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.
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.
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.
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.
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
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.
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.
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.
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.
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> | +------------------------------------+------------------------------+
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.
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)
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.
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)
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.
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.
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.
[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>.
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.