The Use of Non-ASCII Characters in RFCs

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Table of Contents

1. Introduction

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. At the time of the publication of [RFC7997], the increasing need for easily readable, internationalized content suggested that it is time to allow non-ASCII characters in RFCs where necessary. To support this move away from ASCII, RFCs switched to supporting UTF-8 as the default character encoding and allowed support for a broad range of Unicode characters [UnicodeCurrent].¶

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 publishing new RFCs.¶

2. Basic Requirements for Non-ASCII Text in RFCs

The following fundamental requirements inform the guidance and examples provided in this document. They are:¶

• Searches against RFC indexes and database tables should return expected results and support appropriate Unicode string matching behaviors.¶

• RFCs should 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.¶

• As stated in the RFC Style Guide [RFC7322], the language of the RFC Series is English.¶

3. Use of Non-ASCII Text in RFCs

This section describes the guidelines for the use of non-ASCII characters in an RFC. If the RPC identifies areas where the use of non-ASCII characters in an RFC negatively impacts the readability of the text, they can require that the authors supply alternate text or change the non-ASCII characters to better suit the expected readers of the RFC. When the RPC has questions about non-ASCII text in RFCs, the RPC can ask the RFC stream approving bodies for input. The RPC can also consult the RSAB and the RSWG on such matters.¶

In general, using the "U+NNNN" syntax from [BCP137] is the suggested way to show Unicode code points as alternate text.¶

Characters in an RFC will generally appear in Normalization Form C (NFC) as defined in [UnicodeNorm]. If the RFC would be more correct and more understandable with particular characters not in NFC, the RPC can make an exception and use unnormalized text. In such a case, a text note should be included to describe why unnormalized text used.¶

Non-ASCII text can appear in any part of an RFC, such as headings, running text, and artwork. Non-ASCII text in person, company, and postal names are covered later in Section 3.1.¶

When the non-ASCII characters are required for correct protocol operation and understanding, the characters' Unicode code points should also appear in the text in the "U+NNNN" syntax, at least on first use in the RFC. [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.¶

Where the use of non-ASCII characters is purely part of an example and not otherwise required for correct protocol operation, giving the Unicode equivalent of the non-ASCII characters is not required, but it can improve the readability of the RFC. For example, for text that says "The value can be followed by a monetary symbol such as ¥ or €", the RPC might require that it instead say "The value can be followed by a monetary symbol such as ¥ (U+00A5) or € (U+20AC)".¶

Use of the actual non-ASCII character (such as common math symbols like √ and ≤) is encouraged so that a reader can more easily see what the character is. This is done without adding the "U+NNNN" syntax.¶

As another example, [RFC7564] says:¶

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.

This could be replaced with:¶

However, the problem is made more serious by introducing the full
range of Unicode code points into protocol strings.  For example,
the characters "ᏚᎢᎵᎬᎢᎬᏒ" (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.

Code components may have different requirements for using the "U+NNNN" syntax. The use of the "U+NNNN" syntax in code components is recommended, except within a code component where one must follow the rules of the programming language in which the code is being written.¶

4. XML Markup

[[ This section needs revision after community discussion ]]¶

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.¶

5. Internationalization Considerations

The ability to use non-ASCII characters in RFCs in a clear and consistent manner improves the ability to describe internationalized protocols and recognizes the diversity of authors. However, the goal of readability overrides the use of non-ASCII characters within the text.¶

6. Security Considerations

Valid Unicode that matches the expected text must be verified in order to preserve expected behavior and protocol information.¶

Appendix A. Acknowledgements

The acknowledgements from [RFC7997] are to the members of the IAB i18n program, to the RFC Format Design Team: Nevil Brownlee, Tony Hansen, Joe Hildebrand, Paul Hoffman, Ted Lemon, Julian Reschke, Adam Roach, Alice Russo, Robert Sparks, and Dave Thaler.¶

This current document was greatly helped by contributions from the RFC Series Working Group (RSWG), including from Brian Carpenter, Carsten Bormann, Eliot Lear, John Levine, and Martin Thomson.¶

Authors' Addresses