draft-duerst-iri-04.txt   draft-duerst-iri-05.txt 
Network Working Group M. Duerst Network Working Group M. Duerst
Internet-Draft W3C Internet-Draft W3C
Expires: December 28, 2003 M. Suignard Expires: April 25, 2004 M. Suignard
Microsoft Corporation Microsoft Corporation
June 29, 2003 October 26, 2003
Internationalized Resource Identifiers (IRIs) Internationalized Resource Identifiers (IRIs)
draft-duerst-iri-04 draft-duerst-iri-05
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at http:// The list of current Internet-Drafts can be accessed at http://
www.ietf.org/ietf/1id-abstracts.txt. www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on December 28, 2003. This Internet-Draft will expire on April 25, 2004.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2003). 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 URI [RFCYYYY]. An
IRI is a sequence of characters from the Universal Character Set IRI is a sequence of characters from the Universal Character Set
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 6
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 . . . . . . . . . . . . . . 7
3. Relationship between IRIs and URIs . . . . . . . . . . . . . 10 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 . . . . . . . . . . . . . . . . . . 12 3.2 Converting URIs to IRIs . . . . . . . . . . . . . . . . . . 13
3.2.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.2.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 14
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 . . . . . . . . . . 16
4.2 Bidi IRI Structure . . . . . . . . . . . . . . . . . . . . . 16 4.2 Bidi IRI Structure . . . . . . . . . . . . . . . . . . . . . 17
4.3 Input of Bidi IRIs . . . . . . . . . . . . . . . . . . . . . 17 4.3 Input of Bidi IRIs . . . . . . . . . . . . . . . . . . . . . 18
4.4 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.4 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5. IRI Equivalence and Comparison . . . . . . . . . . . . . . . 19 5. IRI Equivalence and Comparison . . . . . . . . . . . . . . . 20
5.1 Simple String Comparison . . . . . . . . . . . . . . . . . . 20 5.1 Simple String Comparison . . . . . . . . . . . . . . . . . . 20
5.2 Conversion to URIs . . . . . . . . . . . . . . . . . . . . . 20 5.2 Conversion to URIs . . . . . . . . . . . . . . . . . . . . . 21
5.3 Normalization . . . . . . . . . . . . . . . . . . . . . . . 20 5.3 Normalization . . . . . . . . . . . . . . . . . . . . . . . 21
5.4 Preferred Forms . . . . . . . . . . . . . . . . . . . . . . 21 5.4 Preferred Forms . . . . . . . . . . . . . . . . . . . . . . 22
6. Use of IRIs . . . . . . . . . . . . . . . . . . . . . . . . 22 6. Use of IRIs . . . . . . . . . . . . . . . . . . . . . . . . 22
6.1 Limitations on UCS Characters Allowed in IRIs . . . . . . . 22 6.1 Limitations on UCS Characters Allowed in IRIs . . . . . . . 23
6.2 Software Interfaces and Protocols . . . . . . . . . . . . . 22 6.2 Software Interfaces and Protocols . . . . . . . . . . . . . 23
6.3 Format of URIs and IRIs in Documents and Protocols . . . . . 23 6.3 Format of URIs and IRIs in Documents and Protocols . . . . . 23
6.4 Use of UTF-8 for Encoding Original Characters . . . . . . . 23 6.4 Use of UTF-8 for Encoding Original Characters . . . . . . . 24
6.5 Relative IRI References . . . . . . . . . . . . . . . . . . 24 6.5 Relative IRI References . . . . . . . . . . . . . . . . . . 25
7. URI/IRI Processing Guidelines (informative) . . . . . . . . 24 7. URI/IRI Processing Guidelines (informative) . . . . . . . . 25
7.1 URI/IRI Software Interfaces . . . . . . . . . . . . . . . . 24 7.1 URI/IRI Software Interfaces . . . . . . . . . . . . . . . . 25
7.2 URI/IRI Entry . . . . . . . . . . . . . . . . . . . . . . . 25 7.2 URI/IRI Entry . . . . . . . . . . . . . . . . . . . . . . . 26
7.3 URI/IRI Transfer Between Applications . . . . . . . . . . . 26 7.3 URI/IRI Transfer Between Applications . . . . . . . . . . . 26
7.4 URI/IRI Generation . . . . . . . . . . . . . . . . . . . . . 26 7.4 URI/IRI Generation . . . . . . . . . . . . . . . . . . . . . 27
7.5 URI/IRI Selection . . . . . . . . . . . . . . . . . . . . . 27 7.5 URI/IRI Selection . . . . . . . . . . . . . . . . . . . . . 27
7.6 Display of URIs/IRIs . . . . . . . . . . . . . . . . . . . . 27 7.6 Display of URIs/IRIs . . . . . . . . . . . . . . . . . . . . 28
7.7 Interpretation of URIs and IRIs . . . . . . . . . . . . . . 28 7.7 Interpretation of URIs and IRIs . . . . . . . . . . . . . . 28
7.8 Upgrading Strategy . . . . . . . . . . . . . . . . . . . . . 28 7.8 Upgrading Strategy . . . . . . . . . . . . . . . . . . . . . 29
8. Security Considerations . . . . . . . . . . . . . . . . . . 29 8. Security Considerations . . . . . . . . . . . . . . . . . . 30
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31
Normative References . . . . . . . . . . . . . . . . . . . . 31 Normative References . . . . . . . . . . . . . . . . . . . . 32
Non-normative References . . . . . . . . . . . . . . . . . . 32 Non-normative References . . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 34 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 35
Full Copyright Statement . . . . . . . . . . . . . . . . . . 35 Full Copyright Statement . . . . . . . . . . . . . . . . . . 36
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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[RFCYYYY], such as URI references. [RFCYYYY], such as URI references.
Using characters outside of A-Z in IRIs brings with it some Using characters outside of A-Z in IRIs brings with it some
difficulties; a discussion of potential problems and workarounds can difficulties; a discussion of potential problems and workarounds can
be found in the later sections of this document. be found in the later sections of this document.
