draft-duerst-iri-06.txt   draft-duerst-iri-07.txt 
Network Working Group M. Duerst Network Working Group M. Duerst
Internet-Draft W3C Internet-Draft W3C
Expires: August 15, 2004 M. Suignard Expires: November 7, 2004 M. Suignard
Microsoft Corporation Microsoft Corporation
February 15, 2004 May 9, 2004
Internationalized Resource Identifiers (IRIs) Internationalized Resource Identifiers (IRIs)
draft-duerst-iri-06 draft-duerst-iri-07
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with By submitting this Internet-Draft, I certify that any applicable
all provisions of Section 10 of RFC2026. patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3668.
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2004). 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 [RFCYYYY]. An Resource Identifier (IRI), as a complement to the Uniform Resource
IRI is a sequence of characters from the Universal Character Set Identifier (URI). An IRI is a sequence of characters from the
[ISO10646]. A mapping from IRIs to URIs is defined, which means that Universal Character Set (Unicode/ISO 10646). A mapping from IRIs to
IRIs can be used instead of URIs where appropriate to identify URIs is defined, which means that IRIs can be used instead of URIs
resources. where appropriate to identify resources.
The approach of defining a new protocol element was chosen, instead The approach of defining a new protocol element was chosen, instead
of extending or changing the definition of URIs, to allow a clear of extending or changing the definition of URIs, to allow a clear
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 Editorial 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 public-iri@w3.org mailing list (publicly discussion, please use the public-iri@w3.org mailing list (publicly
archived at http://lists.w3.org/Archives/Public/public-iri/). An archived at http://lists.w3.org/Archives/Public/public-iri/). An
issues list for this document is maintained at http://www.w3.org/ issues list for this document is maintained at http://www.w3.org/
International/iri-edit#issues. For more information on the topic of International/iri-edit#issues. For more information on the topic of
this document, please also see [W3CIRI] and [Duerst01]. this document, please also see [W3CIRI] and [Duerst01].
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 1.4 Notation . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. IRI Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. IRI Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1 Summary of IRI Syntax . . . . . . . . . . . . . . . . . . . 7 2.1 Summary of IRI Syntax . . . . . . . . . . . . . . . . . . 7
2.2 ABNF for IRI References and IRIs . . . . . . . . . . . . . . 7 2.2 ABNF for IRI References and IRIs . . . . . . . . . . . . . 8
3. Relationship between IRIs and URIs . . . . . . . . . . . . . 9 3. Relationship between IRIs and URIs . . . . . . . . . . . . . . 10
3.1 Mapping of IRIs to URIs . . . . . . . . . . . . . . . . . . 10 3.1 Mapping of IRIs to URIs . . . . . . . . . . . . . . . . . 10
3.2 Converting URIs to IRIs . . . . . . . . . . . . . . . . . . 13 3.2 Converting URIs to IRIs . . . . . . . . . . . . . . . . . 13
3.2.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.2.1 Examples . . . . . . . . . . . . . . . . . . . . . . . 15
4. Bidirectional IRIs for Right-to-left Languages . . . . . . . 15 4. Bidirectional IRIs for Right-to-left Languages . . . . . . . . 16
4.1 Logical Storage and Visual Presentation . . . . . . . . . . 16 4.1 Logical Storage and Visual Presentation . . . . . . . . . 17
4.2 Bidi IRI Structure . . . . . . . . . . . . . . . . . . . . . 17 4.2 Bidi IRI Structure . . . . . . . . . . . . . . . . . . . . 18
4.3 Input of Bidi IRIs . . . . . . . . . . . . . . . . . . . . . 18 4.3 Input of Bidi IRIs . . . . . . . . . . . . . . . . . . . . 19
4.4 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.4 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 19
5. IRI Equivalence and Comparison . . . . . . . . . . . . . . . 20 5. IRI Equivalence and Comparison . . . . . . . . . . . . . . . . 21
5.1 Simple String Comparison . . . . . . . . . . . . . . . . . . 20 5.1 Simple String Comparison . . . . . . . . . . . . . . . . . 21
5.2 Conversion to URIs . . . . . . . . . . . . . . . . . . . . . 21 5.2 Conversion to URIs . . . . . . . . . . . . . . . . . . . . 22
5.3 Normalization . . . . . . . . . . . . . . . . . . . . . . . 21 5.3 Normalization . . . . . . . . . . . . . . . . . . . . . . 22
5.4 Preferred Forms . . . . . . . . . . . . . . . . . . . . . . 22 5.4 Preferred Forms . . . . . . . . . . . . . . . . . . . . . 23
6. Use of IRIs . . . . . . . . . . . . . . . . . . . . . . . . 23 6. Use of IRIs . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.1 Limitations on UCS Characters Allowed in IRIs . . . . . . . 23 6.1 Limitations on UCS Characters Allowed in IRIs . . . . . . 24
6.2 Software Interfaces and Protocols . . . . . . . . . . . . . 23 6.2 Software Interfaces and Protocols . . . . . . . . . . . . 24
6.3 Format of URIs and IRIs in Documents and Protocols . . . . . 23 6.3 Format of URIs and IRIs in Documents and Protocols . . . . 25
6.4 Use of UTF-8 for Encoding Original Characters . . . . . . . 24 6.4 Use of UTF-8 for Encoding Original Characters . . . . . . 25
6.5 Relative IRI References . . . . . . . . . . . . . . . . . . 25 6.5 Relative IRI References . . . . . . . . . . . . . . . . . 26
7. URI/IRI Processing Guidelines (informative) . . . . . . . . 25 7. URI/IRI Processing Guidelines (informative) . . . . . . . . . 26
7.1 URI/IRI Software Interfaces . . . . . . . . . . . . . . . . 25 7.1 URI/IRI Software Interfaces . . . . . . . . . . . . . . . 26
7.2 URI/IRI Entry . . . . . . . . . . . . . . . . . . . . . . . 26 7.2 URI/IRI Entry . . . . . . . . . . . . . . . . . . . . . . 27
7.3 URI/IRI Transfer Between Applications . . . . . . . . . . . 26 7.3 URI/IRI Transfer Between Applications . . . . . . . . . . 28
7.4 URI/IRI Generation . . . . . . . . . . . . . . . . . . . . . 27 7.4 URI/IRI Generation . . . . . . . . . . . . . . . . . . . . 28
7.5 URI/IRI Selection . . . . . . . . . . . . . . . . . . . . . 27 7.5 URI/IRI Selection . . . . . . . . . . . . . . . . . . . . 29
7.6 Display of URIs/IRIs . . . . . . . . . . . . . . . . . . . . 28 7.6 Display of URIs/IRIs . . . . . . . . . . . . . . . . . . . 29
7.7 Interpretation of URIs and IRIs . . . . . . . . . . . . . . 28 7.7 Interpretation of URIs and IRIs . . . . . . . . . . . . . 30
7.8 Upgrading Strategy . . . . . . . . . . . . . . . . . . . . . 29 7.8 Upgrading Strategy . . . . . . . . . . . . . . . . . . . . 30
8. Security Considerations . . . . . . . . . . . . . . . . . . 30 8. Security Considerations . . . . . . . . . . . . . . . . . . . 31
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33
Normative References . . . . . . . . . . . . . . . . . . . . 32 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
Non-normative References . . . . . . . . . . . . . . . . . . 32 10.1 Normative References . . . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 35 10.2 Non-normative References . . . . . . . . . . . . . . . . . . 34
Full Copyright Statement . . . . . . . . . . . . . . . . . . 36 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 36
A. Design Alternatives . . . . . . . . . . . . . . . . . . . . . 37
A.1 New Scheme(s) . . . . . . . . . . . . . . . . . . . . . . 37
A.2 Other Character Encodings than UTF-8 . . . . . . . . . . . 37
A.3 New Encoding Convention . . . . . . . . . . . . . . . . . 38
A.4 Indicating Character Encodings in the URI/IRI . . . . . . 38
Intellectual Property and Copyright Statements . . . . . . . . 39
1. Introduction 1. Introduction
1.1 Overview and Motivation 1.1 Overview and Motivation
A URI is defined in [RFCYYYY] as a sequence of characters chosen from A URI is defined in [RFCYYYY] 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 for IRIs are designed to be compatible with recent recommendations for
new URI schemes [RFC2718]. The compatibility is provided by new URI schemes [RFC2718]. The compatibility is provided by
specifying a well defined and deterministic mapping from the IRI specifying a well defined and deterministic mapping from the IRI
character sequence to the functionally equivalent URI character character sequence to the functionally equivalent URI character
sequence. Practical use of IRIs (or IRI references) in place of URIs sequence. Practical use of IRIs (or IRI references) in place of URIs
(or URI references) depends on the following conditions being met: (or URI references) depends 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
introduce IRIs into contexts that are not defined to accept IRIs into contexts that are not defined to accept them. For
them. For example, XML schema [XMLSchema] has an explicit type example, XML schema [XMLSchema] has an explicit type "anyURI" that
"anyURI" that designates the use of IRIs. designates the use of IRIs.
b) The protocol or format carrying the IRIs should have a b) The protocol or format carrying the IRIs should have a mechanism
mechanism to represent the wide range of characters used in to represent the wide range of characters used in IRIs, either
IRIs, either natively or by some protocol- or format-specific natively or by some protocol- or format-specific escaping
escaping mechanism (for example numeric character references in mechanism (for example numeric character references in [XML1]).
[XML1]).
c) The URI corresponding to the IRI in question has to encode c) The URI corresponding to the IRI in question has to encode
original characters into octets using UTF-8. For new URI original characters into octets using UTF-8. For new URI schemes,
schemes, this is recommended in [RFC2718]. It can apply to a this is recommended in [RFC2718]. It can apply to a whole scheme
whole scheme (e.g. IMAP URLs [RFC2192] and POP URLs [RFC2384], (e.g. IMAP URLs [RFC2192] and POP URLs [RFC2384], or the URN
or the URN syntax [RFC2141]). It can apply to a specific part syntax [RFC2141]). It can apply to a specific part of a URI, such
of a URI, such as the fragment identifier (e.g. [XPointer]). as the fragment identifier (e.g. [XPointer]). It can apply to a
It can apply to a specific URI or part(s) thereof. For specific URI or part(s) thereof. For details, please see Section
details, please see Section 6.4. 6.4.
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,
organization, control, or representation of data. For example, control, or representation of data. For example, "LATIN CAPITAL
"LATIN CAPITAL LETTER A" names a character. 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
character repertoire: A set of characters (in the mathematical character repertoire: A set of characters (in the mathematical sense)
sense)
sequence of characters: A sequence (one after another) of sequence of characters: A sequence (one after another) of characters
characters
sequence of octets: A sequence (one after another) of octets sequence of octets: A sequence (one after another) of octets
(character) encoding: A method of representing a sequence of character encoding: A method of representing a sequence of characters
characters as a sequence of octets (maybe with variants). A as a sequence of octets (maybe with variants). A method of
method of (unambiguously) converting a sequence of octets into (unambiguously) converting a sequence of octets into a sequence of
a sequence of characters. characters.
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 UCS: Universal Character Set; the coded character set defined by ISO/
[ISO10646] and [UNIV4]. IEC 10646 [ISO10646] and the Unicode Standard [UNIV4].
IRI reference: The term "IRI reference" denotes the common usage IRI reference: The term "IRI reference" denotes the common usage of
of an internationalized resource identifier. An IRI reference an internationalized resource identifier. An IRI reference may be
may be absolute or relative. However, the "IRI" that results absolute or relative. However, the "IRI" that results from such a
from such a reference only includes absolute IRIs; any relative reference only includes absolute IRIs; any relative IRIs are
IRIs are resolved to their absolute form. Note that in resolved to their absolute form. Note that in [RFC2396], URIs did
[RFC2396], URIs did not include fragment identifiers, but in not include fragment identifiers, but in [RFCYYYY], fragment
[RFCYYYY], fragment identifiers are part of URIs. identifiers are part of URIs.
running text: Human text (paragraphs, sentences, phrases) with running text: Human text (paragraphs, sentences, phrases) with syntax
syntax according to orthographic conventions of a natural according to orthographic conventions of a natural language, as
language, as opposed to syntax defined for ease of processing opposed to syntax defined for ease of processing by machines
by machines (markup, programming languages,...). (markup, programming languages,...).
protocol element: Any portion of a message which affects processing
of that message by the protocol in question.
presentation element: Presentation form corresponding to a protocol
element, for example using a wider range of characters.
create (an URI or IRI): With respect to URIs and IRIs, the word
'create' is used for the initial creation. This may be the initial
creation of a resource with a certain name, or the initial
exposition of a resource under a particular name.
generate (an URI or IRI): With respect to URIs and IRIs, the word
'generate' is used when the IRI is generated by derivation from
other information.
1.4 Notation 1.4 Notation
RFCs and Internet Drafts currently do not allow any characters RFCs and Internet Drafts currently do not allow any characters
outside the US-ASCII repertoire. Therefore, this document uses outside the US-ASCII repertoire. Therefore, this document uses
various special notations to denote such characters in examples. various special notations to denote such characters in examples.
