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rfc:rfc7997

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.

Flanagan Informational [Page 1] RFC 7997 Non-ASCII in RFCs December 2016

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

Flanagan Informational [Page 2] RFC 7997 Non-ASCII in RFCs December 2016

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;

Flanagan Informational [Page 3] RFC 7997 Non-ASCII in RFCs December 2016

 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.

Flanagan Informational [Page 6] RFC 7997 Non-ASCII in RFCs December 2016

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.

Flanagan Informational [Page 8] RFC 7997 Non-ASCII in RFCs December 2016

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| <&#x3C0;&#xDF;&#xE5;>          | Non-ASCII letters are OK     |
 |   |                                | (e.g., GREEK SMALL LETTER    |
 |   |                                | PI, U+03C0)                  |
 +------------------------------------+------------------------------+
 | 15| <Jack of &#x2666;s>            | Symbols are OK (e.g., BLACK  |
 |   |                                | DIAMOND SUIT, U+2666)        |
 +------------------------------------+------------------------------+
 | 16| <foo&#x1680;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>                    |
 +------------------------------------+------------------------------+

Flanagan Informational [Page 10] RFC 7997 Non-ASCII in RFCs December 2016

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.

Flanagan Informational [Page 11] RFC 7997 Non-ASCII in RFCs December 2016

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)
  1. —–
   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.

Flanagan Informational [Page 12] RFC 7997 Non-ASCII in RFCs December 2016

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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