Internet DRAFT - draft-ietf-iri-3987bis
draft-ietf-iri-3987bis
Internationalized Resource Identifiers M. Duerst
(iri) Aoyama Gakuin University
Internet-Draft M. Suignard
Obsoletes: 3987 (if approved) Unicode Consortium
Intended status: Standards Track L. Masinter
Expires: April 23, 2013 Adobe
October 20, 2012
Internationalized Resource Identifiers (IRIs)
draft-ietf-iri-3987bis-13
Abstract
This document defines the Internationalized Resource Identifier (IRI)
protocol element, as an extension of the Uniform Resource Identifier
(URI). An IRI is a sequence of characters from the Universal
Character Set (Unicode/ISO 10646). Grammar and processing rules are
given for IRIs and related syntactic forms.
Defining IRI as a new protocol element (rather than updating or
extending the definition of URI) allows independent orderly
transitions: protocols and languages that use URIs must explicitly
choose to allow IRIs.
Guidelines are provided for the use and deployment of IRIs and
related protocol elements when revising protocols, formats, and
software components that currently deal only with URIs.
This document is part of a set of documents intended to replace RFC
3987.
RFC Editor: Please remove the next paragraph before publication.
This document, and several companion documents, are intended to
obsolete RFC 3987. For discussion and comments on these drafts,
please join the IETF IRI WG by subscribing to the mailing list
public-iri@w3.org, archives at
http://lists.w3.org/archives/public/public-iri/. 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. 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.
This document is available in (line-printer ready) plaintext ASCII
and PDF. It is also available in HTML from
http://www.sw.it.aoyama.ac.jp/2012/pub/
draft-ietf-iri-3987bis-13.html, and in UTF-8 plaintext from http://
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www.sw.it.aoyama.ac.jp/2012/pub/draft-ietf-iri-3987bis-13.utf8.txt.
While all these versions are identical in their technical content,
the HTML, PDF, and UTF-8 plaintext versions show non-Unicode
characters directly. This often makes it easier to understand
examples, and readers are therefore advised to consult these versions
in preference or as a supplement to the ASCII version.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on April 23, 2013.
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it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Overview and Motivation . . . . . . . . . . . . . . . . . 5
1.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 6
1.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 7
1.4. Notation . . . . . . . . . . . . . . . . . . . . . . . . 8
2. IRI Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1. Summary of IRI Syntax . . . . . . . . . . . . . . . . . . 9
2.2. ABNF for IRI References and IRIs . . . . . . . . . . . . 10
3. Processing IRIs and related protocol elements . . . . . . . . 12
3.1. Converting to UCS . . . . . . . . . . . . . . . . . . . . 13
3.2. Parse the IRI into IRI components . . . . . . . . . . . . 13
3.3. General percent-encoding of IRI components . . . . . . . 13
3.4. Mapping ireg-name . . . . . . . . . . . . . . . . . . . . 14
3.4.1. Mapping using Percent-Encoding . . . . . . . . . . . . 14
3.4.2. Mapping using Punycode . . . . . . . . . . . . . . . . 14
3.4.3. Additional Considerations . . . . . . . . . . . . . . 15
3.5. Mapping query components . . . . . . . . . . . . . . . . 16
3.6. Mapping IRIs to URIs . . . . . . . . . . . . . . . . . . 16
4. Converting URIs to IRIs . . . . . . . . . . . . . . . . . . . 16
4.1. Limitations . . . . . . . . . . . . . . . . . . . . . . . 16
4.2. Conversion . . . . . . . . . . . . . . . . . . . . . . . 17
4.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 18
5. Use of IRIs . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.1. Limitations on UCS Characters Allowed in IRIs . . . . . . 19
5.2. Software Interfaces and Protocols . . . . . . . . . . . . 20
5.3. Format of URIs and IRIs in Documents and Protocols . . . 20
5.4. Use of UTF-8 for Encoding Original Characters . . . . . . 21
5.5. Relative IRI References . . . . . . . . . . . . . . . . . 22
6. Legacy Extended IRIs (LEIRIs) . . . . . . . . . . . . . . . . 23
6.1. Legacy Extended IRI Syntax . . . . . . . . . . . . . . . 23
6.2. Conversion of Legacy Extended IRIs to IRIs . . . . . . . 23
6.3. Characters Allowed in Legacy Extended IRIs but not in
IRIs . . . . . . . . . . . . . . . . . . . . . . . . . . 23
7. Processing of URIs/IRIs/URLs by Web Browsers . . . . . . . . . 25
8. URI/IRI Processing Guidelines (Informative) . . . . . . . . . 26
8.1. URI/IRI Software Interfaces . . . . . . . . . . . . . . . 26
8.2. URI/IRI Entry . . . . . . . . . . . . . . . . . . . . . . 26
8.3. URI/IRI Transfer between Applications . . . . . . . . . . 27
8.4. URI/IRI Generation . . . . . . . . . . . . . . . . . . . 27
8.5. URI/IRI Selection . . . . . . . . . . . . . . . . . . . . 28
8.6. Display of URIs/IRIs . . . . . . . . . . . . . . . . . . 29
8.7. Interpretation of URIs and IRIs . . . . . . . . . . . . . 29
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8.8. Upgrading Strategy . . . . . . . . . . . . . . . . . . . 30
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
10. Security Considerations . . . . . . . . . . . . . . . . . . . 31
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32
12. Main Changes Since RFC 3987 . . . . . . . . . . . . . . . . . 32
12.1. Split out Bidi, processing guidelines, comparison
sections . . . . . . . . . . . . . . . . . . . . . . . . 32
12.2. Major restructuring of IRI processing model . . . . . . . 32
12.2.1. OLD WAY . . . . . . . . . . . . . . . . . . . . . . . 33
12.2.2. NEW WAY . . . . . . . . . . . . . . . . . . . . . . . 33
12.2.3. Extension of Syntax . . . . . . . . . . . . . . . . . 33
12.2.4. More to be added . . . . . . . . . . . . . . . . . . . 34
12.3. Change Log . . . . . . . . . . . . . . . . . . . . . . . 34
12.3.1. Changes after draft-ietf-iri-3987bis-01 . . . . . . . 34
12.3.2. Changes from draft-duerst-iri-bis-07 to
draft-ietf-iri-3987bis-00 . . . . . . . . . . . . . . 34
12.3.3. Changes from -06 to -07 of draft-duerst-iri-bis . . . 34
12.4. Changes from -00 to -01 . . . . . . . . . . . . . . . . . 34
12.5. Changes from -05 to -06 of draft-duerst-iri-bis-00 . . . 34
12.6. Changes from -04 to -05 of draft-duerst-iri-bis . . . . . 35
12.7. Changes from -03 to -04 of draft-duerst-iri-bis . . . . . 35
12.8. Changes from -02 to -03 of draft-duerst-iri-bis . . . . . 35
12.9. Changes from -01 to -02 of draft-duerst-iri-bis . . . . . 35
12.10. Changes from -00 to -01 of draft-duerst-iri-bis . . . . . 35
12.11. Changes from RFC 3987 to -00 of draft-duerst-iri-bis . . 35
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
13.1. Normative References . . . . . . . . . . . . . . . . . . 36
13.2. Informative References . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39
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1. Introduction
1.1. Overview and Motivation
A Uniform Resource Identifier (URI) is defined in [RFC3986] as a
sequence of characters chosen from a limited subset of the repertoire
of US-ASCII [ASCII] characters.
The characters in URIs are frequently used for representing words of
natural languages. This usage has many advantages: Such URIs are
easier to memorize, easier to interpret, easier to transcribe, easier
to create, and easier to guess. For most languages other than
English, however, the natural script uses characters other than A -
Z. For many people, handling Latin characters is as difficult as
handling the characters of other scripts is for those who use only
the Latin script. Many languages with non-Latin scripts are
transcribed with Latin letters. These transcriptions are now often
used in URIs, but they introduce additional difficulties.
The infrastructure for the appropriate handling of characters from
additional scripts is now widely deployed in operating system and
application software. Software that can handle a wide variety of
scripts and languages at the same time is increasingly common. Also,
an increasing number of protocols and formats can carry a wide range
of characters.
URIs are composed out of a very limited repertoire of characters;
this design choice was made to support global transcription (see
[RFC3986] section 1.2.1.). Reliable transition between a URI (as an
abstract protocol element composed of a sequence of characters) and a
presentation of that URI (written on a napkin, read out loud) and
back is relatively straightforward, because of the limited repertoire
of characters used. IRIs are designed to satisfy a different set of
use requirements; in particular, to allow IRIs to be written in ways
that are more meaningful to their users, even at the expense of
global transcribability. However, ensuring reliability of the
transition between an IRI and its presentation and back is more
difficult and complex when dealing with the larger set of Unicode
characters. For example, Unicode supports multiple ways of encoding
complex combinations of characters and accents, with multiple
character sequences that can result in the same presentation.
