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Internet-Draft                                       H. Alvestrand
draft-alvestrand-content-language-02.txt              Cisco Systems
Target Category: Standards Track                           May 2001
Updates: RFC 1766                           Expires: November 2001










Content Language Headers


Status of this Memo
     The file name of this memo is draft-alvestrand-content-language-
     02.txt
     This document is an Internet-Draft and is in full conformance with
     all provisions of Section 10 of RFC 2026.
     Internet-Drafts are working documents of the Internet Engineering
     Task Force (IETF), its areas, and its working groups.  Note that
     other groups may also distribute working documents as Internet-
     Drafts.
     Internet-Drafts are draft documents valid for a maximum of six
     months and may be updated, replaced, or obsoleted by other
     documents at any time.  It is inappropriate to use Internet-
     Drafts as reference material or to cite them other than as "work
     in progress."
     The list of current Internet-Drafts can be accessed at
     http://www.ietf.org/ietf/1id-abstracts.txt
     The list of Internet-Draft Shadow Directories can be accessed at
     http://www.ietf.org/shadow.html.
Comments on this draft should be sent to the mailing list <ietf-
languages@iana.org>

Abstract
This document defines a "Content-language:" header, for use in the case
where one desires to indicate the language of something that has RFC-
822-like headers, like MIME body parts or Web documents, and an
"Accept-Language:" header for use in the case where one wishes to
indicate one's preferences with regard to languages.

1. Introduction
 

Content Language Headers                         Harald Alvestrand
draft-alvestrand-content-language-02.txt     Expires November 2001

There are a number of languages presently or previously used by human
beings in this world.
A great number of these people would prefer to have information
presented in a language which they understand.
In some contexts, it is possible to have information available in more
than one language, or it might be possible to provide tools  (such as
dictionaries) to assist in the understanding of a language.
In other cases, it may be desirable to use a computer program to
convert information from one format (such as plaintext) into another
(such as computer-synthesized speech, or Braille, or high-quality print
renderings).

A prerequisite for any such function is a means of labelling the
information content with an identifier for the language that is used in
this information content, such as is defined by [TAGS].
This document specifies a protocol element for use with protocols that
use RFC-822 like headers for carrying language tags as defined in
[TAGS].
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119].

2. The Content-language header
The "Content-Language" header is intended for use in the case where one
desires to indicate the language(s) of something that has RFC-822-like
headers, such as MIME body parts or Web documents.
The RFC-822 EBNF of the Content-Language header is:
 Content-Language = "Content-Language" ":" 1#Language-tag

Or in RFC 2234 ABNF:

Content-Language = "Content-Language" CFWS ":" Language-List
Language-List = Language-Tag [ CFWS "," CFWS Language-List ]

The Content-Language header may list several languages in a comma-
separated list.
The CFWS construct is intended to function like the whitespace
convention in RFC 822, which means also that one can place
parenthesized comments anywhere in the language sequence, or use
continuation lines. A formal definition is given in RFC 2822 [RFC2822].

2.1 Examples of Content-language values




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Content Language Headers                         Harald Alvestrand
draft-alvestrand-content-language-02.txt     Expires November 2001

Voice recording from Liverpool downtown
   Content-type: audio/basic
   Content-Language: en-scouse

Document in Mingo, an American Indian language which does not have an
ISO 639 code:
   Content-type: text/plain
   Content-Language: i-mingo

An English-French dictionary

   Content-type: application/dictionary
   Content-Language: en, fr (This is a dictionary)

An official European Commission document (in a few of its official
languages)

   Content-type: multipart/alternative
   Content-Language: da, de, el, en, fr, it

An excerpt from Star Trek
   Content-type: video/mpeg
   Content-Language: i-klingon


3. The Accept-Language header
The "Accept-Language" header is intended for use in the case where a
user or a process desires to identify the preferred language(s) when
RFC-822-like headers, such as MIME body parts or Web documents are
used.
The RFC-822 EBNF of the Accept-Language header is:
Accept-Language = "Accept-Language" ":"
                         1#( language-range [ ";" "q" "=" qvalue ] )


The syntax and semantics of language-range is defined in [TAGS].
(Note that RFC-822 EBNF rather than ABNF is used here, in order to
ensure that the syntax is identical with that specified in [RFC 2616]).
The Accept-Language header may list several language-ranges in a comma-
separated list, and each may include a quality value Q.
If no Q values are given, the language-ranges are given in priority
order, with the leftmost language-range being the most preferred
language; this is an extension to the HTTP/1.1 rules, but matches
current practice.