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
providing 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 IRIs into contexts that are not defined to accept introduce IRIs into contexts that are not defined to accept
them. For example, XML schema [XMLSchema] has an explicit type them. For example, XML schema [XMLSchema] has an explicit type
"anyURI" that designates the use of IRIs. "anyURI" that designates the use of IRIs.
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mechanism to represent the wide range of characters used in mechanism to represent the wide range of characters used in
IRIs, either natively or by some protocol- or format-specific IRIs, either natively or by some protocol- or format-specific
escaping mechanism (for example numeric character references in escaping 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, this is recommended in [RFC2718]. It can apply to a schemes, this is recommended in [RFC2718]. It can apply to a
whole scheme (e.g. IMAP URLs [RFC2192] and POP URLs [RFC2384], whole scheme (e.g. IMAP URLs [RFC2192] and POP URLs [RFC2384],
or the URN syntax [RFC2141]). It can apply to a specific part or the URN syntax [RFC2141]). It can apply to a specific part
of an URI, such as the fragment identifier (e.g. [XPointer]). of a URI, such as the fragment identifier (e.g. [XPointer]).
It can apply to a specific URI or part(s) thereoff. For It can apply to a specific URI or part(s) thereof. For
details, please see Section 6.4. details, please see Section 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, control, or representation of data. For example, organization, control, or representation of data. For example,
"LATIN CAPITAL LETTER A" names a character. "LATIN CAPITAL LETTER A" names a character.
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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 as a sequence of octets (maybe with variants). A characters as a sequence of octets (maybe with variants). A
method of (unambiguously) converting a sequence of octets into method of (unambiguously) converting a sequence of octets into
a sequence of characters. a sequence of characters.
code point: A placeholder for a character in a character encoding,
for example to encode additional characters in future versions
of the character encoding.
charset: The name of a parameter or attribute used to identify a charset: The name of a parameter or attribute used to identify a
character encoding. character encoding.
UCS: Universal Character Set; the coded character set defined by UCS: Universal Character Set; the coded character set defined by
[ISO10646] and [UNIV4]. [ISO10646] and [UNIV4].
IRI reference: The term "IRI reference" denotes the common usage IRI reference: The term "IRI reference" denotes the common usage
of an internationalized resource identifier. An IRI reference of an internationalized resource identifier. An IRI reference
may be absolute or relative. However, the "IRI" that results may be absolute or relative. However, the "IRI" that results
from such a reference only includes absolute IRIs; any relative from such a reference only includes absolute IRIs; any relative
IRIs are resolved to their absolute form. Note that in IRIs are resolved to their absolute form. Note that in
[RFC2396], URIs did not include fragment identifiers, but in [RFC2396], URIs did not include fragment identifiers, but in
[RFCYYYY], fragment identifiers are part of URIs. [RFCYYYY], fragment identifiers are part of URIs.
running text: Human text (paragraphs, sentences, phrases) with
syntax according to orthographic conventions of a natural
language, as opposed to syntax defined for ease of processing
by machines (markup, programming languages,...).
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.
To represent characters outside US-ASCII in examples, this document To represent characters outside US-ASCII in examples, this document
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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),
the two hex digits denoting the octet are enclosed in "<" 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).
As with URIs, an IRI is defined as a sequence of characters, not as a As with URIs, an IRI is defined as a sequence of characters, not as a
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these protocols or documents use different character encodings (and/ these protocols or documents use different character encodings (and/
or transfer encodings). Using the same character encoding as the or transfer encodings). Using the same character encoding as the
containing protocol or document assures that the characters in the containing protocol or document assures that the characters in the
IRI can be handled (searched, converted, displayed,...) in the same IRI can be handled (searched, converted, displayed,...) in the same
way as the rest of the protocol or document. way as the rest of the protocol or document.
2.1 Summary of IRI Syntax 2.1 Summary of IRI Syntax
IRIs are defined similarly to URIs in [RFCYYYY], but the class of IRIs are defined similarly to URIs in [RFCYYYY], but the class of
unreserved characters is extended by adding the characters of the UCS unreserved characters is extended by adding the characters of the UCS
(Universal Character Set, [ISO10646]) beyond U+0080, subject to the (Universal Character Set, [ISO10646]) beyond U+007F, subject to the
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
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":" / "&" / "=" / "+" / "$" / "," ) ":" / "&" / "=" / "+" / "$" / "," )
ihost = [ IPv6reference / IPv4address / ihostname ] ihost = [ IPv6reference / IPv4address / ihostname ]
ihostname = idomainlabel iqualified ihostname = idomainlabel iqualified
iqualified = *( "." idomainlabel ) [ "." ] iqualified = *( "." idomainlabel ) [ "." ]
idomainlabel = <<See following production rules>> idomainlabel = <<See following production rules>>
ipath-segments = isegment *( "/" isegment ) ipath-segments = ipath-segment *( "/" ipath-segment )
isegment = *ipchar ipath-segment = *ipchar
ipchar = iunreserved / escaped / ";" / ipchar = iunreserved / escaped / ";" /
":" / "@" / "&" / "=" / "+" / "$" / "," ":" / "@" / "&" / "=" / "+" / "$" / ","
iquery = *( ipchar / iprivate / "/" / "?" ) iquery = *( ipchar / iprivate / "/" / "?" )
ifragment = *( ipchar / "/" / "?" ) ifragment = *( ipchar / "/" / "?" )
iric = reserved / iunreserved / escaped iric = reserved / iunreserved / escaped
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iunreserved = unreserved / ucschar iunreserved = unreserved / 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
The 'idomainlabel' production rule is as follows: The 'idomainlabel' production rule is as follows:
The value 'idomainlabel' is defined as a string of 'ucschar' obeying The value 'idomainlabel' is defined as a string of 'ucschar' obeying
the following rules: the following rules:
a) Given a string of 'ucschar' values, the ToASCII operation a) Given a string of 'ucschar' values, the ToASCII operation
[RFC3490] is performed on that string with the flag [RFC3490] is performed on that string with the flag
UseSTD3ASCIIRules set to TRUE and the flag AllowUnassigned set UseSTD3ASCIIRules set to TRUE and the flag AllowUnassigned set
to FALSE for creating IRIs and set to TRUE otherwise. to FALSE for creating IRIs and set to TRUE otherwise.
b) ToASCII is successful and results in a string conforming to b) ToASCII is successful. (Note: This means that its output
'domainlabel' (see below). conforms to 'domainlabel' as defined below.)
