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Network Working Group C. Weider Request for Comments: 2130 Microsoft Category: Informational C. Preston

                                                     Preston & Lynch
                                                         K. Simonsen
                                                       H. Alvestrand
                                                         R. Atkinson
                                                       Cisco Systems
                                                          M. Crispin
                                            University of Washington
                                                         P. Svanberg
                                                          April 1997
            The Report of the IAB Character Set Workshop
                  held 29 February - 1 March, 1996

Status of this Memo

 This memo provides information for the Internet community.  This memo
 does not specify an Internet standard of any kind.  Distribution of
 this memo is unlimited.


 The authors would like to sincerely thank Information Sciences
 Institute (ISI), and in particular Joyce K. Reynolds for graciously
 hosting this event; Joe Kemp and Jeanine Yamazaki of ISI made sure
 the facilities met our needs.  We also wish to thank the Internet
 Society, which underwrote travel for participants who might not
 otherwise have been able to attend.  Of course, we also wish to thank
 the many experts who participated in the workshop and on the mailing
 list; a complete list of these people can be found in Appendix D.
 Bunyip Information Systems was kind enough to provide mailing list
 facilities for this work.

Table of Contents

 0:    Executive summary..........................................   2
 1:    Introduction...............................................   3
 2:    Character sets on the Internet -- the problem..............   3
 2.1:  Character set handling in existing protocols...............   4
 3:    Architectural model........................................   6
 3.1:  Segments defined...........................................   7
 3.2:  On the wire................................................   8

Weider, et. al. Informational [Page 1] RFC 2130 Character Set Workshop Report April 1997

 3.3:  Determining which values of CCS, CES, and TES are used.....   9
 3.4:  Recommended Defaults.......................................  10
 3.5:  Guidelines for conversions between coded character sets....  13
 4:    Presentation issues........................................  14
 5:    Open issues................................................  14
 5.1:  Language tags..............................................  15
 5.2:  Public identifiers.........................................  16
 5.3:  Bi-directionality..........................................  16
 6:    Security Considerations....................................  16
 7:    Conclusions................................................  16
 8:    Recommendations............................................  17
 8.1:  To the IAB.................................................  17
 8.2:  For new Internet protocols.................................  18
 8.3:  For registration of new character sets.....................  18
 Appendix A: List of protocols affected by character set issues...  20
 Appendix B: Acronyms.............................................  23
 Appendix C: Glossary.............................................  24
 Appendix D: References...........................................  25
 Appendix E: Recommended reading..................................  27
 Appendix F: Workshop attendee list...............................  29
 Appendix G: Authors' Addresses...................................  30


 This report details the conclusions of an IAB-sponsored invitational
 workshop held 29 February  - 1 March, 1996, to discuss the use of
 character sets on the Internet.  It motivates the need to have
 character set handling in Internet protocols which transmit text,
 provides a conceptual framework for specifying character sets,
 recommends the use of MIME tagging for transmitted text, recommends a
 default character set *without* stating that there is no need for
 other character sets, and makes a series of recommendations to the
 IAB, IANA, and the IESG for furthering the integration of the
 character set framework into text transmission protocols.

0: Executive summary

 The term 'Character Set' means many things to many people. Even the
 MIME registry of character sets registers items that have great
 differences in semantics and applicability. This workshop provides
 guidance to the IAB and IETF about the use of character sets on the
 Internet and provides a common framework for interoperability between
 the many characters in use there.
 The framework consists of four components: an architecture model,
 which specifies components necessary for on-the-wire transmission of
 text; recommendations for tagging transmitted (and stored) text;
 recommended defaults for each level of the model; and a set of

Weider, et. al. Informational [Page 2] RFC 2130 Character Set Workshop Report April 1997

 recommendations to the IAB, IANA, and the IESG for furthering the
 integration of  this framework into text transmission protocols.
 The architectural model specifies 7 layers, of which only three are
 required for on-the-wire transmission. The Coded Character Set is a
 mapping from a set of abstract characters to a set of integers. The
 Character Encoding Scheme is a mapping from a Coded Character Set (or
 several) to a set of octets. The Transfer Encoding Syntax is a
 transformation applied to data which has been encoded using a
 Character Encoding Scheme to allow it to be transmitted. These layers
 should be specified in a transmitted text stream by using the MIME
 encoding mechanisms.
 This report recommends the use of ISO 10646 as the default Coded
 Character Set, and UTF-8 as the default Character Encoding Scheme in
 the creation of new protocols or new version of old protocols which
 transmit text. These defaults do not deprecate the use of other
 character sets when and where they are needed; they are simply
 intended to provide guidance and a specification for

1: Introduction

 This is the report of an IAB-sponsored invitational workshop on the
 use of Character Sets on the Internet, held 29 February - 1 March
 1996 at Information Sciences Institute (ISI) in Marina del Rey,
 California.  In addition, this report covers the discussion on the
 mailing list up to and slightly beyond the workshop itself.  The
 goals of this workshop were to provide guidance to the IAB and the
 IETF about the use of character sets on the Internet, and if possible
 a common framework for interoperability between the many character
 sets in use there.  Both goals were achieved.

2: Character sets on the Internet - the problem

 The term 'character set' is typically applied to the contents of a
 wide variety of text transmission and display protocols used on the
 Internet.  Because the term is used to mean different things,
 confusion has arisen.  For example, the MIME registry of character
 sets [MIME] contains items that may differ greatly in their
 applicability and semantics in various Internet protocols.
 In addition, there is a vast profusion of different text encoding
 schemes in use on the Internet.  This per se is not a problem; each
 scheme has evolved to meet real needs.  However, information
 applications such as mail, directories, and the World Wide Web have
 each developed different techniques for dealing with the growing
 number of schemes.  A robust information architecture for the

Weider, et. al. Informational [Page 3] RFC 2130 Character Set Workshop Report April 1997

 Internet requires as much interoperability between these techniques
 as possible.

