draft-ietf-ltru-matching-00.txt   draft-ietf-ltru-matching-01.txt 
Network Working Group A. Phillips, Ed. Network Working Group A. Phillips, Ed.
Internet-Draft Quest Software Internet-Draft Quest Software
Expires: November 14, 2005 M. Davis, Ed. Expires: December 1, 2005 M. Davis, Ed.
IBM IBM
May 13, 2005 May 30, 2005
Matching Language Identifiers Matching Language Identifiers
draft-ietf-ltru-matching-00 draft-ietf-ltru-matching-01
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on November 14, 2005. This Internet-Draft will expire on December 1, 2005.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
This document describes different mechanisms for comparing and This document describes different mechanisms for comparing and
matching the tags for the identification of languages defined by [RFC matching the tags for the identification of languages defined by [RFC
3066bis] [1]. Possible algorithms for language negotiation and 3066bis] [1]. Possible algorithms for language negotiation and
content selection are described. Portions of this document obsolete content selection are described. This document obsoletes portions of
[RFC 3066] [19]. [RFC 3066] [19].
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Language Range . . . . . . . . . . . . . . . . . . . . . . 4 2. The Language Range . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Basic Language Range . . . . . . . . . . . . . . . . . . . 4 2.1 Basic Language Range . . . . . . . . . . . . . . . . . . . 4
2.1.1 Matching . . . . . . . . . . . . . . . . . . . . . . . 5 2.1.1 Matching . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 Lookup . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1.2 Lookup . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Extended Language Range . . . . . . . . . . . . . . . . . 6 2.2 Extended Language Range . . . . . . . . . . . . . . . . . 6
2.2.1 Extended Range Matching . . . . . . . . . . . . . . . 7 2.2.1 Extended Range Matching . . . . . . . . . . . . . . . 7
2.2.2 Extended Range Lookup . . . . . . . . . . . . . . . . 8 2.2.2 Extended Range Lookup . . . . . . . . . . . . . . . . 8
2.2.3 Scored Matching . . . . . . . . . . . . . . . . . . . 9 2.2.3 Scored Matching . . . . . . . . . . . . . . . . . . . 9
2.3 Meaning of Language Tags and Ranges . . . . . . . . . . . 10 2.3 Meaning of Language Tags and Ranges . . . . . . . . . . . 10
2.4 Choosing Between Alternate Matching Schemes . . . . . . . 11 2.4 Choosing Between Alternate Matching Schemes . . . . . . . 11
2.5 Considerations for Private Use Subtags . . . . . . . . . . 11 2.5 Considerations for Private Use Subtags . . . . . . . . . . 11
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 2.6 Length Considerations in Matching . . . . . . . . . . . . 12
4. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 15 4. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6. Character Set Considerations . . . . . . . . . . . . . . . . . 16 5. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6. Character Set Considerations . . . . . . . . . . . . . . . . . 17
7.1 Normative References . . . . . . . . . . . . . . . . . . . 17 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.2 Informative References . . . . . . . . . . . . . . . . . . 18 7.1 Normative References . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 18 7.2 Informative References . . . . . . . . . . . . . . . . . . 19
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 19
Intellectual Property and Copyright Statements . . . . . . . . 20 A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
Intellectual Property and Copyright Statements . . . . . . . . 21
1. Introduction 1. Introduction
Human beings on our planet have, past and present, used a number of Human beings on our planet have, past and present, used a number of
languages. There are many reasons why one would want to identify the languages. There are many reasons why one would want to identify the
language used when presenting or requesting information. language used when presenting or requesting information.
Information about a user's language preferences commonly needs to be Information about a user's language preferences commonly needs to be
identified so that appropriate processing can be applied. For identified so that appropriate processing can be applied. For
example, the user's language preferences in a browser can be used to example, the user's language preferences in a browser can be used to
select web pages appropriately. A choice of language preference can select web pages appropriately. A choice of language preference can
also be used to select among tools (such as dictionaries) to assist also be used to select among tools (such as dictionaries) to assist
in the processing or understanding of content in different languages. in the processing or understanding of content in different languages.
Given a set of language identifiers, such as those defined in Given a set of language identifiers, such as those defined in
RFC3066bis, various mechanisms can be envisioned for performing RFC3066bis [1], various mechanisms can be envisioned for performing
language negotiation and tag matching. The suitability of a language negotiation and tag matching. The suitability of a
particular mechanism to a particular application depends on the needs particular mechanism to a particular application depends on the needs
of that application. of that application.
