draft-ietf-iri-3987bis-05.txt   draft-ietf-iri-3987bis-06.txt 
Internationalized Resource M. Duerst Internationalized Resource Identifiers M. Duerst
Identifiers (iri) Aoyama Gakuin University (iri) Aoyama Gakuin University
Internet-Draft M. Suignard Internet-Draft M. Suignard
Obsoletes: 3987 (if approved) Unicode Consortium Obsoletes: 3987 (if approved) Unicode Consortium
Intended status: Standards Track L. Masinter Intended status: Standards Track L. Masinter
Expires: September 30, 2011 Adobe Expires: February 13, 2012 Adobe
March 29, 2011 August 12, 2011
Internationalized Resource Identifiers (IRIs) Internationalized Resource Identifiers (IRIs)
draft-ietf-iri-3987bis-05 draft-ietf-iri-3987bis-06
Abstract Abstract
This document defines the Internationalized Resource Identifier (IRI) This document defines the Internationalized Resource Identifier (IRI)
protocol element, as an extension of the Uniform Resource Identifier protocol element, as an extension of the Uniform Resource Identifier
(URI). An IRI is a sequence of characters from the Universal (URI). An IRI is a sequence of characters from the Universal
Character Set (Unicode/ISO 10646). Grammar and processing rules are Character Set (Unicode/ISO 10646). Grammar and processing rules are
given for IRIs and related syntactic forms. given for IRIs and related syntactic forms.
In addition, this document provides named additional rule sets for In addition, this document provides named additional rule sets for
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This document is intended to update RFC 3987 and move towards IETF This document is intended to update RFC 3987 and move towards IETF
Draft Standard. For discussion and comments on this draft, please Draft Standard. For discussion and comments on this draft, please
join the IETF IRI WG by subscribing to the mailing list join the IETF IRI WG by subscribing to the mailing list
public-iri@w3.org. For a list of open issues, please see the issue public-iri@w3.org. For a list of open issues, please see the issue
tracker of the WG at http://trac.tools.ietf.org/wg/iri/trac/report/1. tracker of the WG at http://trac.tools.ietf.org/wg/iri/trac/report/1.
For a list of individual edits, please see the change history at For a list of individual edits, please see the change history at
http://trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis. http://trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis.
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF). Note that other groups may also distribute
other groups may also distribute working documents as Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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 This Internet-Draft will expire on February 13, 2012.
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 30, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the BSD License. described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this 10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process. modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
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3.4.3. Additional Considerations . . . . . . . . . . . . . . 16 3.4.3. Additional Considerations . . . . . . . . . . . . . . 16
3.5. Mapping query components . . . . . . . . . . . . . . . . 17 3.5. Mapping query components . . . . . . . . . . . . . . . . 17
3.6. Mapping IRIs to URIs . . . . . . . . . . . . . . . . . . 17 3.6. Mapping IRIs to URIs . . . . . . . . . . . . . . . . . . 17
3.7. Converting URIs to IRIs . . . . . . . . . . . . . . . . . 17 3.7. Converting URIs to IRIs . . . . . . . . . . . . . . . . . 17
3.7.1. Examples . . . . . . . . . . . . . . . . . . . . . . . 19 3.7.1. Examples . . . . . . . . . . . . . . . . . . . . . . . 19
4. Bidirectional IRIs for Right-to-Left Languages . . . . . . . . 20 4. Bidirectional IRIs for Right-to-Left Languages . . . . . . . . 20
4.1. Logical Storage and Visual Presentation . . . . . . . . . 21 4.1. Logical Storage and Visual Presentation . . . . . . . . . 21
4.2. Bidi IRI Structure . . . . . . . . . . . . . . . . . . . 22 4.2. Bidi IRI Structure . . . . . . . . . . . . . . . . . . . 22
4.3. Input of Bidi IRIs . . . . . . . . . . . . . . . . . . . 23 4.3. Input of Bidi IRIs . . . . . . . . . . . . . . . . . . . 23
4.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . 23 4.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . 23
5. Normalization and Comparison . . . . . . . . . . . . . . . . . 25 5. Use of IRIs . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.1. Equivalence . . . . . . . . . . . . . . . . . . . . . . . 26 5.1. Limitations on UCS Characters Allowed in IRIs . . . . . . 25
5.2. Preparation for Comparison . . . . . . . . . . . . . . . 26 5.2. Software Interfaces and Protocols . . . . . . . . . . . . 26
5.3. Comparison Ladder . . . . . . . . . . . . . . . . . . . . 27 5.3. Format of URIs and IRIs in Documents and Protocols . . . 26
5.3.1. Simple String Comparison . . . . . . . . . . . . . . . 27 5.4. Use of UTF-8 for Encoding Original Characters . . . . . . 26
5.3.2. Syntax-Based Normalization . . . . . . . . . . . . . . 28 5.5. Relative IRI References . . . . . . . . . . . . . . . . . 28
5.3.3. Scheme-Based Normalization . . . . . . . . . . . . . . 31 6. Liberal Handling of Otherwise Invalid IRIs . . . . . . . . . . 28
5.3.4. Protocol-Based Normalization . . . . . . . . . . . . . 32 6.1. LEIRI Processing . . . . . . . . . . . . . . . . . . . . 29
6. Use of IRIs . . . . . . . . . . . . . . . . . . . . . . . . . 33 6.2. Web Address Processing . . . . . . . . . . . . . . . . . 29
6.1. Limitations on UCS Characters Allowed in IRIs . . . . . . 33 6.3. Characters Not Allowed in IRIs . . . . . . . . . . . . . 31
6.2. Software Interfaces and Protocols . . . . . . . . . . . . 33 7. URI/IRI Processing Guidelines (Informative) . . . . . . . . . 33
6.3. Format of URIs and IRIs in Documents and Protocols . . . 34 7.1. URI/IRI Software Interfaces . . . . . . . . . . . . . . . 33
6.4. Use of UTF-8 for Encoding Original Characters . . . . . . 34 7.2. URI/IRI Entry . . . . . . . . . . . . . . . . . . . . . . 33
6.5. Relative IRI References . . . . . . . . . . . . . . . . . 36 7.3. URI/IRI Transfer between Applications . . . . . . . . . . 34
7. Liberal Handling of Otherwise Invalid IRIs . . . . . . . . . . 36 7.4. URI/IRI Generation . . . . . . . . . . . . . . . . . . . 34
7.1. LEIRI Processing . . . . . . . . . . . . . . . . . . . . 36 7.5. URI/IRI Selection . . . . . . . . . . . . . . . . . . . . 35
7.2. Web Address Processing . . . . . . . . . . . . . . . . . 37 7.6. Display of URIs/IRIs . . . . . . . . . . . . . . . . . . 36
7.3. Characters Not Allowed in IRIs . . . . . . . . . . . . . 38 7.7. Interpretation of URIs and IRIs . . . . . . . . . . . . . 36
8. URI/IRI Processing Guidelines (Informative) . . . . . . . . . 40 7.8. Upgrading Strategy . . . . . . . . . . . . . . . . . . . 37
8.1. URI/IRI Software Interfaces . . . . . . . . . . . . . . . 40 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
8.2. URI/IRI Entry . . . . . . . . . . . . . . . . . . . . . . 41 9. Security Considerations . . . . . . . . . . . . . . . . . . . 38
8.3. URI/IRI Transfer between Applications . . . . . . . . . . 42 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 39
8.4. URI/IRI Generation . . . . . . . . . . . . . . . . . . . 42 11. Main Changes Since RFC 3987 . . . . . . . . . . . . . . . . . 40
8.5. URI/IRI Selection . . . . . . . . . . . . . . . . . . . . 43 11.1. Major restructuring of IRI processing model . . . . . . . 40
8.6. Display of URIs/IRIs . . . . . . . . . . . . . . . . . . 43 11.1.1. OLD WAY . . . . . . . . . . . . . . . . . . . . . . . 40
8.7. Interpretation of URIs and IRIs . . . . . . . . . . . . . 44 11.1.2. NEW WAY . . . . . . . . . . . . . . . . . . . . . . . 40
8.8. Upgrading Strategy . . . . . . . . . . . . . . . . . . . 44 11.1.3. Extension of Syntax . . . . . . . . . . . . . . . . . 41
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45 11.1.4. More to be added . . . . . . . . . . . . . . . . . . . 41
10. Security Considerations . . . . . . . . . . . . . . . . . . . 46 11.2. Change Log . . . . . . . . . . . . . . . . . . . . . . . 41
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 47 11.2.1. Changes after draft-ietf-iri-3987bis-01 . . . . . . . 41
12. Main Changes Since RFC 3987 . . . . . . . . . . . . . . . . . 47 11.2.2. Changes from draft-duerst-iri-bis-07 to
12.1. Major restructuring of IRI processing model . . . . . . . 47 draft-ietf-iri-3987bis-00 . . . . . . . . . . . . . . 41
12.1.1. OLD WAY . . . . . . . . . . . . . . . . . . . . . . . 48 11.2.3. Changes from -06 to -07 of draft-duerst-iri-bis . . . 41
12.1.2. NEW WAY . . . . . . . . . . . . . . . . . . . . . . . 48 11.3. Changes from -00 to -01 . . . . . . . . . . . . . . . . . 41
12.1.3. Extension of Syntax . . . . . . . . . . . . . . . . . 48 11.4. Changes from -05 to -06 of draft-duerst-iri-bis-00 . . . 42
12.1.4. More to be added . . . . . . . . . . . . . . . . . . . 49 11.5. Changes from -04 to -05 of draft-duerst-iri-bis . . . . . 42
12.2. Change Log . . . . . . . . . . . . . . . . . . . . . . . 49 11.6. Changes from -03 to -04 of draft-duerst-iri-bis . . . . . 42
12.2.1. Changes after draft-ietf-iri-3987bis-01 . . . . . . . 49 11.7. Changes from -02 to -03 of draft-duerst-iri-bis . . . . . 42
12.2.2. Changes from draft-duerst-iri-bis-07 to 11.8. Changes from -01 to -02 of draft-duerst-iri-bis . . . . . 42
draft-ietf-iri-3987bis-00 . . . . . . . . . . . . . . 49 11.9. Changes from -00 to -01 of draft-duerst-iri-bis . . . . . 42
12.2.3. Changes from -06 to -07 of draft-duerst-iri-bis . . . 49 11.10. Changes from RFC 3987 to -00 of draft-duerst-iri-bis . . 43
12.3. Changes from -00 to -01 . . . . . . . . . . . . . . . . . 49 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 43
12.4. Changes from -05 to -06 of draft-duerst-iri-bis-00 . . . 49 12.1. Normative References . . . . . . . . . . . . . . . . . . 43
12.5. Changes from -04 to -05 of draft-duerst-iri-bis . . . . . 50 12.2. Informative References . . . . . . . . . . . . . . . . . 44
12.6. Changes from -03 to -04 of draft-duerst-iri-bis . . . . . 50 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 46
12.7. Changes from -02 to -03 of draft-duerst-iri-bis . . . . . 50
12.8. Changes from -01 to -02 of draft-duerst-iri-bis . . . . . 50
12.9. Changes from -00 to -01 of draft-duerst-iri-bis . . . . . 50
12.10. Changes from RFC 3987 to -00 of draft-duerst-iri-bis . . 50
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 51
13.1. Normative References . . . . . . . . . . . . . . . . . . 51
13.2. Informative References . . . . . . . . . . . . . . . . . 52
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 54
1. Introduction 1. Introduction
1.1. Overview and Motivation 1.1. Overview and Motivation
A Uniform Resource Identifier (URI) is defined in [RFC3986] as a A Uniform Resource Identifier (URI) is defined in [RFC3986] as a
sequence of characters chosen from a limited subset of the repertoire sequence of characters chosen from a limited subset of the repertoire
of US-ASCII [ASCII] characters. of US-ASCII [ASCII] characters.