The following are the same as [RFCYYYY]: The following are the same as [RFCYYYY]:
scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." ) scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
port = *DIGIT port = *DIGIT
domainlabel = alphanum [ 0*61( alphanum | "-" ) alphanum ] domainlabel = alphanum [ 0*61( alphanum | "-" ) alphanum ]
alphanum = ALPHA / DIGIT alphanum = ALPHA / DIGIT
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a) Syntactical: Many URI schemes and components define additional a) Syntactical: Many URI schemes and components define additional
syntactical restrictions not captured in Section 2.2. Such syntactical restrictions not captured in Section 2.2. Such
restrictions can be applied to IRIs by noting that IRIs are restrictions can be applied to IRIs by noting that IRIs are
only valid if they map to syntactically valid URIs. This means only valid if they map to syntactically valid URIs. This means
that such syntactical restrictions do not have to be defined that such syntactical restrictions do not have to be defined
again on the IRI level. again on the IRI level.
b) Interpretational: URIs identify resources in various ways. b) Interpretational: URIs identify resources in various ways.
IRIs also identify resources. When the IRI is used solely for IRIs 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
an URI (see Section 5). However, when an IRI is used for a URI (see Section 5). However, when an IRI is used for
resource retrieval, the resource that the IRI locates is the resource retrieval, the resource that the IRI locates is the
same as the one located by the URI obtained after converting same as the one located by the URI obtained after converting
the IRI according to the procedure defined here. This means the IRI according to the procedure defined here. This means
that there is no need to define resolution separately on the that there is no need to 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 encoding from the original
IRI format. This step has three variants, depending on the IRI format. This step has three variants, depending on the
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from the UCS normalized according to NFC. from the UCS 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 encoding (for
example UTF-8 or UTF-16): Do not normalize. Move example UTF-8 or UTF-16): Do not normalize. Move
directly to Step 2. directly to Step 2.
Step 2) If the IRI contains an 'ihostname' part, replace this Step 2) If the IRI contains an 'ihostname' part, replace this
'ihostname' part by the part converted using the ToASCII 'ihostname' part by the part converted using the ToASCII
operation specified in Section 4.1 of [RFC3490], with the flag operation specified in Section 4.1 of [RFC3490], with the flag
UseSTD3ASCIIRules set to TRUE and the flag AllowUnassigned set UseSTD3ASCIIRules set to TRUE and the flag AllowUnassigned set
to FALSE for creating IRIs and set to TRUE otherwise. to FALSE for creating IRIs and set to TRUE otherwise. The
ToASCII operation may fail, but only if the IRI does not
conform to the rules in Section 2.2.
Step 3) For each character that is disallowed in URI references, Step 3) For each character that is disallowed in URI references,
apply steps 1) through 3) below. The disallowed characters apply steps 1) through 3) below. The disallowed characters
consist of all non-ASCII characters allowed in IRIs. consist of all non-ASCII characters allowed in IRIs.
1) Convert the character to a sequence of one or more octets 1) Convert the character to a sequence of one or more octets
using UTF-8 [RFCXXXX]. using UTF-8 [RFCXXXX].
2) Convert each octet to %HH, where HH is the hexadecimal 2) Convert each octet to %HH, where HH is the hexadecimal
notation of the octet value. Note: This is identical to notation of the octet value. Note: This is identical to
the escaping mechanism in Section 2.4.1 of [RFCYYYY]. the escaping mechanism in Section 2.4.1 of [RFCYYYY]. To
Note: To reduce variability, the hexadecimal notation reduce variability, the hexadecimal notation SHOULD use
SHOULD use upper case letters. upper case letters.
3) Replace the original character by the resulting character 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).
Note that the ToASCII operation in Step 2) may fail, but only if the The above mapping from IRIs to URIs produces URIs fully conforming to
IRI does not conform to the rules in Section 2.2. [RFCYYYY]. The mapping is also an identity transformation for URIs
and is idempotent -- applying the mapping a second time will not
change anything. Every URI is by definition an IRI.
Note: For backwards compatibility with implementations of previous Infrastructure accepting IRIs MAY also deal with 'ihostname' parts
drafts of this specification, infrastructure accepting IRIs MAY also escaped according to Step 3) rather than Step 2). For example, Step
deal with 'ihostname' parts escaped according to Step 3) rather than 2) converts the IRI
Step 2). For example, Step 2) converts the IRI
http://r&#xE9;sum&#xE9;.example.org to http://r&#xE9;sum&#xE9;.example.org to
http://xn--rsum-bpad.example.org. For backwards compatibility, http://xn--rsum-bpad.example.org. For backward compatibility,
http://r%C3%A9sum%C3%A9.example.org would also be converted to http://r%C3%A9sum%C3%A9.example.org would also be converted to
http://xn--rsum-bpad.example.org. http://xn--rsum-bpad.example.org.
Note that Internationalized Domain Names may be contained in parts of Infrastructure accepting IRIs MAY also deal with the printable
an IRI other than the 'ihostname' part. characters in US-ASCII that are not allowed in URIs, namely "<", ">",
'"', Space, "{", "}", "|", "\", "^", and "`", in step 3) above. If
such characters are found but are not converted, then the conversion
SHOULD fail. Please note that the number sign ("#"), the percent
sign ("%"), and the square bracket characters ("[", "]") are not part
of the above list, and MUST NOT be converted. Protocols and formats
that have used earlier definitions of IRIs including these characters
MAY require unescaping of these characters as a preprocessing step to
extract the actual IRI from a given field. Such preprocessing MAY
also be used by applications allowing the user to enter an IRI.