2.1: Related topics deemed out of scope for this workshop

 Successful display of plain text transmitted over the Internet
 requires a lot of information about the text itself, such as the
 underlying character set, language, and so forth.  An additional set
 of formatting information is needed if the receiving application
 wishes to use local (cultural) conventions when it presents the data
 to the user.  This formatting includes information, that provides the
 data necessary to format certain  types of textual data (dates,
 times, numbers and monetary notation) into a form which is familiar
 to the user.  The POSIX [POSIX] notation of locale encompasses
 language, coded character set and cultural conventions.
 To avoid unfruitful discussion, and to make the best use of the time
 available for the workshop, we declared the following  issues out of
 scope for the purposes of this workshop:
  1. glyphs
  2. sorting
  3. culture (e.g. do we present the American or British spelling?)
  4. user interface issues
  5. internal representation of textual data
  6. included characters (why aren't certain characters available in

any character set?)

  1. locale (in the POSIX sense)
  2. font registration
  3. semantics
  4. user input/output issues
  5. Han unification issues
 There are some related issues which were included for discussion,
 most importantly the 'locale' components necessary for transport and
 identification of multilingual texts.

2.2: Character Set handling in existing protocols

 One of the group's overriding concerns was that the framework
 developed for character set handling not break existing protocols.
 With that in mind, the way character sets are being used in existing
 protocols was examined.  See Appendix A for a list of those protocols
 and some recommendations for change.

2.2.1: General comments

 The problem areas here fall into three main categories: protocols,

Weider, et. al. Informational [Page 4] RFC 2130 Character Set Workshop Report April 1997

 identifiers, and data. Protocols

 The protocol machinery SHOULD NOT be changed; allowing, for instance,
 SMTP [SMTP] to use both MAIL FROM and POST FRA is dangerous to the
 protocols' stability.  However, many protocols carry error messages
 and other information that is intended for human consumption; it
 MIGHT be an advantage to allow these to be localized into a specific
 language and character set, rather than staying in English and US-
 ASCII [ASCII].  If this is done, new extensions should follow the
 framework outlined below. Identifiers.

 There is a strong statement of direction from the IAB, RFC 1958 [RFC
 1958],  which states:
      4.3 Public (i.e. widely visible) names should be in case
          independent ASCII.  Specifically, this refers to DNS names,
          and to protocol elements that are transmitted in text format.
      5.4 Designs should be fully international, with support for
          localization (adaptation to local character sets). In
          particular, there should be a uniform approach to character
          set tagging for information content.
 In protocols that up to now have used US-ASCII only, UTF-8 [UTF-8]
 forms a simple upgrade path; however, its use should be negotiated
 either by negotiating a protocol version or by negotiating charset
 usage, and a fallback to a US-ASCII compatible representation such as
 UTF-7 [UTF-7] MUST be available.
 The need for passing application data such as language on individual
 identifiers varies between applications; protocols SHOULD attempt to
 evaluate this need when designing mechanisms.  Applying the ASCII
 requirement for identifiers that are only used in a local context
 (such as private mailbox folder names) is both unrealistic and
 unreasonable; in such cases, methods for consistency in the handling
 of character set should be considered. Data

 Data that require character set handling includes text, databases,
 and HTML [HTML] pages, for example.  In these the support for
 multiple character sets and proper application information is
 absolutely vital, and MUST be supported.

Weider, et. al. Informational [Page 5] RFC 2130 Character Set Workshop Report April 1997

2.3: Architectural requirements

 To address the issues enumerated for this work, first an
 architectural model was created which establishes the components that
 are required to fully specify the transmission of textual data. Many
 of these components are already familiar to the users of encoding
 protocols such as MIME.  Not all of these are discussed in detail in
 this report; we restrict ourselves primarily to those components
 which are required to specify the 'on-the-wire' phase of text
 Mandating a single, all-encompassing character set would not fit well
 with the IETF philosophy of planning for architectural diversity.
 So, the best that can be done is to provide a common *framework* for
 identifying and using the multitude of character sets available on
 the Internet.  It would be an advantage if the total number of Coded
 Character Sets could be kept to a minimum.  This framework should
 meet the following requirements:
  1. it should not break existing protocols (because then the likelihood

of deployment is very small),

  1. it should allow the use of character sets currently used on the

Internet, and

  1. it should be relatively easy to build into new protocols.

3: Architectural model

 The basic architectural model which guided our discussions is shown
 in below.  A distinction was made between those segments which were
 necessary to successfully transmit character set data on-the-wire and
 those needed to present that data to a user in a comprehensible
 manner.  The discussions were primarily restricted to those segments
 of the model which specify the 'on-the-wire' transmission of textual
 User interface issues: these are briefly discussed in Section 3.1.1.
 On-the-wire: see section 3.2 for detailed discussion.
      Transfer Syntax
      Character Encoding Scheme
      Coded Character Set

Weider, et. al. Informational [Page 6] RFC 2130 Character Set Workshop Report April 1997

3.1: Segments defined

3.1:1: User interface Layout

 Layout includes the elements needed for displaying text to the user,
 such as font selection, word-wrapping, etc.  It is similar to the
 'presentation' layer in the 7-layer ISO telecommunications model
 [ISO-7498]. Culture

 Culture includes information about cultural preferences, which affect
 spelling, word choice, and so forth. Locale

 The locale component includes the information necessary to make
 choices about text manipulation which will present the text to the
 user in an expected format.  This information may include the display
 of date, time and monetary symbol preferences.  Notice that locale
 modifications are typically applied to a text stream before it is
 presented to the user, although they also are used to specify input
 formats. Language

 This component specifies the language of the transmitted text.  At
 times and in specific cases, language information may be required to
 achieve a particular level of quality for the purpose of displaying a
 text stream.  For example, UTF-8 encoded Han may require transmission
 of a language tag to select the specific glyphs to be displayed at a
 particular level of quality.
 Note that information other than language may be used to achieve the
 required level of quality in a display process.  In particular, a
 font tag is sufficient to produce identical results.  However, the
 association of a language with a specific block of text has
 usefulness far beyond its use in display.  In particular, as the
 amount of information available in multiple languages on the World
 Wide Web grows, it becomes critical to specify which language is in
 use in particular documents, to assist automatic indexing and
 retrieval of relevant documents.

Weider, et. al. Informational [Page 7] RFC 2130 Character Set Workshop Report April 1997

 The term 'language tag' should be reserved for the short identifier
 of RFC 1766 [RFC-1766] that only serves to identify the language.
 While there may be other text attributes intimately associated with
 the language of the document, such as desired font or text direction,
 these should be specified with other identifiers rather than
 overloading the language tag.

