draft-duerst-iri-01.txt   draft-duerst-iri-02.txt 

Network Working Group M. Duerst Network Working Group M. Duerst
Internet-Draft W3C/Keio University Internet-Draft W3C
Expires: December 30, 2002 M. Suignard Expires: May 4, 2003 M. Suignard
Microsoft Corporation Microsoft Corporation
July 1, 2002 November 3, 2002
Internationalized Resource Identifiers (IRI) Internationalized Resource Identifiers (IRIs)
draft-duerst-iri-01 draft-duerst-iri-02
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
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
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
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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 http:// The list of current Internet-Drafts can be accessed at http://
www.ietf.org/ietf/1id-abstracts.txt. 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 December 30, 2002. This Internet-Draft will expire on May 4, 2003.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved. Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract Abstract
This document defines a new protocol element, the Internationalized This document defines a new protocol element, the Internationalized
Resource Identifier (IRI), as a complement to the URI [RFC2396]. An Resource Identifier (IRI), as a complement to the URI [RFC2396]. An
IRI is a sequence of characters from the Universal Character Set IRI is a sequence of characters from the Universal Character Set
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distinction and to avoid incompatibilities with existing software. distinction and to avoid incompatibilities with existing software.
Guidelines for the use and deployment of IRIs in various protocols, Guidelines for the use and deployment of IRIs in various protocols,
formats, and software components that now deal with URIs are formats, and software components that now deal with URIs are
provided. provided.
NOTE NOTE
This document is a product of the Internationalization Working Group This document is a product of the Internationalization Working Group
(I18N WG) of the World Wide Web Consortium (W3C). For general (I18N WG) of the World Wide Web Consortium (W3C). For general
discussion, please use the www-i18n-comments@w3.org mailing list discussion, please use the www-international@w3.org mailing list
(publicly archived at http://lists.w3.org/Archives/Public/www-i18n- (publicly archived at http://lists.w3.org/Archives/Public/www-
comments/). For more information on the topic of this document, international/). For more information on the topic of this document,
please also see [W3CIRI] and [Duer01]. please also see [W3CIRI] and [Duer01].
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Overview and Motivation . . . . . . . . . . . . . . . . . . . 4 1.1 Overview and Motivation . . . . . . . . . . . . . . . . . . . 4
1.2 Applicability . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Applicability . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4 Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. IRI Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. IRI Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1 Summary of IRI Syntax . . . . . . . . . . . . . . . . . . . . 6 2.1 Summary of IRI Syntax . . . . . . . . . . . . . . . . . . . . 7
2.2 ABNF for IRI References and IRIs . . . . . . . . . . . . . . . 6 2.2 ABNF for IRI References and IRIs . . . . . . . . . . . . . . . 7
2.3 IRI Equivalence and Normalization . . . . . . . . . . . . . . 9 2.3 IRI Equivalence and Normalization . . . . . . . . . . . . . . 10
3. Relationship between IRIs and URIs . . . . . . . . . . . . . . 10 3. Relationship between IRIs and URIs . . . . . . . . . . . . . . 12
3.1 Mapping of IRIs to URIs . . . . . . . . . . . . . . . . . . . 11 3.1 Mapping of IRIs to URIs . . . . . . . . . . . . . . . . . . . 12
3.2 Converting URIs to IRIs . . . . . . . . . . . . . . . . . . . 12 3.2 Converting URIs to IRIs . . . . . . . . . . . . . . . . . . . 14
4. Bidirectional IRIs for Right-to-left Languages . . . . . . . . 13 4. Bidirectional IRIs for Right-to-left Languages . . . . . . . . 15
4.1 Bidi IRI Structure . . . . . . . . . . . . . . . . . . . . . . 14 4.1 Logical Storage and Visual Presentation . . . . . . . . . . . 15
4.2 Visual Rendering of Bidi IRIs . . . . . . . . . . . . . . . . 14 4.2 Bidi IRI Structure . . . . . . . . . . . . . . . . . . . . . . 16
4.3 Input of Bidi IRIs . . . . . . . . . . . . . . . . . . . . . . 15 4.3 Input of Bidi IRIs . . . . . . . . . . . . . . . . . . . . . . 17
5. Use of IRIs . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.4 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.1 Limitations on UCS Character Allowed in IRI . . . . . . . . . 15 5. Use of IRIs . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.2 Software Interfaces and Protocols . . . . . . . . . . . . . . 16 5.1 Limitations on UCS Characters Allowed in IRIs . . . . . . . . 19
5.3 Format of URIs and IRIs in Documents and Protocols . . . . . . 17 5.2 Software Interfaces and Protocols . . . . . . . . . . . . . . 20
5.4 Relative IRI References . . . . . . . . . . . . . . . . . . . 17 5.3 Format of URIs and IRIs in Documents and Protocols . . . . . . 20
6. URI/IRI Processing Guidelines (informative) . . . . . . . . . 17 5.4 Relative IRI References . . . . . . . . . . . . . . . . . . . 21
6.1 URI/IRI Software Interfaces . . . . . . . . . . . . . . . . . 18 6. URI/IRI Processing Guidelines (informative) . . . . . . . . . 21
6.2 URI/IRI Entry . . . . . . . . . . . . . . . . . . . . . . . . 18 6.1 URI/IRI Software Interfaces . . . . . . . . . . . . . . . . . 21
6.3 URI/IRI Generation . . . . . . . . . . . . . . . . . . . . . . 19 6.2 URI/IRI Entry . . . . . . . . . . . . . . . . . . . . . . . . 21
6.4 URI/IRI Selection . . . . . . . . . . . . . . . . . . . . . . 19 6.3 URI/IRI Transfer Between Applications . . . . . . . . . . . . 22
6.5 Display of URIs/IRIs . . . . . . . . . . . . . . . . . . . . . 20 6.4 URI/IRI Generation . . . . . . . . . . . . . . . . . . . . . . 23
6.6 Interpretation of URIs and IRIs . . . . . . . . . . . . . . . 20 6.5 URI/IRI Selection . . . . . . . . . . . . . . . . . . . . . . 23
6.7 Upgrading Strategy . . . . . . . . . . . . . . . . . . . . . . 21 6.6 Display of URIs/IRIs . . . . . . . . . . . . . . . . . . . . . 24
7. Security Considerations . . . . . . . . . . . . . . . . . . . 21 6.7 Interpretation of URIs and IRIs . . . . . . . . . . . . . . . 24
8. Change log . . . . . . . . . . . . . . . . . . . . . . . . . . 22 6.8 Upgrading Strategy . . . . . . . . . . . . . . . . . . . . . . 25
9. Acknowlegdements . . . . . . . . . . . . . . . . . . . . . . . 23 7. Security Considerations . . . . . . . . . . . . . . . . . . . 26
References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 8. Change log . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 26 8.1 Changes from -01 to -02 . . . . . . . . . . . . . . . . . . . 27
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 27 8.2 Changes from -00 to -01 . . . . . . . . . . . . . . . . . . . 27
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27
Normative References . . . . . . . . . . . . . . . . . . . . . 28
Non-normative References . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 31
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 32
1. Introduction 1. Introduction
1.1 Overview and Motivation 1.1 Overview and Motivation
A URI is defined in [RFC2396] as a sequence of characters chosen from A URI is defined in [RFC2396] as a sequence of characters chosen from
a limited subset of the repertoire of US-ASCII characters. a limited subset of the repertoire of US-ASCII characters.
The characters in URIs are frequently used for representing words of The characters in URIs are frequently used for representing words of
natural languages. Such usage has many advantages: such URIs are natural languages. Such usage has many advantages: such URIs are
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1.2 Applicability 1.2 Applicability
IRIs are designed to be compatible with recent recommendations on URI IRIs are designed to be compatible with recent recommendations on URI
syntax [RFC2718]. The compatibility is provided by providing a well syntax [RFC2718]. The compatibility is provided by providing a well
defined and deterministic mapping from the IRI character sequence to defined and deterministic mapping from the IRI character sequence to
the functionally equivalent URI character sequence. Practical use of the functionally equivalent URI character sequence. Practical use of
IRIs (or IRI references) in place of URIs (or URI references) depends IRIs (or IRI references) in place of URIs (or URI references) depends
on the following conditions being met: on the following conditions being met:
a. The protocol or format element used should be explicitly a) The protocol or format element used should be explicitly
designated to carry IRIs. That is, the intent is not to designated to carry IRIs. That is, the intent is not to
introduce IRIs into contexts that are not defined to accept introduce IRIs into contexts that are not defined to accept
them. For example, XML schema [XMLSchema] has an explicit type them. For example, XML schema [XMLSchema] has an explicit type
"anyURI" that designates the use of IRIs. "anyURI" that designates the use of IRIs.
b. The protocol or format carrying the IRIs must have a mechanism b) The protocol or format carrying the IRIs should have a
to represent the wide range of characters used in IRIs, either mechanism to represent the wide range of characters used in
natively or by some protocol- or format-specific escaping IRIs, either natively or by some protocol- or format-specific
mechanism (for example numeric character references in [XML1]). escaping mechanism (for example numeric character references in
[XML1]).
c. Either by definition for all the URIs of a specific URI c) Either by definition for all the URIs of a specific URI scheme,
scheme, or at least for some specific URIs, the encoding of or a specific part of a URI (Reference), such as the fragment
non-ASCII characters has to be based on UTF-8. For new URI identifier, or at least for some specific URIs of a given
schemes, this is recommended in [RFC2718]. This allows IRIs to scheme, the encoding of non-ASCII characters should be based on
be used with the URN syntax [RFC2141] as well as recent URL UTF-8. For new URI schemes, this is recommended in [RFC2718].
scheme definitions based on UTF-8, such as IMAP URLs [RFC2192] This allows IRIs to be used with the URN syntax [RFC2141] as
and POP URLs [RFC2384]. This condition may also apply to only well as recent URL scheme definitions based on UTF-8, such as
a piece of a URI (reference), such as the fragment identifier. IMAP URLs [RFC2192] and POP URLs [RFC2384].
In cases and for pieces where an encoding other than UTF-8 is used, In cases and for pieces where an encoding other than UTF-8 is used,
and for raw binary data encoded in URIs (see [RFC2397]), the octets and for raw binary data encoded in URIs (see [RFC2397]), the octets
have to be %-escaped. In these situations, the ability of IRIs to have to be %-escaped. In these situations, the ability of IRIs to
directly represent a wide character repertoire cannot be used. directly represent a wide character repertoire cannot be used.