Note that in this process (in step 3.3), characters allowed in URI Internationalized Domain Names may be contained in parts of an
IRI other than the 'ihostname' part. In this case, Step 2) is
not used, but Step 3) is applied. This is important to
maintain uniform treatment of URIs. See [Gettys] for an in-
depth discussion. It is the responsibility of scheme-specific
implementations (if the Internationalized Domain Name is part
of the scheme syntax) or of server-side implementations (if the
Internationalized Domain Name is part of 'iquery') to apply the
necessary conversions at the appropriate point. Example:
Trying to validate the Web page at
http://r&#xE9;sum&#xE9;.example.org would lead to an IRI of
http://validator.w3.org/
check?uri=http%3A%2F%2Fr&#xE9;sum&#xE9;.example.org, which
would convert to a URI of
http://validator.w3.org/
check?uri=http%3A%2F%2Fr%C3%A9sum%C3%A9.example.org. The
server side implementation would be responsible to do the
necessary conversions in order to be able to retrieve the Web
page.
In this process (in step 3.3), characters allowed in URI
references as well as existing escape sequences are not escaped references as well as existing escape sequences are not escaped
further. (This mapping is similar to, but different from, the further. (This mapping is similar to, but different from, the
escaping applied when including arbitrary content into some part of a escaping applied when including arbitrary content into some
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 like http://www.example.org/red%09ros%C3%A9#red, not to something
like
http%3A%2F%2Fwww.example.org%2Fred%2509ros%C3%A9%23red. http%3A%2F%2Fwww.example.org%2Fred%2509ros%C3%A9%23red.
Note that some older software transcoding to UTF-8 may produce Some older software transcoding to UTF-8 may produce illegal
illegal output for some input, in particular for characters outside output for some input, in particular for characters outside the
the BMP (Basic Multilingual Plane). As an example, for the following BMP (Basic Multilingual Plane). As an example, for the
IRI with non-BMP characters (in XML Notation): following IRI with non-BMP characters (in XML Notation):
http://example.com/&#x10300;&#x10301;&#x10301; http://example.com/&#x10300;&#x10301;&#x10302;
(the first three letters of the Old Italic alphabet) the correct (the first three letters of the Old Italic alphabet) the
conversion to a URI is: correct 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
The above mapping produces a URI fully conforming to [RFCYYYY] out of
each IRI. The mapping is also an identity transformation for URIs
and is idempotent -- applying the mapping a second time will not
change anything. Every URI is therefore by definition an IRI.
Note: Earlier drafts of this specification allowed the space
character and various delimiters in IRIs and IRI references. The
full list of these characters was: "<", ">", '"', Space, "{", "}",
"|", "\", "^", and "`", i.e. all printable characters in US-ASCII
that are not allowed in URIs. For backwards compatibility,
implementations MAY also include these characters in step 3) above.
If such characters are found but are not converted, then the
conversion SHOULD fail. Please note that the number sign ("#"), the
percent sign ("%"), and the square bracket characters ("[", "]") are
not part of the above list, and MUST not be converted. Protocols and
formats that have used earlier definitions of IRIs including these
characters MAY require unescaping of these characters as a
preprocessing step to extract the actual IRI from a given field.
Such preprocessing MAY also be used by applications allowing the user
to enter an IRI.
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 escape
sequences). However, the IRI resulting from this conversion may not sequences). However, the IRI resulting from this conversion may not
be exactly the same as the original IRI (if there ever was one). be exactly the same as the original IRI (if there ever was one).
skipping to change at page 13, line 32 skipping to change at page 13, line 48
discussion, see [Duerst97].) discussion, 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 in an IRI. See Section 6.1 for further details. appropriate 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) Replace any punycode-encoded domainlabel in the URI by the 2) Apply the ToUnicode operation to each 'domainlabel' in the
result of the ToUnicode function represented as UTF-8. 'hostname' part (if there is one), representing the output as
UTF-8.
3) Convert all hexadecimal escapes (% followed by two hexadecimal 3) Convert all hexadecimal escapes (% 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 corresponding octets. the corresponding octets.
4) Re-escape any octet produced in step 3) that is not part of a 4) Re-escape any octet produced in step 3) that is not part of a
strictly legal UTF-8 octet sequence. strictly legal UTF-8 octet sequence.
5) Re-escape all octets produced in step 3) that in UTF-8 5) Re-escape all octets produced in step 3) that in UTF-8
skipping to change at page 14, line 34 skipping to change at page 15, line 4
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%BCrst 2) http://www.example.org/D%C3%BCrst
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<c3><bc>rst 5) http://www.example.org/D<c3><bc>rst
6) http://www.example.org/D&#xFC;rst 6) 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 encoding. (It might represent other characters in other
encodings. For example, the octet <FC> in iso-8859-5 represents encodings. For example, the octet <fc> in iso-8859-5 represents
U+045C CYRILLIC SMALL LETTER KJE.) Because <FC> is not part of a U+045C CYRILLIC SMALL LETTER KJE.) Because <fc> is not part of a
strictly legal UTF-8 sequence, it is re-escaped in step 2). strictly legal UTF-8 sequence, it is re-escaped in step 2).