3.2: On the wire

 There are three segments of the model which are required for
 completely specifying the content of a transmitted text stream (with
 the occasional exception of the Language component, mentioned above).
 These components are:
 1)  Coded Character Set,
 2)  Character Encoding Scheme, and
 3)  Transfer Encoding Syntax.
 Each of these abstract components must be explicitly specified by the
 transmitter when the data is sent.  There may be instances of an
 implicit specification due to the protocol/standard being used (i.e.
 ANSI/NISO Z39.50).  Also, in MIME, the Coded Character Set and
 Character Encoding Scheme are specified by the Charset parameter to
 the Content-Type header field, and Transfer Encoding Syntax is
 specified by the Content-Transfer-Encoding header field.

3.2.1: Coded Character Set

 A Coded Character Set (CCS) is a mapping from a set of abstract
 characters to a set of integers.  Examples of coded character sets
 are ISO 10646 [ISO-10646], US-ASCII [ASCII], and ISO-8859 series

3.2.2: Character Encoding Scheme

 A Character Encoding Scheme (CES) is a mapping from a Coded Character
 Set or several coded character sets to a set of octets. Examples of
 Character Encoding Schemes are ISO 2022 [ISO-2022] and UTF-8 [UTF-8].
 A given CES is typically associated with a single CCS; for example,
 UTF-8 applies only to ISO 10646.

Weider, et. al. Informational [Page 8] RFC 2130 Character Set Workshop Report April 1997

3.2.3: Transfer Encoding Syntax

 It is frequently necessary to transform encoded text into a format
 which is transmissible by specific protocols.  The Transfer Encoding
 Syntax (TES) is a transformation applied to character data encoded
 using a CCS and possibly a CES to allow it to be transmitted.
 Examples of Transfer Encoding Syntaxes are Base64 Encoding [Base64],
 gzip encoding, and so forth.

3.3: Determining which values of CCS, CES, and TES are used

 To completely specify which CCS, CES, and TES are used in a specific
 text transmission, there needs to be a consistent set of labels for
 specifying which CCS, CES, and TES are used.  Once the appropriate
 mechanisms have been selected, there are six techniques for attaching
 these labels to the data.
 The labels themselves are named and registered, either with IANA
 [IANA] or with some other registry.  Ideally, their definitions are
 retrievable from some registration authority.
 Labels may be determined in one of the following ways:
  1. Determined by guessing, where the receiver of the text has to

guess the values of the CCS, CES, and TES. For example: "I got

    this from Sweden so it's probably  ISO-8859-1."  This is
    obviously not a very foolproof way to decode text.
 -  Determined by the standard, where the protocol used to transmit
    the data has made documented choices of CCS, CES, and TES in the
    standard. Thus, the encodings used are known through the
    access protocol, for example HTTP [HTTP] uses (but is not
    limited to) ISO-8859-1, SMTP uses US-ASCII.
 -  Attached to the transfer envelope, where the descriptive labels are
    attached to the wrapper placed around the text for transport.
    MIME headers are a good example of this technique.
 -  Included in the data stream, where the data stream itself has
    been encoded in such a way as to signal the character set used.
    For example, ISO-2022 encodes the data with escape sequences to
    provide information on the character subset currently being used.
 -  Agreed by prior bilateral agreement, where some out-of-band
    negotiation has allowed the text transmitter and receiver to
    determine the CCS, CES, and  TES for the transmitted text.
 -  Agreed to by negotiation during some phase, typically
    initialization of the protocol.

Weider, et. al. Informational [Page 9] RFC 2130 Character Set Workshop Report April 1997

3.3.1: Recommendations for value specification mechanisms

 While each of these techniques (with the  exception of guessing) is
 useful in particular situations, interoperability requires a more
 consistent set of techniques.  Thus, we recommend that MIME
 registered values be used for all tagging of character sets and
 languages UNLESS there is an existing mechanism for determining the
 required information using one of the other techniques (except
 guessing).  This recommendation will require a fair bit of work on
 the part of protocol designers, implementors, the IETF, the IESG, and
 the IAB.
 However, it is important to point out that the MIME concept of
 'charset' in some cases cuts across several layers of components in
 our model.  While this can be accepted in existing registrations, we
 also recommend that the MIME registration procedure for character
 sets be modified to show how a proposed character set deals with the
 CCS and the CES. Most 'charsets' have a well defined CCS and CES,
 they should merely be teased apart for the registration.
 There are a number of other recommendations, but these will be
 covered in the next sections.

3.4: Recommended Defaults

 For a number of reasons, one cannot define a mandatory set of
 defaults for all Internet protocols.  There is a mass of current
 practice, future protocols are likely to have different purposes,
 which may determine their handling of text, and protocols may need
 specific variation support.  For example, in mail, text is a
 predominant data type and coded character sets then become a major
 issue for the protocol.  Also, since e-mail is ubiquitous and users
 expect to be able to send it to everyone, the mail protocols need to
 be quite adept at handling different character set encodings.  On the
 other hand, if strings are seldom used in a given protocol, there is
 no need to weigh the protocol down with a sophisticated apparatus for
 handling multiple character sets, assuming that the predicated
 character set can handle all the protocol's needs. This observation
 also applies to the specification techniques for character set
 parameters.  If only one character set encoding is needed, it can be
 made explicit in the protocol specification.  Protocols with a
 greater need for character set support will need a more elaborate
 specification technique.

Weider, et. al. Informational [Page 10] RFC 2130 Character Set Workshop Report April 1997

3.4.1: Clarity of specification

 We recommend that each protocol clearly specify what it is using for
 each of the layers of the transmission model.  Users (or clients)
 should never have to guess what the parameter is for a given layer.

3.4.2: Default Coded Character Set:

 The default Coded Character Set is the repertoire of ISO-10646.

3.4.3: Default Character Encoding Scheme

 For text-oriented protocols, new protocols should use UTF-8, and
 protocols that have a backwards compatibility requirement should use
 the default of the existing protocol, e.g. US-ASCII for mail, and
 ISO-8859-1 for HTTP.  The recommended specification scheme is the
 MIME "charset" specification, using the IANA "charset"
 specifications.  The MIME specifications will need to be clarified to
 meet this model in the future.
 For other protocols, the default should be UTF-8 as this initially
 allows US-ASCII to be entered as-is, and enables the full repertoire
 of ISO 10646.
 Some protocols, such as those descended from SGML [SGML], have other
 natural notations for characters outside their "natural" repertoire;
 for instance, HTML [HTML] allows the use of &#nnnn to refer to any
 ISO 10646 character.  Note that this, like all other encodings that
 depend on "escape characters", redefines at least one character from
 the base character set for use as an indicator of "foreign"
 characters.  Use of this approach must be weighed very carefully.