For example, for a document with a URI of http://www.example.org/
r%C3%A9sum%C3%A9.html, it is possible to construct a corresponding
IRI (in XML notation): http://www.example.org/résumé.html
(é stands for the e-acute character, and is the UTF-8 encoded
and escaped representation of that character). On the other hand,
for a document with an URI of http://www.example.org/r%e9sum%e9.html,
the escaped octets cannot be converted to actual characters in an
IRI, because the escaping is based on iso-8859-1 rather than UTF-8.
1.3 Definitions 1.3 Definitions
The following definitions are used in this document; they follow the The following definitions are used in this document; they follow the
terms in [RFC2130], [RFC2277] and [ISO10646]: terms in [RFC2130], [RFC2277] and [ISO10646]:
character: A member of a set of elements used for the character: A member of a set of elements used for the
organization, control, or representation of data. For example, organization, control, or representation of data. For example,
"LATIN CAPITAL LETTER A" names a character. "LATIN CAPITAL LETTER A" names a character.
octet: an ordered sequence of eight bits considered as a unit octet: an ordered sequence of eight bits considered as a unit
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method of (unambiguously) converting a sequence of octets into method of (unambiguously) converting a sequence of octets into
a sequence of characters. a sequence of characters.
code point: A placeholder for a character in a character encoding, code point: A placeholder for a character in a character encoding,
for example to encode additional characters in future versions for example to encode additional characters in future versions
of the character encoding. of the character encoding.
charset: The name of a parameter or attribute used to identify a charset: The name of a parameter or attribute used to identify a
character encoding. character encoding.
UCS: Universal Character Set; the coded character set defined by
[ISO10646] and [UNIV3].
IRI reference: The term "IRI reference" denotes the common usage
of an internationalized resource identifier. An IRI reference
may be absolute or relative, and may have additional
information attached in the form of a fragement identifier.
However, the "IRI" that results from such a reference only
includes the absolute IRI after fragment identifier (if any) is
removed and after any relative IRI is resolved to its absolute
form.
1.4 Notation
In text, characters outside US-ASCII are sometimes referenced by
using a prefix of 'U+', followed by four to six hexadecimal digits.
To represent characters outside US-ASCII in examples, this document
uses two notations called 'XML Notation' and 'Bidi Notation'.
XML Notation uses leading '&#x', trailing ';', and the hexadecimal
number of the character in the UCS in between. Example: Я stands
for CYRILLIC CAPITAL LETTER YA. In this notation, an actual '&' is
denoted by '&amp'.
Bidi Notation is used for bidirectional examples: lower case ASCII
letters stand for Latin letters or other letters that are written
left-to-right, whereas upper case letters represent Arabic or Hebrew
letters that are written right-to-left.
2. IRI Syntax 2. IRI Syntax
This section defines the syntax of Internationalized Resource This section defines the syntax of Internationalized Resource
Identifiers (IRIs). Identifiers (IRIs).
As with URIs, an IRI is defined as a sequence of characters, not as a As with URIs, an IRI is defined as a sequence of characters, not as a
sequence of octets. This definition accommodates the fact that IRIs sequence of octets. This definition accommodates the fact that IRIs
may be written on paper or read over the radio as well as being may be written on paper or read over the radio as well as being
transmitted over the network. The same IRI may be represented as transmitted over the network. The same IRI may be represented as
different sequences of octets in different protocols or documents if different sequences of octets in different protocols or documents if
these protocols or documents use different character encodings and/or these protocols or documents use different character encodings (and/
transfer encodings. Using the same character encoding as the or transfer encodings). Using the same character encoding as the
containing protocol or document assures that the characters in the containing protocol or document assures that the characters in the
IRI can be handled (searched, converted, displayed,...) in the same IRI can be handled (searched, converted, displayed,...) in the same
way as the rest of the protocol or document. way as the rest of the protocol or document.
2.1 Summary of IRI Syntax 2.1 Summary of IRI Syntax
IRIs are defined similarly to URIs in [RFC2396] (as modified by IRIs are defined similarly to URIs in [RFC2396] (as modified by
[RFC2732] and [IDNURI]), but the class of unreserved characters is [RFC2732] and [IDNURI]), but the class of unreserved characters is
extended by adding all the characters of the UCS (Universal Character extended by adding the characters of the UCS (Universal Character
Set, [ISO10646]) beyond U+0080, subject to the limitations given in Set, [ISO10646]) beyond U+0080, subject to the limitations given in
Section 5.1. the syntax rules below and in Section 5.1.
Otherwise, the syntax and use of components and reserved characters Otherwise, the syntax and use of components and reserved characters
is the same as that in [RFC2396]. All the operations defined in is the same as that in [RFC2396]. All the operations defined in
[RFC2396], such as the resolution of relative URIs, can be applied to [RFC2396], such as the resolution of relative URIs, can be applied to
IRIs by IRI-processing software in exactly the same way as this is IRIs by IRI-processing software in exactly the same way as this is
done to URIs by URI-processing software. done to URIs by URI-processing software.
Note: [RFC2396]: Uniform Resource Identifiers (URI): Generic Syntax"
is being revised as [RFC2396bis]. The syntax used in this document
includes bug fixes from [RFC2396bis].
Characters outside the US-ASCII range MUST NOT be used for Characters outside the US-ASCII range MUST NOT be used for
syntactical purposes such as to delimit components in newly defined syntactical purposes such as to delimit components in newly defined
schemes. As an example, it is not allowed to use U+00A2, CENT SIGN, schemes. As an example, it is not allowed to use U+00A2, CENT SIGN,
as a delimiter, because it is in the 'iunreserved' category, in the as a delimiter in IRIs, because it is in the 'iunreserved' category,
same way as it is not possible to use '-' as a delimiter, because it in the same way as it is not possible to use '-' as a delimiter,
is in the 'unreserved' category. because it is in the 'unreserved' category in URIs.
2.2 ABNF for IRI References and IRIs 2.2 ABNF for IRI References and IRIs
While it might be possible to define IRI references and IRIs merely While it might be possible to define IRI references and IRIs merely
by their transformation to URIs, they can also be accepted and by their transformation to URI references and URIs, they can also be
processed directly. Therefore, an ABNF definition for IRI references accepted and processed directly. Therefore, an ABNF definition for
(which are the most general concept and the start of the grammar) and IRI references (which are the most general concept and the start of
IRIs is given here. the grammar) and IRIs is given here. The syntax of this ABNF is
described in [RFC2234]. Character numbers are taken from the UCS,
without implying any actual binary encoding.
The following rules are different from [RFC2396]: The following rules are different from [RFC2396]:
IRI-reference = [ absoluteIRI | relativeIRI ] [ "#" ifragment ] absolute-IRI-reference = absolute-IRI [ "#" ifragment ]
absoluteIRI = scheme ":" ( ihier_part | iopaque_part )
relativeIRI = ( inet_path | iabs_path | irel_path ) IRI-reference = [ absolute-IRI / relative-IRI ]
[ "#" ifragment ]
absolute-IRI = scheme ":" ( ihier-part / iopaque-part )
relative-IRI = [ inet-path / iabs-path / irel-path ]
[ "?" iquery ] [ "?" iquery ]
ihier_part = ( inet_path | iabs_path ) [ "?" iquery ]
iopaque_part = iric_no_slash *iric ihier-part = [ inet-path / iabs-path ] [ "?" iquery ]
iric_no_slash = iunreserved | escaped | ";" | "?" | ":" | "@" | iopaque-part = iric-no-slash *iric
"&" | "=" | "+" | "$" | ","
inet_path = "//" iauthority [ iabs_path ] iric-no-slash = iunreserved / escaped / "[" / "]" / ";" / "?" /
iabs_path = "/" ipath_segments ":" / "@" / "&" / "=" / "+" / "$" / ","
irel_path = irel_segment [ iabs_path ]
irel_segment = 1*( iunreserved | escaped | inet-path = "//" iauthority [ iabs-path ]
";" | "@" | "&" | "=" | "+" | "$" | "," ) iabs-path = "/" ipath-segments
iauthority = iserver | ireg_name irel-path = irel-segment [ iabs-path ]
ireg_name = 1*( iunreserved | escaped | "$" | "," |
";" | ":" | "@" | "&" | "=" | "+" ) irel-segment = 1*( iunreserved / escaped / ";" /
iserver = [ [ userinfo "@" ] ihostport ] "@" / "&" / "=" / "+" / "$" / "," )
iuserinfo = *( iunreserved | escaped |
";" | ":" | "&" | "=" | "+" | "$" | "," ) iauthority = iserver / ireg-name
ireg-name = 1*( iunreserved / escaped / ";" /
":" / "@" / "&" / "=" / "+" / "$" / "," )
iserver = [ [ iuserinfo "@" ] ihostport ]
iuserinfo = *( iunreserved / escaped / ";" /
":" / "&" / "=" / "+" / "$" / "," )
ihostport = ihost [ ":" port ] ihostport = ihost [ ":" port ]
ihost = ihostname | IPv4address | IPv6reference ihost = IPv6reference / IPv4address / ihostname
ihostname = << as specified by [IDNA] >>
ipath_segments = isegment *( "/" isegment ) ihostname = << as specified by [RFCXXXX] >>
isegment = *ipchar *( ";" iparam )
iparam = *ipchar ipath = [ iabs-path / iopaque-part ]
ipchar = iunreserved | escaped | ipath-segments = isegment *( "/" isegment )
":" | "@" | "&" | "=" | "+" | "$" | "," isegment = *ipchar
iquery = *iric
ifragment = *iric ipchar = iunreserved / escaped / ";" /
iric = reserved | iunreserved | escaped ":" / "@" / "&" / "=" / "+" / "$" / ","
iunreserved = ichar | unreserved iquery = *( ipchar / "/" / "?" )
ichar = << allowed character of the UCS [ISO10646] >> | space | delims | unwise ifragment = *( ipchar / "/" / "?" )
iric = reserved / iunreserved / escaped
iunreserved = ichar / unreserved
ichar = idelims / ucschar / " " / "{" / "}" / "|"
/ "\" / "^" / "`"
idelims = "<" / ">" / DQUOTE
ucschar = %xA0-D7FF / %xF900-FDCF / %xFDF0-FFEF /
/ %x10000-1FFFD / %x20000-2FFFD / %x30000-3FFFD
/ %x40000-4FFFD / %x50000-5FFFD / %x60000-6FFFD
/ %x70000-7FFFD / %x80000-8FFFD / %x90000-9FFFD
/ %xA0000-AFFFD / %xB0000-BFFFD / %xC0000-CFFFD
/ %xD0000-DFFFD / %xE1000-EFFFD
Note that the space character and various delimiters are allowed in Note that the space character and various delimiters are allowed in
IRIs and IRI references. This is further discussed in Section 5.1. IRIs and IRI references. This is further discussed in Section 5.1.