The characters in URIs are frequently used for representing words of The characters in URIs are frequently used for representing words of
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This document defines the protocol element called Internationalized This document defines the protocol element called Internationalized
Resource Identifier (IRI), which allow applications of URIs to be Resource Identifier (IRI), which allow applications of URIs to be
extended to use resource identifiers that have a much wider extended to use resource identifiers that have a much wider
repertoire of characters. It also provides corresponding repertoire of characters. It also provides corresponding
"internationalized" versions of other constructs from [RFC3986], such "internationalized" versions of other constructs from [RFC3986], such
as URI references. The syntax of IRIs is defined in Section 2. as URI references. The syntax of IRIs is defined in Section 2.
Using characters outside of A - Z in IRIs adds a number of Using characters outside of A - Z in IRIs adds a number of
difficulties. Section 4 discusses the special case of bidirectional difficulties. Section 4 discusses the special case of bidirectional
IRIs using characters from scripts written right-to-left. Section 5 IRIs using characters from scripts written right-to-left. Section 5
discusses various forms of equivalence between IRIs. Section 6 discusses the use of IRIs in different situations. Section 7 gives
discusses the use of IRIs in different situations. Section 8 gives additional informative guidelines. Section 9 discusses IRI-specific
additional informative guidelines. Section 10 discusses IRI-specific
security considerations. security considerations.
When originally defining IRIs, several design alternatives were When originally defining IRIs, several design alternatives were
considered. Historically interested readers can find an overview in considered. Historically interested readers can find an overview in
Appendix A of [RFC3987]. For some additional background on the Appendix A of [RFC3987]. For some additional background on the
design of URIs and IRIs, please also see [Gettys]. design of URIs and IRIs, please also see [Gettys].
1.2. Applicability 1.2. Applicability
IRIs are designed to allow protocols and software that deal with URIs IRIs are designed to allow protocols and software that deal with URIs
to be updated to handle IRIs. A "URI scheme" (as defined by to be updated to handle IRIs. A "URI scheme" (as defined by
[RFC3986] and registered through the IANA process defined in [RFC3986] and registered through the IANA process defined in
[RFC4395bis] also serves as an "IRI scheme". Processing of IRIs is [RFC4395bis] also serves as an "IRI scheme". Processing of IRIs is
accomplished by extending the URI syntax while retaining (and not accomplished by extending the URI syntax while retaining (and not
expanding) the set of "reserved" characters, such that the syntax for expanding) the set of "reserved" characters, such that the syntax for
any URI scheme may be uniformly extended to allow non-ASCII any URI scheme may be extended to allow non-ASCII characters. In
characters. In addition, following parsing of an IRI, it is possible addition, following parsing of an IRI, it is possible to construct a
to construct a corresponding URI by first encoding characters outside corresponding URI by first encoding characters outside of the allowed
of the allowed URI range and then reassembling the components. URI range and then reassembling the components.
Practical use of IRIs forms in place of URIs forms depends on the Practical use of IRIs forms in place of URIs forms depends on the
following conditions being met: following conditions being met:
a. A protocol or format element MUST be explicitly designated to be a. A protocol or format element MUST be explicitly designated to be
able to carry IRIs. The intent is to avoid introducing IRIs into able to carry IRIs. The intent is to avoid introducing IRIs into
contexts that are not defined to accept them. For example, XML contexts that are not defined to accept them. For example, XML
schema [XMLSchema] has an explicit type "anyURI" that includes schema [XMLSchema] has an explicit type "anyURI" that includes
IRIs and IRI references. Therefore, IRIs and IRI references can IRIs and IRI references. Therefore, IRIs and IRI references can
be in attributes and elements of type "anyURI". On the other be in attributes and elements of type "anyURI". On the other
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c. The URI scheme definition, if it explicitly allows a percent sign c. The URI scheme definition, if it explicitly allows a percent sign
("%") in any syntactic component, SHOULD define the interpretation ("%") in any syntactic component, SHOULD define the interpretation
of sequences of percent-encoded octets (using "%XX" hex octets) as of sequences of percent-encoded octets (using "%XX" hex octets) as
octet from sequences of UTF-8 encoded strings; this is recommended octet from sequences of UTF-8 encoded strings; this is recommended
in the guidelines for registering new schemes, [RFC4395bis]. For in the guidelines for registering new schemes, [RFC4395bis]. For
example, this is the practice for IMAP URLs [RFC2192], POP URLs example, this is the practice for IMAP URLs [RFC2192], POP URLs
[RFC2384] and the URN syntax [RFC2141]). Note that use of [RFC2384] and the URN syntax [RFC2141]). Note that use of
percent-encoding may also be restricted in some situations, for percent-encoding may also be restricted in some situations, for
example, URI schemes that disallow percent-encoding might still be example, URI schemes that disallow percent-encoding might still be
used with a fragment identifier which is percent-encoded (e.g., used with a fragment identifier which is percent-encoded (e.g.,
[XPointer]). See Section 6.4 for further discussion. [XPointer]). See Section 5.4 for further discussion.
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 organization, character: A member of a set of elements used for the organization,
control, or representation of data. For example, "LATIN CAPITAL control, or representation of data. For example, "LATIN CAPITAL
LETTER A" names a character. LETTER A" names a character.
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URL: The term "URL" was originally used [RFC1738] for roughly what URL: The term "URL" was originally used [RFC1738] for roughly what
is now called a "URI". Books, software and documentation often is now called a "URI". Books, software and documentation often
refers to URIs and IRIs using the "URL" term. Some usages refers to URIs and IRIs using the "URL" term. Some usages
restrict "URL" to those URIs which are not URNs. Because of the restrict "URL" to those URIs which are not URNs. Because of the
ambiguity of the term using the term "URL" is NOT RECOMMENDED in ambiguity of the term using the term "URL" is NOT RECOMMENDED in
formal documents. formal documents.
LEIRI (Legacy Extended IRI) processing: This term was used in LEIRI (Legacy Extended IRI) processing: This term was used in
various XML specifications to refer to strings that, although not various XML specifications to refer to strings that, although not
valid IRIs, were acceptable input to the processing rules in valid IRIs, were acceptable input to the processing rules in
Section 7.1. Section 6.1.
(Web Address, Hypertext Reference, HREF): These terms have been (Web Address, Hypertext Reference, HREF): These terms have been
added in this document for convenience, to allow other added in this document for convenience, to allow other
specifications to refer to those strings that, although not valid specifications to refer to those strings that, although not valid
IRIs, are acceptable input to the processing rules in Section 7.2. IRIs, are acceptable input to the processing rules in Section 6.2.
This usage corresponds to the parsing rules of some popular web This usage corresponds to the parsing rules of some popular web
browsing applications. ISSUE: Need to find a good name/ browsing applications. ISSUE: Need to find a good name/
abbreviation for these. abbreviation for these.
running text: Human text (paragraphs, sentences, phrases) with running text: Human text (paragraphs, sentences, phrases) with
syntax according to orthographic conventions of a natural syntax according to orthographic conventions of a natural
language, as opposed to syntax defined for ease of processing by language, as opposed to syntax defined for ease of processing by
machines (e.g., markup, programming languages). machines (e.g., markup, programming languages).
protocol element: Any portion of a message that affects processing protocol element: Any portion of a message that affects processing
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transmitted digitally. The same IRI might be represented as transmitted digitally. The same IRI might be represented as
different sequences of octets in different protocols or documents if different sequences of octets in different protocols or documents if
these protocols or documents use different character encodings these protocols or documents use different character encodings
(and/or transfer encodings). Using the same character encoding as (and/or transfer encodings). Using the same character encoding as
the containing protocol or document ensures that the characters in the containing protocol or document ensures that the characters in
the IRI can be handled (e.g., searched, converted, displayed) in the the IRI can be handled (e.g., searched, converted, displayed) in the
same way as the rest of the protocol or document. same way as the rest of the protocol or document.
2.1. Summary of IRI Syntax 2.1. Summary of IRI Syntax
IRIs are defined by extending the URI syntax in [RFC3986], but The IRI syntax extends the URI syntax in [RFC3986] by extending the
extending the class of unreserved characters by adding the characters class of unreserved characters, primarily by adding the characters of
of the UCS (Universal Character Set, [ISO10646]) beyond U+007F, the UCS (Universal Character Set, [ISO10646]) beyond U+007F, subject
subject to the limitations given in the syntax rules below and in to the limitations given in the syntax rules below and in
Section 6.1. Section 5.1.
The syntax and use of components and reserved characters is the same The syntax and use of components and reserved characters is the same
as that in [RFC3986]. Each "URI scheme" thus also functions as an as that in [RFC3986]. Each "URI scheme" thus also functions as an
"IRI scheme", in that scheme-specific parsing rules for URIs of a "IRI scheme", in that scheme-specific parsing rules for URIs of a
scheme are be extended to allow parsing of IRIs using the same scheme are be extended to allow parsing of IRIs using the same
parsing rules. parsing rules.
All the operations defined in [RFC3986], such as the resolution of All the operations defined in [RFC3986], such as the resolution of
relative references, can be applied to IRIs by IRI-processing relative references, can be applied to IRIs by IRI-processing
software in exactly the same way as they are for URIs by URI- software in exactly the same way as they are for URIs by URI-
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which establish the relationship between the string given and the which establish the relationship between the string given and the
interpreted derivatives. These processing steps apply to both IRIs interpreted derivatives. These processing steps apply to both IRIs
and IRI references (i.e., absolute or relative forms); for IRIs, some and IRI references (i.e., absolute or relative forms); for IRIs, some
steps are scheme specific. steps are scheme specific.
3.1. Converting to UCS 3.1. Converting to UCS
Input that is already in a Unicode form (i.e., a sequence of Unicode Input that is already in a Unicode form (i.e., a sequence of Unicode
characters or an octet-stream representing a Unicode-based character characters or an octet-stream representing a Unicode-based character
encoding such as UTF-8 or UTF-16) should be left as is and not encoding such as UTF-8 or UTF-16) should be left as is and not
normalized (see Section 5.3.2.2). normalized or changed.
An IRI or IRI reference is a sequence of characters from the UCS. An IRI or IRI reference is a sequence of characters from the UCS.