This document defines language ranges and syntax for specifying user This document defines language ranges and syntax for specifying user
preferences in a request for language content. It also specifies a preferences in a request for language content. It also specifies
default algorithm for matching language ranges to content (language various schemes and mechanisms that can be used with language ranges
tags), as well as alternate mechanisms suitable for certain when matching or filtering content based on language tags.
applications.
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119] [5]. document are to be interpreted as described in RFC 2119 [5].
2. The Language Range 2. The Language Range
Language Tags are used to identify the language of some information Language Tags are used to identify the language of some information
item or content. Applications that use language tags are often faced item or content. Applications that use language tags are often faced
with the problem of identifying sets of content that share certain with the problem of identifying sets of content that share certain
language attributes. For example, HTTP 1.1 [10] describes language language attributes. For example, HTTP 1.1 [10] describes language
ranges in its discussion of the Accept-Language header (Section ranges in its discussion of the Accept-Language header (Section
14.4), which is used for selecting content from servers based on the 14.4), which is used for selecting content from servers based on the
language of that content. language of that content.
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then this user will also understand all languages with tags for which then this user will also understand all languages with tags for which
this tag is a prefix. The prefix rule simply allows the use of this tag is a prefix. The prefix rule simply allows the use of
prefix tags if this is the case. prefix tags if this is the case.
When working with tags and ranges you should also note the following: When working with tags and ranges you should also note the following:
1. Private-use and Extension subtags are normally orthogonal to 1. Private-use and Extension subtags are normally orthogonal to
language tag fallback. Implementations should ignore language tag fallback. Implementations should ignore
unrecognized private-use and extension subtags when performing unrecognized private-use and extension subtags when performing
language tag fallback. Since these subtags are always at the end language tag fallback. Since these subtags are always at the end
of the sequence of subtags, they naturally fall out of the of the sequence of subtags, they don't normally interfere with
default fallback pattern (above). Thus a request to match the the use of prefixes for matching in the schemes described below.
tag "en-US-boont-x-1943" would produce exactly the same
information content as the example above.
2. Implementations that choose not to interpret one or more private- 2. Implementations that choose not to interpret one or more private-
use or extension subtags should not remove or modify these use or extension subtags should not remove or modify these
extensions in content that they are processing. When a language extensions in content that they are processing. When a language
tag instance is to be used in a specific, known protocol, and is tag instance is to be used in a specific, known protocol, and is
not being passed through to other protocols, language tags may be not being passed through to other protocols, language tags may be
filtered to remove subtags and extensions that are not supported filtered to remove subtags and extensions that are not supported
by that protocol. This should be done with caution, since it it by that protocol. This should be done with caution, since it is
is removing information that may be relevant if services on the removing information that may be relevant if services on the
other end of the protocol would make use of that information. other end of the protocol would make use of that information.
3. Some applications of language tags may want or need to consider 3. Some applications of language tags may want or need to consider
extensions and private-use subtags when matching tags. If extensions and private-use subtags when matching tags. If
extensions and private-use subtags are included in a matching extensions and private-use subtags are included in a matching or
process that utilizes the default fallback mechanism, then the filtering process that utilizes the one of the schemes described
implementation should canonicalize the language tags and/or in this document, then the implementation should canonicalize the
ranges before performing the matching. Note that language tag language tags and/or ranges before performing the matching. Note
processors that claim to be "well-formed" processors as defined that language tag processors that claim to be "well-formed"
in [1] generally fall into this category. processors as defined in [1] generally fall into this category.
There are two matching schemes that are commonly associated with There are two matching schemes that are commonly associated with
basic language ranges: matching and lookup. basic language ranges: matching and lookup.
2.1.1 Matching 2.1.1 Matching
Language tag matching is used to select all content that matches a Language tag matching is used to select all content that matches a
given prefix. In matching, the language range represents the least given prefix. In matching, the language range represents the least
specific tag which is an acceptable match and every piece of content specific tag which is an acceptable match and every piece of content
that matches is returned. that matches is returned.
For example, if an application is applying a style to all content in For example, if an application is applying a style to all content in
a web page in a particular language, it might use language tag a web page in a particular language, it might use language tag
matching to perform the matching. matching to select the content to which the style is applied.
A language-range matches a language-tag if it exactly equals the tag, A language-range matches a language-tag if it exactly equals the tag,
or if it exactly equals a prefix of the tag such that the first or if it exactly equals a prefix of the tag such that the first
character following the prefix is "-". (That is, the language-range character following the prefix is "-". (That is, the language-range
"en-de" matches the language tag "en-DE-boont", but not the language "en-de" matches the language tag "en-DE-boont", but not the language
tag "en-Deva".) tag "en-Deva".)