The following describe the allowed characters of the UCS [ISO10646] The following are the same as [RFC2396bis]:
using the UCS-4 encoding notation for these characters:
U+00A0-U+D7FF scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
U+F900-U+FDCF port = *DIGIT
U+FDF0-U+FFEF alphanum = ALPHA / DIGIT
U+10000-U+1FFFD
U+20000-U+2FFFD IPv4address = dec-octet 3( "." dec-octet )
U+30000-U+3FFFD dec-octet = DIGIT / ; 0-9
U+40000-U+4FFFD ( %x31-39 DIGIT ) / ; 10-99
U+50000-U+5FFFD ( "1" 2*DIGIT ) / ; 100-199
U+60000-U+6FFFD ( "2" %x30-34 DIGIT ) / ; 200-249
U+70000-U+7FFFD ( "25" %x30-35 ) ; 250-255
U+80000-U+8FFFD
U+90000-U+9FFFD
U+A0000-U+AFFFD
U+B0000-U+BFFFD
U+C0000-U+CFFFD
U+D0000-U+DFFFD
U+E1000-U+EFFFD
The following are the same as [RFC2396] as modified by [RFC2732]:
reserved = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" |
"$" | "," | "[" | "]"
unreserved = alphanum | mark
mark = "-" | "_" | "." | "!" | "~" | "*" | "'" |
"(" | ")"
escaped = "%" hex hex
hex = digit | "A" | "B" | "C" | "D" | "E" | "F" |
"a" | "b" | "c" | "d" | "e" | "f"
IPv6reference = "[" IPv6address "]" IPv6reference = "[" IPv6address "]"
IPv6address = hexpart [ ":" IPv4address ] IPv6address = ( 7( h4 ":" ) h4 ) /
IPv4address = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT ( "::" 0*6( h4 ":" ) [ h4 ] ) /
hexpart = hexseq | hexseq "::" [ hexseq ] | "::" ( h4 "::" 0*5( h4 ":" ) [ h4 ] ) /
[ hexseq ] ( h4 ":" h4 "::" 0*4( h4 ":" ) [ h4 ] ) /
hexseq = hex4 *( ":" hex4) ( h4 2( ":" h4 ) "::" 0*3( h4 ":" ) [ h4 ] ) /
hex4 = 1*4hex ( h4 3( ":" h4 ) "::" 0*2( h4 ":" ) [ h4 ] ) /
port = *DIGIT ( h4 4( ":" h4 ) "::" 0*1( h4 ":" ) [ h4 ] ) /
scheme = alpha *( alpha | digit | "+" | "-" | "." ) ( 6( h4 ":" ) IPv4address )/
alphanum = alpha | digit ( "::" 0*5( h4 ":" ) IPv4address )/
alpha = lowalpha | upalpha ( h4 "::" 0*4( h4 ":" ) IPv4address )/
lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | ( h4 ":" h4 "::" 0*3( h4 ":" ) IPv4address )/
"j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | ( h4 2( ":" h4 ) "::" 0*2( h4 ":" ) IPv4address )/
"s" | "t" | "u" | "v" | "w" | "x" | "y" | "z" ( h4 3( ":" h4 ) "::" 0*1( h4 ":" ) IPv4address )
upalpha = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" |
"J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | h4 = 1*4HEXDIG
"S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z" reserved = "[" / "]" / ";" / "/" / "?" /
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | ":" / "@" / "&" / "=" / "+" / "$" / "," /
"8" | "9" unreserved = ALPHA / DIGIT / mark
space = << US-ASCII coded character 20 hexadecimal >> mark = "-" / "_" / "." / "!" / "~" / "*" / "'" /
delims = "<" | ">" | "#" | "%" | <"> "(" / ")"
unwise = "{" | "}" | "|" | "\" | "^" | "`"
escaped = "%" HEXDIG HEXDIG
2.3 IRI Equivalence and Normalization 2.3 IRI Equivalence and Normalization
There is no general rule or procedure to decide whether two arbitrary There is no general rule or procedure to decide whether two arbitrary
IRIs are equivalent or not (i.e. refer to the same resource or not). IRIs are equivalent or not (i.e. refer to the same resource or not).
Two IRIs that look almost the same may refer to different resources. Two IRIs that look almost the same may refer to different resources.
Two IRIs that look completely different may refer to, and resolve to, Two IRIs that look completely different may refer to, and resolve to,
the same resource. the same resource.
In some scenarios, such as XML Namespaces ([XMLNamespace]), a In some scenarios, such as XML Namespaces ([XMLNamespace]), a
definite answer to the question of IRI equivalence is needed that is definite answer to the question of IRI equivalence is needed that is
independent of the scheme used and always can be calculated quickly independent of the scheme used and always can be calculated quickly
and without accessing a network. In such cases, two IRIs SHOULD be and without accessing a network. In such cases, two IRIs SHOULD be
defined as equivalent if and only if they are character-by-character defined as equivalent if and only if they are character-by-character
equivalent (which is the same as byte-by-byte equivalent if the equivalent. This is the same as being byte-by-byte equivalent if the
character encoding for both IRIs is the same). In such a case, the character encoding for both IRIs is the same. As an example,
comparison function MUST NOT map the IRIs to URIs. http://example.org/~user, http://example.org/%7euser, and
http://example.org/%7Euser would not be equivalent. In such a case,
the comparison function MUST NOT map the IRIs to URIs.
It follows from the above that IRIs SHOULD NOT be modified when being It follows from the above that IRIs SHOULD NOT be modified when being
transported. transported.
For actual resolution, differences in escaping (except for the For actual resolution, differences in escaping (except for the
escaping of reserved characters) MUST always result in the same escaping of reserved characters) MUST always result in the same
resource. For example, foo://example.com/XML, foo://example.com/ resource. For example, http://example.org/~user,
XM%4C, and foo://example.com/XM%4c must resolve to the same resource. http://example.org/%7euser and http://example.org/%7Euser must
If this kind of equivalence is to be tested, the escaping of both resolve to the same resource. If this kind of equivalence is to be
IRIs to be compared has to be aligned, for example by converting both tested, the escaping of both IRIs to be compared has to be aligned,
IRIs to URIs (see Section 3.1) and making sure that the case of the for example by converting both IRIs to URIs (see Section 3.1) and
hexadecimal characters in the %-escape is always the same. Such making sure that the case of the hexadecimal characters in the %-
conversions MUST only be done on the fly, without changing the escape is always the same. Such conversions MUST only be done on the
original IRI. fly, without changing the original IRI.
Specific schemes and resolution mechanisms may define additional Specific schemes and resolution mechanisms may define additional
equivalences. For a specific scheme, two IRIs that e.g. differ only equivalences. For a specific scheme, two IRIs that e.g. differ only
by case may be equivalent. However, this document does not deal with by case may be equivalent. However, this document does not deal with
scheme-specific issues. scheme-specific issues.
The Unicode Standard [UNIV3] defines various equivalences between The Unicode Standard [UNIV3] defines various equivalences between
sequences of characters for various purposes. Unicode Standard Annex sequences of characters for various purposes. Unicode Standard Annex
#15 [UNI15] defines various Normalization Forms for these #15 [UNI15] defines various Normalization Forms for these
equivalences. IRIs SHOULD be created using the Normalization Form C equivalences. IRIs SHOULD be created using Normalization Form C
(NFC). When an IRI is created in an UCS-based encoding without the (NFC). Equivalence of IRIs MUST rely on the IRIs being appropriately
end-user being aware of or interested in Unicode normalization pre-normalized, rather than applying normalization, except when
issues, the IRI MUST be created using the normalization form NFC.
Equivalence of IRIs MUST rely on the IRIs being appropriately pre-
normalized, rather than applying normalization, except when
converting from a non-UCS-based encoding to an UCS-based encoding, converting from a non-UCS-based encoding to an UCS-based encoding,
where a normalizing transcoder using NFC MUST be used. where a normalizing transcoder using NFC MUST be used.
As an example, http://www.example.org/r&#xe9;sum&#xe9;.html (in XML
Notation) is in NFC. On the other hand, http://www.example.org/
re&#x301;sume&#x301;.html is not in NFC. The former uses precombined
e-acute characters, the later uses 'e' characters followed by
combining acute accents, both are defined as canonically equivalent
in [UNIV3].
Various IRI schemes may allow the usage of International Domain Names Various IRI schemes may allow the usage of International Domain Names
(IDN) [IDNA]. When in use in IRIs, those names SHOULD be validated (IDN) [RFCXXXX]. When in use in IRIs, those names SHOULD be
using the rules defined by [Nameprep]. An IRI containing an invalid validated using the ToASCII operation defined in [RFCXXXX], with the
IDN cannot successfully be resolved. For legibility purposes, IDN flags "UseSTD3ASCIIRules" and "AllowUnassigned". An IRI containing
components of IRIs SHOULD not be converted into ASCII Compatible an invalid IDN cannot successfully be resolved. For legibility
Encoding (ACE). However, this conversion may be applied when mapping purposes, IDN components of IRIs SHOULD not be converted into ASCII
an IRI into an URI, see Section 3.1. Compatible Encoding (ACE). However, this conversion may be applied
when mapping an IRI into an URI, see Section 3.1.
3. Relationship between IRIs and URIs 3. Relationship between IRIs and URIs
IRIs are meant to replace URIs in identifying resources for IRIs are meant to replace URIs in identifying resources for
protocols, formats and software components which use a UCS-based protocols, formats and software components which use a UCS-based
character repertoire. These protocols and components may never need character repertoire. These protocols and components may never need
to use URIs directly, especially when the resource identifier is used to use URIs directly, especially when the resource identifier is used
simply for identification purposes. However, when the resource simply for identification purposes. However, when the resource
identifier is used for resource retrieval, it is in many cases identifier is used for resource retrieval, it is in many cases
necessary to determine the associated URI because most retrieval necessary to determine the associated URI because most retrieval
skipping to change at page 11, line 27 skipping to change at page 12, line 38
a) Syntactical: Many URI schemes and components define additional a) Syntactical: Many URI schemes and components define additional
syntactical restrictions not captured in Section 2.2. Such syntactical restrictions not captured in Section 2.2. Such
restrictions can be applied to IRIs by noting that IRIs are restrictions can be applied to IRIs by noting that IRIs are
only valid if they map to syntactically valid URIs. This means only valid if they map to syntactically valid URIs. This means
that such syntactical restrictions do not have to be defined that such syntactical restrictions do not have to be defined
again on the IRI level. again on the IRI level.
b) Interpretational: URIs identify resources in various ways. b) Interpretational: URIs identify resources in various ways.