This document defines the protocol element called Internationalized
Resource Identifier (IRI), which allows applications of URIs to be
extended to use resource identifiers that have a much wider
repertoire of characters. It also provides corresponding
"internationalized" versions of other constructs from [RFC3986], such
as URI references. The syntax of IRIs is defined in Section 2.
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Within this document, Section 5 discusses the use of IRIs in
different situations. Section 8 gives additional informative
guidelines. Section 10 discusses IRI-specific security
considerations.
This specification is part of a collection of specifications intended
to replace [RFC3987]. [Bidi] discusses the special case of
bidirectional IRIs, IRIs using characters from scripts written right-
to-left. [Equivalence] gives guidelines for applications wishing to
determine if two IRIs are equivalent, as well as defining some
equivalence methods. [RFC4395bis] updates the URI scheme
registration guidelines and procedures to note that every URI scheme
is also automatically an IRI scheme and to allow scheme definitions
to be directly described in terms of Unicode characters.
1.2. Applicability
IRIs are designed to allow protocols and software that deal with URIs
to be updated to handle IRIs. Processing of IRIs is accomplished by
extending the URI syntax while retaining (and not expanding) the set
of "reserved" characters, such that the syntax for any URI scheme may
be extended to allow non-ASCII characters. In addition, following
parsing of an IRI, it is possible to construct a corresponding URI by
first encoding characters outside of the allowed URI range and then
reassembling the components.
Practical use of IRIs forms in place of URIs forms depends on the
following conditions being met:
a. A protocol or format element MUST be explicitly designated to be
able to carry IRIs. The intent is to avoid introducing IRIs into
contexts that are not defined to accept them. For example, XML
schema [XMLSchema] has an explicit type "anyURI" that includes
IRIs and IRI references. Therefore, IRIs and IRI references can
be used in attributes and elements of type "anyURI". On the other
hand, in HTTP/1.1 ([RFC2616]) , the Request URI is defined as a
URI, which means that direct use of IRIs is not allowed in HTTP
requests.
b. The protocol or format carrying the IRIs MUST have a mechanism to
represent the wide range of characters used in IRIs, either
natively or by some protocol- or format-specific escaping
mechanism (for example, numeric character references in [XML1]).
c. The URI scheme definition, if it explicitly allows a percent sign
("%") in any syntactic component, SHOULD define the interpretation
of sequences of percent-encoded octets (using "%XX" hex octets) as
octets from sequences of UTF-8 encoded characters; this is
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recommended in the guidelines for registering new schemes,
[RFC4395bis]. For example, this is the practice for IMAP URLs
[RFC2192], POP URLs [RFC2384] and the URN syntax [RFC2141]). Note
that use of percent-encoding may also be restricted in some
situations, for example, URI schemes that disallow percent-
encoding might still be used with a fragment identifier which is
percent-encoded (e.g., [XPointer]). See Section 5.4 for further
discussion.
1.3. Definitions
Various terms used in this document are defined in [RFC6365] and
[RFC3986]. In addition, we define the following terms for use in
this document.
octet: An ordered sequence of eight bits considered as a unit.
sequence of characters: A sequence of characters (one after
another).
sequence of octets: A sequence of octets (one after another).
character encoding: A method of representing a sequence of
characters as a sequence of octets (maybe with variants). Also, a
method of (unambiguously) converting a sequence of octets into a
sequence of characters.
charset: The name of a parameter or attribute used to identify a
character encoding.
UCS: Universal Character Set. The coded character set defined by
ISO/IEC 10646 [ISO10646] and the Unicode Standard [UNIV6].
IRI reference: Denotes the common usage of an Internationalized
Resource Identifier. An IRI reference may be absolute or
relative. However, the "IRI" that results from such a reference
only includes absolute IRIs; any relative IRI references are
resolved to their absolute form. Note that in [RFC2396] URIs did
not include fragment identifiers, but in [RFC3986] fragment
identifiers are part of URIs.
LEIRI (Legacy Extended IRI): This term is used in various XML
specifications to refer to strings that, although not valid IRIs,
are acceptable input to the processing rules in Section 6.2.
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protocol element: Any portion of a message that affects processing
of that message by the protocol in question.
create (a URI or IRI): With respect to URIs and IRIs, the term is
used for the initial creation. This may be the initial creation
of a resource with a certain identifier, or the initial exposition
of a resource under a particular identifier.
generate (a URI or IRI): With respect to URIs and IRIs, the term is
used when the identifier is generated by derivation from other
information.
parsed URI component: When a URI processor parses a URI (following
the generic syntax or a scheme-specific syntax, the result is a
set of parsed URI components, each of which has a type
(corresponding to the syntactic definition) and a sequence of URI
characters.
parsed IRI component: When an IRI processor parses an IRI directly,
following the general syntax or a scheme-specific syntax, the
result is a set of parsed IRI components, each of which has a type
(corresponding to the syntactic definition) and a sequence of IRI
characters. (This definition is analogous to "parsed URI
component".)
IRI scheme: A URI scheme may also be known as an "IRI scheme" if the
scheme's syntax has been extended to allow non-US-ASCII characters
according to the rules in this document.
1.4. Notation
RFCs and Internet Drafts currently do not allow any characters
outside the US-ASCII repertoire. Therefore, this document uses
various special notations for such characters in examples.
In text, characters outside US-ASCII are sometimes referenced by
using a prefix of 'U+', followed by four to six hexadecimal digits.
To represent characters outside US-ASCII in a document format that is
limited to US-ASCII, this document uses 'XML Notation'. XML Notation
uses a leading '&#x', a trailing ';', and the hexadecimal number of
the character in the UCS in between. For example, Я stands for
CYRILLIC CAPITAL LETTER YA. In this notation, an actual '&' is
denoted by '&'. This notation is only used in the ASCII
version(s) of this document, because in the other versions, non-ASCII
characters are used directly.
To denote actual octets in examples (as opposed to percent-encoded
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octets), the two hex digits denoting the octet are enclosed in "<"
and ">". For example, the octet often denoted as 0xc9 is denoted
here as <c9>.
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in [RFC2119].
2. IRI Syntax
This section defines the syntax of Internationalized Resource
Identifiers (IRIs).
As with URIs, an IRI is defined as a sequence of characters, not as a
sequence of octets. This definition accommodates the fact that IRIs
may be written on paper or read over the radio as well as stored or
transmitted digitally. The same IRI might be represented as
different sequences of octets in different protocols or documents if
these protocols or documents use different character encodings
(and/or transfer encodings). Using the same character encoding as
the containing protocol or document ensures that the characters in
the IRI can be handled (e.g., searched, converted, displayed) in the
same way as the rest of the protocol or document.
2.1. Summary of IRI Syntax
The IRI syntax extends the URI syntax in [RFC3986] by extending the
class of unreserved characters, primarily by adding the characters of
the UCS (Universal Character Set, [ISO10646]) beyond U+007F, subject
to the limitations given in the syntax rules below and in
Section 5.1.
The syntax and use of components and reserved characters is the same
as that in [RFC3986]. Each URI scheme thus also functions as an IRI
scheme, in that scheme-specific parsing rules for URIs of a scheme
are extended to allow parsing of IRIs using the same parsing rules.
All the operations defined in [RFC3986], such as the resolution of
relative references, can be applied to IRIs by IRI-processing
software in exactly the same way as they are for URIs by URI-
processing software.
Characters outside the US-ASCII repertoire MUST NOT be reserved and
therefore MUST NOT be used for syntactical purposes, such as to
delimit components in newly defined schemes. For example, U+00A2,
CENT SIGN, is not allowed as a delimiter in IRIs, because it is in
the 'iunreserved' category. This is similar to the fact that it is
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not possible to use '-' as a delimiter in URIs, because it is in the
'unreserved' category.
2.2. ABNF for IRI References and IRIs
An ABNF definition for IRI references (which are the most general
concept and the start of the grammar) and IRIs is given here. The
syntax of this ABNF is described in [STD68]. Character numbers are
taken from the UCS, without implying any actual binary encoding.
Terminals in the ABNF are characters, not octets.