3.4.4: Default Transport Encoding Scheme

 There is no recommended default for this level.  For plain text
 oriented protocols, the bytestream transport format should be 8-bit
 clean, possibly with normalization of end-of-line indicators.  Some
 special cases could be made for protocols that are not 8-bit clean,
 such as encoding it for transport over 7-bit connections.  For binary
 the same recommendation holds as above.  The specification technique
 should either be defined in the  protocol, if only one way is
 permitted, or by use of MIME content-transfer-encoding (CTE)
 techniques, using IANA registered values.

Weider, et. al. Informational [Page 11] RFC 2130 Character Set Workshop Report April 1997

3.4.5: Default Language

 There is no recommended default for the language level.  For human
 readable text, there should always be a way to specify the natural
 language. The specification technique should be a MIME identifier
 with IANA  registered values for languages.  If headers are used, the
 header should be 'Content-Language'.

3.4.6: Default Locale

 The default should be the POSIX locale.  The specification technique
 should use the Cultural register of CEN ENV 12005 [CEN] for the
 values.  If headers are used, the header should be 'Content-Locale'.

3.4.7: Default Culture

 There is no recommended default for the Culture level.  The
 specification  technique should be a MIME or MIME-like identifier
 (e.g. Content-Culture) and should use the Cultural register of CEN
 ENV 12005 for its values.

3.4.8: Default Presentation

 There is no recommended default for the Presentation level.  The
 specification technique should be a MIME or MIME-like identifier
 (e.g.  Content-Layout) and use the glyph register of ISO 10036 and
 other registers for its values.

3.4.9: Multiplexing

 In some cases, text transmission may require the use of a number of
 different values for a given parameter; for example, English
 annotation of Japanese text might well require shifting the Content-
 Language parameter.  The way to switch the value of parameters within
 a single body of text depends on the application.  For instance, the
 HTML I18N [I18N] work defines a language attribute on most of its
 elements, including <SPAN>, <HTML>, and <BODY>, for the purpose of
 switching between different languages.  When only one value is
 needed, this value should be as general as possible, and specified in
 the protocol standard with reference to the IANA or other registry
 value.  All levels should be specified explicitly.

3.4.10: Storage

 Because stored text may very well be stored without any of the
 additional information necessary for decoding, stored text SHOULD be
 tagged in a MIME compliant fashion.  This alleviates the problem of
 being unable to interpret text which has been stored for a long time,

Weider, et. al. Informational [Page 12] RFC 2130 Character Set Workshop Report April 1997

 or text whose provenance is not available.

3.5: Guidelines for conversions between coded character sets

 This section covers various algorithms to convert a source text S,
 encoded in the coded character set CCS(S), to a target text T,
 encoded in the coded character set CCS(T).
 Rep(X) is the character repertoire of coded character set X, i.e. the
 set of characters which can be represented with X.

3.5.1: Exact conversion

 When Rep(CCS(S)) and Rep(CCS(T)) are equal or Rep(CCS(S)) is a subset
 of Rep(CCS(T)), exact conversion is possible; i.e. T is equal to S.
 The octets just need to be remapped.  The algorithm for performing
 this remapping is simple, if the IANA-registered definition tables
 for CCS(S) and CCS(T) are available.

3.5.2: Approximate conversion

 In all other cases, any conversion creates a text T which differs
 from S.  There are different principles for how this inevitable
 difference should be handled.  A choice between them should be made,
 depending on the purpose and requirements of the conversion.  Where
 possible, the client application should be given mechanisms to
 determine what has been done to the text.  Length-modifying conversion for human display
 When the length of the target text T is allowed to differ from the
 length of the source text S, one should use a conversion method in
 which each source character is converted to one or several target
 character(s), using a best resemblance criteria in the choice of that
 target character(s).
    COPYRIGHT SIGN       [*] -> (c) Length-preserving conversion for human display

 Where the text T must be presented and the length of T cannot differ
 from the length of S, one should use a conversion method where each
 source character is converted to one target character, using some
 kind of best  resemblance criteria in the choice of target character.

Weider, et. al. Informational [Page 13] RFC 2130 Character Set Workshop Report April 1997

   COPYRIGHT SIGN        [*] -> C Conversion without data loss

 Where the conversion of the text S into T must be completely
 reversible, apply a Character Encoding Syntax or other reversible
 transformation method.  This case is most frequently met in data
 storage requirements.
   COPYRIGHT SIGN       [*] -> &(C
 An alternate method, which can be used if the size of Rep(CCS(T)) >=
 Rep(CCS(S)), then for each character in Rep(CCS(S)) which is not
 present in Rep(CCS(T)), define a mapping into a character in
 Rep(CCS(T)) which is not present in Rep(CCS(S)).
 Note that conversion without data loss requires redefining some
 member of T to indicate "the introduction of character data outside
 T".  This effectively adds another level of CES on top of CES(T).

4: Presentation issues

 There are a number of considerations to make in selecting the base
 character set.  One such consideration is the protocol's convenience
 to users with limited equipment (for example only ISO 8859-1 or a
 keyboard without the ability to enter all the characters in ISO
 10646).  Alternative representation should be considered for these
 users, both for input and output.  Possible options for the
 representation of characters that can not be displayed include
 transliteration (a la CEN/TC304 or ISO TC46/SC2 ), RFC 1345 [RFC-
 1345] representative icons, or the WG2 short name (u+xxxx).

5: Open issues

 In addition to the issues declared out of scope and enumerated in
 section 2.1, the following issues are still open and will need to be
 addressed in other forums.  These issues: language tags, public
 identifiers such as URL names, and bi-directionality are briefly
 discussed below as they repeatedly encroached the discussion.