1) http://www.example.org/D%FCrst 1) http://www.example.org/D%FCrst
2) http://www.example.org/D%FCrst 2) http://www.example.org/D%FCrst
3) http://www.example.org/D<FC>rst
3) http://www.example.org/D<fc>rst
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
6) http://www.example.org/D%FCrst 6) 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 escaped
UTF-8 encoding of U+202E, RIGHT-TO-LEFT OVERRIDE. Section 4.1 UTF-8 encoding of U+202E, RIGHT-TO-LEFT OVERRIDE. Section 4.1
forbids the direct use of this character in an IRI. Therefore, the forbids the direct use of this character in an IRI. Therefore, the
corresponding octets are re-escaped in step 5). This example shows corresponding octets are re-escaped in step 5). This example shows
that the case (upper or lower) of letters used in escapes may not be that the case (upper or lower) of letters used in escapes may not be
preserved. The example also contains a punycode-encoded domain name preserved. The example also contains a punycode-encoded domain name
label (xn--99zt52a), which is converted to the corresponding label (xn--99zt52a), which is converted to the corresponding
characters U+7D0D U+8C46 (Japanese Natto). characters U+7D0D U+8C46 (Japanese Natto).
1) http://xn--99zt52a.example.org/%e2%80%ae 1) http://xn--99zt52a.example.org/%e2%80%ae
2) http://<E7><B4><8D><E8><B1><86>.example.org/%e2%80%ae 2) http://<e7><b4><8d><e8><b1><86>.example.org/%e2%80%ae
3) http://<E7><B4><8D><E8><B1><86>.example.org/<E2><80><AE> 3) http://<e7><b4><8d><e8><b1><86>.example.org/<e2><80><ae>
4) http://<E7><B4><8D><E8><B1><86>.example.org/<E2><80><AE> 4) http://<e7><b4><8d><e8><b1><86>.example.org/<e2><80><ae>
5) http://<E7><B4><8D><E8><B1><86>.example.org/%E2%80%AE 5) http://<e7><b4><8d><e8><b1><86>.example.org/%E2%80%AE
6) http://&#x7D0D;&#x8C46;.example.org/%E2%80%AE 6) 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
skipping to change at page 16, line 4 skipping to change at page 16, line 22
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 2) the ability to include a wide range of characters in various
parts of the IRI; parts of the IRI;
3) no or not too big 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 with an overall left-to-right (ltr) direction. rendered with an overall left-to-right (ltr) direction.
In text with a left-to-right base directionality or embedding (as In text with a left-to-right base directionality or embedding (such
used for e.g. English or Cyrillic), the Unicode Bidirectional as used for English or Cyrillic), the Unicode Bidirectional Algorithm
Algorithm will automatically use an overall ltr direction for the will automatically use an overall ltr direction for the IRI. In text
IRI. In text with a rtl base directionality or embedding (as used with a rtl base directionality or embedding (such as used for Arabic
e.g. for Arabic or Hebrew), setting a different embedding direction or Hebrew), setting a different embedding direction for the IRI is
for the IRI is needed. Setting the embedding direction can be done needed. Setting the embedding direction can be done in a higher-
in a higher-order protocol (e.g. the dir='ltr' attribute in HTML). order protocol (e.g. the dir='ltr' attribute in HTML). If this is
If this is not available (e.g. in plain text), setting the embedding not available (e.g. in plain text), setting the embedding is done
is done with Unicode bidi formatting codes, i.e. U+202A, LEFT-TO- with Unicode bidi formatting codes, i.e. U+202A, LEFT-TO-RIGHT
RIGHT EMBEDDING (LRE) before the IRI, and U+202C, POP DIRECTIONAL EMBEDDING (LRE) before the IRI, and U+202C, POP DIRECTIONAL
FORMATTING (PDF) after the IRI, both not being part of the IRI FORMATTING (PDF) after the IRI, both not being part of the IRI
itself. itself.
IRIs MUST NOT contain bidirectional formatting characters (LRM, RLM, IRIs MUST NOT contain bidirectional formatting characters (LRM, RLM,
LRE, RLE, LRO, RLO, and PDF). They affect the visual rendering of LRE, RLE, LRO, RLO, and PDF). They affect the visual rendering of
the IRI, but do not themselves appear visually. It would therefore the IRI, but do not themselves appear visually. It would therefore
not be possible to correctly input an IRI with such characters. not be possible to correctly input an IRI with such 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, ihostname, for the purpose of Bidi behavior: iuserinfo, ipath-segment,
iquery, and ifragment. ihostname, 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 the domain name as a component. Even where the components label of the domain name as a component. Even where the components
are not defined formally, it may be helpful to think about some are not defined formally, it may be helpful to think about some
syntax in terms of components and to apply the relevant restrictions. syntax in terms of components and to apply the relevant restrictions.
For example, for the usual name/value syntax in query parts, it is For example, for the usual name/value syntax in query parts, it is
convenient to treat each name and each value as a component. As convenient to treat each name and each value as a component. As
skipping to change at page 17, line 32 skipping to change at page 17, line 50
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.
In some components, the above restrictions may actually be strictly In some components, the above restrictions may actually be
enforced. For example, [RFC3490] requires that these restrictions strictly enforced. For example, [RFC3490] requires that these
apply to the labels of the host name part of an IRI. In some other restrictions apply to the labels of the host name part of an
components, for example path components, following these restrictions IRI. In some other components, for example path components,
may not be too difficult. For other components, such as parts of the following these restrictions may not be too difficult. For
query part, it may be very difficult to enforce the restrictions, other components, such as parts of the query part, it may be
because the values of query parameters may be arbitrary character very difficult to enforce the restrictions, because the values
sequences. of query parameters may be arbitrary character 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 34 skipping to change at page 20, line 4
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: escaped:
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):
logical representation: http://ab.CDEFGH.123/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
difficult to prohibit them), but may interact with adjacent RTL
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 focusses on the main issues and on aspects that are different section focuses on the main issues and on aspects that are different
from [RFCYYYY]; Section 6 of [RFCYYYY] is recommended background from [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.