IRIs also identify resources. When the IRI is used simply for IRIs also identify resources. When the IRI is used simply for
indentification purposes, it is not necessary to map the IRI to identification purposes, it is not necessary to map the IRI to
an URI (see Section 2.3). However, when an IRI is used for an URI (see Section 2.3). However, when an IRI is used for
resource retrieval, the resource that the IRI locates is the resource retrieval, the resource that the IRI locates is the
same as the one located by the URI obtained after converting same as the one located by the URI obtained after converting
the IRI according to the procedure defined here. This means the IRI according to the procedure defined here. This means
that there is no need to define resolution again on the IRI that there is no need to define resolution separately on the
level. IRI level.
This mapping is accomplished in two steps. This mapping is accomplished in two steps.
Step 1) This step generates a UCS-based encoding from the original Step 1) This step generates a UCS-based encoding from the original
IRI format. This step has three variants, depending on the IRI format. This step has three variants, depending on the
form of the input. form of the input.
Variant A) If the IRI is written on paper or read out loud, Variant A) If the IRI is written on paper or read out loud,
or otherwise represented as a sequence of characters or otherwise represented as a sequence of characters
independent of any encoding: Represent the IRI as a independent of any encoding: Represent the IRI as a
skipping to change at page 12, line 19 skipping to change at page 13, line 30
Step 2) For each character that is disallowed in URI references, Step 2) For each character that is disallowed in URI references,
apply steps 1) through 3) below. The disallowed characters apply steps 1) through 3) below. The disallowed characters
consist of all non-ASCII characters, plus the excluded consist of all non-ASCII characters, plus the excluded
characters listed in Section 2.4 of [RFC2396], except for the characters listed in Section 2.4 of [RFC2396], except for the
number sign (#) and percent sign (%) and the square bracket number sign (#) and percent sign (%) and the square bracket
characters re-allowed in [RFC2732]. characters re-allowed in [RFC2732].
1) Convert the character to a sequence of one or more octets 1) Convert the character to a sequence of one or more octets
using UTF-8 [RFC2279]. using UTF-8 [RFC2279].
2) Convert each octet to %HH, where HH is the hexadecimal 2) Convert each octet to %hh, where hh is the hexadecimal
notation of the octet value. Note: This is identical to notation of the octet value. Note: This is identical to
the escaping mechanism in Section 2.4.1 of [RFC2396]. the escaping mechanism in Section 2.4.1 of [RFC2396].
Note: To reduce variability, the hexadecimal notation
SHOULD use lower case letters.
3) Replace the original character by the resulting character 3) Replace the original character by the resulting character
sequence. sequence.
Note that in this process (in step 2.3), characters allowed in URI Note that in this process (in step 2.3), characters allowed in URI
references and existing escape sequences are not escaped further. references and existing escape sequences are not escaped further.
(This mapping is similar to, but different from, the escaping applied (This mapping is similar to, but different from, the escaping applied
when including arbitrary content into some part of a URI.) when including arbitrary content into some part of a URI.) For
example, an IRI of
http://www.example.org/red%09ros&#xe9;#<red> (in XML notation) is
converted to
http://www.example.org/red%09ros%c3%a9#%3cred%3e, not to something
like
http%3a%2f%2fwww.example.org%2fred%2509ros%c3%a9%23red.
Note that some older software transcoding to UTF-8 may produce
illegal output for some input, in particular for characters outside
the BMP (Basic Multilingual Plane). As an example, for the following
IRI with non-BMP characters (in XML Notation):
http://example.com/
(the first three letters of the Old Italic alphabet) the correct
conversion to a URI is:
http://example.com/%F0%90%8C%80%F0%90%8C%81%F0%90%8C%82
The above mapping produces a URI fully conforming to [RFC2396] (as The above mapping produces a URI fully conforming to [RFC2396] (as
amended by [RFC2732] and [IDNURI]) out of each IRI. The mapping is amended by [RFC2732] and [IDNURI]) out of each IRI. The mapping is
also an identity transformation for URIs and is idempotent -- also an identity transformation for URIs and is idempotent --
applying the mapping a second time will not change anything. Every applying the mapping a second time will not change anything. Every
URI is therefore by definition an IRI. URI is therefore by definition an IRI.
Note: For backwards compatibility with infrastructure that does not Note: For backwards compatibility with infrastructure that does not
implement the updates of [IDNURI], converters MAY also convert the implement the updates of [IDNURI], converters MAY also convert the
'ihostname' part of an IRI using the ToASCII operation specified in 'ihostname' part of an IRI using the ToASCII operation specified in
Section 4.1 of [IDNA] between Step 1 and Step 2. Note that the Section 4.1 of [RFCXXXX] between Step 1 and Step 2. Note that the
ToASCII operation may fail. Note that Internationalized Domain Names ToASCII operation may fail. Note that Internationalized Domain Names
may be contained in parts of an IRI other than the 'ihostname' part. may be contained in parts of an IRI other than the 'ihostname' part.
3.2 Converting URIs to IRIs 3.2 Converting URIs to IRIs
In some situations, it may be desirable to try to convert a URI into In some situations, it may be desirable to try to convert a URI into
an equivalent IRI. This section gives a procedure to do such a an equivalent IRI. This section gives a procedure to do such a
conversion. The conversion described in this section will always conversion. The conversion described in this section will always
give an IRI which maps back to the URI that was used as an input for result in an IRI which maps back to the URI that was used as an input
the conversion, but perhaps not exactly the original IRI (if there for the conversion (except for potential case differences in escape
ever was one). sequences). However, the IRI resulting from this conversion may not
be exactly the same as the original IRI (if there ever was one).
URI to IRI conversion removes escape sequences, but not all escaping URI to IRI conversion removes escape sequences, but not all escaping
can be eliminated. There are many reasons for this: can be eliminated. There are several reasons for this:
a. Some escape sequences are necessary to distinguish escaped and a) Some escape sequences are necessary to distinguish escaped and
unescaped uses of reserved characters. unescaped uses of reserved characters.
b. Some escape sequences cannot be interpreted as sequences of b) Some escape sequences cannot be interpreted as sequences of
UTF-8 octets. UTF-8 octets.
(Note: Due to the regularities in the octet patterns of UTF-8, (Note: Due to the regularities in the octet patterns of UTF-8,
there is a very high probability, but no guarantee, that escape there is a very high probability, but no guarantee, that escape
sequences that can be interpreted as sequences of UTF-8 octets sequences that can be interpreted as sequences of UTF-8 octets
actually originated from UTF-8. For a detailed discussion, see actually originated from UTF-8. For a detailed discussion, see
[Duer97].) [Duer97].)
c. The conversion may result in a character that is not c) The conversion may result in a character that is not
appropriate in an IRI. See Section 5.1 for further details. appropriate in an IRI. See Section 5.1 for further details.
Conversion from a URI to an IRI is done using the following steps (or Conversion from a URI to an IRI is done using the following steps (or
any other algorithm that produces the same result): any other algorithm that produces the same result):
1) Represent the URI as a sequence of octets in US-ASCII. 1) Represent the URI as a sequence of octets in US-ASCII.
2) Convert all hexadecimal escapes (% followed by two hexadecimal 2) Convert all hexadecimal escapes (% followed by two hexadecimal
digits) of %80 and higher to the corresponding octets. digits) except those corresponding to '#' and '%' and
characters in 'reserved', to the corresponding octets.
3) Re-escape any octets that are not part of a strictly legal UTF- 3) Re-escape any octets that are not part of a strictly legal UTF-
8 octet sequence. 8 octet sequence.
4) Re-escape all octets that in UTF-8 represent characters that 4) Re-escape all octets that in UTF-8 represent characters that
are not appropriate according to Section 5.1. are not appropriate according to Section 5.1.
5) Interpret the resulting octet sequence as a sequence of 5) Interpret the resulting octet sequence as a sequence of
characters encoded in UTF-8. characters encoded in UTF-8.
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4. Bidirectional IRIs for Right-to-left Languages 4. Bidirectional IRIs for Right-to-left Languages
Some UCS characters, such as those used in the Arabic and Hebrew Some UCS characters, such as those used in the Arabic and Hebrew
script, have an inherent right-to-left writing direction. IRIs script, have an inherent right-to-left writing direction. IRIs
containing such characters (called bidirectional IRIs or Bidi IRIs) containing such characters (called bidirectional IRIs or Bidi IRIs)
require additional attention because of the non-trivial relation require additional attention because of the non-trivial relation
between logical representation (used for digital representation as between logical representation (used for digital representation as
well as when reading/spelling) and visual representation (used for well as when reading/spelling) and visual representation (used for
display/printing). display/printing).
4.1 Bidi IRI Structure Because of the complex interaction between the logical
representation, the visual representation, and the syntax of a Bidi
IRIs have an inherent structure that distinguishes structural IRI, a balance is needed between various requirements. The main
characters (usually punctuation such as '@', '.', ':', '/', and so requirements are (1) user-predictable conversion between visual and
on) called delimiters and payload components (usually consisting logical representation; (2) the ability to include a wide range of
mostly of letters and digits). characters in various parts of the IRI; (3) no or not too big changes
or restrictions for implementations.
ISSUE: Exact definition of components. 4.1 Logical Storage and Visual Presentation
In their internal digital representation, i.e. stored or transmitted In their internal digital representation, i.e. stored or transmitted
for resolution, bidirectional IRIs MUST be in full logical order both for resolution, bidirectional IRIs MUST be in full logical order, and
for the overall structure as well as for the individual components. MUST conform directly to the IRI syntax rules (which includes the
They MUST conform directly to the IRI syntax rules (which includes rules relevant to their scheme). This assures that bidirectional
the rules relevant to their scheme). This is necessary to make sure IRIs can be processed in the same way as other IRIs.
that bidirectional IRIs can be processed in the same way as other
IRIs.
The components have the following restrictions: When rendered, bidirectional IRIs MUST be rendered using the Unicode
Bidirectional Algorithm [UNIV3], [UNI9]. Bidirectional IRIs MUST be
rendered with an overall left-to-right direction.