In text, characters outside US-ASCII are sometimes referenced by In text, characters outside US-ASCII are sometimes referenced by
using a prefix of 'U+', followed by four to six hexadecimal digits. using a prefix of 'U+', followed by four to six hexadecimal digits.
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XML Notation uses leading '&#x', trailing ';', and the hexadecimal XML Notation uses leading '&#x', trailing ';', and the hexadecimal
number of the character in the UCS in between. Example: я number of the character in the UCS in between. Example: я
stands for CYRILLIC CAPITAL LETTER YA. In this notation, an actual stands for CYRILLIC CAPITAL LETTER YA. In this notation, an actual
'&' is denoted by '&'. '&' is denoted by '&'.
Bidi Notation is used for bidirectional examples: lower case ASCII Bidi Notation is used for bidirectional examples: lower case ASCII
letters stand for Latin letters or other letters that are written letters stand for Latin letters or other letters that are written
left-to-right, whereas upper case letters represent Arabic or Hebrew left-to-right, whereas upper case letters represent Arabic or Hebrew
letters that are written right-to-left. letters that are written right-to-left.
To denote actual octets in examples (as opposed to escaped octets), To denote actual octets in examples (as opposed to percent-encoded
the two hex digits denoting the octet are enclosed in "<" and ">". octets), the two hex digits denoting the octet are enclosed in "<"
For example, the octet often denoted as 0xc9 is denoted here as <c9>. and ">". For example, the octet often denoted as 0xc9 is denoted here
as <c9>.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
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).
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limitations given in the syntax rules below and in Section 6.1. limitations given in the syntax rules below and in Section 6.1.
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 [RFCYYYY]. All the operations defined in is the same as that in [RFCYYYY]. All the operations defined in
[RFCYYYY], such as the resolution of relative URIs, can be applied to [RFCYYYY], 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.
Characters outside the US-ASCII range are not reserved and therefore Characters outside the US-ASCII range are not reserved and therefore
MUST NOT be used for syntactical purposes such as to delimit MUST NOT be used for syntactical purposes such as to delimit
components in newly defined schemes. As an example, it is not components in newly defined schemes. As an example, it is not allowed
allowed to use U+00A2, CENT SIGN, as a delimiter in IRIs, because it to use U+00A2, CENT SIGN, as a delimiter in IRIs, because it is in
is in the 'iunreserved' category, in the same way as it is not the 'iunreserved' category, in the same way as it is not possible to
possible to use '-' as a delimiter, because it is in the 'unreserved' use '-' as a delimiter, because it is in the 'unreserved' category in
category in URIs. 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 URI references and URIs, they can also be by their transformation to URI references and URIs, they can also be
accepted and processed directly. Therefore, an ABNF definition for accepted and processed directly. Therefore, an ABNF definition for
IRI references (which are the most general concept and the start of IRI references (which are the most general concept and the start of
the grammar) and IRIs is given here. The syntax of this ABNF is the grammar) and IRIs is given here. The syntax of this ABNF is
described in [RFC2234]. Character numbers are taken from the UCS, described in [RFC2234]. Character numbers are taken from the UCS,
without implying any actual binary encoding. Terminals in the ABNF without implying any actual binary encoding. Terminals in the ABNF
are characters, not bytes. are characters, not bytes.
The following rules are different from [RFCYYYY]: The following rules are different from [RFCYYYY]:
IRI = scheme ":" ["//" iauthority] ipath ["?" iquery] IRI = scheme ":" ihier-part [ "?" iquery ]
["#" ifragment] ["#" ifragment]
IRI-reference = IRI / relative-IRI
relative-IRI = ["//" iauthority] ipath ["?" iquery] ihier-part = "//" iauthority ipath-abempty
["#" ifragment] / ipath-abs
/ ipath-rootless
/ ipath-empty
absolute-IRI = scheme ":" ["//" iauthority] ipath ["?" iquery] IRI-reference = IRI / relative-IRI
iauthority = [ iuserinfo "@" ] ihost [ ":" port ] absolute-IRI = scheme ":" ihier-part [ "?" iquery ]
iuserinfo = *( iunreserved / pct-encoded / sub-delims relative-IRI = irelative-part [ "?" iquery ] [ "#" ifragment ]
/ ":" )
irelative-part = "//" iauthority ipath-abempty
/ ipath-abs
/ ipath-noscheme
/ ipath-empty
iauthority = [ iuserinfo "@" ] ihost [ ":" port ]
iuserinfo = *( iunreserved / pct-encoded / sub-delims / ":" )
ihost = IP-literal / IPv4address / ireg-name ihost = IP-literal / IPv4address / ireg-name
ireg-name = 0*255( iunreserved / pct-encoded / sub-delims ) ireg-name = 0*255( iunreserved / pct-encoded / sub-delims )
ipath = isegment *( "/" isegment ) ipath = ipath-abempty ; begins with "/" or is empty
/ ipath-abs ; begins with "/" but not "//"
/ ipath-noscheme ; begins with a non-colon segment
/ ipath-rootless ; begins with a segment
/ ipath-empty ; zero characters
ipath-abempty = *( "/" isegment )
ipath-abs = "/" [ isegment-nz *( "/" isegment ) ]
ipath-noscheme = isegment-nzc *( "/" isegment )
ipath-rootless = isegment-nz *( "/" isegment )
ipath-empty = 0<ipchar>
isegment = *ipchar isegment = *ipchar
isegment-nz = 1*ipchar
isegment-nzc = 1*( iunreserved / pct-encoded / sub-delims
/ "@" )
ipchar = iunreserved / pct-encoded / sub-delims / ":"
/ "@"
iquery = *( ipchar / iprivate / "/" / "?" ) iquery = *( ipchar / iprivate / "/" / "?" )
ifragment = *( ipchar / "/" / "?" ) ifragment = *( ipchar / "/" / "?" )
ipchar = iunreserved / pct-encoded / sub-delims / ":"
/ "@"
iunreserved = ALPHA / DIGIT / "-" / "." / "_" / "~" / ucschar iunreserved = ALPHA / DIGIT / "-" / "." / "_" / "~" / ucschar
ucschar = %xA0-D7FF / %xF900-FDCF / %xFDF0-FFEF / ucschar = %xA0-D7FF / %xF900-FDCF / %xFDF0-FFEF
/ %x10000-1FFFD / %x20000-2FFFD / %x30000-3FFFD / %x10000-1FFFD / %x20000-2FFFD / %x30000-3FFFD
/ %x40000-4FFFD / %x50000-5FFFD / %x60000-6FFFD / %x40000-4FFFD / %x50000-5FFFD / %x60000-6FFFD
/ %x70000-7FFFD / %x80000-8FFFD / %x90000-9FFFD / %x70000-7FFFD / %x80000-8FFFD / %x90000-9FFFD
/ %xA0000-AFFFD / %xB0000-BFFFD / %xC0000-CFFFD / %xA0000-AFFFD / %xB0000-BFFFD / %xC0000-CFFFD
/ %xD0000-DFFFD / %xE1000-EFFFD / %xD0000-DFFFD / %xE1000-EFFFD
iprivate = %xE000-F8FF / %xF0000-FFFFD / %x100000-10FFFD iprivate = %xE000-F8FF / %xF0000-FFFFD / %x100000-10FFFD
Some productions ambiguous. The "first-match-wins" (a.k.a. Some productions are ambiguous. The "first-match-wins" (a.k.a.
"greedy") algorithm applies. For details, see [RFCYYYY]. "greedy") algorithm applies. For details, see [RFCYYYY].
The following are the same as [RFCYYYY]: The following are the same as in [RFCYYYY]:
scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." ) scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
port = *DIGIT port = *DIGIT
IP-literal = "[" ( IPv6address | IPvFuture ) "]" IP-literal = "[" ( IPv6address / IPvFuture ) "]"
IPvFuture = "v" HEXDIG "." 1*( unreserved / sub-delims / ":" )
IPv6address = 6( h4 ":" ) ls32
/ "::" 5( h4 ":" ) ls32
/ [ h4 ] "::" 4( h4 ":" ) ls32
/ [ *1( h4 ":" ) h4 ] "::" 3( h4 ":" ) ls32
/ [ *2( h4 ":" ) h4 ] "::" 2( h4 ":" ) ls32
/ [ *3( h4 ":" ) h4 ] "::" h4 ":" ls32
/ [ *4( h4 ":" ) h4 ] "::" ls32
/ [ *5( h4 ":" ) h4 ] "::" h4
/ [ *6( h4 ":" ) h4 ] "::"
h4 = 1*4HEXDIG IPvFuture = "v" 1*HEXDIG "." 1*( unreserved / sub-delims
/ ":" )
ls32 = ( h4 ":" h4 ) / IPv4address IPv6address = 6( h16 ":" ) ls32
/ "::" 5( h16 ":" ) ls32
/ [ h16 ] "::" 4( h16 ":" ) ls32
/ [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
/ [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
/ [ *3( h16 ":" ) h16 ] "::" h16 ":" ls32
/ [ *4( h16 ":" ) h16 ] "::" ls32
/ [ *5( h16 ":" ) h16 ] "::" h16
/ [ *6( h16 ":" ) h16 ] "::"
h16 = 1*4HEXDIG
ls32 = ( h16 ":" h16 ) / IPv4address
IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet IPv4address = dec-octet "." dec-octet "." dec-octet
"." dec-octet
dec-octet = DIGIT ; 0-9 dec-octet = DIGIT ; 0-9
/ %x31-39 DIGIT ; 10-99 / %x31-39 DIGIT ; 10-99
/ "1" 2DIGIT ; 100-199 / "1" 2DIGIT ; 100-199
/ "2" %x30-34 DIGIT ; 200-249 / "2" %x30-34 DIGIT ; 200-249
/ "25" %x30-35 ; 250-255 / "25" %x30-35 ; 250-255
pct-encoded = "%" HEXDIG HEXDIG pct-encoded = "%" HEXDIG HEXDIG
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~" unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
skipping to change at page 9, line 48 skipping to change at page 10, line 33
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
mechanisms currently only are defined for URIs. (Additional mechanisms currently only are defined for URIs. In this case, IRIs
can serve as presentation elements for URI protocol elements. An
example would be an address bar in a Web user agent. (Additional
rationale is given in Section 3.1.) rationale is given in Section 3.1.)
3.1 Mapping of IRIs to URIs 3.1 Mapping of IRIs to URIs
This section defines how to map an IRI to a URI. Everything in this This section defines how to map an IRI to a URI. Everything in this
section applies also to IRI references and URI references, as well as section applies also to IRI references and URI references, as well as
components thereof (for example fragment identifiers). components thereof (for example fragment identifiers).
This mapping has two purposes: This mapping has two purposes:
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.
restrictions can be applied to IRIs by noting that IRIs are Scheme-specific restrictions are applied to IRIs by converting
only valid if they map to syntactically valid URIs. This means IRIs to URIs and checking the URIs against the scheme-specific
that such syntactical restrictions do not have to be defined restrictions.
again on the IRI level.
b) Interpretational: URIs identify resources in various ways. b) Interpretational: URIs identify resources in various ways. IRIs
IRIs also identify resources. When the IRI is used solely for also identify resources. When the IRI is used solely for
identification purposes, it is not necessary to map the IRI to identification purposes, it is not necessary to map the IRI to a
a URI (see Section 5). However, when an IRI is used for URI (see Section 5). However, when an IRI is used for resource
resource retrieval, the resource that the IRI locates is the retrieval, the resource that the IRI locates is the same as the
same as the one located by the URI obtained after converting one located by the URI obtained after converting the IRI according
the IRI according to the procedure defined here. This means to the procedure defined here. This means that there is no need to
that there is no need to define resolution separately on the define resolution separately on the IRI level.
IRI level.
Applications MUST map IRIs to URIs using the following two steps. Applications MUST map IRIs to URIs using the following two steps.
Step 1) This step generates a UCS-based encoding from the original Step 1) This step generates a UCS-based character encoding from the
IRI format. This step has three variants, depending on the original IRI format. This step has three variants, depending on
form of the input. the 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
or otherwise represented as a sequence of characters otherwise represented as a sequence of characters independent
independent of any encoding: Represent the IRI as a of any character encoding: Represent the IRI as a sequence of
sequence of characters from the UCS normalized according characters from the UCS normalized according to Normalization
to Normalization Form C (NFC, [UTR15]). Form C (NFC, [UTR15]).
Variant B) If the IRI is in some digital representation Variant B) If the IRI is in some digital representation (e.g. an
(e.g. an octet stream) in some known non-Unicode octet stream) in some known non-Unicode character encoding:
encoding: Convert the IRI to a sequence of characters Convert the IRI to a sequence of characters from the UCS
from the UCS normalized according to NFC. normalized according to NFC.