skipping to change at page 21, line 10 skipping to change at page 21, line 36
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 convertsion from a non- comparing two IRIs. The exceptions are conversion from a non-digital
digital form, and conversion from a non-UCS-based encoding to an UCS- form, and conversion from a non-UCS-based encoding to an UCS-based
based encoding. In these cases, NFC or a normalizing transcoder encoding. In these cases, NFC or a normalizing transcoder using NFC
using NFC MUST be used for interoperability. To avoid false MUST be used for interoperability. To avoid false negatives and
negatives and problems with transcoding, IRIs SHOULD be created using problems with transcoding, IRIs SHOULD be created using NFC. Using
NFC. Using NFKC will avoid even more problems. NFKC may avoid even more problems, for example by choosing half-width
Latin letters instead of full-width, and 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 we do not know how a particular field is treated with respect Because it is unknow how a particular field is being treated
to text normalization, it would be inappropriate to allow third with respect to text normalization, it would be inappropriate
parties to normalize an IRI arbitrarily. This does not contradict to allow third parties to normalize an IRI arbitrarily. This
the recommendation that if you create a resource, and an IRI for that does not contradict the recommendation that when a resource is
resource, you try to be as normalized as possible (i.e. NFKC if created, and an IRI for that resource, you try to be as
possible). This is similar to the upper-case/lower-case problems in normalized as possible (i.e. NFC or even NFKC). This is
URIs. Some parts of an URI are case-insensitive (domain name). For similar to the upper-case/lower-case problems in URIs. Some
others, it is unclear whether they are case-sensitive or case- parts of a URI are case-insensitive (domain name). For others,
insensitive, or something in between (e.g. case-sensitive, but if it is unclear whether they are case-sensitive or case-
you use the wrong case, may not directly get a result, but rather a insensitive, or something in between (e.g. case-sensitive, but
'Multiple choices'). The best recipe we have there is that the if the wrong case is used, a multiple choice selection is
generator uses a reasonable capitalization, and when transfering the provided instead of a direct negative result). The best recipe
URI, you do not change capitalization. is that the generator uses a reasonable capitalization, and
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 using the ToASCII operation defined in [RFC3490], with the validated using the ToASCII operation defined in [RFC3490], with the
flags "UseSTD3ASCIIRules" and "AllowUnassigned". An IRI containing flags "UseSTD3ASCIIRules" and "AllowUnassigned". An IRI containing
an invalid IDN cannot successfully be resolved. For legibility an invalid IDN cannot successfully be resolved. For legibility
purposes, IDN components of IRIs SHOULD not be converted into ASCII purposes, IDN components of IRIs SHOULD NOT be converted into ASCII
Compatible Encoding (ACE). However, this conversion is applied when Compatible Encoding (ACE). However, this conversion is applied when
mapping an IRI into an URI, see Section 3.1. mapping an IRI into a URI, see Section 3.1.
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 generated:
- 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-escaping where it is essential.
- Always use uppercase A-through-F characters when percent- - Always use uppercase A-through-F characters when percent-
escaping. escaping.
- Always provide the hostname, if any, in the form produced when - Always provide the hostname, if any, in the form produced when
applying [RFC3491]. This in particular includes using applying nameprep [RFC3491]. This in particular includes using
lowercase characters rather than uppercase characters where lowercase characters rather than uppercase characters where
applicable. applicable.
- 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.
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
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strong visual look-alikes. Because of the likelihood of strong visual look-alikes. Because of the likelihood of
transcription errors, these also should be avoided. This transcription errors, these also should be avoided. This
includes the full-width equivalents of ASCII characters, half- includes the full-width equivalents of ASCII characters, half-
width Katakana characters for Japanese, and many others. This width Katakana characters for Japanese, and many others. This
also includes many look-alikes of "space", "delims", and also includes many look-alikes of "space", "delims", and
"unwise", characters excluded in [RFC3491]. "unwise", 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 and code points 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
other kinds of code units. Thus, software interfaces and protocols other kinds of code units. Thus, software interfaces and protocols
MUST define which character encoding is used. MUST define which character encoding is used.
Intermediate software interfaces between IRI-capable components and Intermediate software interfaces between IRI-capable components and
URI-only components MUST map the IRIs 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 encoding, and converted accordingly by a parser or interpreter. IRI
characters that are not expressible in the native encoding SHOULD be characters that are not expressible in the native encoding SHOULD be
escaped using the escaping conventions of the document format if such escaped using the escaping conventions of the document format if such
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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
This section discusses details and gives examples for point c) in This section discusses details and gives examples for point c) in
Section 1.2. In order to be able to use IRIs, the URI corresponding Section 1.2. In order to be able to use IRIs, the URI corresponding
to the IRI in question has to encode original characters into octets to the IRI in question has to encode original characters into octets
using UTF-8. This can be specified for all URIs of an URI scheme, or using UTF-8. This can be specified for all URIs of a URI scheme, or
can apply to individual URIs for schemes that do not specify how to can apply to individual URIs for schemes that do not specify how to
encode original characters. It can apply to the whole URI, or only encode original characters. It can apply to the whole URI, or only
some part. some part.
For new URI schemes, using UTF-8 is recommended in [RFC2718]. For new URI schemes, using UTF-8 is recommended in [RFC2718].
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, the IMAP URLs [RFC2192], and POP URLs [RFC2384]. On the other hand,
HTTP URL scheme does not specify how to encode original characters, because the HTTP URL scheme does not specify how to encode original
and therefore IRIs only can be used for some HTTP URLs. characters, only some HTTP URLs can have corresponding but different
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 escaped
representation of that character). On the other hand, for a document representation of that character). On the other hand, for a document
with an URI of http://www.example.org/r%E9sum%E9.html, the escaped with a URI of http://www.example.org/r%E9sum%E9.html, the escaped
octets cannot be converted to actual characters in an IRI, because octets cannot be converted to actual characters in an IRI, because
the escaping is not based on UTF-8. the escaping is not based on UTF-8.
The requirement for the use of UTF-8 applies to all parts of an URI, The requirement for the use of UTF-8 applies to all parts of a URI,
with the exception of the ihostname part. However, it is possible with the exception of the ihostname part. However, it is possible
that the capability of IRIs to represent a wide range of characters that the capability of IRIs to represent a wide range of characters
directly is used just in some parts of the IRI (or IRI reference). directly is used just in some parts of the IRI (or IRI reference).
