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INFORMATIONAL
Internet Architecture Board (IAB) H. Flanagan, Ed.
Request for Comments: 7997 RFC Editor
Updates: 7322 December 2016
Category: Informational
ISSN: 2070-1721
The Use of Non-ASCII Characters in RFCs
Abstract
In order to support the internationalization of protocols and a more
diverse Internet community, the RFC Series must evolve to allow for
the use of non-ASCII characters in RFCs. While English remains the
required language of the Series, the encoding of future RFCs will be
in UTF-8, allowing for a broader range of characters than typically
used in the English language. This document describes the RFC Editor
requirements and gives guidance regarding the use of non-ASCII
characters in RFCs.
This document updates RFC 7322. Please view this document in PDF
form to see the full text.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Architecture Board (IAB)
and represents information that the IAB has deemed valuable to
provide for permanent record. It represents the consensus of the
Internet Architecture Board (IAB). Documents approved for
publication by the IAB are not a candidate for any level of Internet
Standard; see 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
http://www.rfc-editor.org/info/rfc7997.
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Copyright Notice
Copyright (c) 2016 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
(http://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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Basic Requirements . . . . . . . . . . . . . . . . . . . . . 3
3. Rules for the Use of Non-ASCII Characters . . . . . . . . . . 4
3.1. General Usage throughout a Document . . . . . . . . . . . 4
3.2. Person Names . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Company Names . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Body of the Document . . . . . . . . . . . . . . . . . . 7
3.5. Tables . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.6. Code Components . . . . . . . . . . . . . . . . . . . . . 11
3.7. Bibliographic Text . . . . . . . . . . . . . . . . . . . 11
3.8. Keywords and Citation Tags . . . . . . . . . . . . . . . 11
3.9. Address Information . . . . . . . . . . . . . . . . . . . 12
4. Normalization Forms . . . . . . . . . . . . . . . . . . . . . 12
5. XML Markup . . . . . . . . . . . . . . . . . . . . . . . . . 12
6. Internationalization Considerations . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. Informative References . . . . . . . . . . . . . . . . . . . 13
IAB Members at the Time of Approval . . . . . . . . . . . . . . . 14
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
Please review the PDF version of this draft.
For much of the history of the RFC Series, the character encoding
used for RFCs has been ASCII [RFC20]. This was a sensible choice at
the time: the language of the Series has always been English, a
language that primarily uses ASCII-encoded characters (ignoring for a
moment words borrowed from more richly decorated alphabets); and,
ASCII is the "lowest common denominator" for character encoding,
making cross-platform viewing trivial.
There are limits to ASCII, however, that hinder its continued use as
the exclusive character encoding for the Series. The increasing need
for easily readable, internationalized content suggests it is time to
allow non-ASCII characters in RFCs where necessary. To support this
move away from ASCII, RFCs will switch to supporting UTF-8 as the
default character encoding and will allow support for a broad range
of Unicode characters [UnicodeCurrent]. Note that the RFC Editor may
reject any code point that does not render adequately across all
formats or in enough rendering engines using the v3 tooling.
Given the continuing goal of maximum readability across platforms,
the use of non-ASCII characters should be limited to only where
necessary within the text. This document describes the rules under
which non-ASCII characters may be used in an RFC. These rules will
be applied as the necessary changes are made to submission checking
and editorial tools.
This document updates the RFC Style Guide [RFC7322].
The details included in this document are expected to change based on
experience gained in implementing the new publication toolsets.
Revised documents will be published capturing those changes as the
toolsets are completed. Other implementers must not expect those
changes to remain backwards compatible with the details included in
this document.
2. Basic Requirements
Two fundamental requirements inform the guidance and examples
provided in this document. They are:
o Searches against RFC indexes and database tables need to return
expected results and support appropriate Unicode string matching
behaviors;
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o RFCs must be able to be displayed correctly across a wide range of
readers and browsers. People whose systems do not have the fonts
needed to display a particular RFC need to be able to read the
various publication formats and the XML correctly in order to
understand and implement the information described in the
document.