Variant C) If the IRI is in an Unicode-based encoding (for Variant C) If the IRI is in an Unicode-based character encoding
example UTF-8 or UTF-16): Do not normalize. Move (for example UTF-8 or UTF-16): Do not normalize. Move directly
directly to Step 2. to Step 2.
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 2.1 through 2.3 below. The disallowed characters
consist of all non-ASCII characters allowed in IRIs. consist of all non-ASCII characters allowed in IRIs.
1) Convert the character to a sequence of one or more octets 2.1) Convert the character to a sequence of one or more octets
using UTF-8 [RFC3629]. using UTF-8 [RFC3629].
2) Convert each octet to %HH, where HH is the hexadecimal 2.2) 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
the escaping mechanism in Section 2.4.1 of [RFCYYYY]. To percent-encoding mechanism in Section 2.1 of [RFCYYYY]. To
reduce variability, the hexadecimal notation SHOULD use reduce variability, the hexadecimal notation SHOULD use upper
upper case letters. case letters.
3) Replace the original character by the resulting character 2.3) Replace the original character by the resulting character
sequence (i.e. a sequence of %HH triplets). sequence (i.e. a sequence of %HH triplets).
The above mapping from IRIs to URIs produces URIs fully conforming to The above mapping from IRIs to URIs produces URIs fully conforming to
[RFCYYYY]. The mapping is also an identity transformation for URIs [RFCYYYY]. The mapping is also an identity transformation for URIs
and is idempotent -- applying the mapping a second time will not and is idempotent -- applying the mapping a second time will not
change anything. Every URI is by definition an IRI. change anything. Every URI is by definition an IRI.
Infrastructure accepting IRIs MAY also convert the ireg-name Infrastructure accepting IRIs MAY convert the ireg-name component of
component of an IRI as follows (before step 2 above) if it knows that an IRI as follows (before Step 2.2 above) for schemes that are known
the scheme in question uses domain names: Replace the iregname part to use domain names in ireg-name, but where the scheme definition
of the IRI by the part converted using the ToASCII operation does not allow percent-encoding for ireg-name: Replace the ireg-name
specified in Section 4.1 of [RFC3490], with the flag part of the IRI by the part converted using the ToASCII operation
specified in Section 4.1 of [RFC3490] on each dot-separated label,
and using U+002E (FULL STOP) as a label separator, with the flag
UseSTD3ASCIIRules set to TRUE and the flag AllowUnassigned set to UseSTD3ASCIIRules set to TRUE and the flag AllowUnassigned set to
FALSE for creating IRIs and set to TRUE otherwise. The ToASCII FALSE for creating IRIs and set to TRUE otherwise. The ToASCII
operation may fail, but this would mean that the IRI cannot be operation may fail, but this would mean that the IRI cannot be
resolved. For example, the IRI resolved. This conversion SHOULD be used when the goal is to maximize
interoperability with legacy URI resolvers. For example, the IRI
http://r&#xE9;sum&#xE9;.example.org may be converted to http://r&#xE9;sum&#xE9;.example.org may be converted to
http://xn--rsum-bpad.example.org instead of http://xn--rsum-bpad.example.org instead of
http://r%C3%A9sum%C3%A9.example.org. http://r%C3%A9sum%C3%A9.example.org.
Note: The uniform treatment of the whole IRI in step 2) above is An IRI with a scheme that is known to use domain names in ireg-name,
but where the scheme definition does not allow percent-encoding for
ireg-name, meets scheme-specific restrictions if either the
straightforward conversion or the conversion using the ToASCII
operation on ireg-name result in an URI that meets the
scheme-specific restrictions. An IRI with a scheme that is known to
use domain names in ireg-name, but where the scheme definition does
not allow percent-encoding for ireg-name, resolves to the URI
obtained after converting the IRI including using the ToASCII
operation on ireg-name. Implementations do not need to do this
conversion as long as they produce the same result.
Note: The uniform treatment of the whole IRI in Step 2.2 above is
important to not make processing dependent on URI scheme. See important to not make processing dependent on URI scheme. See
[Gettys] for an in-depth discussion. [Gettys] for an in-depth discussion.
Note: In practice, the difference above will not be noticed if Note: In practice, the difference above will not be noticed if
mapping from IRI to URI and resolution is tightly integrated mapping from IRI to URI and resolution is tightly integrated (e.g.
(e.g. carried out in the same user agent). But conversion carried out in the same user agent). But conversion using
using [RFC3490] may be able to better deal with backwards [RFC3490] may be able to better deal with backwards compatibility
compatibility issues in case mapping and resolution are issues in case mapping and resolution are separated, as in the
separated, as in the case of using an HTTP proxy. case of using an HTTP proxy.
Note: Internationalized Domain Names may be contained in parts of Note: Internationalized Domain Names may be contained in parts of an
an IRI other than the ireg-name part. It is the responsibility IRI other than the ireg-name part. It is the responsibility of
of scheme-specific implementations (if the Internationalized scheme-specific implementations (if the Internationalized Domain
Domain Name is part of the scheme syntax) or of server-side Name is part of the scheme syntax) or of server-side
implementations (if the Internationalized Domain Name is part implementations (if the Internationalized Domain Name is part of
of 'iquery') to apply the necessary conversions at the 'iquery') to apply the necessary conversions at the appropriate
appropriate point. Example: Trying to validate the Web page at point. Example: Trying to validate the Web page at
http://r&#xE9;sum&#xE9;.example.org would lead to an IRI of http://r&#xE9;sum&#xE9;.example.org would lead to an IRI of
http://validator.w3.org/ http://validator.w3.org/
check?uri=http%3A%2F%2Fr&#xE9;sum&#xE9;.example.org, which check?uri=http%3A%2F%2Fr&#xE9;sum&#xE9;.example.org, which would
would convert to a URI of convert to a URI of
http://validator.w3.org/ http://validator.w3.org/
check?uri=http%3A%2F%2Fr%C3%A9sum%C3%A9.example.org. The check?uri=http%3A%2F%2Fr%C3%A9sum%C3%A9.example.org. The server
server side implementation would be responsible to do the side implementation would be responsible to do the necessary
necessary conversions in order to be able to retrieve the Web conversions in order to be able to retrieve the Web page.
page.
Infrastructure accepting IRIs MAY also deal with the printable Infrastructure accepting IRIs MAY also deal with the printable
characters in US-ASCII that are not allowed in URIs, namely "<", ">", characters in US-ASCII that are not allowed in URIs, namely "<", ">",
'"', Space, "{", "}", "|", "\", "^", and "`", in step 2) above. If '"', Space, "{", "}", "|", "\", "^", and "`", in Step 2.2 above. If
such characters are found but are not converted, then the conversion such characters are found but are not converted, then the conversion
SHOULD fail. Please note that the number sign ("#"), the percent SHOULD fail. Please note that the number sign ("#"), the percent sign
sign ("%"), and the square bracket characters ("[", "]") are not part ("%"), and the square bracket characters ("[", "]") are not part of
of the above list, and MUST NOT be converted. Protocols and formats the above list, and MUST NOT be converted. Protocols and formats that
that have used earlier definitions of IRIs including these characters have used earlier definitions of IRIs including these characters MAY
MAY require unescaping of these characters as a preprocessing step to require percent-encoding of these characters as a preprocessing step
extract the actual IRI from a given field. Such preprocessing MAY to extract the actual IRI from a given field. Such preprocessing MAY
also be used by applications allowing the user to enter an IRI. also be used by applications allowing the user to enter an IRI.
Note: In this process (in step 2.3), characters allowed in URI Note: In this process (in Step 2.3), characters allowed in URI
references as well as existing escape sequences are not escaped references as well as existing percent-encoded sequences are not
further. (This mapping is similar to, but different from, the encoded further. (This mapping is similar to, but different from,
escaping applied when including arbitrary content into some the encoding applied when including arbitrary content into some
part of a URI.) For example, an IRI of part of a URI.) For example, an IRI of
http://www.example.org/red%09ros&#xE9;#red (in XML notation) is http://www.example.org/red%09ros&#xE9;#red (in XML notation) is
converted to converted to
http://www.example.org/red%09ros%C3%A9#red, not to something http://www.example.org/red%09ros%C3%A9#red, not to something like
like
http%3A%2F%2Fwww.example.org%2Fred%2509ros%C3%A9%23red. http%3A%2F%2Fwww.example.org%2Fred%2509ros%C3%A9%23red.
Note: Some older software transcoding to UTF-8 may produce illegal Note: Some older software transcoding to UTF-8 may produce illegal
output for some input, in particular for characters outside the output for some input, in particular for characters outside the
BMP (Basic Multilingual Plane). As an example, for the BMP (Basic Multilingual Plane). As an example, for the following
following IRI with non-BMP characters (in XML Notation): IRI with non-BMP characters (in XML Notation):
http://example.com/&#x10300;&#x10301;&#x10302; http://example.com/&#x10300;&#x10301;&#x10302;
(the first three letters of the Old Italic alphabet) the (the first three letters of the Old Italic alphabet) the correct
correct conversion to a URI is: conversion to a URI is:
http://example.com/%F0%90%8C%80%F0%90%8C%81%F0%90%8C%82 http://example.com/%F0%90%8C%80%F0%90%8C%81%F0%90%8C%82
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
result in an IRI which maps back to the URI that was used as an input result in an IRI which maps back to the URI that was used as an input
for the conversion (except for potential case differences in escape for the conversion (except for potential case differences in
sequences). However, the IRI resulting from this conversion may not percent-encoding). However, the IRI resulting from this conversion
be exactly the same as the original IRI (if there ever was one). 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 percent-encodings, but not all
can be eliminated. There are several reasons for this: percent-encodings can be eliminated. There are several reasons for
this:
a) Some escape sequences are necessary to distinguish escaped and a) Some percent-encodings are necessary to distinguish
unescaped uses of reserved characters. percent-encoded and unencoded uses of reserved characters.
b) Some escape sequences cannot be interpreted as sequences of b) Some percent-encodings cannot be interpreted as sequences of UTF-8
UTF-8 octets. octets.
(Note: The octet patterns of UTF-8 are highly regular. (Note: The octet patterns of UTF-8 are highly regular. Therefore,
Therefore, there is a very high probability, but no guarantee, there is a very high probability, but no guarantee, that
that escape sequences that can be interpreted as sequences of percent-encodings that can be interpreted as sequences of UTF-8
UTF-8 octets actually originated from UTF-8. For a detailed octets actually originated from UTF-8. For a detailed discussion,
discussion, see [Duerst97].) see [Duerst97].)
c) The conversion may result in a character that is not c) The conversion may result in a character that is not appropriate
appropriate in an IRI. See Section 6.1 for further details. in an IRI. See Section 6.1 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 percent-encodings (% followed by two hexadecimal
digits) except those corresponding to '%', characters in digits) except those corresponding to '%', characters in
'reserved', and characters in US-ASCII not allowed in URIs, to 'reserved', and characters in US-ASCII not allowed in URIs, to the
the corresponding octets. corresponding octets.
3) Re-escape any octet produced in step 2) that is not part of a 3) Re-percent-encode any octet produced in Step 2 that is not part of
strictly legal UTF-8 octet sequence. a strictly legal UTF-8 octet sequence.
4) Re-escape all octets produced in step 3) that in UTF-8 4) Re-percent-encode all octets produced in Step 3 that in UTF-8
represent characters that are not appropriate according to represent characters that are not appropriate according to Section
Section 4.1 and Section 6.1. 4.1 and Section 6.1.
5) Interpret the resulting octet sequence as a sequence of 5) Interpret the resulting octet sequence as a sequence of characters
characters encoded in UTF-8. encoded in UTF-8.
This procedure will convert as many escaped non-ASCII characters as This procedure will convert as many percent-encoded non-ASCII
possible to characters in an IRI. Because there are some choices characters as possible to characters in an IRI. Because there are
when applying step 4) (see Section 6.1), results may vary. some choices when applying Step 4 (see Section 6.1), results may
vary.
Conversions from URIs to IRIs MUST NOT use any other encoding than Conversions from URIs to IRIs MUST NOT use any other character
UTF-8 in steps 3) and 4) above, even if it might be possible from encoding than UTF-8 in Steps 3 and 4 above, even if it might be
context to guess that another encoding than UTF-8 was used in the possible from context to guess that another character encoding than
URI. As an example, the URI http://www.example.org/r%E9sum%E9.html UTF-8 was used in the URI. As an example, the URI http://
might with some guessing be interpreted to contain two e-acute www.example.org/r%E9sum%E9.html might with some guessing be
characters encoded as iso-8859-1. It must not be converted to an IRI interpreted to contain two e-acute characters encoded as iso-8859-1.
containing these e-acute characters. Otherwise, the IRI will in the It must not be converted to an IRI containing these e-acute
future be mapped to http://www.example.org/r%C3%A9sum%C3%A9.html, characters. Otherwise, the IRI will in the future be mapped to http:/
which is a different URI than http://www.example.org/r%E9sum%E9.html. /www.example.org/r%C3%A9sum%C3%A9.html, which is a different URI than
http://www.example.org/r%E9sum%E9.html.