The following grammar closely follows the URI grammar in [RFC3986],
except that the range of unreserved characters is expanded to include
UCS characters, with the restriction that private UCS characters can
occur only in query parts. The grammar is split into two parts:
Rules that differ from [RFC3986] because of the above-mentioned
expansion, and rules that are the same as those in [RFC3986]. For
rules that are different than those in [RFC3986], the names of the
non-terminals have been changed as follows. If the non-terminal
contains 'URI', this has been changed to 'IRI'. Otherwise, an 'i'
has been prefixed. The rule <pct-form> has been introduced in order
to be able to reference it from other parts of the document.
The following rules are different from those in [RFC3986]:
IRI = scheme ":" ihier-part [ "?" iquery ]
[ "#" ifragment ]
ihier-part = "//" iauthority ipath-abempty
/ ipath-absolute
/ ipath-rootless
/ ipath-empty
IRI-reference = IRI / irelative-ref
absolute-IRI = scheme ":" ihier-part [ "?" iquery ]
irelative-ref = irelative-part [ "?" iquery ] [ "#" ifragment ]
irelative-part = "//" iauthority ipath-abempty
/ ipath-absolute
/ ipath-noscheme
/ ipath-empty
iauthority = [ iuserinfo "@" ] ihost [ ":" port ]
iuserinfo = *( iunreserved / pct-form / sub-delims / ":" )
ihost = IP-literal / IPv4address / ireg-name
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pct-form = pct-encoded
ireg-name = *( iunreserved / sub-delims )
ipath = ipath-abempty ; begins with "/" or is empty
/ ipath-absolute ; begins with "/" but not "//"
/ ipath-noscheme ; begins with a non-colon segment
/ ipath-rootless ; begins with a segment
/ ipath-empty ; zero characters
ipath-abempty = *( path-sep isegment )
ipath-absolute = path-sep [ isegment-nz *( path-sep isegment ) ]
ipath-noscheme = isegment-nz-nc *( path-sep isegment )
ipath-rootless = isegment-nz *( path-sep isegment )
ipath-empty = ""
path-sep = "/"
isegment = *ipchar
isegment-nz = 1*ipchar
isegment-nz-nc = 1*( iunreserved / pct-form / sub-delims
/ "@" )
; non-zero-length segment without any colon ":"
ipchar = iunreserved / pct-form / sub-delims / ":"
/ "@"
iquery = *( ipchar / iprivate / "/" / "?" )
ifragment = *( ipchar / "/" / "?" )
iunreserved = ALPHA / DIGIT / "-" / "." / "_" / "~" / ucschar
ucschar = %xA0-D7FF / %xF900-FDCF / %xFDF0-FFEF
/ %x10000-1FFFD / %x20000-2FFFD / %x30000-3FFFD
/ %x40000-4FFFD / %x50000-5FFFD / %x60000-6FFFD
/ %x70000-7FFFD / %x80000-8FFFD / %x90000-9FFFD
/ %xA0000-AFFFD / %xB0000-BFFFD / %xC0000-CFFFD
/ %xD0000-DFFFD / %xE1000-EFFFD
iprivate = %xE000-F8FF / %xE0000-E0FFF / %xF0000-FFFFD
/ %x100000-10FFFD
Some productions are ambiguous. The "first-match-wins" (a.k.a.
"greedy") algorithm applies. For details, see [RFC3986].
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The following rules are the same as those in [RFC3986]:
scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
port = *DIGIT
IP-literal = "[" ( IPv6address / IPvFuture ) "]"
IPvFuture = "v" 1*HEXDIG "." 1*( unreserved / sub-delims / ":" )
IPv6address = 6( h16 ":" ) ls32
/ "::" 5( h16 ":" ) ls32
/ [ h16 ] "::" 4( h16 ":" ) ls32
/ [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
/ [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
/ [ *3( h16 ":" ) h16 ] "::" h16 ":" ls32
/ [ *4( h16 ":" ) h16 ] "::" ls32
/ [ *5( h16 ":" ) h16 ] "::" h16
/ [ *6( h16 ":" ) h16 ] "::"
h16 = 1*4HEXDIG
ls32 = ( h16 ":" h16 ) / IPv4address
IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet
dec-octet = DIGIT ; 0-9
/ %x31-39 DIGIT ; 10-99
/ "1" 2DIGIT ; 100-199
/ "2" %x30-34 DIGIT ; 200-249
/ "25" %x30-35 ; 250-255
pct-encoded = "%" HEXDIG HEXDIG
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
reserved = gen-delims / sub-delims
gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@"
sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="
This syntax does not support IPv6 scoped addressing zone identifiers.
3. Processing IRIs and related protocol elements
IRIs are meant to replace URIs in identifying resources within new
versions of protocols, formats, and software components that use a
UCS-based character repertoire. Protocols and components may use and
process IRIs directly. However, there are still numerous systems and
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protocols which only accept URIs or components of parsed URIs; that
is, they only accept sequences of characters within the subset of US-
ASCII characters allowed in URIs.
This section defines specific processing steps for IRI consumers
which establish the relationship between the string given and the
interpreted derivatives. These processing steps apply to both IRIs
and IRI references (i.e., absolute or relative forms); for IRIs, some
steps are scheme specific.
3.1. Converting to UCS
Input that is already in a Unicode form (i.e., a sequence of Unicode
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
normalized or changed.
An IRI or IRI reference is a sequence of characters from the UCS.
For input from presentations (written on paper, read aloud) or
translation from other representations (a text stream using a legacy
character encoding), convert the input to Unicode. Note that some
character encodings or transcriptions can be converted to or
represented by more than one sequence of Unicode characters. Ideally
the resulting IRI would use a normalized form, such as Unicode
Normalization Form C [UTR15], since that ensures a stable, consistent
representation that is most likely to produce the intended results.
Previous versions of this specification required normalization at
this step. However, attempts to require normalization in other
protocols have met with strong enough resistance that requiring
normalization here was considered impractical. Implementers and
users are cautioned that, while denormalized character sequences are
valid, they might be difficult for other users or processes to
reproduce and might lead to unexpected results.
3.2. Parse the IRI into IRI components
Parse the IRI, either as a relative reference (no scheme) or using
scheme specific processing (according to the scheme given); the
result is a set of parsed IRI components.
3.3. General percent-encoding of IRI components
Except as noted in the following subsections, IRI components are
mapped to the equivalent URI components by percent-encoding those
characters not allowed in URIs. Previous processing steps will have
removed some characters, and the interpretation of reserved
characters will have already been done (with the syntactic reserved
characters outside of the IRI component). This mapping is defined
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for all sequences of Unicode characters, whether or not they are
valid for the component in question.
For each character which is not allowed anywhere in a valid URI apply
the following steps.
Convert to UTF-8: Convert the character to a sequence of one or more
octets using UTF-8 [STD63].
Percent encode: Convert each octet of this sequence to %HH, where HH
is the hexadecimal notation of the octet value. The hexadecimal
notation SHOULD use uppercase letters. (This is the general URI
percent-encoding mechanism in Section 2.1 of [RFC3986].)
Note that the mapping is an identity transformation for parsed URI
components of valid URIs, and is idempotent: applying the mapping a
second time will not change anything.
3.4. Mapping ireg-name
The mapping from <ireg-name> to a <reg-name> requires a choice
between one of the two methods described below.
3.4.1. Mapping using Percent-Encoding
The ireg-name component SHOULD be converted according to the general
procedure for percent-encoding of IRI components described in
Section 3.3.
For example, the IRI
"http://résumé.example.org"
will be converted to
"http://r%C3%A9sum%C3%A9.example.org".
This conversion for ireg-name is in line with Section 3.2.2 of
[RFC3986], which does not mandate a particular registered name lookup
technology. For further background, see [RFC6055] and [Gettys].
3.4.2. Mapping using Punycode
In situations where it is certain that <ireg-name> is intended to be
used as a domain name to be processed by Domain Name Lookup (as per
[RFC5891]), an alternative method MAY be used, converting <ireg-name>
as follows:
If there is any percent-encoding, and the corresponding octets all
represent valid UTF-8 octet sequences, then convert these back to
Unicode character sequences. (If any percent-encodings are not valid
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UTF-8 octet sequences, then leave the entire field as is without any
change, since punycode encoding would not succeed.)
Replace the ireg-name part of the IRI by the part converted using the
Domain Name Lookup procedure (Subsections 5.3 to 5.5) of [RFC5891].
on each dot-separated label, and by using U+002E (FULL STOP) as a
label separator. This procedure may fail, but this would mean that
the IRI cannot be resolved. In such cases, if the domain name
conversion fails, then the entire IRI conversion fails. Processors
that have no mechanism for signalling a failure MAY instead
substitute an otherwise invalid host name, although such processing
SHOULD be avoided.