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Content Language Headers                         Harald Alvestrand
draft-alvestrand-content-language-02.txt     Expires November 2001

If Q values are given, refer to HTTP/1.1 [RFC 2616] for the details on
how to evaluate it.

4. Security Considerations
The only security issue that has been raised with language tags since
the publication of RFC 1766, which stated that "Security issues are
believed to be irrelevant to this memo", is a concern with language
ranges used in content negotiation - that they may be used to infer the
nationality of the sender, and thus identify potential targets for
surveilllance.
This is a special case of the general problem that anything you send is
visible to the receiving party; it is useful to be aware that such
concerns can exist in some cases.
The exact magnitude of the threat, and any possible countermeasures, is
left to each application protocol.

5. Character set considerations
This document adds no new considerations beyond what is mentioned in
[TAGS].

6. Acknowledgements
This document has benefited from many rounds of review and comments in
various fora of the IETF and the Internet working groups.
Any list of contributors is bound to be incomplete; please regard the
following as only a selection from the group of people who have
contributed to make this document what it is today.
In alphabetical order:
Tim Berners-Lee, Nathaniel Borenstein, Sean M. Burke, John Clews, Jim
Conklin, John Cowan, Dave Crocker, Martin Duerst, Michael Everson, Ned
Freed, Tim Goodwin, Dirk-Willem van Gulik, Marion Gunn, Paul Hoffman,
Olle Jarnefors, John Klensin, Keith Moore, Chris Newman, Masataka Ohta,
Keld Jorn Simonsen, Rhys Weatherley, Misha Wolf, Francois Yergeau and
many, many others.

Special thanks must go to Michael Everson, who has served as language
tag reviewer for almost the complete period since the publication of
RFC 1766, and has provided a great deal of input to this revision.

7. Author's Address
Harald Tveit Alvestrand
Cisco Systems
Weidemanns vei 27
7043 Trondheim
NORWAY

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Content Language Headers                         Harald Alvestrand
draft-alvestrand-content-language-02.txt     Expires November 2001

EMail: Harald@Alvestrand.no
Phone: +47 73 50 33 52

8. References

[TAGS]    Alvestrand, H., "Tags for the identification of languages",
RFC 3066
[ISO 639]
     ISO 639:1988 (E/F) - Code for the representation of names of
     languages - The International Organization for Standardization,
     1st edition, 1988-04-01 Prepared by ISO/TC 37 - Terminology
     (principles and coordination).
     Note that a new version (ISO 639-1:2000) is in preparation at the
     time of this writing.
[ISO 639-2]
     ISO 639-2:1998 - Codes for the representation of names of
     languages -- Part 2: Alpha-3 code  - edition 1, 1998-11-01, 66
     pages, prepared by ISO/TC 37/SC 2

[ISO 3166]
     ISO 3166:1988 (E/F) - Codes for the representation of names of
     countries - The International Organization for Standardization,
     3rd edition, 1988-08-15.
[ISO 15924]
     ISO/DIS 15924 - Codes for the representation of names of scripts
     (under development by ISO TC46/SC2)
[RFC 1521]
     Borenstein, N., and N. Freed, "MIME Part One: Mechanisms for
     Specifying and Describing the Format of Internet Message Bodies",
     RFC 1521, Bellcore, Innosoft, September 1993.
[RFC 2119]
     Key words for use in RFCs to Indicate Requirement Levels. S.
     Bradner. March 1997.
[RFC 2234]
     Augmented BNF for Syntax Specifications: ABNF. D. Crocker, Ed., P.
Overell, November 1997.
[RFC 2616]
     Hypertext Transfer Protocol -- HTTP/1.1. R. Fielding, J. Gettys,
     J. Mogul, H. Frystyk, L. Masinter, P. Leach, T. Berners-Lee. June
     1999.
[RFC 2822]

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Content Language Headers                         Harald Alvestrand
draft-alvestrand-content-language-02.txt     Expires November 2001

     Internet Message Format. P. Resnick, Editor. April 2001.

Appendix A: Changes from RFC 1766
The definition of the language tags has been split, and is now RFC 3066
The differences parameter to multipart/alternative is no longer part of
this standard.














































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