3.2.1 Examples 3.2.1 Examples
This section shows various examples of converting URIs to IRIs. The This section shows various examples of converting URIs to IRIs. The
notation <hh> is used to denote octets outside those that can be notation <hh> is used to denote octets outside those that can be
represented in this document. Each example shows the result after represented in this document. Each example shows the result after
applying each of the steps 1) to 5). XML Notation is used for the applying each of the Steps 1 to 5. XML Notation is used for the final
final result. result.
The following example contains the sequence '%C3%BC', which is a The following example contains the sequence '%C3%BC', which is a
strictly legal UTF-8 sequence, and which is converted into the actual strictly legal UTF-8 sequence, and which is converted into the actual
character U+00FC LATIN SMALL LETTER U WITH DIAERESIS (also known as character U+00FC LATIN SMALL LETTER U WITH DIAERESIS (also known as
u-umlaut). u-umlaut).
1) http://www.example.org/D%C3%BCrst 1) http://www.example.org/D%C3%BCrst
2) http://www.example.org/D<c3><bc>rst 2) http://www.example.org/D<c3><bc>rst
3) http://www.example.org/D<c3><bc>rst 3) http://www.example.org/D<c3><bc>rst
4) http://www.example.org/D<c3><bc>rst 4) http://www.example.org/D<c3><bc>rst
5) http://www.example.org/D&#xFC;rst 5) http://www.example.org/D&#xFC;rst
The following example contains the sequence '%FC', which might The following example contains the sequence '%FC', which might
represent U+00FC LATIN SMALL LETTER U WITH DIAERESIS in the represent U+00FC LATIN SMALL LETTER U WITH DIAERESIS in the
iso-8859-1 encoding. (It might represent other characters in other iso-8859-1 character encoding. (It might represent other characters
encodings. For example, the octet <fc> in iso-8859-5 represents in other character encodings. For example, the octet <fc> in
U+045C CYRILLIC SMALL LETTER KJE.) Because <fc> is not part of a iso-8859-5 represents U+045C CYRILLIC SMALL LETTER KJE.) Because <fc>
strictly legal UTF-8 sequence, it is re-escaped in step 3). is not part of a strictly legal UTF-8 sequence, it is
re-percent-encoded in Step 3.
1) http://www.example.org/D%FCrst 1) http://www.example.org/D%FCrst
2) http://www.example.org/D<fc>rst 2) http://www.example.org/D<fc>rst
3) http://www.example.org/D%FCrst 3) http://www.example.org/D%FCrst
4) http://www.example.org/D%FCrst 4) http://www.example.org/D%FCrst
5) http://www.example.org/D%FCrst 5) http://www.example.org/D%FCrst
The following example contains '%e2%80%ae', which is the escaped The following example contains '%e2%80%ae', which is the
UTF-8 encoding of U+202E, RIGHT-TO-LEFT OVERRIDE. Section 4.1 percent-encoded
forbids the direct use of this character in an IRI. Therefore, the UTF-8 character encoding of U+202E, RIGHT-TO-LEFT OVERRIDE. Section
corresponding octets are re-escaped in step 4). This example shows 4.1 forbids the direct use of this character in an IRI. Therefore,
that the case (upper or lower) of letters used in escapes may not be the corresponding octets are re-percent-encoded in Step 4. This
preserved. The example also contains a punycode-encoded domain name example shows that the case (upper or lower) of letters used in
label (xn--99zt52a), which is not converted. percent-encodes may not be preserved. The example also contains a
punycode-encoded domain name label (xn--99zt52a), which is not
converted.
1) http://xn--99zt52a.example.org/%e2%80%ae 1) http://xn--99zt52a.example.org/%e2%80%ae
2) http://xn--99zt52a.example.org/<e2><80><ae> 2) http://xn--99zt52a.example.org/<e2><80><ae>
3) http://xn--99zt52a.example.org/<e2><80><ae> 3) http://xn--99zt52a.example.org/<e2><80><ae>
4) http://xn--99zt52a.example.org/%E2%80%AE 4) http://xn--99zt52a.example.org/%E2%80%AE
5) http://xn--99zt52a.example.org/%E2%80%AE 5) http://xn--99zt52a.example.org/%E2%80%AE
Implementations with scheme-specific knowledge MAY convert punycode- Implementations with scheme-specific knowledge MAY convert
encoded domain name labels to the corresponding characters using the punycode-encoded domain name labels to the corresponding characters
ToUnicode procedure. Thus, for the example above, the label xn-- using the ToUnicode procedure. Thus, for the example above, the label
99zt52a may be converted to U+7D0D U+8C46 (Japanese Natto), leading xn--99zt52a may be converted to U+7D0D U+8C46 (Japanese Natto),
to the overall IRI of leading to the overall IRI of
http://&#x7D0D;&#x8C46;.example.org/%E2%80%AE http://&#x7D0D;&#x8C46;.example.org/%E2%80%AE
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 (rtl) writing direction. IRIs script, have an inherent right-to-left (rtl) 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).
Because of the complex interaction between the logical Because of the complex interaction between the logical
representation, the visual representation, and the syntax of a Bidi representation, the visual representation, and the syntax of a Bidi
IRI, a balance is needed between various requirements. The main IRI, a balance is needed between various requirements. The main
requirements are: requirements are:
1) user-predictable conversion between visual and logical 1) user-predictable conversion between visual and logical
representation; representation;
2) the ability to include a wide range of characters in various
parts of the IRI; 2) the ability to include a wide range of characters in various parts
of the IRI;
3) minor or no changes or restrictions for implementations. 3) minor or no changes or restrictions for implementations.
4.1 Logical Storage and Visual Presentation 4.1 Logical Storage and Visual Presentation
When stored or transmitted in digital representation, bidirectional When stored or transmitted in digital representation, bidirectional
IRIs MUST be in full logical order, and MUST conform to the IRI IRIs MUST be in full logical order, and MUST conform to the IRI
syntax rules (which includes the rules relevant to their scheme). syntax rules (which includes the rules relevant to their scheme).
This assures that bidirectional IRIs can be processed in the same way This assures that bidirectional IRIs can be processed in the same way
as other IRIs. as other IRIs.
When rendered, bidirectional IRIs MUST be rendered using the Unicode When rendered, bidirectional IRIs MUST be rendered using the Unicode
Bidirectional Algorithm [UNIV4], [UNI9]. Bidirectional IRIs MUST be Bidirectional Algorithm [UNIV4], [UNI9]. Bidirectional IRIs MUST be
rendered in the same way as they would be rendered if they were in an rendered in the same way as they would be rendered if they were in an
left-to-right embedding, i.e. as if they were preceded by U+202A, left-to-right embedding, i.e. as if they were preceded by U+202A,
LEFT-TO-RIGHT EMBEDDING (LRE), and followed by U+202C, POP LEFT-TO-RIGHT EMBEDDING (LRE), and followed by U+202C, POP
DIRECTIONAL FORMATTING (PDF). Setting the embedding direction can DIRECTIONAL FORMATTING (PDF). Setting the embedding direction can
also be done in a higher-order protocol (e.g. the dir='ltr' also be done in a higher-order protocol (e.g. the dir='ltr' attribute
attribute in HTML). in HTML).
There is no requirement to actually use the above embedding if the There is no requirement to actually use the above embedding if the
display is still the same without the embedding. For example, a display is still the same without the embedding. For example, a
bidirectional IRI in a text with left-to-right base directionality bidirectional IRI in a text with left-to-right base directionality
(such as used for English or Cyrillic) that is preceded and followed (such as used for English or Cyrillic) that is preceded and followed
by whitespace and strong left-to-right characters does not need an by whitespace and strong left-to-right characters does not need an
embedding. Also, a bidirectional relative IRI that only contains embedding. Also, a bidirectional relative IRI that only contains
strong right-to-left characters and weak characters and that starts strong right-to-left characters and weak characters and that starts
and ends with a strong rigth-to-left character and appears in a text and ends with a strong rigth-to-left character and appears in a text
with right-to-left base directionality (such as used for Arabic or with right-to-left base directionality (such as used for Arabic or
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The Unicode Bidirectional Algorithm ([UNI9], Section 4.3) permits The Unicode Bidirectional Algorithm ([UNI9], Section 4.3) permits
higher-level protocols to influence bidirectional rendering. Such higher-level protocols to influence bidirectional rendering. Such
changes by higher-level protocols MUST NOT be used if they change the changes by higher-level protocols MUST NOT be used if they change the
rendering of IRIs. rendering of IRIs.
The bidirectional formatting characters that may be used before or The bidirectional formatting characters that may be used before or
after the IRI to assure correct display are themselves not part of after the IRI to assure correct display are themselves not part of
the IRI. IRIs MUST NOT contain bidirectional formatting characters the IRI. IRIs MUST NOT contain bidirectional formatting characters
(LRM, RLM, LRE, RLE, LRO, RLO, and PDF). They affect the visual (LRM, RLM, LRE, RLE, LRO, RLO, and PDF). They affect the visual
rendering of the IRI, but do not themselves appear visually. It rendering of the IRI, but do not themselves appear visually. It would
would therefore not be possible to correctly input an IRI with such therefore not be possible to correctly input an IRI with such
characters. characters.
4.2 Bidi IRI Structure 4.2 Bidi IRI Structure
The Unicode Bidirectional Algorithm is designed mainly for running The Unicode Bidirectional Algorithm is designed mainly for running
text. To make sure that it does not affect the rendering of text. To make sure that it does not affect the rendering of
bidirectional IRIs too much, some restrictions on bidirectional IRIs bidirectional IRIs too much, some restrictions on bidirectional IRIs
are necessary. These restrictions are given in terms of delimiters are necessary. These restrictions are given in terms of delimiters
(structural characters, mostly punctuation such as '@', '.', ':', (structural characters, mostly punctuation such as '@', '.', ':',
'/') and components (usually consisting mostly of letters and '/') and components (usually consisting mostly of letters and
digits). digits).
The following syntax rules from Section 2.2 correspond to components The following syntax rules from Section 2.2 correspond to components
for the purpose of Bidi behavior: iuserinfo, isegment, ireg-name, for the purpose of Bidi behavior: iuserinfo, ireg-name, isegment,
iquery, and ifragment. isegment-nz, isegment-nzc, ireg-name, iquery, and ifragment.
Specifications that define the syntax of any of the above components Specifications that define the syntax of any of the above components
MAY divide them further and define smaller parts to be components MAY divide them further and define smaller parts to be components
according to this document. As an example, the restrictions of according to this document. As an example, the restrictions of
[RFC3490] on bidirectional domain names correspond to treating each [RFC3490] on bidirectional domain names correspond to treating each
label of a domain name as a component for those schemes where ireg- label of a domain name as a component for those schemes where
name is a domain name. Even where the components are not defined ireg-name is a domain name. Even where the components are not defined
formally, it may be helpful to think about some syntax in terms of formally, it may be helpful to think about some syntax in terms of
components and to apply the relevant restrictions. For example, for components and to apply the relevant restrictions. For example, for
the usual name/value syntax in query parts, it is convenient to treat 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 each name and each value as a component. As another example, the
extensions in a resource name can be treated as separate components. extensions in a resource name can be treated as separate components.
For each component, the following restrictions apply: For each component, the following restrictions apply:
1) A component SHOULD NOT not use both right-to-left and left-to- 1) A component SHOULD NOT use both right-to-left and left-to-right
right characters. characters.
2) A component using right-to-left characters SHOULD start and end 2) A component using right-to-left characters SHOULD start and end
with right-to-left characters. with right-to-left characters.
The above restrictions are given as shoulds, rather than as musts. The above restrictions are given as shoulds, rather than as musts.
For IRIs that are never presented visually, they are not relevant. For IRIs that are never presented visually, they are not relevant.
However, for IRIs in general, they are very important to insure However, for IRIs in general, they are very important to insure
consistent conversion between visual presentation and logical consistent conversion between visual presentation and logical
representation, in both directions. representation, in both directions.
Note: In some components, the above restrictions may actually be Note: In some components, the above restrictions may actually be
strictly enforced. For example, [RFC3490] requires that these strictly enforced. For example, [RFC3490] requires that these
restrictions apply to the labels of a host name for those restrictions apply to the labels of a host name for those schemes
schemes where ireg-name is a host name. In some other where ireg-name is a host name. In some other components, for
components, for example path components, following these example path components, following these restrictions may not be
restrictions may not be too difficult. For other components, too difficult. For other components, such as parts of the query
such as parts of the query part, it may be very difficult to part, it may be very difficult to enforce the restrictions,
enforce the restrictions, because the values of query because the values of query parameters may be arbitrary character
parameters may be arbitrary character sequences. sequences.
If the above restrictions cannot be satisfied otherwise, the affected If the above restrictions cannot be satisfied otherwise, the affected
component can always be mapped to URI notation as described in component can always be mapped to URI notation as described in
Section 3.1. Please note that the whole component needs to be mapped Section 3.1. Please note that the whole component needs to be mapped
(see also Example 9 below). (see also Example 9 below).