For example, the IRI
"http://résumé.example.org"
is converted to
"http://xn--rsum-bad.example.org".
This conversion for ireg-name will be better able to deal with legacy
infrastructure that cannot handle percent-encoding in domain names.
3.4.3. Additional Considerations
Domain Names can appear in parts of an IRI other than the ireg-name
part. It is the responsibility of scheme-specific implementations
(if the Internationalized Domain Name is part of the scheme syntax)
or of server-side implementations (if the Internationalized Domain
Name is part of 'iquery') to apply the necessary conversions at the
appropriate point. Example: Trying to validate the Web page at
http://résumé.example.org would lead to an IRI of
http://validator.w3.org/check?uri=http%3A%2F%2Frésumé
.example.org, which would convert to a URI of
http://validator.w3.org/check?uri=http%3A%2F%2Fr%C3%A9sum%C3%A9.
example.org. The server-side implementation is responsible for
making the necessary conversions to be able to retrieve the Web page.
In this process, characters allowed in URI references and existing
percent-encoded sequences are not encoded further. (This mapping is
similar to, but different from, the encoding applied when arbitrary
content is included in some part of a URI.) For example, an IRI of
"http://www.example.org/red%09rosé#red" (in XML notation) is
converted to
"http://www.example.org/red%09ros%C3%A9#red", not to something like
"http%3A%2F%2Fwww.example.org%2Fred%2509ros%C3%A9%23red".
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3.5. Mapping query components
For compatibility with existing deployed HTTP infrastructure, the
following special case applies for the schemes "http" and "https"
when an IRI is found in a document whose charset is not based on UCS
(e.g., not UTF-8 or UTF-16). In such a case, the "query" component
of an IRI is mapped into a URI by using the document charset rather
than UTF-8 as the binary representation before percent-encoding.
This mapping is not applied for any other schemes or components.
3.6. Mapping IRIs to URIs
The mapping from an IRI to URI is accomplished by applying the
mapping above (from IRI to URI components) and then reassembling a
URI from the parsed URI components using the original punctuation
that delimited the IRI components.
4. Converting URIs to IRIs
In some situations, for presentation and further processing, it is
desirable to convert a URI into an equivalent IRI without unnecessary
percent encoding. Of course, every URI is already an IRI in its own
right without any conversion. This section gives one possible
procedure for converting a URI to an IRI.
4.1. Limitations
The conversion described in this section, if given a valid URI, will
result in an IRI that maps back to the URI used as an input for the
conversion (except for potential case differences in percent-encoding
and for potential percent-encoded unreserved characters). However,
the IRI resulting from this conversion may differ from the original
IRI (if there ever was one).
URI-to-IRI conversion removes percent-encodings, but not all percent-
encodings can be eliminated. There are several reasons for this:
1. Some percent-encodings are necessary to distinguish percent-
encoded and unencoded uses of reserved characters.
2. Some percent-encodings cannot be interpreted as sequences of UTF-8
octets.
(Note: The octet patterns of UTF-8 are highly regular. Therefore,
there is a very high probability, but no guarantee, that percent-
encodings that can be interpreted as sequences of UTF-8 octets
actually originated from UTF-8. For a detailed discussion, see
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[Duerst97].)
3. The conversion may result in a character that is not appropriate
in an IRI. See Section 2.2, and Section 5.1 for further details.
4. As described in Section 3.5, IRI to URI conversion may work
somewhat differently for query components.
4.2. Conversion
Conversion from a URI to an IRI MAY be done by using the following
steps:
1. Represent the URI as a sequence of octets in US-ASCII.
2. Convert all percent-encodings ("%" followed by two hexadecimal
digits) to the corresponding octets, except those corresponding to
"%", characters in "reserved", and characters in US-ASCII not
allowed in URIs.
3. Re-percent-encode any octet produced in step 2 that is not part of
a strictly legal UTF-8 octet sequence.
4. Re-percent-encode all octets produced in step 3 that in UTF-8
represent characters that are not appropriate according to
Section 2.2 and Section 5.1.
5. Optionally, re-percent-encode octets in the query component if the
scheme is one of those mentioned in Section 3.5.
6. Interpret the resulting octet sequence as a sequence of characters
encoded in UTF-8.
7. URIs known to contain domain names in the reg-name component
SHOULD convert punycode-encoded domain name labels to the
corresponding characters using the ToUnicode procedure.
This procedure will convert as many percent-encoded characters as
possible to characters in an IRI. Because there are some choices in
steps 4 (see also Section 5.1) and 5, results may vary.
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
guess from the context that another character encoding than UTF-8 was
used in the URI. For example, the URI
"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.
It must not be converted to an IRI containing these e-acute
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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
URI from "http://www.example.org/r%E9sum%E9.html".
4.3. Examples
This section shows various examples of converting URIs to IRIs. Each
example shows the result after each of the steps 1 through 6 is
applied. XML Notation is used for the final result. Octets are
denoted by "<" followed by two hexadecimal digits followed by ">".
The following example contains the sequence "%C3%BC", which is a
strictly legal UTF-8 sequence, and which is converted into the actual
character U+00FC, LATIN SMALL LETTER U WITH DIAERESIS (also known as
u-umlaut).
1. http://www.example.org/D%C3%BCrst
2. http://www.example.org/D<c3><bc>rst
3. http://www.example.org/D<c3><bc>rst
4. http://www.example.org/D<c3><bc>rst
5. http://www.example.org/Dürst
6. http://www.example.org/Dürst
The following example contains the sequence "%FC", which might
represent U+00FC, LATIN SMALL LETTER U WITH DIAERESIS, in the
iso-8859-1 character encoding. (It might represent other characters
in other character encodings. For example, the octet <fc> in iso-
8859-5 represents U+045C, CYRILLIC SMALL LETTER KJE.) Because <fc>
is not part of a strictly legal UTF-8 sequence, it is re-percent-
encoded in step 3.
1. http://www.example.org/D%FCrst
2. http://www.example.org/D<fc>rst
3. http://www.example.org/D%FCrst
4. http://www.example.org/D%FCrst
5. http://www.example.org/D%FCrst
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6. http://www.example.org/D%FCrst
The following example contains "%e2%80%ae", which is the percent-
encoded
UTF-8 character encoding of U+202E, RIGHT-TO-LEFT OVERRIDE. The
direct use of this character is forbidden in an IRI. Therefore, the
corresponding octets are re-percent-encoded in step 4. This example
shows that the case (upper- or lowercase) of letters used in percent-
encodings may not be preserved. The example also contains a
punycode-encoded domain name label (xn--99zt52a), which is not
converted.
1. http://xn--99zt52a.example.org/%e2%80%ae
2. http://xn--99zt52a.example.org/<e2><80><ae>
3. http://xn--99zt52a.example.org/<e2><80><ae>
4. http://xn--99zt52a.example.org/%E2%80%AE
5. http://xn--99zt52a.example.org/%E2%80%AE
6. http://納豆.example.org/%E2%80%AE
Note that the label "xn--99zt52a" is converted to U+7D0D U+8C46
(Japanese Natto). ((EDITOR NOTE: There is some inconsistency in this
note.))
5. Use of IRIs
5.1. Limitations on UCS Characters Allowed in IRIs
This section discusses limitations on characters and character
sequences usable for IRIs beyond those given in Section 2.2. The
considerations in this section are relevant when IRIs are created and
when URIs are converted to IRIs.
a. The repertoire of characters allowed in each IRI component is
limited by the definition of that component. For example, the
definition of the scheme component does not allow characters
beyond US-ASCII.
(Note: In accordance with URI practice, generic IRI software
cannot and should not check for such limitations.)
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b. The UCS contains many areas of characters for which there are
strong visual look-alikes. Because of the likelihood of
transcription errors, these also should be avoided. This includes
the full-width equivalents of Latin characters, half-width
Katakana characters for Japanese, and many others. It also
includes many look-alikes of "space", "delims", and "unwise",
characters excluded in [RFC3491].
c. At the start of a component, the use of combining marks is
strongly discouraged. As an example, a COMBINING TILDE OVERLAY
(U+0334) would be very confusing at the start of a <isegment>.
Combined with the preceeding '/', it might look like a solidus
with combining tilde overlay, but IRI processing software will
parse and process the '/' separately.
d. The ZERO WIDTH NON-JOINER (U+200C) and ZERO WIDTH JOINER (U+200D)
are invisible in most contexts, but are crucial in some very
limited contexts. Appendix A of [RFC5892] contains contextual
restrictions for these and some other characters. The use of
these characters are strongly discouraged except in the relevant
contexts.
