave, Ste 322
   Cambridge, MA  02140
   USA

   Phone: +1 617 245 1457
   Email: john-ietf@jck.com


   Patrik Faltstrom
   Netnod
   Franzengatan 5
   Stockholm  112 51
   Sweden

   Phone: +46 70 6059051
   Email: paf@netnod.se










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