Weider, et. al. Informational [Page 14] RFC 2130 Character Set Workshop Report April 1997

5.1: Language tags

 Although the workshop decided not to explicitly address the so-called
 "CJK issue", a few members felt it was necessary to have some
 mechanism to address the problem of correct Han character display in
 the ISO-10646 issue, and that saying that it was a "font issue" would
 not suffice.
 The "CJK issue" refers to the extended discussion about "Han
 unification", the use of a single ISO-10646 codepoint to represent
 multiple national variants of a Chinese (Han) character.  ISO-10646
 can map uniquely to any single CJK national character set, but in the
 absence of additional  information an application can not display an
 ISO-10646 text using the proper national variants for that text.
 It was agreed that language tags would be sufficient to disambiguate
 unified characters. There was not, in our opinion, a significant
 technical difference between the use of different coded character
 sets with overlapping codepoints, and a single coded character set
 with language tags.  Either way, the application has sufficient
 information to display the text properly.
 It was observed that in contemporary usage of MIME charsets, the
 language is implied as well as the coded character set and the
 character encoding syntax.  We agreed that this is excessive
 overloading of MIME charsets.
 To specify the language used in a particular block of text, we
 recommend that the MIME tag "Content-Language" be used.  There are a
 number of questions about this approach that need to be worked out,
  1. Is Content-Language: actually suitable?
  2. Is there an overload between this function and the other

intended functions of Content-Language: as described in RFC

 -  What, precisely, does "Content-Language: zh-tw, ja, ko, zh-cn"
      mean in this context? We believe it means that, in drawing a
      Han character, the Taiwanese variant (presumably traditional
      Han) is preferred, followed by the Japanese, Korean, and
      mainland Chinese (presumably simplified Han) variants. It does
      *NOT* mean "mixed text containing Taiwanese, Japanese, Korean,
      and mainland Chinese text with all the national variants in
      each of these".
 Mixed CJK text, that simultaneously displays different variants
 occupying the same codepoint, requires language tags embedded in the
 data.  Ohta and Handa propose in RFC 1554 [RFC-1554] a MIME charset

Weider, et. al. Informational [Page 15] RFC 2130 Character Set Workshop Report April 1997

 using ISO-2022 shifts between multiple coded character sets; in
 effect this is an encoding that uses coded character sets for
 displaying the appropriate glyphs.
 There is some speculation that states that mixed CJK text is
 relatively infrequent, and that therefore it is acceptable to require
 that such text be represented using a rich text format that can
 support language tags.  In other words, that a simplifying assumption
 can be made for TEXT/PLAIN in  email using ISO-10646 that will not
 require multiple display representations for the same codepoint.  A
 mechanism such as RFC 1554 could address this need if it was
 important; although arguably RFC 1554 should really be identified as
 Note again that we recommend that support for language tagging SHOULD
 be built into new protocols, as this will become a critical component
 of the automated indexing and retrieval in information applications
 of the future.

5.2: Public identifiers

 There is a considerable demand from the user community for the
 ability to use non-ASCII characters in URL names, IMAP mailbox names,
 file names, and other public identifiers. This is still an open

5.3: Bi-directionality

 It was realized that a consistent framework for bi-directional text
 was needed but there was no attempt to work on it in this workshop.

6: Security Considerations

 There are no security considerations associated with character sets.

7: Conclusions

 This paper provides a conceptual framework and a set of
 recommendations which, if adopted, should provide a solid foundation
 for interoperability on the Internet. There are, however, a number of
 open issues which will need to be addressed to provide ever better
 use of text on the Internet.

Weider, et. al. Informational [Page 16] RFC 2130 Character Set Workshop Report April 1997

8: Recommendations

8.1: To the IAB

 There were a number of recommendations to the IAB about making the
 standards process more aware of the need for character set
 interoperability, and about the framework itself.
 A: The IAB should trigger the examination of all RFCs to determine
 the way  they handle character sets, and obsolete or annotate the
 RFCs where necessary.
 B: The IESG should trigger the recommendation of procedures to the
 RFC editor  to encourage RFCs to specify character set handling if
 they specify the  transmission of text.
 C: The IAB should trigger the production of a perspectives document
 on the  character set work that has gone on in the past and relate it
 to the current framework.
 D: Full ISO 10646 has a sufficiently broad repertoire, and scope for
 further extension, that it is sufficient for use in Internet
 Protocols (without excluding the use of existing alternatives).
 There is no need for specific development of character set standards
 for the Internet.
 E: The IAB should encourage the IRTF to create a research group to
 explore the open issues of character sets on the Internet. This group
 should set its sights much higher than this workshop did.
 F: The IANA (perhaps with the help of an IETF or IRTF group) should
 develop  procedures for the registration of new character sets for
 use in the Internet.
 G: Register UTF-8 as a Character Encoding Scheme for MIME.
 H: The current use of the "x-*" format for distinguishing
 experimental tags should be continued for private use among
 consenting parties. All other namespaces should be allocated by IANA.
 I: Application protocol RFCs SHOULD include a section on
 "multilingual Considerations".
 J: Application Protocol RFCs SHOULD indicate how to transfer 'on the
 wire' all characters in the character sets they use. They SHOULD also
 specify how to transfer other information that applications may need
 to know about the data.

Weider, et. al. Informational [Page 17] RFC 2130 Character Set Workshop Report April 1997

 K: The IESG should trigger a set of extensions to RFC 1522 to allow
 language tagging of the free text parts of message headers.

8.2: For new Internet protocols

 New protocols do not suffer from the need to be compatible with old
 7-bit pipes.  New protocol specifications SHOULD use ISO 10646 as the
 base charset unless there is an overriding need to use a different
 base character set.
 New protocols SHOULD use values from the IANA registries when
 referring to parameter values.  The way these values are carried in
 the protocols is protocol dependent; if the protocol uses RFC-822-
 like headers, the header names already in use SHOULD be used.
 For protocols with only a single choice for each component, the
 protocol  should use the most general specification and should be
 specified with reference to the registered value in the protocol
 Protocols SHOULD tag text streams with the language of the text.

8.3: For the registration of new character sets

 Ned Freed will be releasing a new MIME registration document in
 conjunction with this paper.

8.3.1: A definition table for a coded character set

 A definition table for a coded character set A must for each
 character C that is in the repertoire of A give:
 a) if C is present in ISO 10646, the code value (in hexadecimal form)
      for that character.
 b) If C is not present in ISO 10646, but may be constructed using ISO
      10646 combining characters, the series of code values (in
      hexadecimal form) used to construct that character.
 c) if C is not present in ISO 10646, a textual description of the
      character,  and a reference to its origin.