3. Rules for the Use of Non-ASCII Characters
This section describes the guidelines for the use of non-ASCII
characters in an RFC. If the RFC Editor identifies areas where the
use of non-ASCII characters negatively impacts the readability of the
text, they will request alternate text.
The RFC Editor may, in cases of entire words represented in non-ASCII
characters, ask for a set of reviewers to verify the meaning,
spelling, characters, and grammar of the text.
3.1. General Usage throughout a Document
Where the use of non-ASCII characters is purely part of an example
and not otherwise required for correct protocol operation, escaping
the non-ASCII character is not required. Note, however, that as the
language of the RFC Series is English, the use of non-ASCII
characters is based on the spelling of words commonly used in the
English language following the guidance in the Merriam-Webster
dictionary [MerrWeb].
The RFC Editor will use the primary spelling listed in that
dictionary by default.
Example of non-ASCII characters that do not require escaping (example
from Section 3.1.1.12 of RFC 4475 [RFC4475], with a hex dump replaced
by the actual character glyphs):
This particular response contains unreserved and non-ASCII
UTF-8 characters.
This response is well formed. A parser must accept this message.
Message Details : unreason
SIP/2.0 200 = 2**3 * 5**2 (See PDF for non-ASCII character string)
Via: SIP/2.0/UDP 192.0.2.198;branch=z9hG4bK1324923
Call-ID: unreason.1234ksdfak3j2erwedfsASdf
CSeq: 35 INVITE
From: sip:user@example.com;tag=11141343
To: sip:user@example.edu;tag=2229 Content-Length: 154
Content-Type: application/sdp
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3.2. Person Names
Person names may appear in several places within an RFC (e.g., the
header, Acknowledgements, and References). When a script outside the
Unicode Latin blocks [UNICODE-CHART] is used for an individual name,
an author-provided, ASCII-only identifier will appear immediately
after the non-Latin characters, surrounded by parentheses. This will
improve general readability of the text.
Example header:
OLD:
Internet Engineering Task Force (IETF) J. Tong
Request for Comments: 7380 C. Bi, Ed.
Category: Standards Track China Telecom
ISSN: 2070-1721 R. Even
Q. Wu, Ed.
R. Huang
Huawei
November 2014
PROPOSED/NEW:
Internet Engineering Task Force (IETF) J. Tong
Request for Comments: 7380 C. Bi, Ed.
Category: Standards Track China Telecom
ISSN: 2070-1721 (See PDF for non-ASCII character string) (R. Even)
(See PDF for non-ASCII character string) (Q. Wu), Ed.
R. Huang
Huawei
November 2014
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Example Acknowledgements section:
OLD:
The following people contributed significant text to early versions
of this draft: Patrik Faltstrom, William Chan, and Fred Baker.
PROPOSED/NEW:
The following people contributed significant text to early versions
of this draft: Patrik (See PDF for non-ASCII character string)
(Faltstrom), (See PDF for non-ASCII character string) (William Chan),
and Fred Baker.
Example reference entry:
OLD:
[RFC6630] Cao, Z., Deng, H., Wu, Q., and G. Zorn, Ed., "EAP
Re-authentication Protocol Extensions for Authenticated
Anticipatory Keying (ERP/AAK)", RFC 6630, June 2012.
NEW
[RFC6630] Cao, Z., Deng, H., (See PDF for non-ASCII character
string) (Wu, Q.), and G. Zorn, Ed., "EAP
Re-authentication Protocol Extensions for Authenticated
Anticipatory Keying (ERP/AAK)", RFC 6630, June 2012.
3.3. Company Names
Company names may appear in several places within an RFC. In all
cases, valid Unicode is required. For names that include characters
outside of the Unicode Latin and Latin Extended scripts, an author-
provided, ASCII-only identifier is required to assist in searching
and indexing of the document.
