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Versions: 00 01 rfc2277                                                 
draft                       Charset policy                     June 97


               IETF Policy on Character Sets and Languages

                     Sun Jun 15 14:23:36 MET DST 1997


                         Harald Tveit Alvestrand
                                 UNINETT
                      Harald.T.Alvestrand@uninett.no






    Status of this Memo

    This draft document is being circulated for comment.

    Please send comments to the author.

    The following text is required by the Internet-draft rules:

    This document is an Internet Draft.  Internet Drafts are working
    documents of the Internet Engineering Task Force (IETF), its
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    distribute working documents as Internet Drafts.

    Internet Drafts are draft documents valid for a maximum of six
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    Please check the I-D abstract listing contained in each Internet
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    Internet Draft.

    The file name of this version is draft-alvestrand-charset-policy-00.txt











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    1.  Introduction

    The Internet is international.

    With the international Internet follows an absolute requirement to
    interchange data in a multiplicity of languages, which in turn
    utilize a bewildering number of characters or other character-like
    representation mechanisms.

    This document is (INTENDED TO BE) the current policies being
    applied by the Internet Engineering Steering Group towards the
    standardization efforts in the Internet Engineering Task Force in
    order to help Internet protocols fulfil these requirements.

    The document is very much based upon the recommendations of the
    IAB Character Set Workshop of February 29-March 1, 1996, which is
    documented in RFC 2130 [WR]. This document attempts to be concise,
    explicit and clear; people wanting more background are encouraged
    to read RFC 2130.

    The document uses the terms "MUST", "SHOULD" and "MAY", and their
    negatives, in the way described in [RFC 2119]. In this case, "the
    specification" as used by RFC 2119 refers to the processing of
    protocols being submitted to the IETF standards process.


    2.  Where to do internationalization

    Internationalization is for humans. This means that protocols are
    not subject to internationalization; text strings are. Where
    protocols may masquerade as text strings, such as in many IETF
    application layer protocols, protocols MUST specify which parts
    are protocol and which are text. [WR 2.2.1.1]

    Names are a problem, because people feel strongly about them, many
    of them are mostly for local usage, and all of them tend to leak
    out of the local context at times. RFC 1958 [ARCH] recommends US-
    ASCII for all globally visible names.

    This document does not mandate a policy on name
    internationalization, but requires that all protocols describe
    whether names are internationalized or US-ASCII.







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    3.  Character sets

    For a definition of the term "character set", refer to the
    workshop report. Like MIME, this document uses it to mean the
    combination of a coded character set and a character encoding
    scheme.


    3.1.  What character set to use

    All protocols MUST identify, for all character data, which
    character set is in use.

    Protocols MUST be able to use the ISO 10646 coded character set,
    with the UTF-8 character encoding scheme, for all text. (This is
    called "UTF-8" in the rest of this document)

    They MAY specify how to use other character sets or other
    character encoding schemes, such as UTF-16, but lack of an ability
    to use UTF-8 needs clear and solid justification in the protocol
    specification document before being entered into or advanced upon
    the standards track.

    For existing protocols or protocols that move data from existing
    datastores, support of other character sets, or even using a
    default other than UTF-8, may be a requirement. This is
    acceptable, but UTF-8 support MUST be possible.

    When using other character sets than UTF-8, these MUST be
    registered in the IANA character set registry, if necessary by
    registering them when the protocol is published.


    3.2.  How to decide a character set

    In some cases, like HTTP, there is direct or semi-direct
    communication between the producer and the consumer of a character
    set. In this case, it may make sense to negotiate a character set
    before sending data.

    In other cases, like E-mail or stored data, there is no such
    communication, and the best one can do is to make sure the
    character set is clearly identified with the stored data, and
    choosing a character set that is as widely known as possible.





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    Note that a character set is an absolute; for almost all languages
    but English and a few other Latin-based scripts, text cannot be
    rendered comprehensibly without supporting the right character
    set.

    Negotiating a character set may be regarded as an interim
    mechanism that is to be supported until UTF-8 support is
    prevalent; however, the timeframe of "interim" may be at least 50
    years, so there is every reason to think of it as permanent in
    practice.