For IRIs that are not already in a Unicode form (as when written on For resource identifiers that are not already in a Unicode form (as
paper, read aloud, or represented in a text stream using a legacy when written on paper, read aloud, or represented in a text stream
character encoding), convert the IRI to Unicode. Note that some using a legacy character encoding), convert the IRI to Unicode. Note
character encodings or transcriptions can be converted to or that some character encodings or transcriptions can be converted to
represented by more than one sequence of Unicode characters. Ideally or represented by more than one sequence of Unicode characters.
the resulting IRI would use a normalized form, such as Unicode Ideally the resulting IRI would use a normalized form, such as
Normalization Form C [UTR15] (see Section 5.3 Normalization and Unicode Normalization Form C [UTR15], since that ensures a stable,
Comparison), since that ensures a stable, consistent representation consistent representation that is most likely to produce the intended
that is most likely to produce the intended results. Implementers results. Implementers and users are cautioned that, while
and users are cautioned that, while denormalized character sequences denormalized character sequences are valid, they might be difficult
are valid, they might be difficult for other users or processes to for other users or processes to reproduce and might lead to
reproduce and might lead to unexpected results. unexpected results.
In other cases (written on paper, read aloud, or otherwise In other cases (written on paper, read aloud, or otherwise
represented independent of any character encoding) represent the IRI represented independent of any character encoding) represent the IRI
as a sequence of characters from the UCS normalized according to as a sequence of characters from the UCS normalized according to
Unicode Normalization Form C (NFC, [UTR15]). Unicode Normalization Form C (NFC, [UTR15]).
3.2. Parse the IRI into IRI components 3.2. Parse the IRI into IRI components
Parse the IRI, either as a relative reference (no scheme) or using Parse the IRI, either as a relative reference (no scheme) or using
scheme specific processing (according to the scheme given); the scheme specific processing (according to the scheme given); the
skipping to change at page 15, line 32 skipping to change at page 15, line 32
Except as noted in the following subsections, IRI components are Except as noted in the following subsections, IRI components are
mapped to the equivalent URI components by percent-encoding those mapped to the equivalent URI components by percent-encoding those
characters not allowed in URIs. Previous processing steps will have characters not allowed in URIs. Previous processing steps will have
removed some characters, and the interpretation of reserved removed some characters, and the interpretation of reserved
characters will have already been done (with the syntactic reserved characters will have already been done (with the syntactic reserved
characters outside of the IRI component). This mapping is defined characters outside of the IRI component). This mapping is defined
for all sequences of Unicode characters, whether or not they are for all sequences of Unicode characters, whether or not they are
valid for the component in question. valid for the component in question.
For each character which is not allowed anywhere in a valid URI, For each character which is not allowed anywhere in a valid URI apply
apply the following steps. the following steps.
Convert to UTF-8 Convert the character to a sequence of one or more Convert to UTF-8 Convert the character to a sequence of one or more
octets using UTF-8 [RFC3629]. octets using UTF-8 [RFC3629].
Percent encode Convert each octet of this sequence to %HH, where HH Percent encode Convert each octet of this sequence to %HH, where HH
is the hexadecimal notation of the octet value. The hexadecimal is the hexadecimal notation of the octet value. The hexadecimal
notation SHOULD use uppercase letters. (This is the general URI notation SHOULD use uppercase letters. (This is the general URI
percent-encoding mechanism in Section 2.1 of [RFC3986].) percent-encoding mechanism in Section 2.1 of [RFC3986].)
Note that the mapping is an identity transformation for parsed URI Note that the mapping is an identity transformation for parsed URI
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2. Some percent-encodings cannot be interpreted as sequences of UTF-8 2. Some percent-encodings cannot be interpreted as sequences of UTF-8
octets. octets.
(Note: The octet patterns of UTF-8 are highly regular. Therefore, (Note: The octet patterns of UTF-8 are highly regular. Therefore,
there is a very high probability, but no guarantee, that percent- there is a very high probability, but no guarantee, that percent-
encodings that can be interpreted as sequences of UTF-8 octets encodings that can be interpreted as sequences of UTF-8 octets
actually originated from UTF-8. For a detailed discussion, see actually originated from UTF-8. For a detailed discussion, see
[Duerst97].) [Duerst97].)
3. The conversion may result in a character that is not appropriate 3. The conversion may result in a character that is not appropriate
in an IRI. See Section 2.2, Section 4.1, and Section 6.1 for in an IRI. See Section 2.2, Section 4.1, and Section 5.1 for
further details. further details.
4. IRI to URI conversion has different rules for dealing with domain 4. IRI to URI conversion has different rules for dealing with domain
names and query parameters. names and query parameters.
Conversion from a URI to an IRI MAY be done by using the following Conversion from a URI to an IRI MAY be done by using the following
steps: steps:
1. Represent the URI as a sequence of octets in US-ASCII. 1. Represent the URI as a sequence of octets in US-ASCII.
2. Convert all percent-encodings ("%" followed by two hexadecimal 2. Convert all percent-encodings ("%" followed by two hexadecimal
digits) to the corresponding octets, except those corresponding to digits) to the corresponding octets, except those corresponding to
"%", characters in "reserved", and characters in US-ASCII not "%", characters in "reserved", and characters in US-ASCII not
allowed in URIs. allowed in URIs.
3. Re-percent-encode any octet produced in step 2 that is not part of 3. Re-percent-encode any octet produced in step 2 that is not part of
a strictly legal UTF-8 octet sequence. a strictly legal UTF-8 octet sequence.
4. Re-percent-encode all octets produced in step 3 that in UTF-8 4. Re-percent-encode all octets produced in step 3 that in UTF-8
represent characters that are not appropriate according to represent characters that are not appropriate according to
Section 2.2, Section 4.1, and Section 6.1. Section 2.2, Section 4.1, and Section 5.1.
5. Interpret the resulting octet sequence as a sequence of characters 5. Interpret the resulting octet sequence as a sequence of characters
encoded in UTF-8. encoded in UTF-8.
6. URIs known to contain domain names in the reg-name component 6. URIs known to contain domain names in the reg-name component
SHOULD convert punycode-encoded domain name labels to the SHOULD convert punycode-encoded domain name labels to the
corresponding characters using the ToUnicode procedure. corresponding characters using the ToUnicode procedure.
This procedure will convert as many percent-encoded characters as This procedure will convert as many percent-encoded characters as
possible to characters in an IRI. Because there are some choices possible to characters in an IRI. Because there are some choices
when step 4 is applied (see Section 6.1), results may vary. when step 4 is applied (see Section 5.1), results may vary.
Conversions from URIs to IRIs MUST NOT use any character encoding Conversions from URIs to IRIs MUST NOT use any character encoding
other than UTF-8 in steps 3 and 4, even if it might be possible to other than UTF-8 in steps 3 and 4, even if it might be possible to
guess from the context that another character encoding than UTF-8 was guess from the context that another character encoding than UTF-8 was
used in the URI. For example, the URI used in the URI. For example, the URI
"http://www.example.org/r%E9sum%E9.html" might with some guessing be "http://www.example.org/r%E9sum%E9.html" might with some guessing be
interpreted to contain two e-acute characters encoded as iso-8859-1. interpreted to contain two e-acute characters encoded as iso-8859-1.
It must not be converted to an IRI containing these e-acute It must not be converted to an IRI containing these e-acute
characters. Otherwise, in the future the IRI will be mapped to characters. Otherwise, in the future the IRI will be mapped to
"http://www.example.org/r%C3%A9sum%C3%A9.html", which is a different "http://www.example.org/r%C3%A9sum%C3%A9.html", which is a different
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difficult to prohibit them), but these may interact with adjacent RTL difficult to prohibit them), but these may interact with adjacent RTL
components in ways that are not easy to predict. components in ways that are not easy to predict.
Example 11 (allowed but not recommended): Example 11 (allowed but not recommended):
Logical representation: "http://ab.CDEFGH.123ij/kl/mn/op.html" Logical representation: "http://ab.CDEFGH.123ij/kl/mn/op.html"
Visual representation: "http://ab.123.HGFEDCij/kl/mn/op.html" Visual representation: "http://ab.123.HGFEDCij/kl/mn/op.html"
Components consisting of numbers and left-to-right characters are Components consisting of numbers and left-to-right characters are
allowed, but these may interact with adjacent RTL components in ways allowed, but these may interact with adjacent RTL components in ways
that are not easy to predict. that are not easy to predict.
5. Normalization and Comparison 5. Use of IRIs
Note: The structure and much of the material for this section is
taken from section 6 of [RFC3986]; the differences are due to the
specifics of IRIs.
One of the most common operations on IRIs is simple comparison:
Determining whether two IRIs are equivalent, without using the IRIs
to access their respective resource(s). A comparison is performed
whenever a response cache is accessed, a browser checks its history
to color a link, or an XML parser processes tags within a namespace.
Extensive normalization prior to comparison of IRIs may be used by
spiders and indexing engines to prune a search space or reduce
duplication of request actions and response storage.
IRI comparison is performed for some particular purpose. Protocols
or implementations that compare IRIs for different purposes will
often be subject to differing design trade-offs in regards to how
much effort should be spent in reducing aliased identifiers. This
section describes various methods that may be used to compare IRIs,
the trade-offs between them, and the types of applications that might
use them.
5.1. Equivalence
Because IRIs exist to identify resources, presumably they should be
considered equivalent when they identify the same resource. However,
this definition of equivalence is not of much practical use, as there
is no way for an implementation to compare two resources to determine
if they are "the same" unless it has full knowledge or control of
them. For this reason, determination of equivalence or difference of
IRIs is based on string comparison, perhaps augmented by reference to
additional rules provided by URI scheme definitions. We use the
terms "different" and "equivalent" to describe the possible outcomes
of such comparisons, but there are many application-dependent
versions of equivalence.
Even when it is possible to determine that two IRIs are equivalent,
IRI comparison is not sufficient to determine whether two IRIs
identify different resources. For example, an owner of two different
domain names could decide to serve the same resource from both,
resulting in two different IRIs. Therefore, comparison methods are
designed to minimize false negatives while strictly avoiding false
positives.
In testing for equivalence, applications should not directly compare
relative references; the references should be converted to their
respective target IRIs before comparison. When IRIs are compared to
select (or avoid) a network action, such as retrieval of a
representation, fragment components (if any) should be excluded from
the comparison.
Applications using IRIs as identity tokens with no relationship to a
protocol MUST use the Simple String Comparison (see Section 5.3.1).
All other applications MUST select one of the comparison practices
from the Comparison Ladder (see Section 5.3.
5.2. Preparation for Comparison
Any kind of IRI comparison REQUIRES that any additional contextual
processing is first performed, including undoing higher-level
escapings or encodings in the protocol or format that carries an IRI.
This preprocessing is usually done when the protocol or format is
parsed.
Examples of contextual preprocessing steps are described in
Section 7.
Examples of such escapings or encodings are entities and numeric
character references in [HTML4] and [XML1]. As an example,
"http://example.org/rosé" (in HTML),
"http://example.org/rosé" (in HTML or XML), and
"http://example.org/rosé" (in HTML or XML) are all resolved into
what is denoted in this document (see Section 1.4) as
"http://example.org/rosé" (the "é" here standing for the
actual e-acute character, to compensate for the fact that this
document cannot contain non-ASCII characters).