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 4.1. During input, rendering rendering them according to Section 4.1. During input, rendering
skipping to change at page 19, line 11 skipping to change at page 20, line 14
inverted as a whole: inverted as a whole:
logical representation: http://ab.CDE.FGH/ij/kl/mn/op.html logical representation: http://ab.CDE.FGH/ij/kl/mn/op.html
visual representation: http://ab.HGF.EDC/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 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. sequence of rtl words is read rtl in a bidi text.
Example 3: All components of an IRI (except for the scheme) are rtl. Example 3: All components of an IRI (except for the scheme) are rtl.
All rtl components are inverted overall: All rtl components are inverted overall:
logical representation: http://AB.CD.EF/GH/IJ/KL?MN=OP;QR=ST#UV 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 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 The whole IRI (except the scheme) is read rtl. Delimiters between rtl
rtl components stay between the respective components; delimiters components stay between the respective components; delimiters between
between ltr and rtl components don't move. ltr and rtl components don't move.
Example 4: Several sequences of rtl components are each inverted on Example 4: Several sequences of rtl components are each inverted on
their own: their own:
logical representation: http://AB.CD.ef/gh/IJ/KL.html logical representation: http://AB.CD.ef/gh/IJ/KL.html
visual representation: http://DC.BA.ef/gh/LK/JI.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 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. sequence of rtl words in an ltr text is read rtl.
Example 5: Example 2, applied to components of different kinds: Example 5: Example 2, applied to components of different kinds:
logical representation: http://ab.cd.EF/GH/ij/kl.html logical representation: http://ab.cd.EF/GH/ij/kl.html
visual representation: http://ab.cd.HG/FE/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 The inversion of the domain name label and the path component may be
unexpected, but is consistent with other bidi behavior. For unexpected, but is consistent with other bidi behavior. For
reassurance that the domain component really is "ab.cd.EF", it may be reassurance that the domain component really is "ab.cd.EF", it may be
helpful to read aloud the visual representation following the bidi helpful to read aloud the visual representation following the bidi
algorithm. After "http://ab.cd." one reads the RTL block "E-F-slash- algorithm. After "http://ab.cd." one reads the RTL block
G-H", which corresponds to the logical representation. "E-F-slash-G-H", which corresponds to the logical representation.
Example 6: Same as example 5, with more rtl components: Example 6: Same as example 5, with more rtl components:
logical representation: http://ab.CD.EF/GH/IJ/kl.html logical representation: http://ab.CD.EF/GH/IJ/kl.html
visual representation: http://ab.JI/HG/FE.DC/kl.html visual representation: http://ab.JI/HG/FE.DC/kl.html
The inversion of the domain name labels and the path components may The inversion of the domain name labels and the path components may
be easier to identify because the delimiters also move. be easier to identify because the delimiters also move.
Example 7: A single rtl component with included digits: Example 7: A single rtl component with included digits:
logical representation: http://ab.CDE123FGH.ij/kl/mn/op.html logical representation: http://ab.CDE123FGH.ij/kl/mn/op.html
visual representation: http://ab.HGF123EDC.ij/kl/mn/op.html visual representation: http://ab.HGF123EDC.ij/kl/mn/op.html
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Example 8 (not allowed): Numbers at the start or end of a rtl Example 8 (not allowed): Numbers at the start or end of a rtl
component: component:
logical representation: http://ab.cd.ef/GH1/2IJ/KL.html logical representation: http://ab.cd.ef/GH1/2IJ/KL.html
visual representation: http://ab.cd.ef/LK/JI1/2HG.html visual representation: http://ab.cd.ef/LK/JI1/2HG.html
The sequence '1/2' is interpreted by the bidi algorithm as a The sequence '1/2' is interpreted by the bidi algorithm as a
fraction, fragmenting the components and leading to confusion. There fraction, fragmenting the components and leading to confusion. There
are other characters that are interpreted in a special way close to are other characters that are interpreted in a special way close to
numbers, in particular '+', '-', '#', '$', '%', ',', '.', and ':'. numbers, in particular '+', '-', '#', '$', '%', ',', '.', and ':'.
Example 9 (not allowed): The numbers in the previous example are Example 9 (not allowed): The numbers in the previous example are
escaped: percent-encoded:
logical representation: http://ab.cd.ef/GH%31/%32IJ/KL.html, 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 (Hebrew): http://ab.cd.ef/LK/JI%32/%31HG.html
visual representation (Arabic): http://ab.cd.ef/LK/JI32%/31%HG.html visual representation (Arabic): http://ab.cd.ef/LK/JI32%/31%HG.html
Depending on whether the upper-case letters represent Arabic or Depending on whether the upper-case letters represent Arabic or
Hebrew, the visual representation is different. Hebrew, the visual representation is different.
Example 10 (allowed, but not recommended): Example 10 (allowed, but not recommended):
logical representation: http://ab.CDEFGH.123/kl/mn/op.html logical representation: http://ab.CDEFGH.123/kl/mn/op.html
visual representation: http://ab.123.HGFEDC/kl/mn/op.html visual representation: http://ab.123.HGFEDC/kl/mn/op.html
Components consisting of only numbers are allowed (it would be rather Components consisting of only numbers are allowed (it would be rather
difficult to prohibit them), but may interact with adjacent RTL difficult to prohibit them), but may interact with adjacent RTL
components in ways that are not easy to predict. components in ways that are not easy to predict.
5. IRI Equivalence and Comparison 5. IRI Equivalence and Comparison
This section discusses IRI Equivalence and Comparison similar to This section discusses IRI Equivalence and Comparison similar to
Section 6, "Normalization and Comparison", in [RFCYYYY]. This Section 6, "Normalization and Comparison", in [RFCYYYY]. This section
section focuses on the main issues and on aspects that are different focuses on the main issues and on aspects that are different from
from [RFCYYYY]; Section 6 of [RFCYYYY] is recommended background [RFCYYYY]; Section 6 of [RFCYYYY] is recommended background reading.
reading.
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. whether they refer to the same IRIs are equivalent or not (i.e. whether they refer to the same
resource or not). Two IRIs that look almost the same may refer to resource or not). Two IRIs that look almost the same may refer to
different resources. Two IRIs that look completely different may different resources. Two IRIs that look completely different may
refer to the same resource. Each specification or application that refer to the same resource. Each specification or application that
uses IRIs has to decide on the appropriate criterion for IRI uses IRIs has to decide on the appropriate criterion for IRI
equivalence. equivalence.
5.1 Simple String Comparison 5.1 Simple String Comparison
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http://example.org/%7Euser are not equivalent under this definition. http://example.org/%7Euser are not equivalent under this definition.
In such a case, the comparison function MUST NOT map IRIs to URIs, In such a case, the comparison function MUST NOT map IRIs to URIs,
because such a mapping would create additional spurious equivalences. because such a mapping would create additional spurious equivalences.
It follows that IRIs SHOULD NOT be modified when being transported if It follows that IRIs SHOULD NOT be modified when being transported if
there is any chance that this IRI might be used as an identifier in there is any chance that this IRI might be used as an identifier in
the way explained above. the way explained above.
5.2 Conversion to URIs 5.2 Conversion to URIs
For actual resolution, differences in escaping (except for the For actual resolution, differences in percent-encoding (except for
escaping of reserved characters) MUST always result in the same the percent-encoding of reserved characters) MUST always result in
resource. For example, http://example.org/~user, the same resource. For example, http://example.org/~user,
http://example.org/%7euser and http://example.org/%7Euser must http://example.org/%7euser and http://example.org/%7Euser must
resolve to the same resource. resolve to the same resource.
If this kind of equivalence is to be tested, the escaping of both If this kind of equivalence is to be tested, the percent-encoding of
IRIs to be compared has to be aligned, for example by converting both both IRIs to be compared has to be aligned, for example by converting
IRIs to URIs (see Section 3.1) and making sure that the case of the both IRIs to URIs (see Section 3.1) and making sure that the case of
hexadecimal characters in the %-escape is always the same (preferably the hexadecimal characters in the percent-encode is always the same
upper case). For comparison, such conversions MUST only be done on (preferably upper case). For comparison, such conversions MUST only
the fly, while retaining the original IRI. be done on the fly, while retaining the original IRI.
Additional, similar equivalences are possible based on knowledge Additional, similar equivalences are possible based on knowledge
about the generic URI/IRI syntax, such as the fact that the scheme about the generic URI/IRI syntax, such as the fact that the scheme
part is case-insensitive. part is case-insensitive.
5.3 Normalization 5.3 Normalization
The Unicode Standard [UNIV4] defines various equivalences between The Unicode Standard [UNIV4] defines various equivalences between
sequences of characters for various purposes. Unicode Standard Annex sequences of characters for various purposes. Unicode Standard Annex
#15 [UTR15] defines various Normalization Forms for these #15 [UTR15] defines various Normalization Forms for these
equivalences, in particular Normalization Form C (NFC, Canonical equivalences, in particular Normalization Form C (NFC, Canonical
Decomposition, followed by Canonical Composition) and Normalization Decomposition, followed by Canonical Composition) and Normalization
Form KC (NFKC, Compatibility Decomposition, followed by Canonical Form KC (NFKC, Compatibility Decomposition, followed by Canonical
Composition). Composition).
Equivalence of IRIs MUST rely on the assumption that IRIs are Equivalence of IRIs MUST rely on the assumption that IRIs are
appropriately pre-normalized, rather than applying normalization when appropriately pre-normalized, rather than applying normalization when
comparing two IRIs. The exceptions are conversion from a non-digital comparing two IRIs. The exceptions are conversion from a non-digital
form, and conversion from a non-UCS-based encoding to an UCS-based form, and conversion from a non-UCS-based character encoding to an
encoding. In these cases, NFC or a normalizing transcoder using NFC UCS-based character encoding. In these cases, NFC or a normalizing
MUST be used for interoperability. To avoid false negatives and transcoder using NFC MUST be used for interoperability. To avoid
problems with transcoding, IRIs SHOULD be created using NFC. Using false negatives and problems with transcoding, IRIs SHOULD be created
NFKC may avoid even more problems, for example by choosing half-width using NFC. Using NFKC may avoid even more problems, for example by
Latin letters instead of full-width, and full-width Katakana instead choosing half-width Latin letters instead of full-width, and
of half-width. full-width Katakana instead of half-width.
As an example, http://www.example.org/r&#xE9;sum&#xE9;.html (in XML 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/ 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 re&#x301;sume&#x301;.html is not in NFC. The former uses precombined
e-acute characters, the later uses 'e' characters followed by e-acute characters, the later uses 'e' characters followed by
combining acute accents. Both usages are defined to be canonically combining acute accents. Both usages are defined to be canonically
equivalent in [UNIV4]. equivalent in [UNIV4].
Because it is unknow how a particular field is being treated Note: Because it is unknown how a particular field is being treated
with respect to text normalization, it would be inappropriate with respect to text normalization, it would be inappropriate to
to allow third parties to normalize an IRI arbitrarily. This allow third parties to normalize an IRI arbitrarily. This does not
does not contradict the recommendation that when a resource is contradict the recommendation that when a resource is created, its
created, and an IRI for that resource, you try to be as IRI should be as normalized as possible (i.e. NFC or even NFKC).
normalized as possible (i.e. NFC or even NFKC). This is This is similar to the upper-case/lower-case problems in URIs.
similar to the upper-case/lower-case problems in URIs. Some Some parts of a URI are case-insensitive (domain name). For
parts of a URI are case-insensitive (domain name). For others, others, it is unclear whether they are case-sensitive or
it is unclear whether they are case-sensitive or case- case-insensitive, or something in between (e.g. case-sensitive,
insensitive, or something in between (e.g. case-sensitive, but but if the wrong case is used, a multiple choice selection is
if the wrong case is used, a multiple choice selection is provided instead of a direct negative result). The best recipe is
provided instead of a direct negative result). The best recipe that the creator uses a reasonable capitalization, and when
is that the generator uses a reasonable capitalization, and transferring the URI, that capitalization is never changed.
when transfering the URI, that capitalization is never changed.
Various IRI schemes may allow the usage of International Domain Names Various IRI schemes may allow the usage of International Domain Names
(IDN) [RFC3490]. When in use in IRIs, those names SHOULD be (IDN) [RFC3490]. When in use in IRIs, those names SHOULD be validated
validated using the ToASCII operation defined in [RFC3490], with the using the ToASCII operation defined in [RFC3490], with the flags
flags "UseSTD3ASCIIRules" and "AllowUnassigned". An IRI containing "UseSTD3ASCIIRules" and "AllowUnassigned". An IRI containing an
an invalid IDN cannot successfully be resolved. For legibility invalid IDN cannot successfully be resolved. For legibility purposes,
purposes, IDN components of IRIs SHOULD NOT be converted into ASCII IDN components of IRIs SHOULD NOT be converted into ASCII Compatible
Compatible Encoding (ACE). Encoding (ACE).