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3.4. Body of the Document
When the mention of non-ASCII characters is required for correct
protocol operation and understanding, the characters' Unicode code
points must be used in the text. The addition of each character name
is encouraged.
o Non-ASCII characters will require identifying the Unicode code
point.
o Use of the actual UTF-8 character (e.g., (See PDF for non-ASCII
character string)) is encouraged so that a reader can more easily
see what the character is, if their device can render the text.
o The use of the Unicode character names like "INCREMENT" in
addition to the use of Unicode code points is also encouraged.
When used, Unicode character names should be in all capital
letters.
Examples:
OLD [RFC7564]:
However, the problem is made more serious by introducing the full
range of Unicode code points into protocol strings. For example,
the characters U+13DA U+13A2 U+13B5 U+13AC U+13A2 U+13AC U+13D2 from
the Cherokee block look similar to the ASCII characters
"STPETER" as they might appear when presented using a "creative"
font family.
NEW/ALLOWED:
However, the problem is made more serious by introducing the full
range of Unicode code points into protocol strings. For example,
the characters U+13DA U+13A2 U+13B5 U+13AC U+13A2 U+13AC U+13D2
((See PDF for non-ASCII character string)) from the Cherokee
block look similar to the ASCII characters "STPETER" as they might
appear when presented using a "creative" font family.
ALSO ACCEPTABLE:
However, the problem is made more serious by introducing the full
range of Unicode code points into protocol strings. For example,
the characters "(See PDF for non-ASCII character string)" (U+13DA
U+13A2 U+13B5 U+13AC U+13A2 U+13AC U+13D2) from the Cherokee block
look similar to the ASCII characters "STPETER" as they might
appear when presented using a "creative" font family.
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Example of proper identification of Unicode characters in an RFC:
Acceptable:
o Temperature changes in the Temperature Control Protocol are
indicated by the U+2206 character.
Preferred:
1. Temperature changes in the Temperature Control Protocol are
indicated by the U+2206 character ("(See PDF for non-ASCII
character string)").
2. Temperature changes in the Temperature Control Protocol are
indicated by the U+2206 character (INCREMENT).
3. Temperature changes in the Temperature Control Protocol are
indicated by the U+2206 character ("(See PDF for non-ASCII
character string)", INCREMENT).
4. Temperature changes in the Temperature Control Protocol are
indicated by the U+2206 character (INCREMENT, "(See PDF for non-
ASCII character string)").
5. Temperature changes in the Temperature Control Protocol are
indicated by the "Delta" character "(See PDF for non-ASCII
character string)" (U+2206).
6. Temperature changes in the Temperature Control Protocol are
indicated by the character "(See PDF for non-ASCII character
string)" (INCREMENT, U+2206).
Which option of (1), (2), (3), (4), (5), or (6) is preferred may
depend on context and the specific character(s) in question. All are
acceptable within an RFC. "US-ASCII Escaping of Unicode Character"
[BCP137] describes the pros and cons of different options for
identifying Unicode characters and may help authors decide how to
represent the non-ASCII characters in their documents.
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3.5. Tables
Tables follow the same rules for identifiers and characters as in
"Body of the Document" (Section 3.4). If it is sensible (i.e., more
understandable for a reader) for a given document to have two tables,
-- one including the identifiers and non-ASCII characters and a
second with just the non-ASCII characters -- then that will be
allowed at the discretion of the authors.
Original text from "Preparation, Enforcement, and Comparison of
Internationalized Strings Representing Usernames and Passwords"
[RFC7613].