1) A component MUST NOT not use both right-to-left and left-to- In text with a left-to-right base directionality or embedding (e.g
right characters. English, Cyrillic), the Unicode Bidirectional Algorithm will
automatically use an overall left-to-right direction for the IRI. In
text with a right-to-left base directionality or embedding (e.g.
Arabic or Hebrew), some kind of embedding is needed. This may be
Unicode bidi formatting codes (LRE before the IRI, and PDF after the
IRI, both not part of the IRI itself) or equivalent features of a
higher-order protocol (e.g. the dir='ltr' attribute in HTML).
2) A component MUST NOT contain bidirectional formatting IRIs MUST NOT contain bidirectional formatting characters (LRM, RLM,
characters. LRE, RLE, LRO, RLO, and PDF). They affect the visual rendering of
the IRI, but do not itself appear visually. It would therefore not
be possible to again correctly input an IRI with such characters.
3) A component using right-to-left characters MUST NOT use any 4.2 Bidi IRI Structure
other class of characters (e.g. neutrals or numbers).
Note: Restrictions 1) and 2) are not very severe, in that they do not The Unicode Bidirectional Algorithm is designed mainly for running
overly restrict useful identifiers. Also, trying to remove it would text. To make sure that it does not affect the rendering of
make it impossible for humans to predict the logical sequence of bidirectional IRIs too much, some restrictions on bidirectional IRIs
characters inside a single component. On the other hand, it would be are necessary. These restrictions are given in terms of delimiters
very desirable to remove or at least soften restriction 3). (structural characters, mostly punctuation such as
Otherwise, it is impossible to combine Arabic or Hebrew letters with '@', '.', ':', '/') and components (usually consisting mostly of
numbers, or to use a hyphen between two subcomponents of an Arabic letters and digits).
component to avoid the cursive connection of the two subcomponents.
To a certain extent, softening this restriction should be easily
possible by adding additional formatting characters in well defined
ways similar to the provisions in Section 4.2. Feedback on this
issue is particularly welcome.
4.2 Visual Rendering of Bidi IRIs The following syntax rules from Section 2.2 correspond to components
for the purpose of Bidi behavior: iopaquepart, irelsegment, iregname,
iuserinfo, isegment, iparam, ihostname, iquery, and ifragment.
Bidirectional IRIs MUST be rendered visually by rendering each Specifications that define the syntax of any of the above components
component and each structural character from left to right. They MAY divide them further and define smaller parts to be components
MUST render each component according to its natural direction (i.e. according to this document. As an example, the restrictions of
left-to-right for components with left-to-right characters, right-to- [RFCXXXX] on bidirectional domain names correspond to treating each
left for components with right-to-left characters). label of the domain name as a component. Even where the components
are not defined formally, it may be helpful to think about some
syntax in terms of components and to apply the relevant restrictions.
For example, for the usual name/value syntax in query parts, it is
convenient to treat each name and each value as a component. As
another example, the extensions in a resource name can be treated as
separate components.
ISSUE: The alternative is to display a series of right-to-left For each component, the following restrictions apply:
components in their natural (right-to-left) order. This has the
advantage that it will often be easier for native people to read the
components in the right order. The restrictions on individual
components change. In some cases, the correct visual rendering is
automatic (i.e. exactly the same as with the Unicode algorithm), and
so in these cases, no bidi formatting characters have to be added.
In a textual context, i.e. assuming rendering by the Unicode 1) A component SHOULD NOT not use both right-to-left and left-to-
bidirectional algorithm, the visual rendering backing store is done right characters.
as follows:
The visual representation uses some of the following Bidi formatting 2) A component using right-to-left characters SHOULD start and end
characters described by using a XML-style entity notation: with right-to-left characters.
&lrm; U+200E LEFT-TO-RIGHT MARK The above restrictions are given as shoulds, rather than as musts.
&rlm; U+200F RIGHT-TO-LEFT MARK For IRIs that are never presented visually, they are not relevant.
&lre; U+202A LEFT-TO-RIGHT EMBEDDING However, for IRIs in general, they are very important to insure
&rle; U+202B RIGHT-TO-LEFT EMBEDDING consistent conversion between visual presentation and logical
&pdf; U+202C POP DIRECTIONAL FORMATTING representation, in both directions.
&lro; U+202D LEFT-TO-RIGHT OVERRIDE
&rlo; U+202E RIGHT-TO-LEFT OVERRIDE
Each component with right-to-left characters is preceded and In some components, the above restrictions may actually be strictly
followed by an &lrm;. This left-to-right mark provides a left- enforced. For example, [RFCXXXX] requires that these restrictions
to-right context to intervening syntactic characters. apply to the labels of the host name part of an IRI. In some other
components, for example path components, following these restrictions
may not be too difficult. For other components, such as parts of the
query part, it may be very difficult to enforce the restrictions,
because the values of query parameters may be arbitrary character
sequences.
If the overall context (base directionality) is right-to-left, In order to satisfy the above restrictions, the affected component
the identifier is preceded by an &lre; and followed by a &pdf;. can be mapped to URI notation as described in Section 3.1. Please
This makes sure that the components of the identifier are note that the whole component needs to be mapped (see also Example 9
rendered in left-to-right order. This may also be done by below).
using the equivalent features of a higher-order protocol (e.g.
by using the dir='ltr' attribute in HTML).
4.3 Input of Bidi IRIs 4.3 Input of Bidi IRIs
Bidi input methods MUST generate Bidi IRIs in logical order while Bidi input methods MUST generate Bidi IRIs in logical order while
rendering them according to Section 4.2. During input, rendering rendering them according to Section 4.1. During input, rendering
should be updated after every new character that is input to avoid should be updated after every new character that is input to avoid
end user confusion. end user confusion.
4.4 Examples
This section gives examples of bidirectional IRIs, in Bidi Notation.
It shows legal IRIs with the relationship between logical and visual
representation, and explains how certain phenomena in this
relationship may look strange to somebody not familiar with
bidirectional behavior, but familiar to users of Arabic and Hebrew.
It also shows what happens if the restrictions given in Section 4.2
are not followed. The examples below can be seen at [BidiEx], in
Arabic, Hebrew, and Bidi Notation variants.
Example 1: A single component with right-to-left (rtl) characters is
inverted:
logical representation: http://ab.CDEFGH.ij/kl/mn/op.html,
visual representation: http://ab.HGFEDC.ij/kl/mn/op.html.
Components can be read one-by-one, and each component can be read in
its natural direction.
Example 2: More than one consecutive component with rtl characters is
inverted as a whole:
logical representation: http://ab.CDE.FGH/ij/kl/mn/op.html,
visual representation: http://ab.HGF.EDC/ij/kl/mn/op.html.
A sequence of rtl components is read rtl, in the same way as a
sequence of rtl words is read rtl in a bidi text.
Example 3: All components of an IRI (except for the scheme) are rtl.
All rtl components are inverted overall:
logical representation: http://AB.CD.EF/GH/IJ/KL?MN=OP;QR=ST#UV,
visual representation: http://VU#TS=RQ;PO=NM?LK/JI/HG/FE.DC.BA.
The whole IRI (except the scheme) is read rtl. Delimiters between
rtl components stay between the respective components; delimiters
between ltr and rtl components don't move.
Example 4: Several sequences of rtl components are each inverted on
their own:
logical representation: http://AB.CD.ef/gh/IJ/KL.html,
visual representation: http://DC.BA.ef/gh/LK/JI.html.
Each sequence of rtl components is read rtl, in the same way as each
sequence of rtl words in an ltr text is read rtl.
Example 5: Example 2, applied to components of different kinds:
logical representation: http://ab.cd.EF/GH/ij/kl.html,
visual representation: http://ab.cd.HG/FE/ij/kl.html.
The inversion of the domain name label and the path component may be
unexpected, but is consistent with other bidi behavior.
Example 6: Same as example 5, with more rtl components:
logical representation: http://ab.CD.EF/GH/IJ/kl.html,
visual representation: http://ab.JI/HG/FE.DC/kl.html.
The inversion of the domain name labels and the path components may
be easier to identify because the delimiters also move.
Example 7: A single rtl component with included digits:
logical representation: http://ab.CDE123FGH.ij/kl/mn/op.html,
visual representation: http://ab.HGF123EDC.ij/kl/mn/op.html.
Numbers are written ltr in all cases, but are treated as an
additional embedding inside a run of rtl characters. This is
completely consistent with usual bidirectional text.
Example 8 (not allowed): Numbers at the start or end of a rtl
component:
logical representation: http://ab.cd.ef/GH1/2IJ/KL.html,
visual representation: http://ab.cd.ef/LK/JI1/2HG.html.
The sequence '1/2' is interpreted by the bidi algorithm as a
fraction, fragmenting the components and leading to confusion. There
are other characters that are interpreted in a special way close to
numbers, in particular '+', '-', '#', '$', '%', ',', '.', and ':'.
Example 9 (not allowed): The numbers in the previous example are
escaped:
logical representation: http://ab.cd.ef/GH%31/%32IJ/KL.html,
visual representation (Hebrew): http://ab.cd.ef/LK/JI%32/%31HG.html,
visual representation (Arabic): http://ab.cd.ef/LK/JI32%/31%HG.html.
Depending on whether the upper-case letters represent Arabic or
Hebrew, the visual representation is different.
5. Use of IRIs 5. Use of IRIs
5.1 Limitations on UCS Character Allowed in IRI 5.1 Limitations on UCS Characters Allowed in IRIs
This section discusses the limitations on characters and character This section discusses the limitations on characters and character
sequences usable for IRIs. The considerations in this section are sequences usable for IRIs. The considerations in this section are
relevant when creating IRIs and when converting from URIs to IRIs. relevant when creating IRIs and when converting from URIs to IRIs.
a. The repertoire of characters allowed in each IRI component is a) The repertoire of characters allowed in each IRI component is
limited by the definition of that component. For example, the limited by the definition of that component. For example, the
definition of the scheme component does not allow characters definition of the scheme component does not allow characters
beyond US-ASCII. beyond US-ASCII.