The other parts of the IRI may only contain ASCII characters, or they The other parts of the IRI may only contain ASCII characters, or they
may not be based on UTF-8. They may be based on another encoding, or may not be based on UTF-8. They may be based on another encoding, or
they may directly encode raw binary data (see also [RFC2397]). they may directly encode raw binary data (see also [RFC2397]).
For example, it is possible to have an 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;.
@@@@ add something about query parts Similar considerations apply to query parts. The functionality of
IRIs (namely to be able to include non-ASCII characters) can only be
used if the query part is encoded in UTF-8.
6.5 Relative IRI References 6.5 Relative IRI References
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)
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The process of IRI entry must assure, as far as possible, that the The process of IRI entry must assure, as far as possible, that the
restrictions defined in Section 2.2 are met. This may be done by restrictions defined in Section 2.2 are met. This may be done by
choosing appropriate input methods or variants/settings thereof, by choosing appropriate input methods or variants/settings thereof, by
appropriately converting the characters being input, by eliminating appropriately converting the characters being input, by eliminating
characters that cannot be converted, and/or by issuing a warning or characters that cannot be converted, and/or by issuing a warning or
error message to the user. error message to the user.
As an example of variant settings, input method editors for East As an example of variant settings, input method editors for East
Asian Languages usually allow the input of Latin letters and related Asian Languages usually allow the input of Latin letters and related
characters in full-width or half-width versions. For IRI input, the characters in full-width or half-width versions. For IRI input, the
input method editor should be set to half-width input, in order to input method editor should be set so that it produces half-width
produce US-ASCII characters where possible. Latin letters, and full-width Katakana.
An input field primarily or only used for the input of URIs/IRIs An input field primarily or only used for the input of URIs/IRIs may
should allow the user to view an IRI as mapped to a URI. Places allow the user to view an IRI as mapped to a URI. Places where the
where the input of IRIs is frequent should provide the possibility input of IRIs is frequent may provide the possibility for viewing an
for viewing an IRI as mapped to a URI. This will help users when IRI as mapped to a URI. This will help users when some of the
some of the software they use does not yet accept IRIs. software they use does not yet accept IRIs.
An IRI input component that interfaces to components that handle An IRI input component that interfaces to components that handle
URIs, but not IRIs, must map the IRI to a URI before passing it to URIs, but not IRIs, must map the IRI to a URI before passing it to
such a component. such a component.
For the input of IRIs with right-to-left characters, please see For the input of IRIs with right-to-left characters, please see
Section 4.3. Section 4.3.
7.3 URI/IRI Transfer Between Applications 7.3 URI/IRI Transfer Between Applications
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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 non-
ASCII character should not be taken as the indication of the end of ASCII character should not be taken as the indication of the end of
an IRI. Such applications also have to make sure that they correctly an IRI. Such applications also have to make sure that they correctly
convert the detected IRI from the encoding of the document or convert the detected IRI from the encoding of the document or
application where the IRI appears to the encoding used by the system- application where the IRI appears to the encoding used by the system-
wide IRI invocation mechanism, or to an URI (according to Section wide IRI invocation mechanism, or to a URI (according to Section 3.1)
3.1) if the system-wide invocation mechanism only accepts URIs. 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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generate a directory listing for a file directory, and then respond generate a directory listing for a file directory, and then respond
to the generated URIs with the files. to the generated URIs with the files.
Many legacy character encodings are in use in various file systems. Many legacy character encodings are in use in various file systems.
Many currently deployed systems do not transform the local character Many currently deployed systems do not transform the local character
representation of the underlying system before generating URIs. representation of the underlying system before generating URIs.
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 an 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 an 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
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here. As long as names are limited to characters from a single here. As long as names are limited to characters from a single
script, native writers of a given script or language will know best script, native writers of a given script or language will know best
when ambiguities can appear, and how they can be avoided. What may when ambiguities can appear, and how they can be avoided. What may
look ambiguous to a stranger may be completely obvious to the average look ambiguous to a stranger may be completely obvious to the average
native user. On the other hand, in some cases, the UCS contains native user. On the other hand, in some cases, the UCS contains
variants for compatibility reasons, for example for typographic variants for compatibility reasons, for example for typographic
purposes. These should be avoided wherever possible. Although there purposes. These should be avoided wherever possible. Although there
may be exceptions, in general newly created resource names should be may be exceptions, in general newly created resource names should be
in NFKC [UTR15] (which means that they are also in NFC). in NFKC [UTR15] (which means that they are also in NFC).
As an example, the UCS contains codepoint U+FB01 for the 'fi' As an example, the UCS contains the 'fi' ligature at U+FB01 for
ligature for compatibility reasons. Wherever possible, IRIs should compatibility reasons. Wherever possible, IRIs should use the two
use the two letters 'f' and 'i' rather than the 'fi' ligature. An letters 'f' and 'i' rather than the 'fi' ligature. An example where
example where the later may be used is in the query part of an IRI the latter may be used is in the query part of an IRI for an explicit
for an explicit search for a word 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 generated where all the characters in a single component
are used together in a given language. This usually means that all are used together in a given language. This usually means that all
these characters will be from the same script, but there are these characters will be from the same script, but there are
languages that mix characters from different scripts (such as languages that mix characters from different scripts (such as
Japanese). This is similar to the heuristics used to distinguish Japanese). This is similar to the heuristics used to distinguish
between letters and numbers in the examples above. Also, for Latin, between letters and numbers in the examples above. Also, for Latin,
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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 encodings to
convert non-ASCII characters to URIs. Whether this is necessary, and convert non-ASCII characters to URIs. Whether this is necessary and
what character encodings to cover, depends on a number of factors, what character encodings to cover, depends on a number of factors,
such as the legacy character encodings used locally and the such as the legacy character encodings used locally and the
distribution of various versions of user agents. For example, distribution of various versions of user agents. For example,
software for Japanese may accept URIs in Shift_JIS and/or EUC-JP in software for Japanese may accept URIs in Shift_JIS and/or EUC-JP in
addition to UTF-8. addition to UTF-8.