Similar considerations apply to encodings such as Transfer Codings in
HTTP (see [RFC2616]) and Content Transfer Encodings in MIME
([RFC2045]), although in these cases, the encoding is based not on
characters but on octets, and additional care is required to make
sure that characters, and not just arbitrary octets, are compared
(see Section 5.3.1).
5.3. Comparison Ladder
In practice, a variety of methods are used to test IRI equivalence.
These methods fall into a range distinguished by the amount of
processing required and the degree to which the probability of false
negatives is reduced. As noted above, false negatives cannot be
eliminated. In practice, their probability can be reduced, but this
reduction requires more processing and is not cost-effective for all
applications.
If this range of comparison practices is considered as a ladder, the
following discussion will climb the ladder, starting with practices
that are cheap but have a relatively higher chance of producing false
negatives, and proceeding to those that have higher computational
cost and lower risk of false negatives.
5.3.1. Simple String Comparison
If two IRIs, when considered as character strings, are identical,
then it is safe to conclude that they are equivalent. This type of
equivalence test has very low computational cost and is in wide use
in a variety of applications, particularly in the domain of parsing.
It is also used when a definitive answer to the question of IRI
equivalence is needed that is independent of the scheme used and that
can be calculated quickly and without accessing a network. An
example of such a case is XML Namespaces ([XMLNamespace]).
Testing strings for equivalence requires some basic precautions.
This procedure is often referred to as "bit-for-bit" or "byte-for-
byte" comparison, which is potentially misleading. Testing strings
for equality is normally based on pair comparison of the characters
that make up the strings, starting from the first and proceeding
until both strings are exhausted and all characters are found to be
equal, until a pair of characters compares unequal, or until one of
the strings is exhausted before the other.
This character comparison requires that each pair of characters be
put in comparable encoding form. For example, should one IRI be
stored in a byte array in UTF-8 encoding form and the second in a
UTF-16 encoding form, bit-for-bit comparisons applied naively will
produce errors. It is better to speak of equality on a character-
for-character rather than on a byte-for-byte or bit-for-bit basis.
In practical terms, character-by-character comparisons should be done
codepoint by codepoint after conversion to a common character
encoding form. When comparing character by character, the comparison
function MUST NOT map IRIs to URIs, because such a mapping would
create additional spurious equivalences. It follows that an IRI
SHOULD NOT be modified when being transported if there is any chance
that this IRI might be used in a context that uses Simple String
Comparison.
False negatives are caused by the production and use of IRI aliases.
Unnecessary aliases can be reduced, regardless of the comparison
method, by consistently providing IRI references in an already
normalized form (i.e., a form identical to what would be produced
after normalization is applied, as described below). Protocols and
data formats often limit some IRI comparisons to simple string
comparison, based on the theory that people and implementations will,
in their own best interest, be consistent in providing IRI
references, or at least be consistent enough to negate any efficiency
that might be obtained from further normalization.
5.3.2. Syntax-Based Normalization
Implementations may use logic based on the definitions provided by
this specification to reduce the probability of false negatives.
This processing is moderately higher in cost than character-for-
character string comparison. For example, an application using this
approach could reasonably consider the following two IRIs equivalent:
example://a/b/c/%7Bfoo%7D/rosé
eXAMPLE://a/./b/../b/%63/%7bfoo%7d/ros%C3%A9
Web user agents, such as browsers, typically apply this type of IRI
normalization when determining whether a cached response is
available. Syntax-based normalization includes such techniques as
case normalization, character normalization, percent-encoding
normalization, and removal of dot-segments.
5.3.2.1. Case Normalization
For all IRIs, the hexadecimal digits within a percent-encoding
triplet (e.g., "%3a" versus "%3A") are case-insensitive and therefore
should be normalized to use uppercase letters for the digits A-F.
When an IRI uses components of the generic syntax, the component
syntax equivalence rules always apply; namely, that the scheme and
US-ASCII only host are case insensitive and therefore should be
normalized to lowercase. For example, the URI
"HTTP://www.EXAMPLE.com/" is equivalent to "http://www.example.com/".
Case equivalence for non-ASCII characters in IRI components that are
IDNs are discussed in Section 5.3.3. The other generic syntax
components are assumed to be case sensitive unless specifically
defined otherwise by the scheme.
Creating schemes that allow case-insensitive syntax components
containing non-ASCII characters should be avoided. Case
normalization of non-ASCII characters can be culturally dependent and
is always a complex operation. The only exception concerns non-ASCII
host names for which the character normalization includes a mapping
step derived from case folding.
5.3.2.2. Character Normalization
The Unicode Standard [UNIV6] defines various equivalences between
sequences of characters for various purposes. Unicode Standard Annex
#15 [UTR15] defines various Normalization Forms for these
equivalences, in particular Normalization Form C (NFC, Canonical
Decomposition, followed by Canonical Composition) and Normalization
Form KC (NFKC, Compatibility Decomposition, followed by Canonical
Composition).
IRIs already in Unicode MUST NOT be normalized before parsing or
interpreting. In many non-Unicode character encodings, some text
cannot be represented directly. For example, the word "Vietnam" is
natively written "Việt Nam" (containing a LATIN SMALL LETTER E
WITH CIRCUMFLEX AND DOT BELOW) in NFC, but a direct transcoding from
the windows-1258 character encoding leads to "Việt Nam"
(containing a LATIN SMALL LETTER E WITH CIRCUMFLEX followed by a
COMBINING DOT BELOW). Direct transcoding of other 8-bit encodings of
Vietnamese may lead to other representations.
Equivalence of IRIs MUST rely on the assumption that IRIs are
appropriately pre-character-normalized rather than apply character
normalization when comparing two IRIs. The exceptions are conversion
from a non-digital form, and conversion from a non-UCS-based
character encoding to a UCS-based character encoding. In these
cases, NFC or a normalizing transcoder using NFC MUST be used for
interoperability. To avoid false negatives and problems with
transcoding, IRIs SHOULD be created by using NFC. Using NFKC may
avoid even more problems; for example, by choosing half-width Latin
letters instead of full-width ones, and full-width instead of half-
width Katakana.
As an example, "http://www.example.org/résumé.html" (in XML
Notation) is in NFC. On the other hand,
"http://www.example.org/résumé.html" is not in NFC.
The former uses precombined e-acute characters, and the latter uses
"e" characters followed by combining acute accents. Both usages are
defined as canonically equivalent in [UNIV6].
Note: Because it is unknown how a particular sequence of characters
is being treated with respect to character normalization, it would
be inappropriate to allow third parties to normalize an IRI
arbitrarily. This does not contradict the recommendation that
when a resource is created, its IRI should be as character
normalized as possible (i.e., NFC or even NFKC). This is similar
to the uppercase/lowercase problems. Some parts of a URI are case
insensitive (for example, the domain name). For others, it is
unclear whether they are case sensitive, case insensitive, or
something in between (e.g., case sensitive, but with a multiple
choice selection if the wrong case is used, instead of a direct
negative result). The best recipe is that the creator use a
reasonable capitalization and, when transferring the URI,
capitalization never be changed.
Various IRI schemes may allow the usage of Internationalized Domain
Names (IDN) [RFC5890] either in the ireg-name part or elsewhere.
Character Normalization also applies to IDNs, as discussed in
Section 5.3.3.
5.3.2.3. Percent-Encoding Normalization
The percent-encoding mechanism (Section 2.1 of [RFC3986]) is a
frequent source of variance among otherwise identical IRIs. In
addition to the case normalization issue noted above, some IRI
producers percent-encode octets that do not require percent-encoding,
resulting in IRIs that are equivalent to their nonencoded
counterparts. These IRIs should be normalized by decoding any
percent-encoded octet sequence that corresponds to an unreserved
character, as described in section 2.3 of [RFC3986].
For actual resolution, differences in percent-encoding (except for
the percent-encoding of reserved characters) MUST always result in
the same resource. For example, "http://example.org/~user",
"http://example.org/%7euser", and "http://example.org/%7Euser", must
resolve to the same resource.
If this kind of equivalence is to be tested, the percent-encoding of
both IRIs to be compared has to be aligned; for example, by
converting both IRIs to URIs (see Section 3.1), eliminating escape
differences in the resulting URIs, and making sure that the case of
the hexadecimal characters in the percent-encoding is always the same
(preferably upper case). If the IRI is to be passed to another
application or used further in some other way, its original form MUST
be preserved. The conversion described here should be performed only
for local comparison.
5.3.2.4. Path Segment Normalization
The complete path segments "." and ".." are intended only for use
within relative references (Section 4.1 of [RFC3986]) and are removed
as part of the reference resolution process (Section 5.2 of
[RFC3986]). However, some implementations may incorrectly assume
that reference resolution is not necessary when the reference is
already an IRI, and thus fail to remove dot-segments when they occur
in non-relative paths. IRI normalizers should remove dot-segments by
applying the remove_dot_segments algorithm to the path, as described
in Section 5.2.4 of [RFC3986].
5.3.3. Scheme-Based Normalization
The syntax and semantics of IRIs vary from scheme to scheme, as
described by the defining specification for each scheme.
Implementations may use scheme-specific rules, at further processing
cost, to reduce the probability of false negatives. For example,
because the "http" scheme makes use of an authority component, has a
default port of "80", and defines an empty path to be equivalent to
"/", the following four IRIs are equivalent:
http://example.com
http://example.com/
http://example.com:/
http://example.com:80/
In general, an IRI that uses the generic syntax for authority with an
empty path should be normalized to a path of "/". Likewise, an
explicit ":port", for which the port is empty or the default for the
scheme, is equivalent to one where the port and its ":" delimiter are
elided and thus should be removed by scheme-based normalization. For
example, the second IRI above is the normal form for the "http"
scheme.
Another case where normalization varies by scheme is in the handling
of an empty authority component or empty host subcomponent. For many
scheme specifications, an empty authority or host is considered an
error; for others, it is considered equivalent to "localhost" or the
end-user's host. When a scheme defines a default for authority and
an IRI reference to that default is desired, the reference should be
normalized to an empty authority for the sake of uniformity, brevity,
and internationalization. If, however, either the userinfo or port
subcomponents are non-empty, then the host should be given explicitly
even if it matches the default.
Normalization should not remove delimiters when their associated
component is empty unless it is licensed to do so by the scheme
specification. For example, the IRI "http://example.com/?" cannot be
assumed to be equivalent to any of the examples above. Likewise, the
presence or absence of delimiters within a userinfo subcomponent is
usually significant to its interpretation. The fragment component is
not subject to any scheme-based normalization; thus, two IRIs that
differ only by the suffix "#" are considered different regardless of
the scheme.
Some IRI schemes allow the usage of Internationalized Domain Names
(IDN) [RFC5890] either in their ireg-name part or elswhere. When in
use in IRIs, those names SHOULD conform to the definition of U-Label
in [RFC5890]. An IRI containing an invalid IDN cannot successfully
be resolved. For legibility purposes, they SHOULD NOT be converted
into ASCII Compatible Encoding (ACE).