5.4 Preferred Forms 5.4 Preferred Forms
The following are the preferred forms for IRIs when generated: The following are the preferred forms for IRIs when created:
- Always provide the URI scheme in lowercase characters. - Always provide the URI scheme in lowercase characters.
- Only perform percent-escaping where it is essential. - Only perform percent-encoding where it is essential.
- Always use uppercase A-through-F characters when percent- - Always use uppercase A-through-F characters when percent-encoding.
escaping.
- Always provide the hostname, if any, in the form produced when - For those schemes where ireg-name is a domain name, always provide
applying nameprep [RFC3491]. This in particular includes using the individual labels, in the form produced when applying nameprep
lowercase characters rather than uppercase characters where [RFC3491]. This in particular includes using lowercase characters
applicable. rather than uppercase characters where applicable. Also, always
use US-ASCII '.' as a separator.
- Where possible, provide IRI components in NFKC or NFC. - Where possible, provide IRI components in NFKC or NFC.
- Prevent /./ and /../ from appearing in non-relative URI paths. - Prevent /./ and /../ from appearing in non-relative URI paths.
- For schemes that define an empty path to be equivalent to a - For schemes that define an empty path to be equivalent to a path
path of "/", use "/". of "/", use "/".
6. Use of IRIs 6. Use of IRIs
6.1 Limitations on UCS Characters Allowed in IRIs 6.1 Limitations on UCS Characters Allowed in IRIs
This section discusses limitations on characters and character This section discusses 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) The UCS contains many areas of characters for which there are b) 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
includes the full-width equivalents of ASCII characters, half- the full-width equivalents of ASCII characters, half-width
width Katakana characters for Japanese, and many others. This Katakana characters for Japanese, and many others. This also
also includes many look-alikes of "space", "delims", and includes many look-alikes of "space", "delims", and "unwise",
"unwise", characters excluded in [RFC3491]. characters excluded in [RFC3491].
Additional information is available from [UNIXML]. [UNIXML] is Additional information is available from [UNIXML]. [UNIXML] is
written in the context of running text rather than in the context of written in the context of running text rather than in the context of
identifiers. Nevertheless, it discusses many of the categories of identifiers. Nevertheless, it discusses many of the categories of
characters not appropriate for IRIs. characters not appropriate for IRIs.
6.2 Software Interfaces and Protocols 6.2 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 or interfaces for URIs typically function on sequences of octets or
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URI-only components MUST map the IRIs per Section 3.1, when URI-only components MUST map the IRIs 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.
6.3 Format of URIs and IRIs in Documents and Protocols 6.3 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
the transport of IRIs. In those cases where the document as a whole the transport of IRIs. In those cases where the document as a whole
has a native character encoding, IRIs MUST also be encoded in this has a native character encoding, IRIs MUST also be encoded in this
encoding, and converted accordingly by a parser or interpreter. IRI character encoding, and converted accordingly by a parser or
characters that are not expressible in the native encoding SHOULD be interpreter. IRI characters that are not expressible in the native
escaped using the escaping conventions of the document format if such character encoding SHOULD be escaped using the escaping conventions
conventions are available. Alternatively, they MAY be escaped of the document format if such conventions are available.
according to Section 3.1. For example, in HTML or XML, numeric Alternatively, they MAY be percent-encoded according to Section 3.1.
character references SHOULD be used. If a document as a whole has a For example, in HTML or XML, numeric character references SHOULD be
native character encoding, and that character encoding is not UTF-8, used. If a document as a whole has a native character encoding, and
then IRIs MUST NOT be placed into the document in the UTF-8 character that character encoding is not UTF-8, then IRIs MUST NOT be placed
encoding. into the document in the UTF-8 character encoding.
Note: Some formats already accommodate IRIs, although they use Note: Some formats already accommodate IRIs, although they use
different terminology. HTML 4.0 [HTML4] defines the conversion from different terminology. HTML 4.0 [HTML4] defines the conversion from
IRIs to URIs as error-avoiding behavior. XML 1.0 [XML1], XLink IRIs to URIs as error-avoiding behavior. XML 1.0 [XML1], XLink
[XLink], and XML Schema [XMLSchema] and specifications based upon [XLink], and XML Schema [XMLSchema] and specifications based upon
them allow IRIs. Also, it is expected that all relevant new W3C them allow IRIs. Also, it is expected that all relevant new W3C
formats and protocols will be required to handle IRIs [CharMod]. formats and protocols will be required to handle IRIs [CharMod].
6.4 Use of UTF-8 for Encoding Original Characters 6.4 Use of UTF-8 for Encoding Original Characters
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Examples where this is already used are the URN syntax [RFC2141], Examples where this is already used are the URN syntax [RFC2141],
IMAP URLs [RFC2192], and POP URLs [RFC2384]. On the other hand, IMAP URLs [RFC2192], and POP URLs [RFC2384]. On the other hand,
because the HTTP URL scheme does not specify how to encode original because the HTTP URL scheme does not specify how to encode original
characters, only some HTTP URLs can have corresponding but different characters, only some HTTP URLs can have corresponding but different
IRIs. IRIs.
For example, for a document with a URI of For example, for a document with a URI of
http://www.example.org/r%C3%A9sum%C3%A9.html, it is possible to http://www.example.org/r%C3%A9sum%C3%A9.html, it is possible to
construct a corresponding IRI (in XML notation, see Section 1.4): construct a corresponding IRI (in XML notation, see Section 1.4):
http://www.example.org/r&#xE9;sum&#xE9;.html (&#xE9; stands for the http://www.example.org/r&#xE9;sum&#xE9;.html (&#xE9; stands for the
e-acute character, and %C3%A9 is the UTF-8 encoded and escaped e-acute character, and %C3%A9 is the UTF-8 encoded and
representation of that character). On the other hand, for a document percent-encoded representation of that character). On the other hand,
with a URI of http://www.example.org/r%E9sum%E9.html, the escaped for a document with a URI of http://www.example.org/r%E9sum%E9.html,
octets cannot be converted to actual characters in an IRI, because the percent-encoding octets cannot be converted to actual characters
the escaping is not based on UTF-8. in an IRI, because the percent-encoding is not based on UTF-8.
The requirement for the use of UTF-8 applies to all parts of a URI. The requirement for the use of UTF-8 applies to all parts of a URI
However, it is possible that the capability of IRIs to represent a (with the potential exception of the ireg-name part, see Section
wide range of characters directly is used just in some parts of the 3.1). However, it is possible that the capability of IRIs to
IRI (or IRI reference). The other parts of the IRI may only contain represent a wide range of characters directly is used just in some
ASCII characters, or they may not be based on UTF-8. They may be parts of the IRI (or IRI reference). The other parts of the IRI may
based on another encoding, or they may directly encode raw binary only contain ASCII characters, or they may not be based on UTF-8.
data (see also [RFC2397]). They may be based on another character encoding, or they may directly
encode raw binary data (see also [RFC2397]).
For example, it is possible to have a URI reference of For example, it is possible to have a URI reference of
http://www.example.org/r%E9sum%E9.xml#r%C3%A9sum%C3%A9, where the http://www.example.org/r%E9sum%E9.xml#r%C3%A9sum%C3%A9, where the
document name is encoded in iso-8859-1 based on server settings, but document name is encoded in iso-8859-1 based on server settings, but
the fragment identifier is encoded in UTF-8 according to [XPointer]. the fragment identifier is encoded in UTF-8 according to [XPointer].
The IRI corresponding to the above URI would be (in XML notation) The IRI corresponding to the above URI would be (in XML notation)
http://www.example.org/r%E9sum%E9.xml#r&#xE9;sum&#xE9;. http://www.example.org/r%E9sum%E9.xml#r&#xE9;sum&#xE9;.
Similar considerations apply to query parts. The functionality of Similar considerations apply to query parts. The functionality of
IRIs (namely to be able to include non-ASCII characters) can only be IRIs (namely to be able to include non-ASCII characters) can only be
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Processing of relative forms of IRIs against a base is handled Processing of relative forms of IRIs against a base is handled
straightforwardly; the algorithms of [RFCYYYY] can be applied straightforwardly; the algorithms of [RFCYYYY] can be applied
directly, treating the characters additionally allowed in IRIs in the directly, treating the characters additionally allowed in IRIs in the
same way as unreserved characters in URIs. same way as unreserved characters in URIs.
7. URI/IRI Processing Guidelines (informative) 7. URI/IRI Processing Guidelines (informative)
This informative section provides guidelines for supporting IRIs in This informative section provides guidelines for supporting IRIs in
the same software components and operations that currently process the same software components and operations that currently process
URIs: software interfaces that handle URIs, software that allows URIs: software interfaces that handle URIs, software that allows
users to enter URIs, software that generates URIs, software that users to enter URIs, software that creates or generates URIs,
displays URIs, formats and protocols that transport URIs, and software that displays URIs, formats and protocols that transport
software that interprets URIs. These may all require more or less URIs, and software that interprets URIs. These may all require more
modification before functioning properly with IRIs. The or less modification before functioning properly with IRIs. The
considerations in this section also apply to URI references and IRI considerations in this section also apply to URI references and IRI
references. references.
7.1 URI/IRI Software Interfaces 7.1 URI/IRI Software Interfaces
Software interfaces that handle URIs, such as URI-handling APIs and Software interfaces that handle URIs, such as URI-handling APIs and
protocols transferring URIs, need interfaces and protocol elements protocols transferring URIs, need interfaces and protocol elements
that are designed to carry IRIs. that are designed to carry IRIs.
In case the current handling in an API or protocol is based on US- In case the current handling in an API or protocol is based on
ASCII, UTF-8 is recommended as the encoding for IRIs, because this is US-ASCII, UTF-8 is recommended as the character encoding for IRIs,
compatible with US-ASCII, is in accordance with the recommendations because this is compatible with US-ASCII, is in accordance with the
of [RFC2277], and makes it easy to convert to URIs where necessary. recommendations of [RFC2277], and makes it easy to convert to URIs
In any case, the API or protocol definition must clearly define the where necessary. In any case, the API or protocol definition must
encoding to be used. clearly define the character encoding to be used.
The transfer from URI-only to IRI-capable components requires no The transfer from URI-only to IRI-capable components requires no
mapping, although the conversion described in Section 3.2 above may mapping, although the conversion described in Section 3.2 above may
be performed. It is preferable not to perform this inverse be performed. It is preferable not to perform this inverse conversion
conversion when there is a chance that this cannot be done correctly. when there is a chance that this cannot be done correctly.
7.2 URI/IRI Entry 7.2 URI/IRI Entry
There are components that allow users to enter URIs into the system, There are components that allow users to enter URIs into the system,
for example by typing or dictation. This software must be updated to for example by typing or dictation. This software must be updated to
allow for IRI entry. allow for IRI entry.
A person viewing a visual representation of an IRI (as a sequence of A person viewing a visual representation of an IRI (as a sequence of
glyphs, in some order, in some visual display) or hearing an IRI, glyphs, in some order, in some visual display) or hearing an IRI,
will use a entry method for characters in the user's language to will use a entry method for characters in the user's language to
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7.3 URI/IRI Transfer Between Applications 7.3 URI/IRI Transfer Between Applications
Many applications, in particular many mail user agents, try to detect Many applications, in particular many mail user agents, try to detect
URIs appearing in plain text. For this, they use some heuristics 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 based on URI syntax. They then allow the user to click on such URIs
and retrieve the corresponding resource in an appropriate (usually and retrieve the corresponding resource in an appropriate (usually
scheme-dependent) application. scheme-dependent) application.
Such applications have to be upgraded to use the IRI syntax rather 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- than the URI syntax as a base for heuristics. In particular, a
ASCII character should not be taken as the indication of the end of non-ASCII character should not be taken as the indication of the end
an IRI. Such applications also have to make sure that they correctly of an IRI. Such applications also have to make sure that they
convert the detected IRI from the encoding of the document or correctly convert the detected IRI from the character encoding of the
application where the IRI appears to the encoding used by the system- document or application where the IRI appears to the character
wide IRI invocation mechanism, or to a URI (according to Section 3.1) encoding used by the system-wide IRI invocation mechanism, or to a
if the system-wide invocation mechanism only accepts URIs. 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 The clipboard is another frequently used way to transfer URIs and
IRIs from one application to another. On most platforms, the IRIs from one application to another. On most platforms, the
clipboard is able to store and transfer text in many languages and clipboard is able to store and transfer text in many languages and
scripts. Correctly used, the clipboard transfers characters, not scripts. Correctly used, the clipboard transfers characters, not
bytes, which will do the right thing with IRIs. bytes, which will do the right thing with IRIs.
7.4 URI/IRI Generation 7.4 URI/IRI Generation
Systems that offer resources through the Internet, where those Systems that offer resources through the Internet, where those
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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.