Weider, et. al. Informational [Page 18] RFC 2130 Character Set Workshop Report April 1997

8.3.2: A definition of a character encoding scheme

 A definition of a character encoding scheme consists of:
  1. A description of an algorithm which transforms every possible

sequence of octets to either a sequence of pairs <CCS, code

      value> or to the  error state "illegal octet sequence"
 -  Specifications, either by reference to CCS's registered by IANA or
    in text, of each CCS upon which this CES is based.

Weider, et. al. Informational [Page 19] RFC 2130 Character Set Workshop Report April 1997

Appendix A:

A-1: IETF Protocols

 The following list describes how various existing protocols handle
 multiple character set information.
      See 8.2. ESMTP makes it easy to negotiate the use of alternate
      language and encoding if it is needed.
      RFC 1522 forms an adequate framework for supporting text; UTF-8
      alone is not a possible solution, because the mail pathways are
      assumed to be 7-bit 'forever'. However, RFC 1522 should be
      extended to allow language tagging of the free text parts of
      message headers.
      Selection of charset parameters for Email text bodies is
      reasonably well covered by the charset= parameter on Text/* MIME
      types.  Language is defined by the Content-language header of
      RFC 1766.  Other information will have to be added using body
      part headers; due to the way MIME differentiates between body
      part headers and message headers, these will all have to have
      names starting with Content- .
      See 8.2. No strong tradition for negotiation of encoding in NNTP
    NetNews Messages
      These should be able to leverage off the mechanisms defined for
      Email.  One difference is that nearly all NNTP channels are 8-
      bit clean; some NNTP newsgroups have a tradition of using 8-bit
      charsets in both headers and bodies. Defining character set
      default on a per newsgroup basis might be a suitable approach.
      The identifiers carried as information about parties are already
      defined to be in UTF-8.

Weider, et. al. Informational [Page 20] RFC 2130 Character Set Workshop Report April 1997

      See 8.2. The common use of welcome banners in the login response
      means that there might be strong reason here to allow client and
      server to negotiate a language different from the default for
      greetings and error messages. This should be a simple protocol
      Many fileservers now how have the capability of using non-ASCII
      characters in filenames, while the "dir" and "get" commands of
      are defined in terms of US-ASCII only. One possible solution
      would be to define a "UTF-8" mode for the transfer of filenames
      and directory information; this would need to be a negotiated
      facility, with fallback to US-ASCII if not negotiated. The
      important point here is consistency between all implementations;
      a single charset is better here than the ability to handle
      multiple charsets.
 World Wide Web
      See 8.2. The single-shot stype of HTTP makes negotiation more
      complex than it would otherwise be.
      Internationalization of HTML [I18N] seems fairly well covered in
      the current "I18N" document. It needs review to see if it needs
      more specific details in order to carry application information
      apart from the language.
      URLs are "input identifiers", and powerful arguments should be
      made if they are ever to be anything but US-ASCII.
      IMAP's information objects are MIME Email objects, and therefore
      are able to use that standard's methods. However, IMAP folder
      names are local identifiers; there is strong reason to allow
      non-ASCII characters in these. A UTF-8 negotiation might be the
      most appropriate thing, however, UTF-8 is awkward to use.
      Unfortunately, UTF-7 isn't suitable because it conflicts with
      popular hierarchy delimiters. The most recent IMAP work in
      progress specification describes a modified UTF-7 which avoids
      this problem.

Weider, et. al. Informational [Page 21] RFC 2130 Character Set Workshop Report April 1997

      DNS names are the prime example of identifiers that need to stay
      in US-ASCII for global interoperability. However, some DNS
      information, in particular TXT records, may represent
      information (such as names) that is outside the ASCII range. A
      single solution is the best; problems resulting from UTF-8
      should be investigated.
      WHOIS++ version 1 is defined to use ISO 8859-1. The next version
      will use UTF-8. The currently designed changes will also allow
      the specification of individual attributes on attribute names;
      these will make the passing of application information about the
      values (such as language) easier. No immediate action seems
      This has been a stable protocol for so many years now that it
      seems unwise to suggest that it be modified. Furthermore,
      compatible extensions exist in RWHOIS and WHOIS++; modification
      should rather be made to these protocols than to the WHOIS
      protocol itself.
      This is a prime example of protocol where character set support
      is necessary and nonexistent. The current work in progress on
      character set negotiation in Telnet seems adequate to the task;
      the question of passing other application data that might be
      useful is still open.

A-2: Non-IETF protocols

 For these protocols, the IETF does not have any power to change them.
 However, the guidelines developed by the workshop may still be useful
 as input to the further development of the protocols.
 Gopher: Gopher, Gopher+
 Prospero (Archie)
 NFS:  Filesystem
 CORBA, Finger, GEDI, IRC, ISO 10160/1, Kerberos, LPR, RSTAT, RWhois,
 SGML, TFTP, X11, X.500, Z39.50

Weider, et. al. Informational [Page 22] RFC 2130 Character Set Workshop Report April 1997

Appendix B: Acronyms

 ASCII       American National Standard Code for Information Character
 CCS         Coded Character Sets
 CEN ENV     European Committee for Standardisation (CEN) European
               pre-standard (ENV)
 CES         Character Encoding Scheme
 CJK         Chinese Japanese Korean
 CORBA       Common Object Request Broker Architecture
 CTE         Content Transfer Encoding
 DNS         Domain Name Service
 ESMTP       Extended SMTP
 FTP         File Transfer Protocol
 HTML        Hypertext Transfer Protocol
 I18N        Internationalization (or 18 characters between the first
               (I) and last (n)character)
 IAB         Internet Activities Board
 IANA        Internet Assigned Numbers Authority
 IESG        Internet Engineering Steering Group
 IETF        Internet Engineering Task Force
 IMAP        Internet Message Access Protocol
 IRC         Internet Relay Chat
 IRTF        Internet Research Task Force
 ISI         Information Sciences Institute
 ISO         International Standards Organization
 MIME        Multipurpose Internet Mail Extensions
 NFS         Networked File Server
 NNTP        Net News Transfer Protocol
 POSIX       Portable Operating System Interface
 RFC         Request for Comments (Internet standards documents)
 RPC         Remote Procedure Call
 RSTAT       Remote Statistics
 RTCP        Real-Time Transport Control Protocol
 Rwhois      Referral Whois
 SGML        Standard Generalized Mark-up Language
 SMTP        Simple Mail Transfer Protocol
 TES         Transfer Encoding Syntax
 TFTP        Trivial File Transfer Protocol
 URL         Uniform Resource Locator
 UTF         Universal Text/Translation Format