Additional information is available from [UNIXML]. [UNIXML] is
written in the context of general purpose text rather than in that of
identifiers. Nevertheless, it discusses many of the categories of
characters not appropriate for IRIs.
5.2. Software Interfaces and Protocols
Although an IRI is defined as a sequence of characters, software
interfaces for URIs typically function on sequences of octets or
other kinds of code units. Thus, software interfaces and protocols
MUST define which character encoding is used.
Intermediate software interfaces between IRI-capable components and
URI-only components MUST map the IRIs per Section 3.6, when
transferring from IRI-capable to URI-only components. This mapping
SHOULD be applied as late as possible. It SHOULD NOT be applied
between components that are known to be able to handle IRIs.
5.3. Format of URIs and IRIs in Documents and Protocols
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
native character encoding, IRIs MUST also be encoded in this
character encoding and converted accordingly by a parser or
interpreter. IRI characters not expressible in the native character
encoding SHOULD be escaped by using the escaping conventions of the
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document format if such conventions are available. Alternatively,
they MAY be percent-encoded according to Section 3.6. For example,
in HTML or XML, numeric character references SHOULD be used. If a
document as a whole has a native character encoding and that
character encoding is not UTF-8, then IRIs MUST NOT be placed into
the document in the UTF-8 character encoding.
((UPDATE THIS NOTE)) Note: Some formats already accommodate IRIs,
although they use different terminology. HTML 4.0 [HTML4] defines
the conversion from IRIs to URIs as error-avoiding behavior. XML 1.0
[XML1], XLink [XLink], XML Schema [XMLSchema], and specifications
based upon them allow IRIs. Also, it is expected that all relevant
new W3C formats and protocols will be required to handle IRIs
[CharMod].
5.4. Use of UTF-8 for Encoding Original Characters
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
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
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
to some part. For background information on encoding characters into
URIs, see also Section 2.5 of [RFC3986].
For new URI/IRI schemes, using UTF-8 is recommended in [RFC4395bis].
Examples where UTF-8 is already used are the URN syntax [RFC2141],
IMAP URLs [RFC2192], POP URLs [RFC2384], XMPP URLs [RFC5122], and the
'mailto:' scheme [RFC6068]. On the other hand, because the HTTP URI
scheme does not specify how to encode original characters, only some
HTTP URLs can have corresponding but different IRIs.
For example, for a document with a URI of
"http://www.example.org/r%C3%A9sum%C3%A9.html", it is possible to
construct a corresponding IRI (in XML notation, see Section 1.4):
"http://www.example.org/résumé.html" ("é" stands for
the e-acute character, and "%C3%A9" is the UTF-8 encoded and percent-
encoded representation of that character). On the other hand, for a
document with a URI of "http://www.example.org/r%E9sum%E9.html", the
percent-encoded octets cannot be converted to actual characters in an
IRI, as the percent-encoding is not based on UTF-8.
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
upgrading makes sense is when a scheme definition, or a particular
component of a scheme, is strictly limited to the use of US-ASCII
characters with no provision to include non-ASCII characters/octets
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via percent-encoding, or if a scheme definition currently uses highly
scheme-specific provisions for the encoding of non-ASCII characters.
Scheme definitions can impose restrictions on the syntax of scheme-
specific URIs; i.e., URIs that are admissible under the generic URI
syntax [RFC3986] may not be admissible due to narrower syntactic
constraints imposed by a URI scheme specification. URI scheme
definitions cannot broaden the syntactic restrictions of the generic
URI syntax; otherwise, it would be possible to generate URIs that
satisfied the scheme-specific syntactic constraints without
satisfying the syntactic constraints of the generic URI syntax.
However, additional syntactic constraints imposed by URI scheme
specifications are applicable to IRI, as the corresponding URI
resulting from the mapping defined in Section 3.6 MUST be a valid URI
under the syntactic restrictions of generic URI syntax and any
narrower restrictions imposed by the corresponding URI scheme
specification.
The requirement for the use of UTF-8 generally applies to all parts
of a URI. However, it is possible that the capability of IRIs to
represent a wide range of characters directly is used just in some
parts of the IRI (or IRI reference). The other parts of the IRI may
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
encode raw binary data (see also [RFC2397]).
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
document name is encoded in iso-8859-1 based on server settings, but
where the fragment identifier is encoded in UTF-8 according to
[XPointer]. The IRI corresponding to the above URI would be (in XML
notation)
"http://www.example.org/r%E9sum%E9.xml#résumé".
Similar considerations apply to query parts. The functionality of
IRIs (namely, to be able to include non-ASCII characters) can only be
used if the query part is encoded in UTF-8.
5.5. Relative IRI References
Processing of relative IRI references against a base is handled
straightforwardly; the algorithms of [RFC3986] can be applied
directly, treating the characters additionally allowed in IRI
references in the same way that unreserved characters are treated in
URI references.
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6. Legacy Extended IRIs (LEIRIs)
In some cases, there have been formats which have used a protocol
element which is a variant of the IRI definition; these variants have
usually been somewhat less restricted in syntax. This section
provides a definition and a name (Legacy Extended IRI or LEIRI) for
one of these variants used widely in XML-based protocols. This
variant has to be used with care; it requires further processing
before being fully interchangeable as IRIs. New protocols and
formats SHOULD NOT use Legacy Extended IRIs. Even where Legacy
Extended IRIs are allowed, only IRIs fully conforming to the syntax
definition in Section 2.2 SHOULD be created, generated, and used.
The provisions in this section also apply to Legacy Extended IRI
references.
6.1. Legacy Extended IRI Syntax
This section defines Legacy Extended IRIs (LEIRIs). The syntax of
Legacy Extended IRIs is the same as that for <IRI-reference>, except
that the ucschar production is replaced by the leiri-ucschar
production:
leiri-ucschar = " " / "<" / ">" / '"' / "{" / "}" / "|"
/ "\" / "^" / "`" / %x0-1F / %x7F-D7FF
/ %xE000-FFFD / %x10000-10FFFF
The restriction on bidirectional formatting characters in [Bidi] is
lifted. The iprivate production becomes redundant.
Likewise, the syntax for Legacy Extended IRI references (LEIRI
references) is the same as that for IRI references with the above
replacement of ucschar with leiri-ucschar.
6.2. Conversion of Legacy Extended IRIs to IRIs
To convert a Legacy Extended IRI (reference) to an IRI (reference),
each character allowed in a Legacy Extended IRI (reference) but not
allowed in an IRI (reference) (see Section 6.3) MUST be percent-
encoded by applying the steps in Section 3.3.
6.3. Characters Allowed in Legacy Extended IRIs but not in IRIs
This section provides a list of the groups of characters and code
points that are allowed in Legacy Extedend IRIs, but are not allowed
in IRIs 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, concentrating on the reasons for why not to use them.
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Space (U+0020): Some formats and applications use space as a
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 printing long URIs; the same applies to long IRIs.
Spaces might disappear, or a single Legacy Extended IRI might
incorrectly be interpreted as two or more separate ones.
Delimiters "<" (U+003C), ">" (U+003E), and '"' (U+0022): Appendix
C of [RFC3986] suggests the use of double-quotes
("http://example.com/") and angle brackets (<http://example.com/>)
as delimiters for URIs in plain text. These conventions are often
used, and also apply to IRIs. Legacy Extended IRIs using these
characters might be cut off at the wrong place.
Unwise characters "\" (U+005C), "^" (U+005E), "`" (U+0060), "{"
(U+007B), "|" (U+007C), and "}" (U+007D): These characters
originally were excluded from URIs because the respective
codepoints are assigned to different graphic characters in some
7-bit or 8-bit encoding. Despite the move to Unicode, some of
these characters are still occasionally displayed differently on
some systems, e.g., U+005C as a Japanese Yen symbol. Also, the
fact that these characters are not used in URIs or IRIs has
encouraged their use outside URIs or IRIs in contexts that may
include URIs or IRIs. In case a Legacy Extended IRI with such a
character is used in such a context, the Legacy Extended IRI will
be interpreted piecemeal.
The controls (C0 controls, DEL, and C1 controls, #x0 - #x1F #x7F -
#x9F): There is no way to transmit these characters reliably
except potentially in electronic form. Even when in electronic
form, some software components might silently filter out some of
these characters, or may stop processing alltogether when
encountering some of them. These characters may affect text
display in subtle, unnoticable ways or in drastic, global, and
irreversible ways depending on the hardware and software involved.
The use of some of these characters may allow malicious users to
manipulate the display of a Legacy Extended IRI and its context.