Scheme-based normalization may also consider IDN components and their
conversions to punycode as equivalent. As an example,
"http://résumé.example.org" may be considered equivalent to
"http://xn--rsum-bpad.example.org".
Other scheme-specific normalizations are possible.
5.3.4. Protocol-Based Normalization
Substantial effort to reduce the incidence of false negatives is
often cost-effective for web spiders. Consequently, they implement
even more aggressive techniques in IRI comparison. For example, if
they observe that an IRI such as
http://example.com/data
redirects to an IRI differing only in the trailing slash
http://example.com/data/
they will likely regard the two as equivalent in the future. This
kind of technique is only appropriate when equivalence is clearly
indicated by both the result of accessing the resources and the
common conventions of their scheme's dereference algorithm (in this
case, use of redirection by HTTP origin servers to avoid problems
with relative references).
6. Use of IRIs
6.1. Limitations on UCS Characters Allowed in IRIs 5.1. Limitations on UCS Characters Allowed in IRIs
This section discusses limitations on characters and character This section discusses limitations on characters and character
sequences usable for IRIs beyond those given in Section 2.2 and sequences usable for IRIs beyond those given in Section 2.2 and
Section 4.1. The considerations in this section are relevant when Section 4.1. The considerations in this section are relevant when
IRIs are created and when URIs are converted to IRIs. IRIs are created and when URIs are converted to IRIs.
a. The repertoire of characters allowed in each IRI component is a. The repertoire of characters allowed in each IRI component is
limited by the definition of that component. For example, the limited by the definition of that component. For example, the
definition of the scheme component does not allow characters definition of the scheme component does not allow characters
beyond US-ASCII. beyond US-ASCII.
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the full-width equivalents of Latin characters, half-width the full-width equivalents of Latin characters, half-width
Katakana characters for Japanese, and many others. It also Katakana characters for Japanese, and many others. It also
includes many look-alikes of "space", "delims", and "unwise", includes many look-alikes of "space", "delims", and "unwise",
characters excluded in [RFC3491]. characters excluded in [RFC3491].
Additional information is available from [UNIXML]. [UNIXML] is Additional information is available from [UNIXML]. [UNIXML] is
written in the context of running text rather than in that of written in the context of running text rather than in that of
identifiers. Nevertheless, it discusses many of the categories of identifiers. Nevertheless, it discusses many of the categories of
characters not appropriate for IRIs. characters not appropriate for IRIs.
6.2. Software Interfaces and Protocols 5.2. Software Interfaces and Protocols
Although an IRI is defined as a sequence of characters, software Although an IRI is defined as a sequence of characters, software
interfaces for URIs typically function on sequences of octets 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 3.6, when URI-only components MUST map the IRIs per Section 3.6, when
transferring from IRI-capable to URI-only components. This mapping transferring from IRI-capable to URI-only components. This 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 5.3. Format of URIs and IRIs in Documents and Protocols
Document formats that transport URIs may have to be upgraded to allow Document formats that transport URIs may have to be upgraded to allow
the transport of IRIs. In cases where the document as a whole has a the transport of IRIs. In cases where the document as a whole has a
native character encoding, IRIs MUST also be encoded in this native character encoding, IRIs MUST also be encoded in this
character encoding and converted accordingly by a parser or character encoding and converted accordingly by a parser or
interpreter. IRI characters not expressible in the native character interpreter. IRI characters not expressible in the native character
encoding SHOULD be escaped by using the escaping conventions of the encoding SHOULD be escaped by using the escaping conventions of the
document format if such conventions are available. Alternatively, document format if such conventions are available. Alternatively,
they MAY be percent-encoded according to Section 3.6. For example, they MAY be percent-encoded according to Section 3.6. For example,
in HTML or XML, numeric character references SHOULD be used. If a in HTML or XML, numeric character references SHOULD be used. If a
skipping to change at page 34, line 30 skipping to change at page 26, line 48
the document in the UTF-8 character encoding. the document in the UTF-8 character encoding.
((UPDATE THIS NOTE)) Note: Some formats already accommodate IRIs, ((UPDATE THIS NOTE)) Note: Some formats already accommodate IRIs,
although they use different terminology. HTML 4.0 [HTML4] defines although they use different terminology. HTML 4.0 [HTML4] defines
the conversion from IRIs to URIs as error-avoiding behavior. XML 1.0 the conversion from IRIs to URIs as error-avoiding behavior. XML 1.0
[XML1], XLink [XLink], XML Schema [XMLSchema], and specifications [XML1], XLink [XLink], XML Schema [XMLSchema], and specifications
based upon them allow IRIs. Also, it is expected that all relevant based upon them allow IRIs. Also, it is expected that all relevant
new W3C formats and protocols will be required to handle IRIs new W3C formats and protocols will be required to handle IRIs
[CharMod]. [CharMod].
6.4. Use of UTF-8 for Encoding Original Characters 5.4. 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. To be able to use IRIs, the URI corresponding to the Section 1.2. To be able to use IRIs, the URI corresponding to the
IRI in question has to encode original characters into octets by IRI in question has to encode original characters into octets by
using UTF-8. This can be specified for all URIs of a 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
to some part. For background information on encoding characters into to some part. For background information on encoding characters into
URIs, see also Section 2.5 of [RFC3986]. URIs, see also Section 2.5 of [RFC3986].
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For most URI schemes, there is no need to upgrade their scheme For most URI schemes, there is no need to upgrade their scheme
definition in order for them to work with IRIs. The main case where definition in order for them to work with IRIs. The main case where
upgrading makes sense is when a scheme definition, or a particular upgrading makes sense is when a scheme definition, or a particular
component of a scheme, is strictly limited to the use of US-ASCII component of a scheme, is strictly limited to the use of US-ASCII
characters with no provision to include non-ASCII characters/octets characters with no provision to include non-ASCII characters/octets
via percent-encoding, or if a scheme definition currently uses highly via percent-encoding, or if a scheme definition currently uses highly
scheme-specific provisions for the encoding of non-ASCII characters. scheme-specific provisions for the encoding of non-ASCII characters.
An example of this is the mailto: scheme [RFC2368]. An example of this is the mailto: scheme [RFC2368].
This specification updates the IANA registry of URI schemes to note This specification updates the IANA registry of URI schemes to note
their applicability to IRIs, see Section 9. All IRIs use URI their applicability to IRIs, see Section 8. All IRIs use URI
schemes, and all URIs with URI schemes can be used as IRIs, even schemes, and all URIs with URI schemes can be used as IRIs, even
though in some cases only by using URIs directly as IRIs, without any though in some cases only by using URIs directly as IRIs, without any
conversion. conversion.
Scheme definitions can impose restrictions on the syntax of scheme- Scheme definitions can impose restrictions on the syntax of scheme-
specific URIs; i.e., URIs that are admissible under the generic URI specific URIs; i.e., URIs that are admissible under the generic URI
syntax [RFC3986] may not be admissible due to narrower syntactic syntax [RFC3986] may not be admissible due to narrower syntactic
constraints imposed by a URI scheme specification. URI scheme constraints imposed by a URI scheme specification. URI scheme
definitions cannot broaden the syntactic restrictions of the generic definitions cannot broaden the syntactic restrictions of the generic
URI syntax; otherwise, it would be possible to generate URIs that URI syntax; otherwise, it would be possible to generate URIs that
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represent a wide range of characters directly is used just in some represent a wide range of characters directly is used just in some
parts of the IRI (or IRI reference). The other parts of the IRI may parts of the IRI (or IRI reference). The other parts of the IRI may
only contain US-ASCII characters, or they may not be based on UTF-8. only contain US-ASCII characters, or they may not be based on UTF-8.
They may be based on another character encoding, or they may directly They may be based on another character encoding, or they may directly
encode raw binary data (see also [RFC2397]). encode raw binary data (see also [RFC2397]).
For example, it is possible to have a URI reference of For example, it is possible to have a URI reference of
"http://www.example.org/r%E9sum%E9.xml#r%C3%A9sum%C3%A9", where the "http://www.example.org/r%E9sum%E9.xml#r%C3%A9sum%C3%A9", where the
document name is encoded in iso-8859-1 based on server settings, but document name is encoded in iso-8859-1 based on server settings, but
where the fragment identifier is encoded in UTF-8 according to where the fragment identifier is encoded in UTF-8 according to
[XPointer]. The IRI corresponding to the above URI would be (in XML [XPointer]. The IRI corresponding to the above URI would be (in XML
notation) notation)
"http://www.example.org/r%E9sum%E9.xml#résumé". "http://www.example.org/r%E9sum%E9.xml#résumé".
Similar considerations apply to query parts. The functionality of Similar considerations apply to query parts. The functionality of
IRIs (namely, to be able to include non-ASCII characters) can only be IRIs (namely, to be able to include non-ASCII characters) can only be
used if the query part is encoded in UTF-8. used if the query part is encoded in UTF-8.
6.5. Relative IRI References 5.5. Relative IRI References
Processing of relative IRI references against a base is handled Processing of relative IRI references against a base is handled
straightforwardly; the algorithms of [RFC3986] can be applied straightforwardly; the algorithms of [RFC3986] can be applied
directly, treating the characters additionally allowed in IRI directly, treating the characters additionally allowed in IRI
references in the same way that unreserved characters are in URI references in the same way that unreserved characters are in URI
references. references.
7. Liberal Handling of Otherwise Invalid IRIs 6. Liberal Handling of Otherwise Invalid IRIs
(EDITOR NOTE: This Section may move to an appendix.) Some technical (EDITOR NOTE: This Section may move to an appendix.) Some technical
specifications and widely-deployed software have allowed additional specifications and widely-deployed software have allowed additional
variations and extensions of IRIs to be used in syntactic components. variations and extensions of IRIs to be used in syntactic components.
This section describes two widely-used preprocessing agreements. This section describes two widely-used preprocessing agreements.
Other technical specifications may wish to reference a syntactic Other technical specifications may wish to reference a syntactic
component which is "a valid IRI or a string that will map to a valid component which is "a valid IRI or a string that will map to a valid
IRI after this preprocessing algorithm". These two variants are IRI after this preprocessing algorithm". These two variants are
known as Legacy Extended IRI or LEIRI [LEIRI], and Web Address known as Legacy Extended IRI or LEIRI [LEIRI], and Web Address
[HTML5]). [HTML5]).
Future technical specifications SHOULD NOT allow conforming producers Future technical specifications SHOULD NOT allow conforming producers
to produce, or conforming content to contain, such forms, as they are to produce, or conforming content to contain, such forms, as they are
not interoperable with other IRI consuming software. not interoperable with other IRI consuming software.