For maximum interoperability, systems that generate resource For maximum interoperability, systems that generate resource
identifiers should do the appropriate transformations. For example, identifiers should do the appropriate transformations. For example,
if a file system contains a file named r&#xE9;sum&#xE9;.html, a if a file system contains a file named r&#xE9;sum&#xE9;.html, a
server should expose this as r%C3%A9sum%C3%A9.html in a URI, which server should expose this as r%C3%A9sum%C3%A9.html in a URI, which
allows to use r&#xE9;sum&#xE9;.html in an IRI, even if the file name allows to use r&#xE9;sum&#xE9;.html in an IRI, even if the file name
locally is kept in an encoding other than UTF-8. locally is kept in a character encoding other than UTF-8.
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].
7.5 URI/IRI Selection 7.5 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
is easily confused with the digit one "1", and the upper-case oh "O" easily confused with the digit one "1", and the upper-case oh "O" is
is easily confused with the digit zero "0". Publishers should avoid easily confused with the digit zero "0". Publishers should avoid
confusing users with "br0ken" or "1ame" identifiers. confusing users with "br0ken" or "1ame" identifiers.
Outside of the US-ASCII range, there are many more opportunities for Outside of the US-ASCII range, there are many more opportunities for
confusion; a complete set of guidelines is too lengthy to include confusion; a complete set of guidelines is too lengthy to include
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
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As an example, the UCS contains the 'fi' ligature at U+FB01 for As an example, the UCS contains the 'fi' ligature at U+FB01 for
compatibility reasons. Wherever possible, IRIs should use the two compatibility reasons. Wherever possible, IRIs should use the two
letters 'f' and 'i' rather than the 'fi' ligature. An example where letters 'f' and 'i' rather than the 'fi' ligature. An example where
the latter may be used is in the query part of an IRI for an explicit the latter may be used is in the query part of an IRI for an explicit
search for a word written containing the 'fi' ligature. search for a word written containing the 'fi' ligature.
In certain cases, there is a chance that characters from different 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 characters in a single component should be created where all the characters in a single component are
are used together in a given language. This usually means that all used together in a given language. This usually means that all these
these characters will be from the same script, but there are characters will be from the same script, but there are languages that
languages that mix characters from different scripts (such as mix characters from different scripts (such as Japanese). This is
Japanese). This is similar to the heuristics used to distinguish similar to the heuristics used to distinguish between letters and
between letters and numbers in the examples above. Also, for Latin, numbers in the examples above. Also, for Latin, Greek, and Cyrillic,
Greek, and Cyrillic, using lower-case letters results in fewer using lower-case letters results in fewer ambiguities than using
ambiguities than using upper-case letters. upper-case letters.
7.6 Display of URIs/IRIs 7.6 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 percent-encoded before being
displayed.
For display of Bidi IRIs, please see Section 4.1. For display of Bidi IRIs, please see Section 4.1.
7.7 Interpretation of URIs and IRIs 7.7 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
do not conform to this specification and use legacy encodings to do not conform to this specification and use legacy character
convert non-ASCII characters to URIs. Whether this is necessary and encodings to convert non-ASCII characters to URIs. Whether this is
what character encodings to cover, depends on a number of factors, necessary and what character encodings to cover, depends on a number
such as the legacy character encodings used locally and the of factors, such as the legacy character encodings used locally and
distribution of various versions of user agents. For example, the 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
how currently some servers treat URIs as case-insensitive, or perform currently some servers treat URIs as case-insensitive, or perform
additional matching 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, percent-encoded and
escaped parts of IRIs can always clearly be distinguished. Also, the not percent-encoded parts of IRIs can always clearly be
regularity of UTF-8 (see [Duerst97]) makes the potential for distinguished. Also, the regularity of UTF-8 (see [Duerst97]) makes
collisions lower than it may seem at first sight. the potential for collisions lower than it may seem at first sight.
7.8 Upgrading Strategy 7.8 Upgrading Strategy
Where 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 created,
or transported. This suggests that upgrading URI interpreting generated, or transported. This suggests that upgrading URI
software to accept IRIs should have highest priority. interpreting 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
entered and transported very widely. entered and transported very widely.
Therefore, IRIs benefit most from a broad upgrade of software to be Therefore, IRIs benefit most from a broad upgrade of software to be
able to enter and transport IRIs, but before publishing any able to enter and transport IRIs, but before publishing any
individual IRI, care should be taken to upgrade the corresponding individual IRI, care should be taken to upgrade the corresponding
interpreting software in order to cover the forms expected to be interpreting software in order to cover the forms expected to be
received by various versions of entry and transport software. received by various versions of entry and transport software.
The upgrade of generating software to generate IRIs instead of a The upgrade of generating software to generate IRIs instead of using
local encoding should happen only after the service is upgraded to a local character encoding should happen only after the service is
accept IRIs. Similarly, IRIs should only be generated when the upgraded to accept IRIs. Similarly, IRIs should only be generated
service accepts IRIs and the intervening infrastructure and protocol when the service accepts IRIs and the intervening infrastructure and
is known to transport them safely. protocol is known to transport them safely.
Display software should be upgraded only after upgraded entry Display software should be upgraded only after upgraded entry
software has been widely deployed to the population that will see the software has been widely deployed to the population that will see the
displayed result. displayed result.
It is often possible to reduce the effort and dependencies for
upgrading to IRIs by using UTF-8 rather than another character
encoding where there is a free choice of character encodings. For
example, when setting up a new file-based Web server, using UTF-8 as
the character encoding for file names will make the transition to
IRIs easier. Likewise, when setting up a new Web form using UTF-8 as
the character encoding of the form page, the returned query URIs will
use UTF-8 as the character encoding (unless the user, for whatever
reason, changes the character encoding) and will therefore be
compatible with IRIs.
These recommendations, when taken together, will allow for the These recommendations, when taken together, will allow for the
extension from URIs to IRIs in order to handle scripts other than extension from URIs to IRIs in order to handle scripts other than
ASCII while minimizing interoperability problems. ASCII while minimizing interoperability problems.
8. Security Considerations 8. Security Considerations
Incorrect escaping or unescaping can lead to security problems. In The security considerations discussed in [RFCYYYY] also apply to
IRIs. In addition, the following issues require particular care for
IRIs.
Incorrect encoding or decoding can lead to security problems. In
particular, some UTF-8 decoders do not check against overlong byte particular, some UTF-8 decoders do not check against overlong byte
sequences. As an example, a '/' is encoded with the byte 0x2F both sequences. As an example, a '/' is encoded with the byte 0x2F both in
in UTF-8 and in ASCII, but some UTF-8 decoders also wrongly interpret UTF-8 and in ASCII, but some UTF-8 decoders also wrongly interpret
the sequence 0xC0 0xAF as a '/'. A sequence such as '%C0%AF..' may the sequence 0xC0 0xAF as a '/'. A sequence such as '%C0%AF..' may
pass some security tests and then be interpreted as '/..' in a path pass some security tests and then be interpreted as '/..' in a path
if UTF-8 decoders are fault-tolerant, if conversion and checking are if UTF-8 decoders are fault-tolerant, if conversion and checking are
not done in the right order, and/or if reserved characters and not done in the right order, and/or if reserved characters and
unreserved characters are not clearly distinguished. unreserved characters are not clearly distinguished.
There are various ways in which "spoofing" can occur with IRIs. There are various ways in which "spoofing" can occur with IRIs.
"Spoofing" means that somebody may add a resource name that looks the "Spoofing" means that somebody may add a resource name that looks the
same or similar to the user, but points to a different resource. The same or similar to the user, but points to a different resource. The
added resource may pretend to be the real resource by looking very added resource may pretend to be the real resource by looking very
similar, but may contain all kinds of changes that may be difficult similar, but may contain all kinds of changes that may be difficult
to spot and can cause all kinds of problems. Most spoofing to spot and can cause all kinds of problems. Most spoofing
possibilities for IRIs are extensions of those for URIs. possibilities for IRIs are extensions of those for URIs.
Spoofing can occur for various reasons. A first reason is that Spoofing can occur for various reasons. A first reason is that
normalization expectations of a user or actual normalization when normalization expectations of a user or actual normalization when
entering an IRI, or when transcoding an IRI from a legacy encoding, entering an IRI, or when transcoding an IRI from a legacy character
do not match the normalization used on the server side. encoding, do not match the normalization used on the server side.
Conceptually, this is no different from the problems surrounding the Conceptually, this is no different from the problems surrounding the
use of case-insensitive web servers. For example, a popular web page use of case-insensitive web servers. For example, a popular web page
with a mixed case name (http://big.site/PopularPage.html) might be with a mixed case name (http://big.site/PopularPage.html) might be
"spoofed" by someone who is able to create http://big.site/ "spoofed" by someone who is able to create http://big.site/
popularpage.html. However, the introduction of character popularpage.html. However, the use of unnormalized character
normalization, and of additional mappings for user convenience, may sequences, and of additional mappings for user convenience, may
increase the chance for spoofing. Protocols and servers that allow increase the chance for spoofing. Protocols and servers that allow
the creation of resources with unnormalized names, and resources with the creation of resources with unnormalized names, and resources with
names that are not normalized, are particularly vulnerable to such names that are not normalized, are particularly vulnerable to such
attacks. This is an inherent security problem of the relevant attacks. This is an inherent security problem of the relevant
protocol, server, or resource, and not specific to IRIs, but protocol, server, or resource, and not specific to IRIs, but
mentioned here for completeness. mentioned here for completeness.
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 [RFC3491]. For the path part, administrators of sites part, see [RFC3491]. For the path part, administrators of sites which
which allow independent users to create resources in the same subarea allow independent users to create resources in the same subarea may
may need to be careful to check for spoofing. need to be careful to check for spoofing.
Spoofing can occur because in the UCS, there are many characters that Spoofing can occur because in the UCS, there are many characters that
look very similar. Details are discussed in Section 7.5. Again, look very similar. Details are discussed in Section 7.5. Again, this
this is very similar to spoofing possibilities on US-ASCII, e.g. is very similar to spoofing possibilities on US-ASCII, e.g. using
using 'br0ken' or '1ame' URIs. 'br0ken' or '1ame' URIs.
Spoofing can occur when URIs in various encodings are accepted to Spoofing can occur when URIs with percent-encodings based on various
deal with older user agents. In some cases, in particular for Latin- character encodings are accepted to deal with older user agents. In
based resource names, this is usually easy to detect because UTF-8- some cases, in particular for Latin-based resource names, this is
encoded names, when interpreted and viewed as legacy encodings, usually easy to detect because UTF-8-encoded names, when interpreted
produce mostly garbage. In other cases, when concurrently used and viewed as legacy character encodings, produce mostly garbage. In
encodings have a similar structure, but there are no characters that other cases, when concurrently used character encodings have a
have exactly the same encoding, detection is more difficult. similar structure, but there are no characters that have exactly the
same encoding, detection is more difficult.
Spoofing can occur with bidirectional IRIs, if the restrictions in Spoofing can occur with bidirectional IRIs, if the restrictions in
Section 4.2 are not followed. The same visual representation may be Section 4.2 are not followed. The same visual representation may be
interpreted as different logical representations, and vice versa. It interpreted as different logical representations, and vice versa. It
is also very important that a correct Unicode bidirectional is also very important that a correct Unicode bidirectional
implementation is used. implementation is used.
9. Acknowledgements 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 discussion on the issue addressed here has started a long time The discussion on the issue addressed here has started a long time
ago. There was a thread in the HTML working group in August 1995 ago. There was a thread in the HTML working group in August 1995
(under the topic of "Globalizing URIs") and in the www-international (under the topic of "Globalizing URIs") and in the www-international
mailing list in July 1996 (under the topic of "Internationalization mailing list in July 1996 (under the topic of "Internationalization
and URLs"), and ad-hoc meetings at the Unicode conferences in and URLs"), and ad-hoc meetings at the Unicode conferences in
September 1995 and September 1997. September 1995 and September 1997.
Thanks to Francois Yergeau, Matti Allouche, Roy Fielding, Tim Many thanks go to Francois Yergeau, Matitiahu Allouche, Roy Fielding,
Berners-Lee, Mark Davis, M.T. Carrasco Benitez, James Clark, Tim Tim Berners-Lee, Mark Davis, M.T. Carrasco Benitez, James Clark, Tim
Bray, Chris Wendt, Yaron Goland, Andrea Vine, Misha Wolf, Leslie Bray, Chris Wendt, Yaron Goland, Andrea Vine, Misha Wolf, Leslie
Daigle, Ted Hardie, Makoto MURATA, Steven Atkin, Ryan Stansifer, Tex Daigle, Ted Hardie, Makoto MURATA, Steven Atkin, Ryan Stansifer, Tex
Texin, Graham Klyne, Bjoern Hoehrmann, Chris Lilley, Ian Jacobs, Adam Texin, Graham Klyne, Bjoern Hoehrmann, Chris Lilley, Ian Jacobs, Adam
Costello, Dan Oscarson, Elliotte Rusty Harold, Mike J. Brown, Andrea Costello, Dan Oscarson, Elliotte Rusty Harold, Mike J. Brown, Andrea
Vine, Roy Badami, Simon Josefsson, Carlos Viegas Damasio, and many Vine, Roy Badami, Jonathan Rosenne, Asmus Freytag, Simon Josefsson,
Carlos Viegas Damasio, Chris Haynes, Walter Underwood, and many
others for help with understanding the issues and possible solutions, others for help with understanding the issues and possible solutions,
and getting the details right. Thanks also to the members of the W3C and getting the details right. Thanks also to the members of the W3C
I18N Working Group and Interest Group for their contributions and I18N Working Group and Interest Group for their contributions and
their work on [CharMod], to the members of many other W3C WGs for their work on [CharMod], to the members of many other W3C WGs for
adopting the ideas, and to the members of the Montreal IAB Workshop adopting IRIs, and to the members of the Montreal IAB Workshop on
on Internationalization and Localization for their review. Internationalization and Localization for their review.