Bidi formatting characters (U+200E, U+200F, U+202A-202E): These
characters affect the display ordering of characters. Displayed
Legacy Extended IRIs containing these characters cannot be
converted back to electronic form (logical order) unambiguously.
These characters may allow malicious users to manipulate the
display of a Legacy Extended IRI and its context.
Specials (U+FFF0-FFFD): These code points provide functionality
beyond that useful in a Legacy Extended IRI, for example byte
order identification, annotation, and replacements for unknown
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characters and objects. Their use and interpretation in a Legacy
Extended IRI serves no purpose and may lead to confusing display
variations.
Private use code points (U+E000-F8FF, U+F0000-FFFFD, U+100000-
10FFFD): Display and interpretation of these code points is by
definition undefined without private agreement. Therefore, these
code points are not suited for use on the Internet. They are not
interoperable and may have unpredictable effects.
Tags (U+E0000-E0FFF): These characters provide a way to language
tag in Unicode plain text. They are not appropriate for Legacy
Extended IRIs because language information in identifiers cannot
reliably be input, transmitted (e.g., on a visual medium such as
paper), or recognized.
Non-characters (U+FDD0-FDEF, U+1FFFE-1FFFF, U+2FFFE-2FFFF,
U+3FFFE-3FFFF, U+4FFFE-4FFFF, U+5FFFE-5FFFF, U+6FFFE-6FFFF,
U+7FFFE-7FFFF, U+8FFFE-8FFFF, U+9FFFE-9FFFF, U+AFFFE-AFFFF,
U+BFFFE-BFFFF, U+CFFFE-CFFFF, U+DFFFE-DFFFF, U+EFFFE-EFFFF,
U+FFFFE-FFFFF, U+10FFFE-10FFFF): These code points are defined as
non-characters. Applications may use some of them internally, but
are not prepared to interchange them.
For reference, we here also list the code points and code units not
even allowed in Legacy Extended IRIs:
Surrogate code units (D800-DFFF): These do not represent Unicode
codepoints.
Non-characters (U+FFFE-FFFF): These are not allowed in XML nor
LEIRIs.
7. Processing of URIs/IRIs/URLs by Web Browsers
For legacy reasons, many web browsers exhibit some irregularities
when processing URIs, IRIs, and URLs. This is being documented in
[HTMLURL], in the hope that it will lead to more uniform
implementations of these irregularities across web browsers.
As far as currently known, creators of content for web browsers (such
as HTML) can use all URIs without problems. They can also use all
IRIs without problems except that they should be aware of the fact
that query parts for HTTP/HTTPS IRIs should be percent-escaped.
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8. URI/IRI Processing Guidelines (Informative)
This informative section provides guidelines for supporting IRIs in
the same software components and operations that currently process
URIs: Software interfaces that handle URIs, software that allows
users to enter URIs, software that creates or generates URIs,
software that displays URIs, formats and protocols that transport
URIs, and software that interprets URIs. These may all require
modification before functioning properly with IRIs. The
considerations in this section also apply to URI references and IRI
references.
8.1. URI/IRI Software Interfaces
Software interfaces that handle URIs, such as URI-handling APIs and
protocols transferring URIs, need interfaces and protocol elements
that are designed to carry IRIs.
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
is compatible with US-ASCII, is in accordance with the
recommendations of [RFC2277], and makes converting to URIs easy. In
any case, the API or protocol definition must clearly define the
character encoding to be used.
The transfer from URI-only to IRI-capable components requires no
mapping, although the conversion described in Section 4 above may be
performed. It is preferable not to perform this inverse conversion
unless it is certain this can be done correctly.
8.2. URI/IRI Entry
Some components allow users to enter URIs into the system by typing
or dictation, for example. This software must be updated to allow
for IRI entry.
A person viewing a visual presentation of an IRI (as a sequence of
glyphs, in some order, in some visual display) will 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 be a more
or less complicated process.
The process of IRI entry must ensure, as much as possible, that the
restrictions defined in Section 2.2 are met. This may be done by
choosing appropriate input methods or variants/settings thereof, by
appropriately converting the characters being input, by eliminating
characters that cannot be converted, and/or by issuing a warning or
error message to the user.
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As an example of variant settings, input method editors for East
Asian Languages usually allow the input of Latin letters and related
characters in full-width or half-width versions. For IRI input, the
input method editor should be set so that it produces half-width
Latin letters and punctuation and full-width Katakana.
An input field primarily or solely used for the input of URIs/IRIs
might allow the user to view an IRI as it is mapped to a URI. Places
where the input of IRIs is frequent may provide the possibility for
viewing an IRI as mapped to a URI. This will help users when some of
the software they use does not yet accept IRIs.
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
components.
For the input of IRIs with right-to-left characters, please see
[Bidi].
8.3. URI/IRI Transfer between Applications
Many applications (for example, mail user agents) try to detect URIs
appearing in plain text. For this, they use some heuristics based on
URI syntax. They then allow the user to click on such URIs and
retrieve the corresponding resource in an appropriate (usually
scheme-dependent) application.
Such applications would need to be upgraded, in order to use the IRI
syntax as a base for heuristics. In particular, a non-ASCII
character should not be taken as the indication of the end of an IRI.
Such applications also would need to make sure that they correctly
convert the detected IRI from the character encoding of the document
or application where the IRI appears, to the character encoding used
by the system-wide IRI invocation mechanism, or to a URI (according
to Section 3.6) if the system-wide invocation mechanism only accepts
URIs.
The clipboard is another frequently used way to transfer URIs and
IRIs from one application to another. On most platforms, the
clipboard is able to store and transfer text in many languages and
scripts. Correctly used, the clipboard transfers characters, not
octets, which will do the right thing with IRIs.
8.4. URI/IRI Generation
Systems that offer resources through the Internet, where those
resources have logical names, sometimes automatically generate URIs
for the resources they offer. For example, some HTTP servers can
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generate a directory listing for a file directory and then respond to
the generated URIs with the files.
Many legacy character encodings are in use in various file systems.
Many currently deployed systems do not transform the local character
representation of the underlying system before generating URIs.
For maximum interoperability, systems that generate resource
identifiers should make the appropriate transformations. For
example, if a file system contains a file named "résum&#
xE9;.html", a server should expose this as "r%C3%A9sum%C3%A9.html" in
a URI, which allows use of "résumé.html" in an IRI, even if
locally the file name is kept in a character encoding other than
UTF-8.
This recommendation particularly applies to HTTP servers. For FTP
servers, similar considerations apply; see [RFC2640].
8.5. URI/IRI Selection
In some cases, resource owners and publishers have control over the
IRIs used to identify their resources. This control is mostly
executed by controlling the resource names, such as file names,
directly.
In these cases, it is recommended to avoid choosing IRIs that are
easily confused. For example, for US-ASCII, the lower-case ell ("l")
is easily confused with the digit one ("1"), and the upper-case oh
("O") is easily confused with the digit zero ("0"). Publishers
should avoid confusing users with "br0ken" or "1ame" identifiers.
Outside the US-ASCII repertoire, there are many more opportunities
for confusion; a complete set of guidelines is too lengthy to include
here. As long as names are limited to characters from a single
script, native writers of a given script or language will know best
when ambiguities can appear, and how they can be avoided. What may
look ambiguous to a stranger may be completely obvious to the average
native user. On the other hand, in some cases, the UCS contains
variants for compatibility reasons; for example, for typographic
purposes. These should be avoided wherever possible. Although there
may be exceptions, newly created resource names should generally be
in NFKC [UTR15] (which means that they are also in NFC).
As an example, the UCS contains the "fi" ligature at U+FB01 for
compatibility reasons. Wherever possible, IRIs should use the two
letters "f" and "i" rather than the "fi" ligature. An example where
the latter may be used is in the query part of an IRI for an explicit
search for a word written containing the "fi" ligature.
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In certain cases, there is a chance that characters from different
scripts look the same. The best known example is the similarity of
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
single component are used together in a given language. This usually
means that all of these characters will be from the same script, but
there are languages that mix characters from different scripts (such
as Japanese). This is similar to the heuristics used to distinguish
between letters and numbers in the examples above. Also, for Latin,
Greek, and Cyrillic, using lowercase letters results in fewer
ambiguities than using uppercase letters would.
8.6. Display of URIs/IRIs
In situations where the rendering software is not expected to display
non-ASCII parts of the IRI correctly using the available layout and
font resources, these parts should be percent-encoded before being
displayed.
For display of Bidi IRIs, please see [Bidi].