    4.  Languages


    4.1.  The need for language information

    All human-readable text has a language.

    Many operations, including high quality formatting, text-to-speech
    synthesis, searching, sorting, spellchecking and so on need access
    to information about the language of a piece of text. [WC
    3.1.1.4].

    Humans have some tolerance for foreign languages, but are
    generally dissatisfied with being presented text in a language
    they do not understand; this is why negotiation of language is
    needed.

    In most cases, machines cannot deduce the language by themselves;
    the protocol must specify how to transfer the language information
    if it is to be available at all.

    (Some items, like domain names and other names, may in some cases
    be very useful without this information.)

    The interaction between language and processing is complex; for
    instance, if I compare "hosta(lang=en)" to "hosta(lang=no)" I will
    generally expect a match, while "aasmund" sorts after "attaboy"
    according to Norwegian rules, but before it using English rules.
    (the "aa" is sorted together with "latin letter a with ring
    above", which is at the end of the Norwegian alphabet).







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    4.2.  How to identify a language

    The RFC 1766 language tag is at the moment the most flexible tool
    available for identifying a language; protocols SHOULD use this,
    or provide clear and solid justification for doing otherwise in
    the document.


    4.3.  Considerations for negotiation

    Protocols that transfer human-readable text MUST provide for
    multiple languages.

    In some cases, a negotiation where the client proposes a set of
    languages and the server replies with one is appropriate; in other
    cases, supplying information in all available languages is a
    better solution; most sites will either have very few languages
    installed or be willing to pay the overhead of sending error
    messages in many languages at once.

    Negotiation is useful in the case where one side of the protocol
    exchange is able to present text in multiple languages to the
    other side, and the other side has a preference for one of these;
    the most common example is the text part of error responses, or
    Web pages that are available in multiple languages.

    Negotiating a language should be regarded as a permanent
    requirement of the protocol that will not go away at any time in
    the future.

    In most cases, it should be possible to include it as part of the
    connection establishment, together with authentication and other
    preferences negotiation.


    4.4.  Default Language

    When human-readable text must be presented in a context where the
    sender has no knowledge of the recipient's language preferences
    (such as login failures or E-mailed warnings, or prior to language
    negotiation), text SHOULD be presented in Default Language.

    The Default Language is English, since this is the language which
    most people will be able to get adequate help in interpreting when





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    working with computers.

    Note that negotiating English is NOT the same as Default Language;
    Default Language is an emergency measure in otherwise unmanageable
    situations.


    5.  Locale

    POSIX defines a concept called a "locale", which includes a lot of
    information about collating order, date format, currency format
    and so on.

    In some cases, and especially with text where the user is expected
    to do processing on the text, locale information may be usefully
    attached to the text.

    This document does not require the communication of locale
    information on all text, but encourages its inclusion when
    appropriate.

    Note that the language and character set will often be present as
    parts of a locale tag (such as no_NO.iso-8859-1; the language is
    before the _ and the character set is after the dot); care must be
    taken to define precisely which specification of character set and
    language applies to any one text item.

    The default locale is the POSIX locale.


    6.  Security considerations

    Apart from the fact that security warnings in a foreign language
    may cause inappropriate behaviour from the user, and the fact that
    multilingual systems usually have problems with consistency
    between language variants, no security considerations relevant
    have been identified.


    7.  References


    [RFC 2119]
         S. Bradner, "Key words for use in RFCs to Indicate





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         Requirement Levels", 03/26/1997 - RFC 2119

    [WR] C. Weider, C. Preston, K. Simonsen, H. Alvestrand, R.
         Atkinson, M. Crispin, P. Svanberg, "The Report of the IAB
         Character Set Workshop held 29 February - 1 March, 1996",
         04/21/1997, RFC 2130

    [ARCH]
         B. Carpenter, "Architectural Principles of the Internet",
         06/06/1996, RFC 1958


    8.  Author's address

    Harald Tveit Alvestrand
    UNINETT
    P.O.Box 6883 Elgeseter
    N-7002 TRONDHEIM
    NORWAY

    +47 73 59 70 94
    Harald.T.Alvestrand@uninett.no



























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