Internet Engineering Task Force (IETF) J. Klensin
Request for Comments: 8753
Updates: 5892 P. Fältström
Category: Standards Track Netnod
ISSN: 2070-1721 April 2020
Internationalized Domain Names for Applications (IDNA) Review for New
Unicode Versions
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 versions 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 to clarify the various relationships involved. It
also makes other minor adjustments to align that document with
experience.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8753.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction
2. Brief History of IDNA Versions, the Review Requirement, and RFC
5982
3. The Review Model
3.1. Review Model Part I: Algorithmic Comparison
3.2. Review Model Part II: New Code Point Analysis
4. IDNA Assumptions and Current Practice
5. Derived Tables Published by IANA
6. Editorial Clarification to RFC 5892
7. IANA Considerations
8. Security Considerations
9. References
9.1. Normative References
9.2. Informative References
Appendix A. Summary of Changes to RFC 5892
Appendix B. Background and Rationale for Expert Review Procedure
for New Code Point Analysis
Acknowledgments
Authors' Addresses
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 versions 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 (see Section 3 and Section 4 for additional
discussion of the question of appropriate decisions and the history
of these reviews). 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 to clarify the various relationships involved.
This specification does not change the requirement that registries at
all levels of the DNS tree take responsibility for the labels they
insert in the DNS, a level of responsibility that requires allowing
only a subset of the code points and strings allowed by the IDNA
protocol itself. That requirement is discussed in more detail in a
companion document [RegRestr].
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
earlier version are explicit only where they are necessary for
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 IDNA2003
standard would have required the creation of a new profile for each
new version of Unicode, or the tables would have fallen further and
further behind.
When IDNA2003 was superseded by the current version, 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
values. 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).
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
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 team concludes that there
are special problems or unusual circumstances, these reviews will be
performed only for major Unicode versions (those numbered NN.0, e.g.,
12.0) and not for minor updates (e.g., 12.1).
As can be seen in the detailed descriptions in the following
subsections, proper review will require a team of experts that has
both broad and specific skills in reviewing Unicode characters and
their properties in relation to both the written standards and
operational needs. The IESG will need to appoint experts who can
draw on the broader community to obtain the necessary skills for
particular situations. See the IANA Considerations (Section 7) for
details.
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, which was for
Unicode 6.0, found only three incompatibilities; the consensus was to
ignore them (not create exceptions in IDNA2008) and to 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 Unicode compatibility, rather
than IDNA 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 were 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, which is not clearly explained in RFC
5892, is intended to identify cases in which newly added or recently
discovered problematic code points violate the design assumptions of
IDNA, to identify defects in those assumptions, or to identify
inconsistencies (from an IDNA perspective) with Unicode commitments
about assignment, properties, and stability of newly added code
points. One example of this type of review was the discovery of new
code points after Unicode 7.0 that were potentially visually
equivalent, in the same script, to previously available code point
sequences [IAB-Unicode7-2015] [IDNA-Unicode7].
Because multiple perspectives on Unicode and writing systems are
required, this review will not be successful unless it is done by a
team. Finding one all-knowing expert is improbable, and a single
expert is unlikely to produce an adequate analysis. Rather than any
single expert being the sole source of analysis, the designated
expert (DE) team needs to understand that there will always be gaps
in their knowledge, to know what they don't know, and to work to find
the expertise that each review requires. It is also important that
the DE team maintains close contact with the Area Directors (ADs) and
that the ADs remain aware of the team's changing needs, examining and
adjusting the team's membership over time, with periodic
reexamination at least annually. 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 security risks (opportunities for
attacks and inadvertent confusion as expected matches do not occur),
or to cause 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 to 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 to provide IANA with corresponding tables,
with warnings about code points whose status is uncertain until there
is IETF consensus 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.
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 [RFC5892a].
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] and in the cumulative review
leading to tables for Unicode 11.0 [IDNA-Unicode11]. In all of those
cases, the decision was made to maintain compatibility with Unicode
properties rather than with prior versions of IDNA.
If an algorithmic review detects changes in Unicode after version
12.0 that would break compatibility with derived properties
associated with prior versions of Unicode or changes that would
preserve compatibility within IDNA at the cost of departing from
current Unicode specifications, those changes must be captured in
documents expected to be published as Standards Track RFCs so that
the IETF can review those changes and maintain a historical record.