(Note: In accordance with URI practice, generic IRI software (Note: In accordance with URI practice, generic IRI software
cannot and should not check for such limitations.) cannot and should not check for such limitations.)
b. In the URI syntax, characters that are likely to be used to b) In the URI syntax, characters that are likely to be used to
delimit URIs in text and print ("space", "delims", and delimit URIs in text and print ("space", "delims", and
"unwise") were excluded. They are included in the IRI syntax, "unwise") were excluded. They are included in the IRI syntax
for the following reasons: (with the exception of '%', which cannot be used directly, and
'#', which is used in IRI references), for the following
reasons:
1) The syntax includes many other characters that are not 1) The syntax includes many other characters that are not
appropriate in many cases. appropriate in many cases.
2) Some implementation practice already allows them in URI 2) Some implementation practice already allows them in URI
references (for example spaces in fragment identifiers). references (for example spaces in fragment identifiers).
3) It is very convenient in some cases, for example for 3) It is very convenient in some cases, for example for
XPointers in XML attributes. XPointers in XML attributes.
4) Considering context is already necessary in the case of 4) Considering context is already necessary in the case of
URIs, for example for "&" in XML. URIs, for example for "&amp;" in XML.
However, these characters should be used carefully. Whenever However, these characters should be avoided where possible.
there is a chance that an IRI will be used in a component where Whenever there is a chance that an IRI will be used in a
these characters can be harmful, they should be escaped. component where these characters can be harmful, they should be
escaped from the start.
c. The UCS contains many areas of characters for which there are c) The UCS contains many areas of characters for which there are
strong visual look-alikes. Because of the likelihood of strong visual look-alikes. Because of the likelihood of
transcription errors, these also should be avoided. This transcription errors, these also should be avoided. This
includes the full-width equivalents of ASCII characters, half- includes the full-width equivalents of ASCII characters, half-
width Katakana characters for Japanese, and many others. This width Katakana characters for Japanese, and many others. This
also includes many look-alikes of "space", "delims", and also includes many look-alikes of "space", "delims", and
"unwise", characters excluded in [RFC2396]. "unwise", characters excluded in [RFC2396].
Additional information is available from [UNIXML]. Although [UNIXML] Additional information is available from [UNIXML]. [UNIXML] is
is written in a different context, it discusses many of the written in the context of running text rather than in the context of
categories of characters and code points not appropriate for IRIs. identifiers. Nevertheless, it discusses many of the categories of
characters and code points not appropriate for IRIs.
5.2 Software Interfaces and Protocols 5.2 Software Interfaces and Protocols
Although an IRI is defined as a sequence of characters, software Although an IRI is defined as a sequence of characters, software
interfaces for URIs typically function on sequences of octets. Thus, interfaces for URIs typically function on sequences of octets or
software interfaces and protocols MUST define which character other kinds of code units. Thus, software interfaces and protocols
encoding is used. MUST define which character encoding is used.
Intermediate software interfaces between IRI-capable components and Intermediate software interfaces between IRI-capable components and
URI-only components MUST map the IRIs as per Section 3.1, when URI-only components MUST map the IRIs as per Section 3.1, when
transferring from IRI-capable to URI-only components. Such a mapping transferring from IRI-capable to URI-only components. Such a mapping
SHOULD be applied as late as possible. It should not be applied SHOULD be applied as late as possible. It should not be applied
between components that are known to be able to handle IRIs. between components that are known to be able to handle IRIs.
5.3 Format of URIs and IRIs in Documents and Protocols 5.3 Format of URIs and IRIs in Documents and Protocols
Document formats that transport URIs may need to be upgraded to allow Document formats that transport URIs may need to be upgraded to allow
skipping to change at page 18, line 41 skipping to change at page 22, line 13
input the IRI. Depending on the script and the input method used, input the IRI. Depending on the script and the input method used,
this may be a more or less complicated process. this may be a more or less complicated process.
The process of IRI entry must assure, as far as possible, that the The process of IRI entry must assure, as far as possible, that the
restrictions defined in Section 2.2 are met. This may be done by restrictions defined in Section 2.2 are met. This may be done by
choosing appropriate input methods or variants/settings thereof, by choosing appropriate input methods or variants/settings thereof, by
appropriately converting the characters being input, by eliminating appropriately converting the characters being input, by eliminating
characters that cannot be converted, and/or by issuing a warning or characters that cannot be converted, and/or by issuing a warning or
error message to the user. error message to the user.
As an example of variant settings, input method editors for East
Asian Languages usually allow to input Latin letters and related
characters in full-width or half-width versions. For IRI input, the
input method editor should be set to half-width input, in order to
produce US-ASCII characters where possible.
An input field primarily or only used for the input of URIs/IRIs An input field primarily or only used for the input of URIs/IRIs
should allow the user to view an IRI as converted to a URI. Places should allow the user to view an IRI as mapped to a URI. Places
where the input of IRIs is frequent should provide the possibility where the input of IRIs is frequent should provide the possibility
for viewing an IRI as converted to a URI. This will help users when for viewing an IRI as mapped to a URI. This will help users when
some of the software they use does not yet accept IRIs. some of the software they use does not yet accept IRIs.
An IRI input component that interfaces to components that handle An IRI input component that interfaces to components that handle
URIs, but not IRIs, must escape the IRI before passing it to such a URIs, but not IRIs, must map the the IRI to an URI before passing it
component. to such a component.
For the input of IRIs with right-to-left characters, please see For the input of IRIs with right-to-left characters, please see
Section 4. Section 4.3.
6.3 URI/IRI Generation 6.3 URI/IRI Transfer Between Applications
Many applications, in particular many mail user agents, try to detect
URIs appearing in plain text. For this, they use some heuristics
based on URI syntax. They then allow the user to click on such URIs
and retrieve the corresponding resource in an appropriate (usually
scheme-dependent) application.
Such applications have to be upgraded to use the IRI syntax rather
than the URI syntax as a base for heuristics. In particular, a non-
ASCII character should not be taken as the indication of the end of
an IRI. Such applications also have to make sure that they correctly
convert the detected IRI from the encoding of the document or
application where the IRI appears to the encoding used by the system-
wide IRI invocation mechanism, or to an URI (according to Section
3.1) if the system-wide invocation mechanism only accepts URIs.
The clipboard is another frequently used way to transfer URIs and
IRIs from one application to another. On most platforms, the
clipboard is able to store and transfer text in many languages and
scripts. Correctly used, the clipboard transfers characters, not
bytes, which will do the right thing with IRIs.
6.4 URI/IRI Generation
Systems that are offering resources through the Internet, where those Systems that are offering resources through the Internet, where those
resources have logical names, sometimes automatically generate URIs resources have logical names, sometimes automatically generate URIs
for the resources they offer. For example, some HTTP servers can for the resources they offer. For example, some HTTP servers can
generate a directory listing for a file directory, and then respond generate a directory listing for a file directory, and then respond
to the generated URIs with the files. to the generated URIs with the files.
Many legacy character encodings are in use in various file systems. Many legacy character encodings are in use in various file systems.
Many currently deployed systems do not transform the local character Many currently deployed systems do not transform the local character
representation of the underlying system before generating URIs. representation of the underlying system before generating URIs.
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use IRIs converted to URIs in cases where it cannot be expected that use IRIs converted to URIs in cases where it cannot be expected that
the recipient is able to handle IRIs. Due to the way most user the recipient is able to handle IRIs. Due to the way most user
agents currently work, native IRIs, encoded in UTF-8, may be used if agents currently work, native IRIs, encoded in UTF-8, may be used if
the recipient announces that it can interpret UTF-8. This requires the recipient announces that it can interpret UTF-8. This requires
that the whole page is sent as UTF-8. If this is not possible, that the whole page is sent as UTF-8. If this is not possible,
escaping can always be used. escaping can always be used.
This recommendation in particular applies to HTTP servers. For FTP This recommendation in particular applies to HTTP servers. For FTP
servers, similar considerations apply, see in particular [RFC2640]. servers, similar considerations apply, see in particular [RFC2640].
6.4 URI/IRI Selection 6.5 URI/IRI Selection
In some cases, resource owners and publishers have control over the In some cases, resource owners and publishers have control over the
IRIs used to identify their resources. Such control is mostly IRIs used to identify their resources. Such control is mostly
executed by controlling the resource names, such as file names, executed by controlling the resource names, such as file names,
directly. directly.
In such cases, it is recommended to avoid choosing IRIs that are In such cases, it is recommended to avoid choosing IRIs that are
easily confused. For example, for US-ASCII, the lower-case ell "l" easily confused. For example, for US-ASCII, the lower-case ell "l"
is easily confused with the digit one "1", and the upper-case oh "O" is easily confused with the digit one "1", and the upper-case oh "O"
is easily confused with the digit zero "0". Publishers should avoid is easily confused with the digit zero "0". Publishers should avoid
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here. As long as names are limited to characters from a single here. As long as names are limited to characters from a single
script, native writers of a given script or language will know best script, native writers of a given script or language will know best
when ambiguities can appear, and how they can be avoided. What may when ambiguities can appear, and how they can be avoided. What may
look ambiguous to a stranger may be completely obvious to the average look ambiguous to a stranger may be completely obvious to the average
native user. On the other hand, in some cases, the UCS contains native user. On the other hand, in some cases, the UCS contains
variants for compatibility reasons, for example for typographic variants for compatibility reasons, for example for typographic
purposes. These should be avoided wherever possible. Although there purposes. These should be avoided wherever possible. Although there
may be exceptions, in general newly created resource names should be may be exceptions, in general newly created resource names should be
in NFKC [UNI15] (which means that they are also in NFC). in NFKC [UNI15] (which means that they are also in NFC).
In certain cases, there is a chance that letters from different As an example, the UCS contains a codepoint for the 'fi' ligature.
Wherever possible, IRIs should use the two letters 'f' and 'i' rather
than the 'fi' ligature. An example where the later may be used is in
the query part of an IRI for an explicit search for a word containing
the 'fi' ligature.
In certain cases, there is a chance that characters from different
scripts look the same. The best known example is the Latin 'A', the scripts look the same. The best known example is the Latin 'A', the
Greek 'Alpha', and the Cyrillic 'A'. To avoid such cases, only IRIs Greek 'Alpha', and the Cyrillic 'A'. To avoid such cases, only IRIs
should be generated where all the letters in a single component are should be generated where all the characters in a single component
from the same script. This is similar to the heuristics used to are used together in a given language. This usually means that all
distinguish between letters and numbers in the examples above. Also, these characters will be from the same script, but there are
for the above three scripts, using lower-case letters results in languages that mix characters from different scripts (such as
fewer ambiguities than using upper-case letters. Japanese). This is similar to the heuristics used to distinguish
between letters and numbers in the examples above. Also, for Latin,
Greek, and Cyrillic, using lower-case letters results in fewer
ambiguities than using upper-case letters.