The special range "*" matches any tag. A protocol which uses The special range "*" matches any tag. A protocol which uses
language ranges may specify additional rules about the semantics of language ranges may specify additional rules about the semantics of
"*"; for instance, HTTP/1.1 specifies that the range "*" matches only "*"; for instance, HTTP/1.1 specifies that the range "*" matches only
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Prefix matching using a Basic Language Range, as described above, is Prefix matching using a Basic Language Range, as described above, is
not always the most appropriate way to access the information not always the most appropriate way to access the information
contained in language tags when selecting or filtering content. Some contained in language tags when selecting or filtering content. Some
applications may wish to define a more granular matching scheme and applications may wish to define a more granular matching scheme and
such a matching scheme requires the ability to specify the various such a matching scheme requires the ability to specify the various
attributes of a language tag in the language range. An extended attributes of a language tag in the language range. An extended
language range can be represented by the following ABNF: language range can be represented by the following ABNF:
extended-language-range = grandfathered / privateuse / range extended-language-range = grandfathered / privateuse / range
range = ( lang [ "-" script ] [ "-" region ] *( "-" variant ) range = ( lang [ "-" script ] [ "-" region ] *( "-" variant )
[ "-" privateuse ] ) [ "-" privateuse ] )
lang = ( 2*8ALPHA *[ *( "-" extlang ] ) ) / "*" lang = ( 2*8ALPHA *[ "-" extlang ] ) / "*"
extlang = 3ALPHA / "*" extlang = 3ALPHA / "*"
script = 4ALPHA / "*" script = 4ALPHA / "*"
region = 2ALPHA / 3DIGIT / "*" region = 2ALPHA / 3DIGIT / "*"
variant = 5*8alphanum / ( DIGIT 3alphanum ) / "*" variant = 5*8alphanum / ( DIGIT 3alphanum ) / "*"
privateuse = ( "x" / "X" ) 1*( "-" ( 1*8alphanum ) ) privateuse = ( "x" / "X" ) 1*( "-" ( 1*8alphanum ) )
grandfathered = 1*3ALPHA 1*2( "-" ( 2*8alphanum ) ) grandfathered = 1*3ALPHA 1*2( "-" ( 2*8alphanum ) )
alphanum = ( ALPHA / DIGIT ) alphanum = ( ALPHA / DIGIT )
In an extended language range, the identifier takes the form of a In an extended language range, the identifier takes the form of a
series of subtags which must consist of well-formed subtags or the series of subtags which must consist of well-formed subtags or the
special subtag "*". For example, the language range "en-*-US" special subtag "*". For example, the language range "en-*-US"
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subtag). Extended Range Matching is an extension of basic matching subtag). Extended Range Matching is an extension of basic matching
(Section 2.1.1): the language range represents the least specific tag (Section 2.1.1): the language range represents the least specific tag
which is an acceptable match. which is an acceptable match.
By default all extensions and their subtags are ignored for extended By default all extensions and their subtags are ignored for extended
language range matching. language range matching.
Private use subtags may be specified in the language range and MUST Private use subtags may be specified in the language range and MUST
NOT be ignored when matching. NOT be ignored when matching.
Subtags not specified, included those at the end of the language Subtags not specified, including those at the end of the language
range, are assigned the value "*". This makes each range into a range, are assigned the value "*". This makes each range into a
prefix much like that used in basic language range matching. For prefix much like that used in basic language range matching. For
example, the extended language range "zh-*-CN" matches all of the example, the extended language range "zh-*-CN" matches all of the
following tags because the unspecified variant field is expanded to following tags because the unspecified variant field is expanded to
"*": "*":
zh-Hant-CN zh-Hant-CN
zh-CN zh-CN
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A language tag defines a language as spoken (or written, signed or A language tag defines a language as spoken (or written, signed or
otherwise signaled) by human beings for communication of information otherwise signaled) by human beings for communication of information
to other human beings. to other human beings.
If a language tag B contains language tag A as a prefix, then B is If a language tag B contains language tag A as a prefix, then B is
typically "narrower" or "more specific" than A. For example, "zh- typically "narrower" or "more specific" than A. For example, "zh-
Hant-TW" is more specific than "zh-Hant". Hant-TW" is more specific than "zh-Hant".