The community has now made decisions and updated tables for Unicode
6.0 [RFC6452], done catch-up work between it and Unicode 11.0
[IDNA-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].
These actions were not only at variance with the language in RFC 5892
but were also inconsistent with commitments to the registry and user
communities to ensure that IDN labels that were once valid under
IDNA2008 would remain valid, and previously invalid labels would
remain invalid, except for those labels that were invalid because
they contained unassigned code points.
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 preserve 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
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
This section updates RFC 5892 to provide fixes for known applicable
errata and omissions. In particular, verified RFC Editor Erratum
3312 [Err3312] provides a clarification to Appendix A and A.1 in RFC
5892. That clarification is incorporated 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.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;
7. 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 to supply derived property tables to IANA. As
provided in Section 5.2 of the Guidelines for Writing IANA
Considerations [RFC8126], the designated expert is expected to
consult additional sources of expertise as needed. For the code
point review, the expertise will be supplied by an IESG-designated
expert team as discussed in Section 3.2 and Appendix B. 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 of 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, IANA has modified the IDNA tables
collection [IANA-IDNA-Tables] by identifying them clearly as non-
normative, so that a "current" or "correct" version of those tables
is not implied, and by pointing to this document for an explanation.
IANA has published tables supplied by the IETF for all Unicode
versions through 11.0, retaining all older versions and making them
available. Newer tables will be constructed as specified in this
document and then made available by IANA. IANA has changed the title
of that registry from "IDNA Parameters", which is misleading, to
"IDNA Rules and Derived Property Values".
The "Note" in that registry says:
| 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 in 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.
As long as the intent is preserved, the text of that note may be
changed in the future 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.
8. Security Considerations
Applying 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.
9. References
9.1. Normative References
[IANA-IDNA-Tables]
IANA, "IDNA Rules and Derived Property Values",
<https://www.iana.org/assignments/idna-tables>.
[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>.
[RFC5892a] Faltstrom, P., Ed., "The Unicode Code Points and
Internationalized Domain Names for Applications (IDNA)",
Section 2.7, RFC 5892, August 2010,
<https://www.rfc-editor.org/rfc/rfc5892.txt>.
[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)", <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", Section 3.5, 2018,
<https://www.unicode.org/versions/Unicode11.0.0/>.
9.2. Informative References
[Err3312] RFC Errata, Erratum ID 3312, RFC 5892,
<https://www.rfc-editor.org/errata/eid3312>.
[IAB-Unicode-2018]
Internet Architecture Board (IAB), "IAB Statement on
Identifiers and Unicode", 15 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", 11 February 2015,
<https://www.iab.org/documents/correspondence-reports-
documents/2015-2/iab-statement-on-identifiers-and-unicode-
7-0-0/>.
[ICANN-LGR-SLA]
Internet Corporation for Assigned Names and Numbers
(ICANN), "Proposed IANA SLAs for Publishing LGRs/IDN
Tables", 10 June 2019, <https://www.icann.org/public-
comments/proposed-iana-sla-lgr-idn-tables-2019-06-10-en>.
[IDNA-Unicode7]
Klensin, J. and P. Faltstrom, "IDNA Update for Unicode 7.0
and Later Versions", Work in Progress, Internet-Draft,
draft-klensin-idna-5892upd-unicode70-05, 8 October 2017,
<https://tools.ietf.org/html/draft-klensin-idna-5892upd-
unicode70-05>.
[IDNA-Unicode11]
Faltstrom, P., "IDNA2008 and Unicode 11.0.0", Work in
Progress, Internet-Draft, draft-faltstrom-unicode11-08, 11
March 2019, <https://tools.ietf.org/html/draft-faltstrom-
unicode11-08>.
[IDNA-Unicode12]
Faltstrom, P., "IDNA2008 and Unicode 12.0.0", Work in
Progress, Internet-Draft, draft-faltstrom-unicode12-00, 11
March 2019, <https://tools.ietf.org/html/draft-faltstrom-
unicode12-00>.
[RegRestr] Klensin, J. and A. Freytag, "Internationalized Domain
Names in Applications (IDNA): Registry Restrictions and
Recommendations", Work in Progress, Internet-Draft, draft-
klensin-idna-rfc5891bis-05, 29 August 2019,
<https://tools.ietf.org/html/draft-klensin-idna-
rfc5891bis-05>.
[RFC1766] Alvestrand, H., "Tags for the Identification of
Languages", RFC 1766, DOI 10.17487/RFC1766, March 1995,
<https://www.rfc-editor.org/info/rfc1766>.