Weider, et. al. Informational [Page 23] RFC 2130 Character Set Workshop Report April 1997

Appendix C: Glossary

 Bi-directionality -  A property of some text where text written right-
       to- left (Arabic or Hebrew) and text written left-to-right
       (e.g. Latin) are intermixed in one and the same line.
 Character - A single graphic symbol represented by sequence of one or
      more bytes.
 Character Encoding Scheme - The mapping from a coded character set to
      an encoding which may be more suitable for specific purpose. For
      example, UTF-8 is a character encoding scheme for ISO 10646.
 Character Set - An enumerated group of symbols (e.g., letters, numbers
      or glyphs)
 Coded Character Set - The mapping from a set of integers to the
      characters of a character set.
 Culture - Preferences in the display of text based on cultural norms,
      such as spelling and word choice.
 Language - The words and combinations of words the constitute a system
      of expression and communication among people with a shared
      history or set of traditions.
 Layout - Information needed to display text to the user, similar to
      the presentation layer in the ISO telecommunications model.
 Locale - The attributes of communication, such as language, character
      set and cultural conventions.
 On-the-wire -  The data that actually gets put into packets for
      transmission to other computers.
 Transfer Encoding Syntax -  The mapping from a coded character set
      which has been encoded in a Character Encoding Scheme to an
      encoding which may be more suitable for transmission using
      specific protocols. For example, Base64 is a transfer encoding

Weider, et. al. Informational [Page 24] RFC 2130 Character Set Workshop Report April 1997

Appendix D: References

[*] Non-ASCII character

[ASCII] ANSI X3.4:1986 "Coded Character Sets - 7 Bit American

   National Standard Code for Information Interchange (7-bit ASCII)"

[Base64] Freed, N., and N. Borenstein, "Multipurpose Internet

   Mail Extensions (MIME) Part One: Format of Internet Message
   Bodies", RFC 2045, November 1996.

[CEN] see for current status.

[HTML] Berners-Lee, T., and D. Connolly, "Hypertext Markup Language -

   2.0", RFC 1866, November 1995.

[HTTP] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext

   Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.

[I18N] Yergeau, F.,, "Internationalization of the Hypertext

   Markup Language", RFC 2070, January 1997.

[IANA] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC

   1700, ISI, October 1994.

[ISO-2022] ISO/IEC 2022:1994, "Information technology – Character

   Code Structure and Extension Techniques",  JTC1/SC2.

[ISO-7498] ISO/IEC 7498-1:1994, "Information technology - Open Systems

   Interconnection - Basic Reference Model:  The Basic Model".

[ISO-8859] Information Processing – 8-bit Single-Byte Coded Graphic

   Character Sets -- Part 1: Latin Alphabet no. 1,
   ISO 8859-1:1987(E). Part 2: Latin Alphabet no. 2, ISO 8859-2
   1987(E). Part 3: Latin Alphabet no. 3, ISO 8859-3:1988(E).
   Part 4: Latin Alphabet no. 4, ISO 8859-4, 1988(E). Part 5:
   Latin/Cyrillic Alphabet ISO 8859-5, 1988(E). Part 6:
   Latin/Arabic Alphabet, ISO 8859-6, 1987(E). Part 7: Latin/Greek
   Alphabet, ISO 8859-7, 1987(E). Part 8: Latin/Hebrew Alphabet, ISO
   8859-8-1988(E).Part 9: Latin Alphabet no. 5, ISO 8859-9, 1990(E).
   Part 10: Latin Alphabet no. 6, ISO 8859-10:1992(E).

[ISO-10646] ISO/IEC 10646-1:1993(E ), "Information technology –

   Universal Multiple-Octet Coded Character Set (UCS) -- Part 1:
   Architecture and Basic Multilingual Plane".  JTC1/SC2, 1993

Weider, et. al. Informational [Page 25] RFC 2130 Character Set Workshop Report April 1997

[MIME] See [Base64]

[POSIX] Institute of Electrical and Electronics Engineers. "IEEE

   standard interpretations for IEEE standard portable operating
   systems interface for computer environments". IEEE Std 1003.1
   -1988/Int, 1992 edition.  Sponsor, Technical Committee on Operating
   Systems of the IEEE Computer Society.  New York, NY: Institute of
   Electrical and Electronic Engineers, 1992.

RFC 1340 See [IANA]

[RFC-1345] Simonsen, K., "Character Mnemonics & Character Sets",

   RFC 1345, Rationel Alim Planlaegning, June 1992.

[RFC-1554] Ohta, M., and K. Handa, "ISO-2022-JP-2: Multilingual

   Extension of ISO-2022-JP",  Tokyo Institute of Technology, ETL,
   December 1993.

RFC 1642 See [UTF-7]

[RFC-1766] Alvestrad, H., "Tags for the Identification of Languages",

   RFC 1766, UNINETT, March 1995.

[RFC 1958] Carpenter, B. (ed.) "Architectural Principles of the

   Internet", RFC 1958, IAB, June 1996.

[SGML] ISO 8879:1986 "Information Processing - Text and Office Systems

  1. Standard Generalized Markup Language (SGML)"

[SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,

   August, 1982.

[Unicode] "The Unicode standard, version 2.0. Unicode Consortium.

   Reading, Mass.: Addison-Wesley Developers Press, 1996

[UTF-7] Goldsmith, D., and M. Davis, "UTF-7: A Mail Safe

   Transformation Format of Unicode", RFC 1642, Taligent, Inc., July

[UTF-8] International Standards Organization, Joint Technical

   Committee 1 (ISO/JTC1), "Amendment 2:1993, UCS Transformation
   Format 8 (UTF-8)", in ISO/IEC 10646-1:1993 Information technology
   - Universal Multiple-Octet Coded Character Set (UCS) -- Part 1:
   Architecture and Basic Multilingual Plane.  JTC1/SC2, 1993.