Third, it may include additional mappings to be more user-friendly Third, it may include additional mappings to be more user-friendly
and robust against transmission errors. These would be similar to and robust against transmission errors. These would be similar to
how currently some servers treat URIs as case-insensitive, or perform how currently some servers treat URIs as case-insensitive, or perform
additional matching to account for spelling errors. For characters additional matching to account for spelling errors. For characters
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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 but 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 encoding,
do not match the normalization used on the server side. 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 introduction of character
normalization, and of additional mappings for user convenience, may normalization, 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
part or a path part. For considerations specific to the domain name
part, see [RFC3491]. For the path part, administrators of sites
which allow independent users to create resources in the same subarea
may 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 is very similar to spoofing possibilities on US-ASCII, e.g. this is very similar to spoofing possibilities on US-ASCII, e.g.
using 'br0ken' or '1ame' URIs. using 'br0ken' or '1ame' URIs.
Spoofing can occur when URIs in various encodings are accepted to Spoofing can occur when URIs in various encodings are accepted to
deal with older user agents. In some cases, in particular for Latin- deal with older user agents. In some cases, in particular for Latin-
based resource names, this is usually easy to detect because UTF-8- based resource names, this is usually easy to detect because UTF-8-
encoded names, when interpreted and viewed as legacy encodings, encoded names, when interpreted and viewed as legacy encodings,
produce mostly garbage. In other cases, when concurrently used produce mostly garbage. In other cases, when concurrently used
encodings have a similar structure, but there are no characters that encodings have a similar structure, but there are no characters that
have exactly the same encoding, detection is more difficult. have exactly the same encoding, detection is more difficult.
Spoofing can occur in various IRI components, such as the domain name
part or a path part. For considerations specific to the domain name
part, see [RFC3491]. For the path part, administrators of sites
which allow independent users to create resources in the same subarea
may need to be careful to check for spoofing.
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).
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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 Thanks to Francois Yergeau, Matti Allouche, Roy Fielding, Tim
Berners-Lee, Mark Davis, M.T. Carrasco Benitez, James Clark, 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, Dan Texin, Graham Klyne, Bjoern Hoehrmann, Chris Lilley, Ian Jacobs, Adam
Oscarson, Elliotte Rusty Harold, Mike J. Brown, Simon Josefsson, Costello, Dan Oscarson, Elliotte Rusty Harold, Mike J. Brown, Andrea
Carlos Viegas Damasio, and many others for help with understanding Vine, Roy Badami, Simon Josefsson, Carlos Viegas Damasio, and many
the issues and possible solutions, and getting the details right. others for help with understanding the issues and possible solutions,
Thanks also to the members of the W3C I18N Working Group and Interest and getting the details right. Thanks also to the members of the W3C
Group for their contributions and their work on [CharMod], to the I18N Working Group and Interest Group for their contributions and
members of many other W3C WGs for adopting the ideas, and to the their work on [CharMod], to the members of many other W3C WGs for
members of the Montreal IAB Workshop on Internationalization and adopting the ideas, and to the members of the Montreal IAB Workshop
Localization for their review. on Internationalization and Localization for their review.
Normative References Normative References
[ISO10646] International Organization for Standardization, [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
skipping to change at page 32, line 14 skipping to change at page 32, line 46
[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 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., [CharMod] Duerst, M., Yergeau, F., Ishida, R., Wolf, M. and T.
Freytag, A. and T. Texin, "Character Model for the Texin, "Character Model for the World Wide Web",
World Wide Web", World Wide Web Consortium Working World Wide Web Consortium Working Draft, August 2003,
Draft, April 2002, <http://www.w3.org/TR/charmod>. <http://www.w3.org/TR/charmod>.
[Duerst97] Duerst, M., "The Properties and Promises of UTF-8", [Duerst97] Duerst, M., "The Properties and Promises of UTF-8",
Proc. 11th International Unicode Conference, San Jose Proc. 11th International Unicode Conference, San Jose
, September 1997, <http://www.ifi.unizh.ch/mml/ , September 1997, <http://www.ifi.unizh.ch/mml/
mduerst/papers/PDF/IUC11-UTF-8.pdf>. mduerst/papers/PDF/IUC11-UTF-8.pdf>.
[Duerst01] Duerst, M., "Internationalized Resource Identifiers: [Duerst01] Duerst, M., "Internationalized Resource Identifiers:
From Specification to Testing", Proc. 19th From Specification to Testing", Proc. 19th
International Unicode Conference, San Jose , International Unicode Conference, San Jose ,
September 2001, <http://www.w3.org/2001/Talks/0912- September 2001, <http://www.w3.org/2001/Talks/0912-
IUC-IRI/paper.html>. IUC-IRI/paper.html>.
[Gettys] Gettys, J., "URI Model Consequences", <http://
www.w3.org/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, December 1999, <http://www.w3.org/TR/ Recommendation, December 1999, <http://www.w3.org/TR/
REC-html40/appendix/notes.html#h-B.2>. REC-html40/appendix/notes.html#h-B.2>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2130] Weider, C., Preston, C., Simonsen, K., Alvestrand, [RFC2130] Weider, C., Preston, C., Simonsen, K., Alvestrand,
H., Atkinson, R., Crispin, M. and P. Svanberg, "The H., Atkinson, R., Crispin, M. and P. Svanberg, "The
skipping to change at page 34, line 30 skipping to change at page 35, line 17
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 200 Technology Square
Cambridge, MA 02139 Cambridge, MA 02139
U.S.A. U.S.A.
Phone: +1 617 253 5509 Phone: +1 617 253 5509
Fax: +1 617 258 5999 Fax: +1 617 258 5999
EMail: 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 escaped form of an IRI.)
Michel Suignard Michel Suignard
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
U.S.A. U.S.A.
 End of changes. 

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