7.1. LEIRI Processing 6.1. LEIRI Processing
This section defines Legacy Extended IRIs (LEIRIs). The syntax of This section defines Legacy Extended IRIs (LEIRIs). The syntax of
Legacy Extended IRIs is the same as that for <IRI-reference>, except Legacy Extended IRIs is the same as that for <IRI-reference>, except
that the ucschar production is replaced by the leiri-ucschar that the ucschar production is replaced by the leiri-ucschar
production: production:
leiri-ucschar = " " / "<" / ">" / '"' / "{" / "}" / "|" leiri-ucschar = " " / "<" / ">" / '"' / "{" / "}" / "|"
/ "\" / "^" / "`" / %x0-1F / %x7F-D7FF / "\" / "^" / "`" / %x0-1F / %x7F-D7FF
/ %xE000-FFFD / %x10000-10FFFF / %xE000-FFFD / %x10000-10FFFF
Among other extensions, processors based on this specification also Among other extensions, processors based on this specification also
did not enforce the restriction on bidirectional formatting did not enforce the restriction on bidirectional formatting
characters in Section 4.1, and the iprivate production becomes characters in Section 4.1, and the iprivate production becomes
redundant. redundant.
To convert a string allowed as a LEIRI to an IRI, each character To convert a string allowed as a LEIRI to an IRI, each character
allowed in leiri-ucschar but not in ucschar must be percent-encoded allowed in leiri-ucschar but not in ucschar must be percent-encoded
using Section 3.3. using Section 3.3.
7.2. Web Address Processing 6.2. Web Address Processing
Many popular web browsers have taken the approach of being quite Many popular web browsers have taken the approach of being quite
liberal in what is accepted as a "URL" or its relative forms. This liberal in what is accepted as a "URL" or its relative forms. This
section describes their behavior in terms of a preprocessor which section describes their behavior in terms of a preprocessor which
maps strings into the IRI space for subsequent parsing and maps strings into the IRI space for subsequent parsing and
interpretation as an IRI. interpretation as an IRI.
In some situations, it might be appropriate to describe the syntax In some situations, it might be appropriate to describe the syntax
that a liberal consumer implementation might accept as a "Web that a liberal consumer implementation might accept as a "Web
Address" or "Hypertext Reference" or "HREF". However, technical Address" or "Hypertext Reference" or "HREF". However, technical
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2. strip all characters in href-strip. 2. strip all characters in href-strip.
3. Percent-encode all characters in href-ucschar not in ucschar. 3. Percent-encode all characters in href-ucschar not in ucschar.
4. Replace occurrences of "%" not followed by two hexadecimal digits 4. Replace occurrences of "%" not followed by two hexadecimal digits
by "%25". by "%25".
5. Convert backslashes ('\') matching href-path-sep to forward 5. Convert backslashes ('\') matching href-path-sep to forward
slashes ('/'). slashes ('/').
7.3. Characters Not Allowed in IRIs 6.3. Characters Not Allowed in IRIs
This section provides a list of the groups of characters and code This section provides a list of the groups of characters and code
points that are allowed by LEIRI or HREF but are not allowed in IRIs points that are allowed by LEIRI or HREF but are not allowed in IRIs
or are allowed in IRIs only in the query part. For each group of or are allowed in IRIs only in the query part. For each group of
characters, advice on the usage of these characters is also given, characters, advice on the usage of these characters is also given,
concentrating on the reasons for why they are excluded from IRI use. concentrating on the reasons for why they are excluded from IRI use.
Space (U+0020): Some formats and applications use space as a Space (U+0020): Some formats and applications use space as a
delimiter, e.g. for items in a list. Appendix C of [RFC3986] also delimiter, e.g. for items in a list. Appendix C of [RFC3986] also
mentions that white space may have to be added when displaying or mentions that white space may have to be added when displaying or
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U+BFFFE-BFFFF, U+CFFFE-CFFFF, U+DFFFE-DFFFF, U+EFFFE-EFFFF, U+BFFFE-BFFFF, U+CFFFE-CFFFF, U+DFFFE-DFFFF, U+EFFFE-EFFFF,
U+FFFFE-FFFFF, U+10FFFE-10FFFF): These code points are defined as U+FFFFE-FFFFF, U+10FFFE-10FFFF): These code points are defined as
non-characters. Applications may use some of them internally, but non-characters. Applications may use some of them internally, but
are not prepared to interchange them. are not prepared to interchange them.
LEIRI preprocessing disallowed some code points and code units: LEIRI preprocessing disallowed some code points and code units:
Surrogate code units (D800-DFFF): These do not represent Unicode Surrogate code units (D800-DFFF): These do not represent Unicode
codepoints. codepoints.
8. URI/IRI Processing Guidelines (Informative) 7. URI/IRI Processing Guidelines (Informative)
This informative section provides guidelines for supporting IRIs in This informative section provides guidelines for supporting IRIs in
the same software components and operations that currently process the same software components and operations that currently process
URIs: Software interfaces that handle URIs, software that allows URIs: Software interfaces that handle URIs, software that allows
users to enter URIs, software that creates or generates URIs, users to enter URIs, software that creates or generates URIs,
software that displays URIs, formats and protocols that transport software that displays URIs, formats and protocols that transport
URIs, and software that interprets URIs. These may all require URIs, and software that interprets URIs. These may all require
modification before functioning properly with IRIs. The modification before functioning properly with IRIs. The
considerations in this section also apply to URI references and IRI considerations in this section also apply to URI references and IRI
references. references.
8.1. URI/IRI Software Interfaces 7.1. URI/IRI Software Interfaces
Software interfaces that handle URIs, such as URI-handling APIs and Software interfaces that handle URIs, such as URI-handling APIs and
protocols transferring URIs, need interfaces and protocol elements protocols transferring URIs, need interfaces and protocol elements
that are designed to carry IRIs. that are designed to carry IRIs.
In case the current handling in an API or protocol is based on US- In case the current handling in an API or protocol is based on US-
ASCII, UTF-8 is recommended as the character encoding for IRIs, as it ASCII, UTF-8 is recommended as the character encoding for IRIs, as it
is compatible with US-ASCII, is in accordance with the is compatible with US-ASCII, is in accordance with the
recommendations of [RFC2277], and makes converting to URIs easy. In recommendations of [RFC2277], and makes converting to URIs easy. In
any case, the API or protocol definition must clearly define the any case, the API or protocol definition must clearly define the
character encoding to be used. character encoding to be used.
The transfer from URI-only to IRI-capable components requires no The transfer from URI-only to IRI-capable components requires no
mapping, although the conversion described in Section 3.7 above may mapping, although the conversion described in Section 3.7 above may
be performed. It is preferable not to perform this inverse be performed. It is preferable not to perform this inverse
conversion unless it is certain this can be done correctly. conversion unless it is certain this can be done correctly.
8.2. URI/IRI Entry 7.2. URI/IRI Entry
Some components allow users to enter URIs into the system by typing Some components allow users to enter URIs into the system by typing
or dictation, for example. This software must be updated to allow or dictation, for example. This software must be updated to allow
for IRI entry. for IRI entry.
A person viewing a visual representation of an IRI (as a sequence of A person viewing a visual representation of an IRI (as a sequence of
glyphs, in some order, in some visual display) or hearing an IRI will glyphs, in some order, in some visual display) or hearing an IRI will
use an entry method for characters in the user's language to input use an entry method for characters in the user's language to input
the IRI. Depending on the script and the input method used, this may the IRI. Depending on the script and the input method used, this may
be a more or less complicated process. be a more or less complicated process.
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viewing an IRI as mapped to a URI. This will help users when some of viewing an IRI as mapped to a URI. This will help users when some of
the software they use does not yet accept IRIs. the software they use does not yet accept IRIs.
An IRI input component interfacing to components that handle URIs, An IRI input component interfacing to components that handle URIs,
but not IRIs, must map the IRI to a URI before passing it to these but not IRIs, must map the IRI to a URI before passing it to these
components. components.
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.
8.3. URI/IRI Transfer between Applications 7.3. URI/IRI Transfer between Applications
Many applications (for example, mail user agents) try to detect URIs Many applications (for example, mail user agents) try to detect URIs
appearing in plain text. For this, they use some heuristics based on appearing in plain text. For this, they use some heuristics based on
URI syntax. They then allow the user to click on such URIs and URI syntax. They then allow the user to click on such URIs and
retrieve the corresponding resource in an appropriate (usually retrieve the corresponding resource in an appropriate (usually
scheme-dependent) application. scheme-dependent) application.
Such applications would need to be upgraded, in order to use the IRI Such applications would need to be upgraded, in order to use the IRI
syntax as a base for heuristics. In particular, a non-ASCII syntax as a base for heuristics. In particular, a non-ASCII
character should not be taken as the indication of the end of an IRI. character should not be taken as the indication of the end of an IRI.
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by the system-wide IRI invocation mechanism, or to a URI (according by the system-wide IRI invocation mechanism, or to a URI (according
to Section 3.6) if the system-wide invocation mechanism only accepts to Section 3.6) if the system-wide invocation mechanism only accepts
URIs. 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
octets, which will do the right thing with IRIs. octets, which will do the right thing with IRIs.
8.4. 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
resources have logical names, sometimes automatically generate URIs resources have logical names, sometimes automatically generate URIs
for the resources they offer. For example, some HTTP servers can for the resources they offer. For example, some HTTP servers can
generate a directory listing for a file directory and then respond to generate a directory listing for a file directory and then respond to
the generated URIs with the files. the generated URIs with the files.
Many legacy character encodings are in use in various file systems. Many legacy character encodings are in use in various file systems.
Many currently deployed systems do not transform the local character Many currently deployed systems do not transform the local character
representation of the underlying system before generating URIs. representation of the underlying system before generating URIs.
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identifiers should make the appropriate transformations. For identifiers should make the appropriate transformations. For
example, if a file system contains a file named "r&#xE9;sum&# example, 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 xE9;.html", a server should expose this as "r%C3%A9sum%C3%A9.html" in
a URI, which allows use of "r&#xE9;sum&#xE9;.html" in an IRI, even if a URI, which allows use of "r&#xE9;sum&#xE9;.html" in an IRI, even if
locally the file name is kept in a character encoding other than locally the file name is kept in a character encoding other than
UTF-8. UTF-8.
This recommendation particularly applies to HTTP servers. For FTP This recommendation particularly applies to HTTP servers. For FTP
servers, similar considerations apply; see [RFC2640]. servers, similar considerations apply; see [RFC2640].
8.5. 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. This control is mostly IRIs used to identify their resources. This control is mostly
executed by controlling the resource names, such as file names, executed by controlling the resource names, such as file names,
directly. directly.
In these cases, it is recommended to avoid choosing IRIs that are In these cases, it is recommended to avoid choosing IRIs that are
easily confused. For example, for US-ASCII, the lower-case ell ("l") easily confused. For example, for US-ASCII, the lower-case ell ("l")
is easily confused with the digit one ("1"), and the upper-case oh is easily confused with the digit one ("1"), and the upper-case oh
("O") is easily confused with the digit zero ("0"). Publishers ("O") is easily confused with the digit zero ("0"). Publishers
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the Latin "A", the Greek "Alpha", and the Cyrillic "A". To avoid the Latin "A", the Greek "Alpha", and the Cyrillic "A". To avoid
such cases, IRIs should only be created where all the characters in a such cases, IRIs should only be created where all the characters in a
single component are used together in a given language. This usually single component are used together in a given language. This usually
means that all of these characters will be from the same script, but means that all of these characters will be from the same script, but
there are languages that mix characters from different scripts (such there are languages that mix characters from different scripts (such
as Japanese). This is similar to the heuristics used to distinguish as 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,
Greek, and Cyrillic, using lowercase letters results in fewer Greek, and Cyrillic, using lowercase letters results in fewer
ambiguities than using uppercase letters would. ambiguities than using uppercase letters would.