Normative References 10. References
[ISO10646] International Organization for Standardization, 10.1 Normative References
[ISO10646]
International Organization for Standardization,
"Information Technology - Universal Multiple-Octet Coded "Information Technology - Universal Multiple-Octet Coded
Character Set (UCS) - Part 1: Architecture and Basic Character Set (UCS) - Part 1: Architecture and Basic
Multilingual Plane - Part 2: Supplementary Planes", ISO Multilingual Plane - Part 2: Supplementary Planes", ISO
Standard 10646, with amendment, July 2002. Standard 10646, with amendment, July 2002.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997. Specifications: ABNF", RFC 2234, November 1997.
[RFC3490] Faltstrom, P., Hoffman, P. and A. Costello, [RFC3490] Faltstrom, P., Hoffman, P. and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)", "Internationalizing Domain Names in Applications (IDNA)",
skipping to change at page 32, line 32 skipping to change at page 34, line 17
[RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep [RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names (IDN)", RFC Profile for Internationalized Domain Names (IDN)", RFC
3491, March 2003. 3491, March 2003.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003, <http:// 10646", STD 63, RFC 3629, November 2003, <http://
www.ietf.org/rfc/rfc3629.txt>. www.ietf.org/rfc/rfc3629.txt>.
[RFCYYYY] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform [RFCYYYY] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", draft- Resource Identifier (URI): Generic Syntax",
fielding-uri-rfc2396bis-03.txt (work in progress), June draft-fielding-uri-rfc2396bis-03.txt (work in progress),
2003. June 2003.
[UTR15] Davis, M. and M. Duerst, "Unicode Normalization Forms", [UTR15] Davis, M. and M. Duerst, "Unicode Normalization Forms",
Unicode Standard Annex #15, March 2001, <http:// Unicode Standard Annex #15, March 2001, <http://
www.unicode.org/unicode/reports/tr15/tr15-21.html>. www.unicode.org/unicode/reports/tr15/tr15-21.html>.
Non-normative References 10.2 Non-normative References
[BidiEx] "Examples of bidirectional IRIs", <http://www.w3.org/ [BidiEx] "Examples of bidirectional IRIs", <http://www.w3.org/
International/iri-edit/BidiExamples>. International/iri-edit/BidiExamples>.
[CharMod] Duerst, M., Yergeau, F., Ishida, R., Wolf, M. and T. [CharMod] Duerst, M., Yergeau, F., Ishida, R., Wolf, M. and T.
Texin, "Character Model for the World Wide Web", Texin, "Character Model for the World Wide Web", World
World Wide Web Consortium Working Draft, August 2003, Wide Web Consortium Working Draft, August 2003, <http://
<http://www.w3.org/TR/charmod>. www.w3.org/TR/charmod>.
[Duerst97] Duerst, M., "The Properties and Promises of UTF-8", [Duerst01]
Proc. 11th International Unicode Conference, San Jose Duerst, M., "Internationalized Resource Identifiers: From
, September 1997, <http://www.ifi.unizh.ch/mml/ Specification to Testing", Proc. 19th International
mduerst/papers/PDF/IUC11-UTF-8.pdf>. Unicode Conference, San Jose , September 2001, <http://
www.w3.org/2001/Talks/0912-IUC-IRI/paper.html>.
[Duerst01] Duerst, M., "Internationalized Resource Identifiers: [Duerst97]
From Specification to Testing", Proc. 19th Duerst, M., "The Properties and Promises of UTF-8", Proc.
International Unicode Conference, San Jose , 11th International Unicode Conference, San Jose ,
September 2001, <http://www.w3.org/2001/Talks/0912- September 1997, <http://www.ifi.unizh.ch/mml/mduerst/
IUC-IRI/paper.html>. papers/PDF/IUC11-UTF-8.pdf>.
[Gettys] Gettys, J., "URI Model Consequences", <http:// [Gettys] Gettys, J., "URI Model Consequences", <http://www.w3.org/
www.w3.org/DesignIssues/ModelConsequences>. DesignIssues/ModelConsequences>.
[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,
Recommendation, December 1999, <http://www.w3.org/TR/ December 1999, <http://www.w3.org/TR/REC-html40/appendix/
REC-html40/appendix/notes.html#h-B.2>. notes.html#h-B.2>.
[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.,
H., Atkinson, R., Crispin, M. and P. Svanberg, "The Atkinson, R., Crispin, M. and P. Svanberg, "The Report of
Report of the IAB Character Set Workshop held 29 the IAB Character Set Workshop held 29 February - 1 March,
February - 1 March, 1996", RFC 2130, April 1997. 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.
[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, [RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
"Uniform Resource Identifiers (URI): Generic Syntax", Resource Identifiers (URI): Generic Syntax", RFC 2396,
RFC 2396, August 1998.
[RFC2397] Masinter, L., "The "data" URL scheme", RFC 2397,
August 1998. August 1998.
[RFC2397] Masinter, L., "The "data" URL scheme", RFC 2397, 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
"Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, 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
Transfer Protocol", RFC 2640, July 1999. Protocol", RFC 2640, July 1999.
[RFC2718] Masinter, L., Alvestrand, H., Zigmond, D. and R. [RFC2718] Masinter, L., Alvestrand, H., Zigmond, D. and R. Petke,
Petke, "Guidelines for new URL Schemes", RFC 2718, "Guidelines for new URL Schemes", RFC 2718, November 1999.
November 1999.
[UNIV4] The Unicode Consortium, "The Unicode Standard, [UNI9] Davis, M., "The Bidirectional Algorithm", Unicode Standard
Version 4.0", Addison-Wesley, Reading, MA , 2003. Annex #9, March 2002, <http://www.unicode.org/unicode/
reports/tr9>.
[UNI9] Davis, M., "The Bidirectional Algorithm", Unicode [UNIV4] The Unicode Consortium, "The Unicode Standard, Version
Standard Annex #9, March 2002, <http:// 4.0", Addison-Wesley, Reading, MA , 2003.
www.unicode.org/unicode/reports/tr9>.
[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
World Wide Web Consortium Note, February 2002, Wide Web Consortium Note, February 2002, <http://
<http://www.w3.org/TR/unicode-xml/>. www.w3.org/TR/unicode-xml/>.
[W3CIRI] Duerst, M., "Internationalization - URIs and other [W3CIRI] Duerst, M., "Internationalization - URIs and other
identifiers", World Wide Web Consortium Note, identifiers", World Wide Web Consortium Note, September
September 2002, <http://www.w3.org/International/O- 2002, <http://www.w3.org/International/
URL-and-ident.html>. 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
Consortium Recommendation, June 2001, <http:// Recommendation, June 2001, <http://www.w3.org/TR/xlink/
www.w3.org/TR/xlink/#link-locators>. #link-locators>.
[XML1] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. [XML1] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
Maler, "Extensible Markup Language (XML) 1.0 (Second "Extensible Markup Language (XML) 1.0 (Second Edition)",
Edition)", World Wide Web Consortium Recommendation, World Wide Web Consortium Recommendation, including
including Erratum 26 at http://www.w3.org/XML/xml- Erratum 26 at http://www.w3.org/XML/xml-V10-2e-errata#E26,
V10-2e-errata#E26, October 2000, <http://www.w3.org/ October 2000, <http://www.w3.org/TR/
TR/REC-xml#sec-external-ent>. REC-xml#sec-external-ent>.
[XMLNamespace] Bray, T., Hollander, D. and A. Layman, "Namespaces in [XMLNamespace]
XML", World Wide Web Consortium Recommendation, Bray, T., Hollander, D. and A. Layman, "Namespaces in
January 1999, <http://www.w3.org/TR/REC-xml#sec- XML", World Wide Web Consortium Recommendation, January
external-ent>. 1999, <http://www.w3.org/TR/REC-xml#sec-external-ent>.
[XMLSchema] Biron, P. and A. Malhotra, "XML Schema Part 2: [XMLSchema]
Datatypes", World Wide Web Consortium Recommendation, Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes",
May 2001, <http://www.w3.org/TR/xmlschema-2/#anyURI>. World Wide Web Consortium Recommendation, May 2001,
<http://www.w3.org/TR/xmlschema-2/#anyURI>.
[XPointer] Grosso, P., Maler, E., Marsh, J. and N. Walsh, [XPointer]
"XPointer Framework", World Wide Web Consortium Grosso, P., Maler, E., Marsh, J. and N. Walsh, "XPointer
Recommendation, March 2003, <http://www.w3.org/TR/ Framework", World Wide Web Consortium Recommendation,
xptr-framework/#escaping>. March 2003, <http://www.w3.org/TR/xptr-framework/
#escaping>.
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 World Wide Web Consortium
200 Technology Square 5322 Endo
Cambridge, MA 02139 Fujisawa, Kanagawa 252-8520
U.S.A. Japan
Phone: +1 617 253 5509 Phone: +81 466 49 1170
Fax: +1 617 258 5999 Fax: +81 466 49 1171
EMail: mailto:duerst@w3.org EMail: mailto: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 percent-encoded 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.
Phone: +1 425 882-8080 Phone: +1 425 882-8080
EMail: mailto:michelsu@microsoft.com EMail: mailto:michelsu@microsoft.com
URI: http://www.suignard.com URI: http://www.suignard.com
Full Copyright Statement Appendix A. Design Alternatives
Copyright (C) The Internet Society (2004). All Rights Reserved. This section shortly summarizes major design alternatives and the
reasons for why they were not chosen.
This document and translations of it may be copied and furnished to Appendix A.1 New Scheme(s)
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be Introducing new schemes (for example httpi:, ftpi:,...) or a new
revoked by the Internet Society or its successors or assigns. metascheme (e.g. i:, leading to URI/IRI prefixes such as i:http:,
i:ftp:,...) was proposed to make IRI-to-URI conversion
scheme-dependent or to distinguish between percent-encodings
resulting from IRI-to-URI conversion and percent-encodings from
legacy character encodings.
This document and the information contained herein is provided on an New schemes are not needed to distinguish URIs from true IRIs (i.e.
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING IRIs that contain non-ASCII characters). The benefit of being able to
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING detect the origin of percent-encodings is marginal, also because
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION UTF-8 can be detected with very high reliably. Deploying new schemes
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF is extremely hard. Not needing new schemes for IRIs makes deployment
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. of IRIs vastly easier. Making conversion scheme-dependent is highly
unadvisable. Using an uniform convention for conversion from IRIs to
URIs makes IRI implementation orthogonal from the introduction of
acual new schemes.
Acknowledgement Appendix A.2 Other Character Encodings than UTF-8
At an early stage, UTF-7 was considered as an alternative to UTF-8
when converting IRIs to URIs. UTF-7 would not have needed
percent-encoding, and would in most cases have been shorter than
percent-encoded UTF-8.
UTF-8 avoids a double layering and overloading of the use of the "+"
character. UTF-8 is fully compatible with US-ASCII, and has therefore
been recommended by the IETF, and is being used widely, while UTF-7
has never been used much and is now clearly being discouraged.
Appendix A.3 New Encoding Convention
Instead of using the existing percent-encoding convention of URIs,
which is based on octets, the idea was to create a new encoding
convention, for example to use '%u' to introduce UCS code points.
Using the existing octet-based percent-encoding mechanism does not
need an upgrade of the URI syntax, and does not need corresponding
server upgrades.
Appendix A.4 Indicating Character Encodings in the URI/IRI
Some proposals suggested indicating the character encodings used in
an URI or IRI with some new syntactic convention in the URI itself,
similar to the 'charset' parameter for emails and Web pages. As an
example, the label in square brackets in http://www.example.org/
ros[iso-8859-1]&#xE9; indicated that the following &#xE9; had to be
interpreted as iso-8859-1.
Using UTF-8 only does not need an upgrade to the URI syntax. It
avoids potentially multiple labels that have to be copied correctly
in all cases, even on the side of a bus or on a napkin, leading to
usability problems to the extent of being prohibitively annoying.
Using UTF-8 only also reduces transcoding errors and confusions.
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The IETF invites any interested party to bring to its attention any
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this standard. Please address the information to the IETF at
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Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
 End of changes. 

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