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Table 3: A sample of legal passwords
+------------------------------------+------------------------------+
| # | Password | Notes |
+------------------------------------+------------------------------+
| 12| <correct horse battery staple> | ASCII space is allowed |
+------------------------------------+------------------------------+
| 13| <Correct Horse Battery Staple> | Different from example 12 |
+------------------------------------+------------------------------+
| 14| <πßå> | Non-ASCII letters are OK |
| | | (e.g., GREEK SMALL LETTER |
| | | PI, U+03C0) |
+------------------------------------+------------------------------+
| 15| <Jack of ♦s> | Symbols are OK (e.g., BLACK |
| | | DIAMOND SUIT, U+2666) |
+------------------------------------+------------------------------+
| 16| <foo bar> | OGHAM SPACE MARK, U+1680, is |
| | | mapped to U+0020 and thus |
| | | the full string is mapped to |
| | | <foo bar> |
+------------------------------------+------------------------------+
Preferred text:
Table 3: A sample of legal passwords
+------------------------------------+------------------------------+
| # | Password | Notes |
+------------------------------------+------------------------------+
| 12| <correct horse battery staple> | ASCII space is allowed |
+------------------------------------+------------------------------+
| 13| <Correct Horse Battery Staple> | Different from example 12 |
+------------------------------------+------------------------------+
| 14| <(See PDF for non-ASCII | Non-ASCII letters are OK |
| | character string)> | (e.g., GREEK SMALL LETTER |
| | | PI, U+03C0; LATIN SMALL |
| | | LETTER SHARP S, U+00DF; THAI |
| | | DIGIT SEVEN, U+0E57) |
+------------------------------------+------------------------------+
| 15| <Jack of (See PDF for non- | Symbols are OK (e.g., BLACK |
| | ASCII character string)s> | DIAMOND SUIT, U+2666) |
+------------------------------------+------------------------------+
| 16| <foo(See PDF for non-ASCII | OGHAM SPACE MARK, U+1680, is |
| | character string)bar> | mapped to U+0020 and thus |
| | | the full string is mapped to |
| | | <foo bar> |
+------------------------------------+------------------------------+
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3.6. Code Components
The RFC Editor encourages the use of the U+ notation except within a
code component where one must follow the rules of the programming
language in which the code is being written.
Code components are generally expected to use fixed-width fonts.
Where such fonts are not available for a particular script, the best
script-appropriate font will be used for that part of the code
component.
3.7. Bibliographic Text
The reference entry must be in English; whatever subfields are
present must be available in ASCII-encoded characters. For
references to RFCs and Internet-Drafts, the author's name will be
formatted in the reference as per current RFC Style Guide
recommendations. As long as good sense is used, the reference entry
may also include non-ASCII characters at the author's discretion and
as provided by the author. The RFC Editor may request that a third
party, such as a language specialist or subject matter expert, review
of any non-ASCII reference. This applies to both normative and
informative references.
Example:
[GOST3410] "Information technology. Cryptographic data security.
Signature and verification processes of [electronic]
digital signature.", GOST R 34.10-2001, Gosudarstvennyi
Standard of Russian Federation, Government Committee of
Russia for Standards, 2001. (In Russian)
Allowable addition to the above citation:
(See PDF for non-ASCII character strings)
Alternatively:
[GOST3410] "Information technology. Cryptographic data security.
Signature and verification processes of [electronic]
digital signature.", GOST R 34.10-2001, Gosudarstvennyi
Standard of Russian Federation, (See PDF for non-ASCII
character strings) (Government Committee of
Russia for Standards), 2001. (In Russian)
3.8. Keywords and Citation Tags
Keywords (as tagged with the <keyword> element in XML) and citation
tags (as defined in the anchor attributes of <reference> elements)
must contain only ASCII characters.
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3.9. Address Information
The purpose of providing address information, either postal or email,
is to assist readers of an RFC in contacting the author or authors.
Authors may include the official postal address as recognized by
their company or local postal service without additional non-ASCII
character escapes. If the email address includes non-ASCII
characters and is a valid email address at the time of publication,
non-ASCII character escapes are not required.
Example:
Qin Wu (editor)
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Additional contact information:
(See PDF for non-ASCII character strings)
------
Roni Even
Huawei
14 David Hamelech
Tel Aviv 64953
Israel
Additional contact information:
(See PDF for non-ASCII character strings)
4. Normalization Forms
Authors should not expect normalization forms [UNICODE-NORM]to be
preserved. If a particular normalization form is expected, note that
in the text of the RFC.