8.6. Display of URIs/IRIs 7.6. Display of URIs/IRIs
In situations where the rendering software is not expected to display In situations where the rendering software is not expected to display
non-ASCII parts of the IRI correctly using the available layout and non-ASCII parts of the IRI correctly using the available layout and
font resources, these parts should be percent-encoded before being font resources, these parts should be percent-encoded before being
displayed. displayed.
For display of Bidi IRIs, please see Section 4.1. For display of Bidi IRIs, please see Section 4.1.
8.7. Interpretation of URIs and IRIs 7.7. Interpretation of URIs and IRIs
Software that interprets IRIs as the names of local resources should Software that interprets IRIs as the names of local resources should
accept IRIs in multiple forms and convert and match them with the accept IRIs in multiple forms and convert and match them with the
appropriate local resource names. appropriate local resource names.
First, multiple representations include both IRIs in the native First, multiple representations include both IRIs in the native
character encoding of the protocol and also their URI counterparts. character encoding of the protocol and also their URI counterparts.
Second, it may include URIs constructed based on character encodings Second, it may include URIs constructed based on character encodings
other than UTF-8. These URIs may be produced by user agents that do other than UTF-8. These URIs may be produced by user agents that do
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beyond the US-ASCII repertoire, this may, for example, include beyond the US-ASCII repertoire, this may, for example, include
ignoring the accents on received IRIs or resource names. Please note ignoring the accents on received IRIs or resource names. Please note
that such mappings, including case mappings, are language dependent. that such mappings, including case mappings, are language dependent.
It can be difficult to identify a resource unambiguously if too many It can be difficult to identify a resource unambiguously if too many
mappings are taken into consideration. However, percent-encoded and mappings are taken into consideration. However, percent-encoded and
not percent-encoded parts of IRIs can always be clearly not percent-encoded parts of IRIs can always be clearly
distinguished. Also, the regularity of UTF-8 (see [Duerst97]) makes distinguished. Also, the regularity of UTF-8 (see [Duerst97]) makes
the potential for collisions lower than it may seem at first. the potential for collisions lower than it may seem at first.
8.8. Upgrading Strategy 7.8. Upgrading Strategy
Where this recommendation places further constraints on software for Where this recommendation places further constraints on software for
which many instances are already deployed, it is important to which many instances are already deployed, it is important to
introduce upgrades carefully and to be aware of the various introduce upgrades carefully and to be aware of the various
interdependencies. interdependencies.
If IRIs cannot be interpreted correctly, they should not be created, If IRIs cannot be interpreted correctly, they should not be created,
generated, or transported. This suggests that upgrading URI generated, or transported. This suggests that upgrading URI
interpreting software to accept IRIs should have highest priority. interpreting software to accept IRIs should have highest priority.
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encoding for file names will make the transition to IRIs easier. encoding for file names will make the transition to IRIs easier.
Likewise, when a new Web form is set up using UTF-8 as the character Likewise, when a new Web form is set up using UTF-8 as the character
encoding of the form page, the returned query URIs will use UTF-8 as encoding of the form page, the returned query URIs will use UTF-8 as
the character encoding (unless the user, for whatever reason, changes the character encoding (unless the user, for whatever reason, changes
the character encoding) and will therefore be compatible with IRIs. the character encoding) and will therefore be compatible with IRIs.
These recommendations, when taken together, will allow for the These recommendations, when taken together, will allow for the
extension from URIs to IRIs in order to handle characters other than extension from URIs to IRIs in order to handle characters other than
US-ASCII while minimizing interoperability problems. For US-ASCII while minimizing interoperability problems. For
considerations regarding the upgrade of URI scheme definitions, see considerations regarding the upgrade of URI scheme definitions, see
Section 6.4. Section 5.4.
9. IANA Considerations 8. IANA Considerations
RFC Editor and IANA note: Please Replace RFC XXXX with the number of RFC Editor and IANA note: Please Replace RFC XXXX with the number of
this document when it issues as an RFC. this document when it issues as an RFC.
IANA maintains a registry of "URI schemes". A "URI scheme" also IANA maintains a registry of "URI schemes". A "URI scheme" also
serves an "IRI scheme". serves an "IRI scheme".
To clarify that the URI scheme registration process also applies to To clarify that the URI scheme registration process also applies to
IRIs, change the description of the "URI schemes" registry header to IRIs, change the description of the "URI schemes" registry header to
say "[RFC4395] defines an IANA-maintained registry of URI Schemes. say "[RFC4395] defines an IANA-maintained registry of URI Schemes.
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RFC Editor and IANA note: Please Replace RFC XXXX with the number of RFC Editor and IANA note: Please Replace RFC XXXX with the number of
this document when it issues as an RFC. this document when it issues as an RFC.
IANA maintains a registry of "URI schemes". A "URI scheme" also IANA maintains a registry of "URI schemes". A "URI scheme" also
serves an "IRI scheme". serves an "IRI scheme".
To clarify that the URI scheme registration process also applies to To clarify that the URI scheme registration process also applies to
IRIs, change the description of the "URI schemes" registry header to IRIs, change the description of the "URI schemes" registry header to
say "[RFC4395] defines an IANA-maintained registry of URI Schemes. say "[RFC4395] defines an IANA-maintained registry of URI Schemes.
These registries include the Permanent and Provisional URI Schemes. These registries include the Permanent and Provisional URI Schemes.
RFC XXXX updates this registry to designate that schemes may also RFC XXXX updates this registry to designate that schemes may also
indicate their usability as IRI schemes. indicate their usability as IRI schemes.
Update "per RFC 4395" to "per RFC 4395 and RFC XXXX". Update "per RFC 4395" to "per RFC 4395 and RFC XXXX".
10. Security Considerations 9. Security Considerations
The security considerations discussed in [RFC3986] also apply to The security considerations discussed in [RFC3986] also apply to
IRIs. In addition, the following issues require particular care for IRIs. In addition, the following issues require particular care for
IRIs. IRIs.
Incorrect encoding or decoding can lead to security problems. For Incorrect encoding or decoding can lead to security problems. For
example, some UTF-8 decoders do not check against overlong byte example, some UTF-8 decoders do not check against overlong byte
sequences. See [UTR36] Section 3 for details. sequences. See [UTR36] Section 3 for details.
There are serious difficulties with relying on a human to verify that There are serious difficulties with relying on a human to verify that
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normalization expectations, use of percent-encoding with various normalization expectations, use of percent-encoding with various
legacy encodings, and bidirectionality issues. See also [UTR36]. legacy encodings, and bidirectionality issues. See also [UTR36].
Confusion can occur in various IRI components, such as the domain Confusion can occur in various IRI components, such as the domain
name part or the path part, or between IRI components. For name part or the path part, or between IRI components. For
considerations specific to the domain name part, see [RFC5890]. For considerations specific to the domain name part, see [RFC5890]. For
considerations specific to particular protocols or schemes, see the considerations specific to particular protocols or schemes, see the
security sections of the relevant specifications and registration security sections of the relevant specifications and registration
templates. Administrators of sites that allow independent users to templates. Administrators of sites that allow independent users to
create resources in the same sub area have to be careful. Details create resources in the same sub area have to be careful. Details
are discussed in Section 8.5. are discussed in Section 7.5.
Confusion can occur with bidirectional IRIs, if the restrictions in Confusion 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 be used. implementation be used.
The characters additionally allowed in Legacy Extended IRIs introduce The characters additionally allowed in Legacy Extended IRIs introduce
additional security issues. For details, see Section 7.3. additional security issues. For details, see Section 6.3.
11. Acknowledgements 10. Acknowledgements
This document was derived from [RFC3987]; the acknowledgments from This document was derived from [RFC3987]; the acknowledgments from
that specification still apply. that specification still apply.
We would like to thank Ian Hickson, Michael Sperberg-McQueen, and Dan We would like to thank Ian Hickson, Michael Sperberg-McQueen, and Dan
Connolly for their work on HyperText References, and Norman Walsh, Connolly for their work on HyperText References, and Norman Walsh,
Richard Tobin, Henry S. Thomson, John Cowan, Paul Grosso, and the XML Richard Tobin, Henry S. Thomson, John Cowan, Paul Grosso, and the XML
Core Working Group of the W3C for their work on LEIRIs. Core Working Group of the W3C for their work on LEIRIs.
In addition, this document was influenced by contributions from (in In addition, this document was influenced by contributions from (in
no particular order) Chris Lilley, Bjoern Hoehrmann, Felix Sasaki, no particular order) Chris Lilley, Bjoern Hoehrmann, Felix Sasaki,
Jeremy Carroll, Frank Ellermann, Michael Everson, Cary Karp, Jeremy Carroll, Frank Ellermann, Michael Everson, Cary Karp,
Matitiahu Allouche, Richard Ishida, Addison Phillips, Jonathan Matitiahu Allouche, Richard Ishida, Addison Phillips, Jonathan
Rosenne, Najib Tounsi, Debbie Garside, Mark Davis, Sarmad Hussain, Rosenne, Najib Tounsi, Debbie Garside, Mark Davis, Sarmad Hussain,
Ted Hardie, Konrad Lanz, Thomas Roessler, Lisa Dusseault, Julian Ted Hardie, Konrad Lanz, Thomas Roessler, Lisa Dusseault, Julian
Reschke, Giovanni Campagna, Anne van Kesteren, Mark Nottingham, Erik Reschke, Giovanni Campagna, Anne van Kesteren, Mark Nottingham, Erik
van der Poel, Marcin Hanclik, Marcos Caceres, Roy Fielding, Greg van der Poel, Marcin Hanclik, Marcos Caceres, Roy Fielding, Greg
Wilkins, Pieter Hintjens, Daniel R. Tobias, Marko Martin, Maciej Wilkins, Pieter Hintjens, Daniel R. Tobias, Marko Martin, Maciej
Stanchowiak, Wil Tan, Yui Naruse, Michael A. Puls II, Dave Thaler, Stanchowiak, Wil Tan, Yui Naruse, Michael A. Puls II, Dave Thaler,
Tom Petch, John Klensin, Shawn Steele, Peter Saint-Andre, Geoffrey Tom Petch, John Klensin, Shawn Steele, Peter Saint-Andre, Geoffrey
Sneddon, Chris Weber, Alex Melnikov, Slim Amamou, SM, Tim Berners- Sneddon, Chris Weber, Alex Melnikov, Slim Amamou, S. Moonesamy, Tim
Lee, Yaron Goland, Sam Ruby, Adam Barth, Abdulrahman I. ALGhadir, Berners-Lee, Yaron Goland, Sam Ruby, Adam Barth, Abdulrahman I.