This relationship is not guaranteed in all cases: specifically, This relationship is not guaranteed in all cases: specifically,
languages that begin with the same sequence of subtags are NOT languages that begin with the same sequence of subtags are NOT
guaranteed to be mutually intelligible, although they may be. For guaranteed to be mutually intelligible, although they may be.
example, the tag "az" shares a prefix with both "az-Latn"
For example, the tag "az" shares a prefix with both "az-Latn"
(Azerbaijani written using the Latin script) and "az-Cyrl" (Azerbaijani written using the Latin script) and "az-Cyrl"
(Azerbaijani written using the Cyrillic script). A person fluent in (Azerbaijani written using the Cyrillic script). A person fluent in
one script may not be able to read the other, even though the text one script may not be able to read the other, even though the text
might be otherwise identical. Content tagged as "az" most probably might be otherwise identical. Content tagged as "az" most probably
is written in just one script and thus might not be intelligible to a is written in just one script and thus might not be intelligible to a
reader familiar with the other script. reader familiar with the other script.
The relationship between the tag and the information it relates to is Variant subtags in particular seem to represent specific divisions in
defined by the standard describing the context in which it appears. mutual understanding, since they often encode dialects or other
Accordingly, this section can only give possible examples of its idiosyncratic variations within a language.
usage.
The relationship between the language tag and the information it
relates to is defined by the standard describing the context in which
it appears. Accordingly, this section can only give possible
examples of its usage.
o For a single information object, the associated language tags o For a single information object, the associated language tags
might be interpreted as the set of languages that is required for might be interpreted as the set of languages that is required for
a complete comprehension of the complete object. Example: Plain a complete comprehension of the complete object. Example: Plain
text documents. text documents.
o For an aggregation of information objects, the associated language o For an aggregation of information objects, the associated language
tags could be taken as the set of languages used inside components tags could be taken as the set of languages used inside components
of that aggregation. Examples: Document stores and libraries. of that aggregation. Examples: Document stores and libraries.
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that intend to use or exchange language tags that use them and great that intend to use or exchange language tags that use them and great
caution should be used in employing them in content or protocols caution should be used in employing them in content or protocols
intended for general use. Private-use subtags are simply useless for intended for general use. Private-use subtags are simply useless for
information exchange without prior arrangement. information exchange without prior arrangement.
The value and semantic meaning of private-use tags and of the subtags The value and semantic meaning of private-use tags and of the subtags
used within such a language tag are not defined. Matching private used within such a language tag are not defined. Matching private
use tags using language ranges or extended language ranges may result use tags using language ranges or extended language ranges may result
in unpredictable content being returned. in unpredictable content being returned.
2.6 Length Considerations in Matching
Although there is no upper bound on the number of subtags in a
language tag and it is possible to envision quite long and complex
subtag sequences, in practice these are rare because of the various
considerations discussed in Section 2.1.1 of [1].
A matching implementation MAY choose not to support the storage or
matching of language tags and ranges which exceed a specified length.
Any such limitation SHOULD be clearly documented, and such
documentation SHOULD include the disposition of any longer tags or
ranges (for example, whether an error value is generated or the
language tag is truncated). If truncation is permitted it must not
permit a subtag to be divided, since this changes the semantics of
the tag or range being matched and may result in false positives or
negatives. Implementations that restrict storage should consider
removing extensions before matching. A protocol that allows tags or
ranges to be truncated at an arbitrary limit, without giving any
indication of what that limit is, has the potential for causing harm
by changing the meaning of values in substantial ways.
In practice, tags and ranges are limited to a sequence of four
subtags, and thus a maximum length of 26 characters (excluding any
extensions or private use sequences). This is because subtags are
limited to a length of eight characters and the extlang, script, and
region subtags are additionally limited to even fewer characters. In
addition, the Language Subtag Registry provides guidance on the use
of subtags (via fields such as Suppress-Script and Recommended-
Prefix) which further limit useful combination of subtags in a
language tag or range.
Longer tags are possible. The longest practical tags (excluding
extensions) could have a length of up to 58 characters, as shown
below. Implementations MUST be able to handle matching tags of this
length. Support for tags and ranges of up to 64 characters is
RECOMMENDED. Implementations MAY support longer tags, including
matching extensive sets of private use or extension subtags.
Here is how the 58-character length of the longest practical tag
(excluding extensions) is derived:
language = 3
extlang1 = 4 (currently undefined)
extlang2 = 4 (unlikely)
script = 5
region = 4 (UN M.49)
variant = 9
variant = 9 (unlikely)
private use 1 = 11
private use 2 = 9
total = 58 characters
Figure 4: Derviation of the Longest Tag
3. IANA Considerations 3. IANA Considerations
This document presents no new or existing considerations for IANA. This document presents no new or existing considerations for IANA.