8.7. Interpretation of URIs and IRIs
Software that interprets IRIs as the names of local resources should
accept IRIs in multiple forms and convert and match them with the
appropriate local resource names.
First, multiple representations include both IRIs in the native
character encoding of the protocol and also their URI counterparts.
Second, it may include URIs constructed based on character encodings
other than UTF-8. These URIs may be produced by user agents that do
not conform to this specification and that use legacy character
encodings to convert non-ASCII characters to URIs. Whether this is
necessary, and what character encodings to cover, depends on a number
of factors, such as the legacy character encodings used locally and
the distribution of various versions of user agents. For example,
software for Japanese may accept URIs in Shift_JIS and/or EUC-JP in
addition to UTF-8.
Third, it may include additional mappings to be more user-friendly
and robust against transmission errors. These would be similar to
how some servers currently treat URIs as case insensitive or perform
additional matching to account for spelling errors. For characters
beyond the US-ASCII repertoire, this may, for example, include
ignoring the accents on received IRIs or resource names. Please note
that such mappings, including case mappings, are language dependent.
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It can be difficult to identify a resource unambiguously if too many
mappings are taken into consideration. However, percent-encoded and
not percent-encoded parts of IRIs can always be clearly
distinguished. Also, the regularity of UTF-8 (see [Duerst97]) makes
the potential for collisions lower than it may seem at first.
8.8. Upgrading Strategy
Where this recommendation places further constraints on software for
which many instances are already deployed, it is important to
introduce upgrades carefully and to be aware of the various
interdependencies.
If IRIs cannot be interpreted correctly, they should not be created,
generated, or transported. This suggests that upgrading URI
interpreting software to accept IRIs should have highest priority.
On the other hand, a single IRI is interpreted only by a single or
very few interpreters that are known in advance, although it may be
entered and transported very widely.
Therefore, IRIs benefit most from a broad upgrade of software to be
able to enter and transport IRIs. However, before an individual IRI
is published, care should be taken to upgrade the corresponding
interpreting software in order to cover the forms expected to be
received by various versions of entry and transport software.
The upgrade of generating software to generate IRIs instead of using
a local character encoding should happen only after the service is
upgraded to accept IRIs. Similarly, IRIs should only be generated
when the service accepts IRIs and the intervening infrastructure and
protocol is known to transport them safely.
Software converting from URIs to IRIs for display should be upgraded
only after upgraded entry software has been widely deployed to the
population that will see the displayed result.
Where there is a free choice of character encodings, it is often
possible to reduce the effort and dependencies for upgrading to IRIs
by using UTF-8 rather than another encoding. For example, when a new
file-based Web server is set up, using UTF-8 as the character
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
encoding of the form page, the returned query URIs will use UTF-8 as
the character encoding (unless the user, for whatever reason, changes
the character encoding) and will therefore be compatible with IRIs.
These recommendations, when taken together, will allow for the
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extension from URIs to IRIs in order to handle characters other than
US-ASCII while minimizing interoperability problems. For
considerations regarding the upgrade of URI scheme definitions, see
Section 5.4.
9. IANA Considerations
This specification does not affect IANA. For details on how to
define a URI/IRI scheme and register it with IANA, see [RFC4395bis].
10. Security Considerations
The security considerations discussed in [RFC3986] also apply to
IRIs. In addition, the following issues require particular care for
IRIs.
Incorrect encoding or decoding can lead to security problems. For
example, some UTF-8 decoders do not check against overlong byte
sequences. See [UTR36] Section 3 for details.
There are serious difficulties with relying on a human to verify that
a an IRI (whether presented visually or aurally) is the same as
another IRI or is the one intended. These problems exist with ASCII-
only URIs (bl00mberg.com vs. bloomberg.com) but are strongly
exacerbated when using the much larger character repertoire of
Unicode. For details, see Section 2 of [UTR36]. Using
administrative and technical means to reduce the availability of such
exploits is possible, but they are difficult to eliminate altogether.
User agents SHOULD NOT rely on visual or perceptual comparison or
verification of IRIs as a means of validating or assuring safety,
correctness or appropriateness of an IRI. Other means of presenting
users with the validity, safety, or appropriateness of visited sites
are being developed in the browser community as an alternative means
of avoiding these difficulties.
Besides the large character repertoire of Unicode, reasons for
confusion include different forms of normalization and different
normalization expectations, use of percent-encoding with various
legacy encodings, and bidirectionality issues. See also [Bidi].
Confusion can occur in various IRI components, such as the domain
name part or the path part, or between IRI components. For
considerations specific to the domain name part, see [RFC5890]. For
considerations specific to particular protocols or schemes, see the
security sections of the relevant specifications and registration
templates. Administrators of sites that allow independent users to
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create resources in the same sub area have to be careful. Details
are discussed in Section 8.5.
The characters additionally allowed in Legacy Extended IRIs introduce
additional security issues. For details, see Section 6.3.
11. Acknowledgements
This document was derived from [RFC3987]; the acknowledgments from
that specification still apply.
In addition, this document was influenced by contributions from (in
no particular order) Norman Walsh, Richard Tobin, Henry S. Thomson,
John Cowan, Paul Grosso, the XML Core Working Group of the W3C, Chris
Lilley, Bjoern Hoehrmann, Felix Sasaki, Jeremy Carroll, Frank
Ellermann, Michael Everson, Cary Karp, Matitiahu Allouche, Richard
Ishida, Addison Phillips, Jonathan Rosenne, Najib Tounsi, Debbie
Garside, Mark Davis, Sarmad Hussain, Ted Hardie, Konrad Lanz, Thomas
Roessler, Lisa Dusseault, Julian Reschke, Giovanni Campagna, Anne van
Kesteren, Mark Nottingham, Erik van der Poel, Marcin Hanclik, Marcos
Caceres, Roy Fielding, Greg Wilkins, Pieter Hintjens, Daniel R.
Tobias, Marko Martin, Maciej Stanchowiak, Wil Tan, Yui Naruse,
Michael A. Puls II, Dave Thaler, Tom Petch, John Klensin, Shawn
Steele, Peter Saint-Andre, Geoffrey Sneddon, Chris Weber, Alex
Melnikov, Slim Amamou, S. Moonesamy, Tim Berners-Lee, Yaron Goland,
Sam Ruby, Adam Barth, Abdulrahman I. ALGhadir, Aharon Lanin, Thomas
Milo, Murray Sargent, Marc Blanchet, and Mykyta Yevstifeyev.
Anne van Kesteren is also gratefully acknowledged for his ongoing
work documenting browser behavior with respect to URIs/URIs/URLs (see
[HTMLURL]).
12. Main Changes Since RFC 3987
This section describes the main changes since [RFC3987].
12.1. Split out Bidi, processing guidelines, comparison sections
Move some components (comparison, bidi, processing) into separate
documents.
12.2. Major restructuring of IRI processing model
Major restructuring of IRI processing model to make scheme-specific
translation necessary to handle IDNA requirements and for consistency
with web implementations.
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Starting with IRI, you want one of:
a IRI components (IRI parsed into UTF8 pieces)
b URI components (URI parsed into ASCII pieces, encoded correctly)
c whole URI (for passing on to some other system that wants whole
URIs)
12.2.1. OLD WAY
1. Percent-encoding on the whole thing to a URI. (c1) If you want a
(maybe broken) whole URI, you might stop here.
2. Parsing the URI into URI components. (b1) If you want (maybe
broken) URI components, stop here.
3. Decode the components (undoing the percent-encoding). (a) if you
want IRI components, stop here.
4. reencode: Either using a different encoding some components (for
domain names, and query components in web pages, which depends on
the component, scheme and context), and otherwise using percent-
encoding. (b2) if you want (good) URI components, stop here.
5. reassemble the reencoded components. (c2) if you want a (*good*)
whole URI stop here.
12.2.2. NEW WAY
1. Parse the IRI into IRI components using the generic syntax. (a)
if you want IRI components, stop here.
2. Encode each components, using percent-encoding, IDN encoding, or
special query part encoding depending on the component scheme or
context. (b) If you want URI components, stop here.
3. reassemble the a whole URI from URI components. (c) if you want a
whole URI stop here.
12.2.3. Extension of Syntax
Added the tag range (U+E0000-E0FFF) to the iprivate production. Some
IRIs generated with the new syntax may fail to pass very strict
checks relying on the old syntax. But characters in this range
should be extremely infrequent anyway.
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12.2.4. More to be added
TODO: There are more main changes that need to be documented in this
section.
12.3. Change Log
Note to RFC Editor: Please completely remove this section before
publication.