Aharon Lanin, Thomas Milo, Murray Sargent, Marc Blanchet, and Mykyta ALGhadir, Aharon Lanin, Thomas Milo, Murray Sargent, Marc Blanchet,
Yevstifeyev. and Mykyta Yevstifeyev.
12. Main Changes Since RFC 3987 11. Main Changes Since RFC 3987
This section describes the main changes since [RFC3987]. This section describes the main changes since [RFC3987].
12.1. Major restructuring of IRI processing model 11.1. Major restructuring of IRI processing model
Major restructuring of IRI processing model to make scheme-specific Major restructuring of IRI processing model to make scheme-specific
translation necessary to handle IDNA requirements and for consistency translation necessary to handle IDNA requirements and for consistency
with web implementations. with web implementations.
Starting with IRI, you want one of: Starting with IRI, you want one of:
a IRI components (IRI parsed into UTF8 pieces) a IRI components (IRI parsed into UTF8 pieces)
b URI components (URI parsed into ASCII pieces, encoded correctly) b URI components (URI parsed into ASCII pieces, encoded correctly)
c whole URI (for passing on to some other system that wants whole c whole URI (for passing on to some other system that wants whole
URIs) URIs)
12.1.1. OLD WAY 11.1.1. OLD WAY
1. Pct-encoding on the whole thing to a URI. (c1) If you want a 1. Pct-encoding on the whole thing to a URI. (c1) If you want a
(maybe broken) whole URI, you might stop here. (maybe broken) whole URI, you might stop here.
2. Parsing the URI into URI components. (b1) If you want (maybe 2. Parsing the URI into URI components. (b1) If you want (maybe
broken) URI components, stop here. broken) URI components, stop here.
3. Decode the components (undoing the pct-encoding). (a) if you want 3. Decode the components (undoing the pct-encoding). (a) if you want
IRI components, stop here. IRI components, stop here.
4. reencode: Either using a different encoding some components (for 4. reencode: Either using a different encoding some components (for
domain names, and query components in web pages, which depends on domain names, and query components in web pages, which depends on
the component, scheme and context), and otherwise using pct- the component, scheme and context), and otherwise using pct-
encoding. (b2) if you want (good) URI components, stop here. encoding. (b2) if you want (good) URI components, stop here.
5. reassemble the reencoded components. (c2) if you want a (*good*) 5. reassemble the reencoded components. (c2) if you want a (*good*)
whole URI stop here. whole URI stop here.
12.1.2. NEW WAY 11.1.2. NEW WAY
1. Parse the IRI into IRI components using the generic syntax. (a) 1. Parse the IRI into IRI components using the generic syntax. (a)
if you want IRI components, stop here. if you want IRI components, stop here.
2. Encode each components, using pct-encoding, IDN encoding, or 2. Encode each components, using pct-encoding, IDN encoding, or
special query part encoding depending on the component scheme or special query part encoding depending on the component scheme or
context. (b) If you want URI components, stop here. context. (b) If you want URI components, stop here.
3. reassemble the a whole URI from URI components. (c) if you want a 3. reassemble the a whole URI from URI components. (c) if you want a
whole URI stop here. whole URI stop here.
12.1.3. Extension of Syntax 11.1.3. Extension of Syntax
Added the tag range (U+E0000-E0FFF) to the iprivate production. Some Added the tag range (U+E0000-E0FFF) to the iprivate production. Some
IRIs generated with the new syntax may fail to pass very strict IRIs generated with the new syntax may fail to pass very strict
checks relying on the old syntax. But characters in this range checks relying on the old syntax. But characters in this range
should be extremely infrequent anyway. should be extremely infrequent anyway.
12.1.4. More to be added 11.1.4. More to be added
TODO: There are more main changes that need to be documented in this TODO: There are more main changes that need to be documented in this
section. section.
12.2. Change Log 11.2. Change Log
Note to RFC Editor: Please completely remove this section before Note to RFC Editor: Please completely remove this section before
publication. publication.
12.2.1. Changes after draft-ietf-iri-3987bis-01 11.2.1. Changes after draft-ietf-iri-3987bis-01
Changes from draft-ietf-iri-3987bis-01 onwards are available as Changes from draft-ietf-iri-3987bis-01 onwards are available as
changesets in the IETF tools subversion repository at http:// changesets in the IETF tools subversion repository at http://
trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis/ trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis/
draft-ietf-iri-3987bis.xml. draft-ietf-iri-3987bis.xml.
12.2.2. Changes from draft-duerst-iri-bis-07 to 11.2.2. Changes from draft-duerst-iri-bis-07 to
draft-ietf-iri-3987bis-00 draft-ietf-iri-3987bis-00
Changed draft name, date, last paragraph of abstract, and titles in Changed draft name, date, last paragraph of abstract, and titles in
change log, and added this section in moving from change log, and added this section in moving from
draft-duerst-iri-bis-07 (personal submission) to draft-duerst-iri-bis-07 (personal submission) to
draft-ietf-iri-3987bis-00 (WG document). draft-ietf-iri-3987bis-00 (WG document).
12.2.3. Changes from -06 to -07 of draft-duerst-iri-bis 11.2.3. Changes from -06 to -07 of draft-duerst-iri-bis
Major restructuring of the processing model, see Section 12.1. Major restructuring of the processing model, see Section 11.1.
12.3. Changes from -00 to -01 11.3. Changes from -00 to -01
o Removed 'mailto:' before mail addresses of authors. o Removed 'mailto:' before mail addresses of authors.
o Added "<to be done>" as right side of 'href-strip' rule. Fixed o Added "<to be done>" as right side of 'href-strip' rule. Fixed
'|' to '/' for alternatives. '|' to '/' for alternatives.
12.4. Changes from -05 to -06 of draft-duerst-iri-bis-00 11.4. Changes from -05 to -06 of draft-duerst-iri-bis-00
o Add HyperText Reference, change abstract, acks and references for o Add HyperText Reference, change abstract, acks and references for
it it
o Add Masinter back as another editor. o Add Masinter back as another editor.
o Masinter integrates HRef material from HTML5 spec. o Masinter integrates HRef material from HTML5 spec.
o Rewrite introduction sections to modernize. o Rewrite introduction sections to modernize.
12.5. Changes from -04 to -05 of draft-duerst-iri-bis 11.5. Changes from -04 to -05 of draft-duerst-iri-bis
o Updated references. o Updated references.
o Changed IPR text to pre5378Trust200902. o Changed IPR text to pre5378Trust200902.
12.6. Changes from -03 to -04 of draft-duerst-iri-bis 11.6. Changes from -03 to -04 of draft-duerst-iri-bis
o Added explicit abbreviation for LEIRIs. o Added explicit abbreviation for LEIRIs.
o Mentioned LEIRI references. o Mentioned LEIRI references.
o Completed text in LEIRI section about tag characters and about o Completed text in LEIRI section about tag characters and about
specials. specials.
12.7. Changes from -02 to -03 of draft-duerst-iri-bis 11.7. Changes from -02 to -03 of draft-duerst-iri-bis
o Updated some references. o Updated some references.
o Updated Michel Suginard's coordinates. o Updated Michel Suginard's coordinates.
12.8. Changes from -01 to -02 of draft-duerst-iri-bis 11.8. Changes from -01 to -02 of draft-duerst-iri-bis
o Added tag range to iprivate (issue private-include-tags-115). o Added tag range to iprivate (issue private-include-tags-115).
o Added Specials (U+FFF0-FFFD) to Legacy Extended IRIs. o Added Specials (U+FFF0-FFFD) to Legacy Extended IRIs.
12.9. Changes from -00 to -01 of draft-duerst-iri-bis 11.9. Changes from -00 to -01 of draft-duerst-iri-bis
o Changed from "IRIs with Spaces/Controls" to "Legacy Extended IRI" o Changed from "IRIs with Spaces/Controls" to "Legacy Extended IRI"
based on input from the W3C XML Core WG. Moved the relevant based on input from the W3C XML Core WG. Moved the relevant
subsections to the back and promoted them to a section. subsections to the back and promoted them to a section.
o Added some text re. Legacy Extended IRIs to the security section. o Added some text re. Legacy Extended IRIs to the security section.
o Added a IANA Consideration Section. o Added a IANA Consideration Section.
o Added this Change Log Section. o Added this Change Log Section.
o Added a section about "IRIs with Spaces/Controls" (converting from o Added a section about "IRIs with Spaces/Controls" (converting from
a Note in RFC 3987). a Note in RFC 3987).
12.10. Changes from RFC 3987 to -00 of draft-duerst-iri-bis 11.10. Changes from RFC 3987 to -00 of draft-duerst-iri-bis
Fixed errata (see Fixed errata (see
http://www.rfc-editor.org/cgi-bin/errataSearch.pl?rfc=3987). http://www.rfc-editor.org/cgi-bin/errataSearch.pl?rfc=3987).
13. References 12. References
13.1. Normative References 12.1. Normative References
[ASCII] American National Standards Institute, "Coded Character [ASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986. Interchange", ANSI X3.4, 1986.
[ISO10646] [ISO10646]
International Organization for Standardization, "ISO/IEC International Organization for Standardization, "ISO/IEC
10646:2003: Information Technology - Universal Multiple- 10646:2003: Information Technology - Universal Multiple-
Octet Coded Character Set (UCS)", ISO Standard 10646, Octet Coded Character Set (UCS)", ISO Standard 10646,
December 2003. December 2003.
skipping to change at page 52, line 11 skipping to change at page 44, line 22
[UNIV6] The Unicode Consortium, "The Unicode Standard, Version [UNIV6] The Unicode Consortium, "The Unicode Standard, Version
6.0.0 (Mountain View, CA, The Unicode Consortium, 2011, 6.0.0 (Mountain View, CA, The Unicode Consortium, 2011,
ISBN 978-1-936213-01-6)", October 2010. ISBN 978-1-936213-01-6)", October 2010.
[UTR15] Davis, M. and M. Duerst, "Unicode Normalization Forms", [UTR15] Davis, M. and M. Duerst, "Unicode Normalization Forms",
Unicode Standard Annex #15, March 2008, Unicode Standard Annex #15, March 2008,
<http://www.unicode.org/unicode/reports/tr15/ <http://www.unicode.org/unicode/reports/tr15/
tr15-23.html>. tr15-23.html>.
13.2. Informative References 12.2. Informative References
[BidiEx] "Examples of bidirectional IRIs", [BidiEx] "Examples of bidirectional IRIs",
<http://www.w3.org/International/iri-edit/BidiExamples>. <http://www.w3.org/International/iri-edit/BidiExamples>.
[CharMod] Duerst, M., Yergeau, F., Ishida, R., Wolf, M., and T. [CharMod] Duerst, M., Yergeau, F., Ishida, R., Wolf, M., and T.
Texin, "Character Model for the World Wide Web: Resource Texin, "Character Model for the World Wide Web: Resource
Identifiers", World Wide Web Consortium Candidate Identifiers", World Wide Web Consortium Candidate
Recommendation, November 2004, Recommendation, November 2004,
<http://www.w3.org/TR/charmod-resid>. <http://www.w3.org/TR/charmod-resid>.
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