4. Changes 4. Changes
This is the first version of this document. Changes from the This is the first version of this document.
reference work (draft-phillips-matching-00) are too numerious to
record. The following changes were put into this document since draft-00:
Fixed text in the introduction that is no longer accurate.
Specifically, there no longer is a default matching algorithm.
(A.Phillips)
Fixed text in Section 2.1 which incorrectly discussed the default
fallback mechanism. (A.Phillips)
Minor changes to Section 2.3, in particular, the addition of the
'variant' paragraph and some tidying of the text. (A.Phillips)
Fixed a minor glitch in the ABNF caused by taking the output of
Bill Fenner's parser and not looking too closely at it (M. Patton)
Fixed some minor reference problems. (M.Patton)
Added Section 2.6 on length considerations in matching.
(R.Presuhn)
5. Security Considerations 5. Security Considerations
The only security issue that has been raised with language tags since The only security issue that has been raised with language tags since
the publication of RFC 1766, which stated that "Security issues are the publication of RFC 1766, which stated that "Security issues are
believed to be irrelevant to this memo", is a concern with language believed to be irrelevant to this memo", is a concern with language
ranges used in content negotiation - that they may be used to infer ranges used in content negotiation - that they may be used to infer
the nationality of the sender, and thus identify potential targets the nationality of the sender, and thus identify potential targets
for surveillance. for surveillance.
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The following people (in alphabetical order) contributed to this The following people (in alphabetical order) contributed to this
document or to RFCs 1766 and 3066: document or to RFCs 1766 and 3066:
Glenn Adams, Harald Tveit Alvestrand, Tim Berners-Lee, Marc Blanchet, Glenn Adams, Harald Tveit Alvestrand, Tim Berners-Lee, Marc Blanchet,
Nathaniel Borenstein, Eric Brunner, Sean M. Burke, Jeremy Carroll, Nathaniel Borenstein, Eric Brunner, Sean M. Burke, Jeremy Carroll,
John Clews, Jim Conklin, Peter Constable, John Cowan, Mark Crispin, John Clews, Jim Conklin, Peter Constable, John Cowan, Mark Crispin,
Dave Crocker, Martin Duerst, Michael Everson, Doug Ewell, Ned Freed, Dave Crocker, Martin Duerst, Michael Everson, Doug Ewell, Ned Freed,
Tim Goodwin, Dirk-Willem van Gulik, Marion Gunn, Joel Halpren, Tim Goodwin, Dirk-Willem van Gulik, Marion Gunn, Joel Halpren,
Elliotte Rusty Harold, Paul Hoffman, Richard Ishida, Olle Jarnefors, Elliotte Rusty Harold, Paul Hoffman, Richard Ishida, Olle Jarnefors,
Kent Karlsson, John Klensin, Alain LaBonte, Eric Mader, Keith Moore, Kent Karlsson, John Klensin, Alain LaBonte, Eric Mader, Keith Moore,
Chris Newman, Masataka Ohta, George Rhoten, Markus Scherer, Keld Jorn Chris Newman, Masataka Ohta, Michael S. Patton, Randy Presuhn, George
Simonsen, Thierry Sourbier, Otto Stolz, Tex Texin, Andrea Vine, Rhys Rhoten, Markus Scherer, Keld Jorn Simonsen, Thierry Sourbier, Otto
Weatherley, Misha Wolf, Francois Yergeau and many, many others. Stolz, Tex Texin, Andrea Vine, Rhys Weatherley, Misha Wolf, Francois
Yergeau and many, many others.
Very special thanks must go to Harald Tveit Alvestrand, who Very special thanks must go to Harald Tveit Alvestrand, who
originated RFCs 1766 and 3066, and without whom this document would originated RFCs 1766 and 3066, and without whom this document would
not have been possible. Special thanks must go to Michael Everson, not have been possible. Special thanks must go to Michael Everson,
who has served as language tag reviewer for almost the complete who has served as language tag reviewer for almost the complete
period since the publication of RFC 1766. Special thanks to Doug period since the publication of RFC 1766. Special thanks to Doug
Ewell, for his production of the first complete subtag registry, and Ewell, for his production of the first complete subtag registry, and
his work in producing a test parser for verifying language tags. his work in producing a test parser for verifying language tags.
For this particular document, John Cowan originated the scheme For this particular document, John Cowan originated the scheme
 End of changes. 

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