5. XML Markup
As described above, use of non-ASCII characters in areas such as
email, company name, address, and name is allowed. In order to make
it easier for code to identify the appropriate ASCII alternatives,
authors must include an "ascii" attribute to their XML markup when an
ASCII alternative is required. See [RFC7991] for more detail on how
to tag ASCII alternatives.
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6. Internationalization Considerations
The ability to use non-ASCII characters in RFCs in a clear and
consistent manner will improve the ability to describe
internationalized protocols and will recognize the diversity of
authors. However, the goal of readability will override the use of
non-ASCII characters within the text.
7. Security Considerations
Valid Unicode that matches the expected text must be verified in
order to preserve expected behavior and protocol information.
8. Informative References
[BCP137] Klensin, J., "ASCII Escaping of Unicode Characters",
BCP 137, RFC 5137, February 2008,
<http://www.rfc-editor.org/info/bcp137>.
[MerrWeb] Merriam-Webster, Inc., "Merriam-Webster's Collegiate
Dictionary, 11th Edition", 2009.
[RFC20] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969,
<http://www.rfc-editor.org/info/rfc20>.
[RFC4475] Sparks, R., Ed., Hawrylyshen, A., Johnston, A., Rosenberg,
J., and H. Schulzrinne, "Session Initiation Protocol (SIP)
Torture Test Messages", RFC 4475, DOI 10.17487/RFC4475,
May 2006, <http://www.rfc-editor.org/info/rfc4475>.
[RFC7322] Flanagan, H. and S. Ginoza, "RFC Style Guide", RFC 7322,
DOI 10.17487/RFC7322, September 2014,
<http://www.rfc-editor.org/info/rfc7322>.
[RFC7564] Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
Preparation, Enforcement, and Comparison of
Internationalized Strings in Application Protocols",
RFC 7564, DOI 10.17487/RFC7564, May 2015,
<http://www.rfc-editor.org/info/rfc7564>.
[RFC7613] Saint-Andre, P. and A. Melnikov, "Preparation,
Enforcement, and Comparison of Internationalized Strings
Representing Usernames and Passwords", RFC 7613,
DOI 10.17487/RFC7613, August 2015,
<http://www.rfc-editor.org/info/rfc7613>.
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[RFC7991] Hoffman, P., "The "xml2rfc" Version 3 Vocabulary",
RFC 7991, DOI 10.17487/RFC7991, December 2016,
<http://www.rfc-editor.org/info/rfc7991>.
[UNICODE-CHART]
The Unicode Consortium, "The Unicode Standard",
<http://www.unicode.org/charts>.
[UNICODE-NORM]
The Unicode Consortium, "Unicode Standard Annex #15:
Unicode Normalization Forms", 2016,
<http://www.unicode.org/reports/tr15/>.
[UnicodeCurrent]
The Unicode Consortium, "The Unicode Standard",
<http://www.unicode.org/versions/latest/>.
IAB Members at the Time of Approval
The IAB members at the time this memo was approved were (in
alphabetical order):
Jari Arkko
Ralph Droms
Ted Hardie
Joe Hildebrand
Russ Housley
Lee Howard
Erik Nordmark
Robert Sparks
Andrew Sullivan
Dave Thaler
Martin Thomson
Brian Trammell
Suzanne Woolf
Acknowledgements
With many thanks to the members of the IAB i18n program. Also, many
thanks to the RFC Format Design Team for their efforts in making this
transition successful: Nevil Brownlee (ISE), Tony Hansen, Joe
Hildebrand, Paul Hoffman, Ted Lemon, Julian Reschke, Adam Roach,
Alice Russo, Robert Sparks (Tools Team liaison), and Dave Thaler.
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Author's Address
Heather Flanagan (editor)
RFC Editor
Email: rse@rfc-editor.org
URI: http://orcid.org/0000-0002-2647-2220
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