[RFC3282] Alvestrand, H., "Content Language Headers", RFC 3282,
DOI 10.17487/RFC3282, May 2002,
<https://www.rfc-editor.org/info/rfc3282>.
[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>.
[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>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
[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>.
[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <https://www.rfc-editor.org/info/rfc5646>.
[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 of
[RFC5892], particularly Section 5.1 of [RFC5892]. 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.
This document also restores the original (but so far unobserved)
default for actions when code point derived properties change. For
this reason, this document effectively replaces Section 5.1 of
[RFC5892] and adds or changes some text so that the replacement makes
better sense.
Changes or clarifications that may be considered important include:
* Separated the new Unicode version review into two explicit parts
and provided for different review methods and, potentially,
asynchronous outcomes.
* Specified a DE team, not a single designated expert, for the code
point review.
* 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.
* Created the "Status" field in the IANA tables to inform the
community about specific potentially problematic code points.
This change creates the ability to add information about such code
points before IETF review is completed instead of having the
review process hold up the use of the new Unicode version.
* 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 internationalization 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.
Appendix B. Background and Rationale for Expert Review Procedure for
New Code Point Analysis
The expert review procedure for new code point analysis described in
Section 3.2 is somewhat unusual compared to the examples presented in
the Guidelines for Writing IANA Considerations [RFC8126]. This
appendix explains that choice and provides the background for it.
Development of specifications to support use of languages and writing
systems other than English (and Latin script) -- so-called
"internationalization" or "i18n" -- has always been problematic in
the IETF, especially when requirements go beyond simple coding of
characters (e.g., RFC 3629 [RFC3629]) or simple identification of
languages (e.g., RFC 3282 [RFC3282] and the earlier RFC 1766
[RFC1766]). A good deal of specialized knowledge is required,
knowledge that comes from multiple fields and that requires multiple
perspectives. The work is not obviously more complex than routing,
especially if one assumes that routing work requires a solid
foundation in graph theory or network optimization, or than security
and cryptography, but people working in those areas are drawn to the
IETF and people from the fields that bear on internationalization
typically are not.
As a result, we have often thought we understood a problem, generated
a specification or set of specifications, but then have been
surprised by unanticipated (by the IETF) issues. We then needed to
tune and often revise our specification. The language tag work that
started with RFC 1766 is a good example of this: broader
considerations and requirements led to later work and a much more
complex and finer-grained system [RFC5646].
Work on IDNs further increased the difficulties because many of the
decisions that led to the current version of IDNA require
understanding the DNS, its constraints, and, to at least some extent,
the commercial market of domain names, including various ICANN
efforts.
The net result of these factors is that it is extremely unlikely that
the IESG will ever find a designated expert whose knowledge and
understanding will include everything that is required.
Consequently, Section 7 and other discussions in this document
specify a DE team that is expected to have the broad perspective,
expertise, and access to information and community in order to review
new Unicode versions and to make consensus recommendations that will
serve the Internet well. While we anticipate that the team will have
one or more leaders, the structure of the team differs from the
suggestions given in Section 5.2 of the Guidelines for Writing IANA
Considerations [RFC8126] since neither the team's formation nor its
consultation is left to the discretion of the designated expert, nor
is the designated expert solely accountable to the community. A team
that contains multiple perspectives is required, the team members are
accountable as a group, and any nontrivial recommendations require
team consensus. This also differs from the common practice in the
IETF of "review teams" from which a single member is selected to
perform a review: the principle for these reviews is team effort.
Acknowledgments
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. Careful reviews by Joel Halpern and text suggestions from
Barry Leiba resulted in some clarifications.
Thanks to Christopher Wood for catching some editorial errors that
persisted until rather late in the document's life cycle and to
Benjamin Kaduk for catching and raising a number of questions during
Last Call. Some of the issues they raised have been reflected in the
document; others did not appear to be desirable modifications after
further discussion, but the questions were definitely worth raising
and discussing.
Authors' Addresses
John C Klensin
1770 Massachusetts Ave, Ste 322
Cambridge, MA 02140
United States of America
Phone: +1 617 245 1457
Email: john-ietf@jck.com
Patrik Fältström
Netnod
Greta Garbos Väg 13
SE-169 40 Solna
Sweden
Phone: +46 70 6059051
Email: paf@netnod.se