6.5 Display of URIs/IRIs 6.6 Display of URIs/IRIs
In situations where the rendering software is not expected to display In situations where the rendering software is not expected to display
non-ASCII parts of the IRI correctly using the available layout and non-ASCII parts of the IRI correctly using the available layout and
font resources, these parts should be escaped before being displayed. font resources, these parts should be escaped before being displayed.
For display of Bidi IRIs, please see Section 4.2. For display of Bidi IRIs, please see Section 4.1.
6.6 Interpretation of URIs and IRIs 6.7 Interpretation of URIs and IRIs
Software that interprets IRIs as the names of local resources should Software that interprets IRIs as the names of local resources should
accept IRIs in multiple forms, and convert and match them with the accept IRIs in multiple forms, and convert and match them with the
appropriate local resource names. appropriate local resource names.
First, multiple representations include both IRIs in the native First, multiple representations include both IRIs in the native
character encoding of the protocol and also their URI counterparts. character encoding of the protocol and also their URI counterparts.
Second, it may include URIs constructed based on other character Second, it may include URIs constructed based on other character
encodings than UTF-8. Such URIs may be produced by user agents that encodings than UTF-8. Such URIs may be produced by user agents that
skipping to change at page 20, line 44 skipping to change at page 25, line 8
convert non-ASCII characters to URIs. Whether this is necessary, and convert non-ASCII characters to URIs. Whether this is necessary, and
what character encodings to cover, depends on a number of factors, what character encodings to cover, depends on a number of factors,
such as the legacy character encodings used locally and the such as the legacy character encodings used locally and the
distribution of various versions of user agents. For example, distribution of various versions of user agents. For example,
software for Japanese may accept URIs in Shift_JIS and/or EUC-JP in software for Japanese may accept URIs in Shift_JIS and/or EUC-JP in
addition to UTF-8. addition to UTF-8.
Third, it may include additional mappings to be more user-friendly Third, it may include additional mappings to be more user-friendly
and robust against transmission errors. These would be similar to and robust against transmission errors. These would be similar to
how currently some servers treat URIs as case-insensitive, or perform how currently some servers treat URIs as case-insensitive, or perform
additional matchings to account for spelling errors. For characters additional matching to account for spelling errors. For characters
beyond the ASCII repertoire, this may for example include ignoring beyond the ASCII repertoire, this may for example include ignoring
the accents on received IRIs or resource names where appropriate. the accents on received IRIs or resource names where appropriate.
Please note that such mappings, including case mappings, are Please note that such mappings, including case mappings, are
language-dependent. language-dependent.
It can be difficult to unambiguously identify a resource if too many It can be difficult to unambiguously identify a resource if too many
mappings are taken into consideration. However, escaped and non- mappings are taken into consideration. However, escaped and non-
escaped parts of IRIs can always clearly be distinguished. Also, the escaped parts of IRIs can always clearly be distinguished. Also, the
regularity of UTF-8 (see [Duer97] makes the potential for collisions regularity of UTF-8 (see [Duer97]) makes the potential for collisions
lower than it may seem at first sight. lower than it may seem at first sight.
6.7 Upgrading Strategy 6.8 Upgrading Strategy
As this recommendation places further constraints on software for Where this recommendation places further constraints on software for
which many instances are already deployed, it is important to which many instances are already deployed, it is important to
introduce upgrades carefully, and to be aware of the various introduce upgrades carefully, and to be aware of the various
interdependencies. interdependencies.
If IRIs cannot be interpreted correctly, they should not be generated If IRIs cannot be interpreted correctly, they should not be generated
or transported. This suggests that upgrading URI interpreting or transported. This suggests that upgrading URI interpreting
software to accept IRIs should have highest priority. software to accept IRIs should have highest priority.
On the other hand, a single IRI is interpreted only by a single or On the other hand, a single IRI is interpreted only by a single or
very few interpreters that are known in advance, while it may be very few interpreters that are known in advance, while it may be
skipping to change at page 22, line 25 skipping to change at page 26, line 37
normalization expectations of a user or actual normalization when normalization expectations of a user or actual normalization when
entering an IRI do not match the normalization used on the server entering an IRI do not match the normalization used on the server
side. Conceptually, this is no different from the problems side. Conceptually, this is no different from the problems
surrounding the use of case-insensitive web servers. For example, a surrounding the use of case-insensitive web servers. For example, a
popular web page with a mixed case name (http://big.site/ popular web page with a mixed case name (http://big.site/
PopularPage.html) might be "spoofed" by someone who obtains access to PopularPage.html) might be "spoofed" by someone who obtains access to
http://big.site/popularpage.html. However, the introduction of http://big.site/popularpage.html. However, the introduction of
character normalization, and of additional mappings for user character normalization, and of additional mappings for user
convenience, may increase the chance for spoofing. convenience, may increase the chance for spoofing.
Spoofing can occur due to the fact that in the UCS, there are many Spoofing can occur because in the UCS, there are many characters that
characters that look very similar. Details are discussed in Section look very similar. Details are discussed in Section 6.5. Again,
6.4. Again, this is very similar to spoofing possibilities on US- this is very similar to spoofing possibilities on US-ASCII, e.g.
ASCII, e.g. using 'br0ken' or '1ame' URIs. using 'br0ken' or '1ame' URIs.
Spoofing can occur when URIs in various encodings are accepted to Spoofing can occur when URIs in various encodings are accepted to
deal with older user agents. In some cases, in particular for Latin- deal with older user agents. In some cases, in particular for Latin-
based resource names, this is usually easy to detect because UTF-8- based resource names, this is usually easy to detect because UTF-8-
encoded names, when interpreted and viewed as legacy encodings, encoded names, when interpreted and viewed as legacy encodings,
produce mostly garbage. In other cases, when concurrently used produce mostly garbage. In other cases, when concurrently used
encodings have a similar structure, but there are no characters that encodings have a similar structure, but there are no characters that
have exactly the same encoding, detection is more difficult. have exactly the same encoding, detection is more difficult.
Spoofing can occur in various IRI components, such as the domain name Spoofing can occur in various IRI components, such as the domain name
part or a path part. For considerations specific to the domain name part or a path part. For considerations specific to the domain name
part, see [Nameprep]. For the path part, administrators of sites part, see [Nameprep]. For the path part, administrators of sites
which allow independent users to create resources in the same subarea which allow independent users to create resources in the same subarea
may need to be careful to check for spoofing. may need to be careful to check for spoofing.
Spoofing can occur with bidirectional IRIs, if the restrictions in
Section 4.2 are not followed. The same visual representation may be
interpreted as different logical representations, and vice versa. It
is also very important that a correct Unicode bidirectional
implementation is used.
8. Change log 8. Change log
Changes from -00 to -01 8.1 Changes from -01 to -02
- New approach for Bidi section, many examples.
- Created idelims, removed '%' and '#'. Changed userinfo to
iuserinfo in iserver.
- Changed to ABNF defined by [RFC2234].
- Included bug fixes from [RFC2396bis].
- Additions to Acknowledgements.
8.2 Changes from -00 to -01
- Re-integrated the section on Bidi, some issues left. - Re-integrated the section on Bidi, some issues left.
- Integrated IDN, changed syntax (host, userinfo,....). - Integrated IDN, changed syntax (host, userinfo,....).
- Moved some text around, marked some as informational. - Moved some text around, marked some as informational.
- Made a clear distinction of IRI use for identification only and - Made a clear distinction of IRI use for identification only and
for resource resolution. for resource resolution.
- Fixed various details in wording, spelling,... - Fixed various details in wording, spelling,...
9. Acknowlegdements 9. Acknowledgements
We would like to thank Larry Masinter for his work as coauthor of We would like to thank Larry Masinter for his work as coauthor of
many earlier versions of this document (draft-masinter-url-i18n-xx). many earlier versions of this document (draft-masinter-url-i18n-xx).
The issue addressed here has been discussed at numerous times over The discussion on the issue addressed here has started a long time
the last years; for example, there was a thread in the HTML working ago. There was a thread in the HTML working group in August 1995
group in August 1995 (under the topic of "Globalizing URIs") in the (under the topic of "Globalizing URIs") and in the www-international
www-international mailing list in July 1996 (under the topic of mailing list in July 1996 (under the topic of "Internationalization
"Internationalization and URLs"), and ad-hoc meetings at the Unicode and URLs"), and ad-hoc meetings at the Unicode conferences in
conferences in September 1995 and September 1997. September 1995 and September 1997.
Thanks to Francois Yergeau, Chris Wendt, Yaron Goland, Graham Klyne, Thanks to Francois Yergeau, Matti Allouche, Roy Fielding, Tim
Roy Fielding, Tim Berners-Lee, M.T. Carrasco Benitez, James Clark, Berners-Lee, Mark Davis, M.T. Carrasco Benitez, James Clark, Tim
Andrea Vine, Misha Wolf, Leslie Daigle, Makoto MURATA, Tex Texin, Bray, Chris Wendt, Yaron Goland, Andrea Vine, Misha Wolf, Leslie
Bjoern Hoehrmann, Dan Oscarson, and many others for help with Daigle, Ted Hardie, Makoto MURATA, Steven Atkin, Ryan Stansifer, Tex
understanding the issues and possible solutions. Thanks also to the Texin, Graham Klyne, Bjoern Hoehrmann, Chris Lilly, Dan Oscarson,
members of the W3C I18N Working Group and Interest Group for their Elliotte Rusty Harold, Mike J. Brown, Carlos Viegas Damasio, and
many others for help with understanding the issues and possible
solutions, and getting the details right. Thanks also to the members
of the W3C I18N Working Group and Interest Group for their
contributions and their work on [CharMod], to the members of many contributions and their work on [CharMod], to the members of many
other W3C WGs for adopting the ideas, and to the members of the other W3C WGs for adopting the ideas, and to the members of the
Montreal IAB Workshop on Internationalization and Localization for Montreal IAB Workshop on Internationalization and Localization for
their review. their review.
References Normative References
[ISO10646] International Organization for Standardization,
"Information Technology - Universal Multiple-Octet Coded
Character Set (UCS) - Part 1: Architecture and Basic
Multilingual Plane - Part 2: Supplementary Planes", ISO
Standard 10646, with amendment, July 2002.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 2279, January 1998.
[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[RFC2732] Hinden, R., Carpenter, B. and L. Masinter, "Format for
Literal IPv6 Addresses in URL's", RFC 2732, December
1999.