12.3.1. Changes after draft-ietf-iri-3987bis-01
Changes from draft-ietf-iri-3987bis-01 onwards are available as
changesets in the IETF tools subversion repository at http://
trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis/
draft-ietf-iri-3987bis.xml.
12.3.2. Changes from draft-duerst-iri-bis-07 to
draft-ietf-iri-3987bis-00
Changed draft name, date, last paragraph of abstract, and titles in
change log, and added this section in moving from
draft-duerst-iri-bis-07 (personal submission) to
draft-ietf-iri-3987bis-00 (WG document).
12.3.3. Changes from -06 to -07 of draft-duerst-iri-bis
Major restructuring of the processing model, see Section 12.2.
12.4. Changes from -00 to -01
o Removed 'mailto:' before mail addresses of authors.
o Added "<to be done>" as right side of 'href-strip' rule. Fixed
'|' to '/' for alternatives.
12.5. Changes from -05 to -06 of draft-duerst-iri-bis-00
o Add HyperText Reference, change abstract, acks and references for
it
o Add Masinter back as another editor.
o Masinter integrates HRef material from HTML5 spec.
o Rewrite introduction sections to modernize.
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12.6. Changes from -04 to -05 of draft-duerst-iri-bis
o Updated references.
o Changed IPR text to pre5378Trust200902.
12.7. Changes from -03 to -04 of draft-duerst-iri-bis
o Added explicit abbreviation for LEIRIs.
o Mentioned LEIRI references.
o Completed text in LEIRI section about tag characters and about
specials.
12.8. Changes from -02 to -03 of draft-duerst-iri-bis
o Updated some references.
o Updated Michel Suginard's coordinates.
12.9. Changes from -01 to -02 of draft-duerst-iri-bis
o Added tag range to iprivate (issue private-include-tags-115).
o Added Specials (U+FFF0-FFFD) to Legacy Extended IRIs.
12.10. Changes from -00 to -01 of draft-duerst-iri-bis
o Changed from "IRIs with Spaces/Controls" to "Legacy Extended IRI"
based on input from the W3C XML Core WG. Moved the relevant
subsections to the back and promoted them to a section.
o Added some text re. Legacy Extended IRIs to the security section.
o Added a IANA Consideration Section.
o Added this Change Log Section.
o Added a section about "IRIs with Spaces/Controls" (converting from
a Note in RFC 3987).
12.11. Changes from RFC 3987 to -00 of draft-duerst-iri-bis
Fixed errata (see
http://www.rfc-editor.org/cgi-bin/errataSearch.pl?rfc=3987).
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13. References
13.1. Normative References
[ASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
[ISO10646]
International Organization for Standardization, "ISO/IEC
10646:2011: Information Technology - Universal Multiple-
Octet Coded Character Set (UCS)", ISO Standard 10646,
March 20011, <http://standards.iso.org/ittf/
PubliclyAvailableStandards/
c051273_ISO_IEC_10646_2011(E).zip>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names (IDN)",
RFC 3491, March 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891, August 2010.
[RFC5892] Faltstrom, P., "The Unicode Code Points and
Internationalized Domain Names for Applications (IDNA)",
RFC 5892, August 2010.
[STD63] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[STD68] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[UNIV6] The Unicode Consortium, "The Unicode Standard, Version
6.2.0 (Mountain View, CA, The Unicode Consortium, 2012,
ISBN 978-1-936213-07-8)", October 2012.
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[UTR15] Davis, M. and M. Duerst, "Unicode Normalization Forms",
Unicode Standard Annex #15, March 2008,
<http://www.unicode.org/unicode/reports/tr15/
tr15-23.html>.
13.2. Informative References
[Bidi] Duerst, M., Masinter, L., and A. Allawi, "Guidelines for
Internationalized Resource Identifiers with Bi-directional
Characters (Bidi IRIs)", draft-ietf-iri-bidi-guidelines-02
(work in progress), March 2012.
[CharMod] Duerst, M., Yergeau, F., Ishida, R., Wolf, M., and T.
Texin, "Character Model for the World Wide Web 1.0:
Resource Identifiers", W3C Candidate Recommendation CR-
charmod-resid-20041122, November 2004,
<http://www.w3.org/TR/2004/CR-charmod-resid/>.
[Duerst97]
Duerst, M., "The Properties and Promises of UTF-8", Proc.
11th International Unicode Conference, San Jose ,
September 1997,
<http://www.sw.it.aoyama.ac.jp/2012/pub/IUC11-UTF-8.pdf>.
[Equivalence]
Masinter, L. and M. Duerst, "Equivalence and
Canonicalization of Internationalized Resource Identifiers
(IRIs)", draft-ietf-iri-comparison-01 (work in progress),
March 2012.
[Gettys] Gettys, J., "URI Model Consequences",
<http://www.w3.org/DesignIssues/ModelConsequences>.
[HTML4] Raggett, D., Le Hors, A., and I. Jacobs, "HTML 4.01
Specification", W3C Recommendation REC-html401-19991224,
December 1999, <http://www.w3.org/TR/1999/REC-html401>.
[HTMLURL] van Kesteren, A., "URL", October 2012,
<http://url.spec.whatwg.org/>.
[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.
[RFC2192] Newman, C., "IMAP URL Scheme", RFC 2192, September 1997.
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.
[RFC2384] Gellens, R., "POP URL Scheme", RFC 2384, August 1998.
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[RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[RFC2397] Masinter, L., "The "data" URL scheme", RFC 2397,
August 1998.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2640] Curtin, B., "Internationalization of the File Transfer
Protocol", RFC 2640, July 1999.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[RFC4395bis]
Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
Registration Procedures for New URI/IRI Schemes",
draft-ietf-iri-4395bis-irireg-04 (work in progress),
December 2011.
[RFC5122] Saint-Andre, P., "Internationalized Resource Identifiers
(IRIs) and Uniform Resource Identifiers (URIs) for the
Extensible Messaging and Presence Protocol (XMPP)",
RFC 5122, February 2008.
[RFC6055] Thaler, D., Klensin, J., and S. Cheshire, "IAB Thoughts on
Encodings for Internationalized Domain Names", RFC 6055,
February 2011.
[RFC6068] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto'
URI Scheme", RFC 6068, October 2010.
[RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in
Internationalization in the IETF", BCP 166, RFC 6365,
September 2011.
[UNIXML] Duerst, M. and A. Freytag, "Unicode in XML and other
Markup Languages", Unicode Technical Report #20, World
Wide Web Consortium Note, June 2003,
<http://www.w3.org/TR/unicode-xml/>.
[UTR36] Davis, M. and M. Suignard, "Unicode Security
Considerations", Unicode Technical Report #36,
August 2010, <http://unicode.org/reports/tr36/>.
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[XLink] DeRose, S., Maler, E., Orchard, D., and N. Walsh, "XML
Linking Language (XLink) Version 1.1", W3C
Recommendation REC-xlink11-20100506, May 2010,
<http://www.w3.org/TR/xlink11/#link-locators>.
[XML1] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", W3C Recommendation REC-xml-20081126,
November 2008, <http://www.w3.org/TR/2008/REC-xml/>.
[XMLSchema]
Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes
Second Edition", W3C Recommendation REC-xmlschema-2-
20041028, October 2004,
<http://www.w3.org/TR/xmlschema-2/#anyURI>.
[XPointer]
Grosso, P., Maler, E., Marsh, J., and N. Walsh, "XPointer
Framework", W3C Recommendation REC-xptr-framework-
20030325, March 2003,
<http://www.w3.org/TR/xptr-framework/#escaping>.
Authors' Addresses
Martin J. Duerst (Note: Please write "Duerst" with u-umlaut wherever
possible, for example as "Dürst" in XML and HTML.)
Aoyama Gakuin University
5-10-1 Fuchinobe
Chuo-ku
Sagamihara, Kanagawa 252-5258
Japan
Phone: +81 42 759 6329
Fax: +81 42 759 6495
Email: duerst@it.aoyama.ac.jp
URI: http://www.sw.it.aoyama.ac.jp/D%C3%BCrst/
(Note: This is the percent-encoded form of an IRI)
Michel Suignard
Unicode Consortium
P.O. Box 391476
Mountain View, CA 94039-1476
U.S.A.
Phone: +1-650-693-3921
Email: michel@unicode.org
URI: http://www.suignard.com
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Larry Masinter
Adobe
345 Park Ave
San Jose, CA 95110
U.S.A.
Phone: +1-408-536-3024
Email: masinter@adobe.com
URI: http://larry.masinter.net
Duerst, et al. Expires April 23, 2013 [Page 40]