Weider, et. al. Informational [Page 26] RFC 2130 Character Set Workshop Report April 1997

Appendix E: Recommended reading

Alvestrand, H., "Tags for the Identification of Languages", RFC 1766,

   UNINETT, March 1995.

Alvestrand, H., "X.400 Use of Extended Character Sets", RFC 1502,

   SINTEF DELAB, August 1993.

Borenstein, N., "Implications of MIME for Internet Mail Gateways",

   RFC 1344, Bellcore, June 1992.

Freed, N., and N. Borenstein, "Multipurpose Internet

   Mail Extensions (MIME) Part One: Format of Internet Message
   Bodies", RFC 2045, November 1996.

Chernov, A., "Registration of a Cyrillic Character Set", RFC 1489,

   RELCOM Development Team, July 1993.

Choi, U., and K. Chan, "Korean Character Encoding for Internet

   Messages", RFC 1557, KAIST, December 1993.

Freed, N., and N. Borenstein, "Multipurpose Internet Mail Extensions

   (MIME) Part Two: Media Types", RFC 2046, November 1996.

Goldsmith, D., and M. Davis, "Transformation Format for Unicode",

   RFC 1642, Taligent, Inc., July 1994.

Goldsmith, D., and M. Davis, "Using Unicode with MIME", RFC 1641,

   Taligent, Inc., July 1994.

Jerman-Blazic, B. "Character handling in computer communication" in

   "user needs in information technology standards", Computer Weekly
   Professional service, eds. C.D. Evans, B.L. Meed & R.S. Walker,
   P.C. Butterworth Heineman, 1993, Oxford, Boston, p. 102-129.

Jerman-Blazic, B. "Tool supporting the internationalization of the

   generic network services", Computer Networks and ISDN Systems,
   No. 27 (1994), p. 429-435.

Jerman-Blazic, B., A. Gogala and D. Gabrijelcic, "Transparent language

   processing: A solution for internationalization of Internet
   services", The LISA Forum Newsletter, 5 (1996) p. 12-21

Lee, F., "HZ - A Data Format for Exchanging Files of Arbitrarily Mixed

   Chinese and ASCII Characters", RFC 1843, Stanford University,
   August 1995.

Weider, et. al. Informational [Page 27] RFC 2130 Character Set Workshop Report April 1997

McCarthy, J., "Arbitrary Character Sets", RFC 373, Stanford

   University, July 1972.

Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part Two:

   Message Header Extensions for Non-ASCII Text", RFC 1522,
   September 1993.  (Obsoleted by RFC 2047.)

Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part Three:

   Message Header Extensions for Non-ASCII Text", RFC 2047,
   University of Tennessee, November 1996.

Murai, J., Crispin, M., and E. von der Poel. "Japanese Character

   Encoding for Internet Messages", RFC 1468, Keio University &
   Panda Programming, June 1993.

Nussbacher, H., "Handling of Bi-directional Texts in MIME", Israeli

   Inter-University, December 1993.

Nussbacher, H., and Y. Bourvine, "Hebrew Character Encoding for

   Internet Messages", RFC 1555, Israeli Inter-University and
   Hebrew University, December 1993.

Ohta, M., "Character Sets ISO-10646 and ISO-10646-J-1", RFC 1815,

   Tokyo Institute of Technology, July 1995.

Postel, J., and J. Reynolds, "File Transfer Protocol (FTP)", STD 9,

   RFC 959, ISI, October 1985.

Postel, J., and J. Reynolds, "Telnet Protocol Specification", STD 8,

   RFC 854, ISI, May 1983.

Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1700,

   ISI, October 1994. p.100-117.

Rose, M., "The Internet Message", Prentice Hall, 1992.

Simonsen, K., "Character Mnemonics & Character Sets", RFC 1345,

   Rationel Almen Planlaegning, June 1992.

Unicode Consortium. "The Unicode standard, version 2.0. Reading,

   Mass.: Addison-Wesley Developers Press, 1996

Wei, U., "ASCII Printable Characters-Based Chinese Character

   Encoding for Internet Messages", RFC 1842, AsiInfo Services,
   Inc.,  August 1995.

Yergeau, F. "UTF-8, a transformation format of Unicode and ISO 10646",

   RFC 2044, ALIS Technologies, October 1996.

Weider, et. al. Informational [Page 28] RFC 2130 Character Set Workshop Report April 1997

Zhu, H.,, "Chinese Character Encoding for Internet Messages",

   RFC 1922, Tsinghua University,, March 1996.

Appendix F: Workshop attendee list

 These people were participants on the workshop mailing list.
 An * indicates that the person attended the workshop in person.
   Glenn Adams <>
 * Joan Aliprand <>
 * Harald Alvestrand <>
 * Ran Atkinson <>
 * Bert Bos <>
 * Brian Carpenter <>
 * Mark Crispin <>
   Makx Dekkers <>
   Robert Elz <>
   Patrik Faltstrom <>
 * Zhu Haifeng <>
   Keniichi Handa<>
   Olle Jarnefors <>
   Borka Jerman-Blazic <>
   John Klensin <>
 * Larry Masinter <>
 * Rick McGowan <>
 * Keith Moore <>
 * Lisa Moore <>
   Ruth Moulton <>
 * Cecilia Preston <>
 * Joyce K. Reynolds <>
 * Keld Simonsen <>
 * Gary Smith <>
 * Peter Svanberg <>
 * Chris Weider < >

Weider, et. al. Informational [Page 29] RFC 2130 Character Set Workshop Report April 1997

Appendix G: Authors' Addresses

 Chris Weider
 Microsoft Corp.
 1 Microsoft Way
 Redmond, WA 98052
 Cecilia Preston
 Preston & Lynch
 PO Box 8310
 Emeryville, CA 94662
 Keld Simonsen
 Freubjergvey 3
 DK-2100 Kxbenhavn X
 Harald T. Alvestrand
 P.O.Box 6883 Elgeseter
 Randall Atkinson
 cisco Systems
 170 West Tasman Drive
 San Jose, CA 95134-1706

Weider, et. al. Informational [Page 30] RFC 2130 Character Set Workshop Report April 1997

 Mark Crispin
 Networks & Distributed Computing
 University of Washington
 4545 15th Avenue NE
 Seattle, WA  98105-4527
 Peter Svanberg
 Dept. of Numberical Analysis and Computing Science (Nada)
 Royal Institute of Technology

Weider, et. al. Informational [Page 31]

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