[RFCXXXX] Faltstrom, P., Hoffman, P. and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
draft-ietf-idn-idna-14.txt (work in progress), October
2002, <http://www.ietf.org/internet-drafts/draft-ietf-
idn-idna-14.txt>.
[UNI15] Davis, M. and M. Duerst, "Unicode Normalization Forms",
Unicode Standard Annex #15, March 2001, <http://
www.unicode.org/unicode/reports/tr15/tr15-21.html>.
Non-normative References
[BidiEx] "Examples of bidirectional IRIs", <http://www.w3.org/
International/iri-edit/BidiExamples>.
[CharMod] Duerst, M., Yergeau, F., Ishida, R., Wolf, M., [CharMod] Duerst, M., Yergeau, F., Ishida, R., Wolf, M.,
Freytag, A. and T. Texin, "Character Model for the Freytag, A. and T. Texin, "Character Model for the
World Wide Web", World Wide Web Consortium Working World Wide Web", World Wide Web Consortium Working
Draft, April 2002, <http://www.w3.org/TR/charmod>. Draft, April 2002, <http://www.w3.org/TR/charmod>.
[Duer97] Duerst, M., "The Properties and Promises of UTF-8", [Duer97] Duerst, M., "The Properties and Promises of UTF-8",
Proc. 11th International Unicode Conference, San Jose Proc. 11th International Unicode Conference, San Jose
, September 1997, <http://www.ifi.unizh.ch/mml/ , September 1997, <http://www.ifi.unizh.ch/mml/
mduerst/papers/PDF/IUC11-UTF-8.pdf>. mduerst/papers/PDF/IUC11-UTF-8.pdf>.
skipping to change at page 24, line 11 skipping to change at page 29, line 33
International Unicode Conference, San Jose , International Unicode Conference, San Jose ,
September 2001, <http://www.w3.org/2001/Talks/0912- September 2001, <http://www.w3.org/2001/Talks/0912-
IUC-IRI/paper.html>. IUC-IRI/paper.html>.
[HTML4] Raggett, D., Le Hors, A. and I. Jacobs, "HTML 4.01 [HTML4] Raggett, D., Le Hors, A. and I. Jacobs, "HTML 4.01
Specification", World Wide Web Consortium Specification", World Wide Web Consortium
Recommendation, December 1999, <http://www.w3.org/TR/ Recommendation, December 1999, <http://www.w3.org/TR/
REC-html40/appendix/notes.html#h-B.2>. REC-html40/appendix/notes.html#h-B.2>.
[IDNURI] Duerst, M., "Internationalized Domain Names in URIs", [IDNURI] Duerst, M., "Internationalized Domain Names in URIs",
draft-ietf-idn-uri-02.txt (work in progress), July draft-ietf-idn-uri-03.txt (work in progress), July
2002, <http://www.ietf.org/internet-drafts/draft- 2002, <http://www.ietf.org/internet-drafts/draft-
ietf-idn-uri-02.txt>. ietf-idn-uri-03.txt>.
[IDNA] Faltstrom, P., Hoffman, P. and A. Faltstrom,
"Internationalizing Domain Names in Applications
(IDNA)", draft-ietf-idn-idna-09.txt (work in
progress), May 2002, <http://www.ietf.org/internet-
drafts/draft-ietf-idn-idna-09.txt>.
[ISO10646] International Organization for Standardization,
"Information Technology - Universal Multiple-Octet
Coded Character Set (UCS) - Part 1: Architecture and
Basic Multilingual Plane", ISO Standard 10646-1, with
amendments, October 2000.
[Nameprep] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep [Nameprep] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names", draft- Profile for Internationalized Domain Names", draft-
ietf-idn-nameprep-10.txt (work in progress), May ietf-idn-nameprep-11.txt (work in progress), June
2002, <http://www.ietf.org/internet-drafts/draft- 2002, <http://www.ietf.org/internet-drafts/draft-
ietf-idn-nameprep-10.txt>. ietf-idn-nameprep-11.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2130] Weider, C., Preston, C., Simonsen, K., Alvestrand, [RFC2130] Weider, C., Preston, C., Simonsen, K., Alvestrand,
H., Atkinson, R., Crispin, M. and P. Svanberg, "The H., Atkinson, R., Crispin, M. and P. Svanberg, "The
Report of the IAB Character Set Workshop held 29 Report of the IAB Character Set Workshop held 29
February - 1 March, 1996", RFC 2130, April 1997. February - 1 March, 1996", RFC 2130, April 1997.
[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997. [RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.
[RFC2192] Newman, C., "IMAP URL Scheme", RFC 2192, September [RFC2192] Newman, C., "IMAP URL Scheme", RFC 2192, September
1997. 1997.
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998. Languages", BCP 18, RFC 2277, January 1998.
[RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 2279, January 1998.
[RFC2384] Gellens, R., "POP URL Scheme", RFC 2384, August 1998. [RFC2384] Gellens, R., "POP URL Scheme", RFC 2384, August 1998.
[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, [RFC2396bis] Berners-Lee, T., Fielding, R. and L. Masinter,
"Uniform Resource Identifiers (URI): Generic Syntax", "Uniform Resource Identifier (URI): Generic Syntax",
RFC 2396, August 1998. Internet-Draft (work in progress), October 2002.
[RFC2397] Masinter, L., "The "data" URL scheme", RFC 2397, [RFC2397] Masinter, L., "The "data" URL scheme", RFC 2397,
August 1998. August 1998.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., [RFC2616] Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
Masinter, L., Leach, P. and T. Berners-Lee, Masinter, L., Leach, P. and T. Berners-Lee,
"Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616,
June 1999. June 1999.
[RFC2640] Curtin, B., "Internationalization of the File [RFC2640] Curtin, B., "Internationalization of the File
Transfer Protocol", RFC 2640, July 1999. Transfer Protocol", RFC 2640, July 1999.
[RFC2718] Masinter, L., Alvestrand, H., Zigmond, D. and R. [RFC2718] Masinter, L., Alvestrand, H., Zigmond, D. and R.
Petke, "Guidelines for new URL Schemes", RFC 2718, Petke, "Guidelines for new URL Schemes", RFC 2718,
November 1999. November 1999.
[RFC2732] Hinden, R., Carpenter, B. and L. Masinter, "Format
for Literal IPv6 Addresses in URL's", RFC 2732,
December 1999.
[UNIV3] The Unicode Consortium, "The Unicode Standard Version [UNIV3] The Unicode Consortium, "The Unicode Standard Version
3.0", Addison-Wesley, Reading, MA , 2000. 3.0", Addison-Wesley, Reading, MA , 2000.
[UNI15] Davis, M. and M. Duerst, "Unicode Normalization [UNI9] Davis, M., "The Bidirectional Algorithm", Unicode
Forms", Unicode Standard Annex #15, March 2001, Standard Annex #9, March 2002, <http://
<http://www.unicode.org/unicode/reports/tr15/tr15- www.unicode.org/unicode/reports/tr9>.
21.html>.
[UNIXML] Duerst, M. and A. Freytag, "Unicode in XML and other [UNIXML] Duerst, M. and A. Freytag, "Unicode in XML and other
Markup Languages", Unicode Technical Report #20, Markup Languages", Unicode Technical Report #20,
World Wide Web Consortium Note, Februar 2002, <http:/ World Wide Web Consortium Note, February 2002,
/www.w3.org/TR/unicode-xml/>. <http://www.w3.org/TR/unicode-xml/>.
[W3CIRI] "Internationalization - URIs and other identifiers", [W3CIRI] Duerst, M., "Internationalization - URIs and other
<http://www.w3.org/International/O-URL-and- identifiers", World Wide Web Consortium Note,
ident.html>. September 2002, <http://www.w3.org/International/O-
URL-and-ident.html>.
[XLink] DeRose, S., Maler, E. and D. Orchard, "XML Linking [XLink] DeRose, S., Maler, E. and D. Orchard, "XML Linking
Language (XLink) Version 1.0", World Wide Web Language (XLink) Version 1.0", World Wide Web
Consortium Recommendation, June 2001, <http:// Consortium Recommendation, June 2001, <http://
www.w3.org/TR/xlink/#link-locators>. www.w3.org/TR/xlink/#link-locators>.
[XML1] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. [XML1] Bray, T., Paoli, J., Sperberg-McQueen, C. and E.
Maler, "Extensible Markup Language (XML) 1.0 (Second Maler, "Extensible Markup Language (XML) 1.0 (Second
Edition)", World Wide Web Consortium Recommendation, Edition)", World Wide Web Consortium Recommendation,
including Erratum 26 at http://www.w3.org/XML/xml- including Erratum 26 at http://www.w3.org/XML/xml-
skipping to change at page 26, line 19 skipping to change at page 31, line 23
XML", World Wide Web Consortium Recommendation, XML", World Wide Web Consortium Recommendation,
January 1999, <http://www.w3.org/TR/REC-xml#sec- January 1999, <http://www.w3.org/TR/REC-xml#sec-
external-ent>. external-ent>.
[XMLSchema] Biron, P. and A. Malhotra, "XML Schema Part 2: [XMLSchema] Biron, P. and A. Malhotra, "XML Schema Part 2:
Datatypes", World Wide Web Consortium Recommendation, Datatypes", World Wide Web Consortium Recommendation,
May 2001, <http://www.w3.org/TR/xmlschema-2/#anyURI>. May 2001, <http://www.w3.org/TR/xmlschema-2/#anyURI>.
Authors' Addresses Authors' Addresses
Martin Duerst (Note: Please write "Duerst" with u-umlaut wherever Martin Duerst (Note: Please write "Duerst" with u-umlaut wherever possible, for example as "D&#252;rst in XML and HTML.)
possible, for example as "D&#252;rst in XML and HTML.) World Wide Web Consortium
W3C/Keio University 200 Technology Square
5322 Endo Cambridge, MA 02139
Fujisawa 252-8520 U.S.A.
Japan
Phone: +81 466 49 1170 Phone: +1 617 253 5509
Fax: +81 466 49 1171 Fax: +1 617 258 5999
EMail: duerst@w3.org EMail: duerst@w3.org
URI: http://www.w3.org/People/D%C3%BCrst/ URI: http://www.w3.org/People/D%C3%BCrst/
(Note: This is the escaped form of an IRI.) (Note: This is the escaped form of an IRI.)
Michel Suignard Michel Suignard
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
U.S.A. U.S.A.
 End of changes. 

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