source: draft-ietf-iri-3987bis/draft-ietf-iri-3987bis.xml @ 82

Last change on this file since 82 was 82, checked in by duerst@…, 8 years ago

edits to address issue #5, plus some other minor edits

  • Property svn:executable set to *
File size: 86.7 KB
[20]1<?xml version="1.0"?>
2<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
3<!ENTITY rfc2045 SYSTEM "">
4<!ENTITY rfc2119 SYSTEM "">
5<!ENTITY rfc2130 SYSTEM "">
6<!ENTITY rfc2141 SYSTEM "">
7<!ENTITY rfc2192 SYSTEM "">
8<!ENTITY rfc2277 SYSTEM "">
9<!ENTITY rfc2368 SYSTEM "">
10<!ENTITY rfc2384 SYSTEM "">
11<!ENTITY rfc2396 SYSTEM "">
12<!ENTITY rfc2397 SYSTEM "">
13<!ENTITY rfc2616 SYSTEM "">
14<!ENTITY rfc2640 SYSTEM "">
15<!ENTITY rfc3491 SYSTEM "">
16<!ENTITY rfc3629 SYSTEM "">
17<!ENTITY rfc3986 SYSTEM "">
[29]18<!ENTITY rfc3987 SYSTEM "">
[20]19<!ENTITY rfc5890 SYSTEM "">
20<!ENTITY rfc5891 SYSTEM "">
[64]21<!ENTITY rfc6055 SYSTEM "">
[72]22<!ENTITY rfc6082 SYSTEM "">
24<?rfc strict='yes'?>
[20]26<?xml-stylesheet type='text/css' href='rfc2629.css' ?>
27<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
28<?rfc symrefs='yes'?>
29<?rfc sortrefs='yes'?>
30<?rfc iprnotified="no" ?>
31<?rfc toc='yes'?>
32<?rfc compact='yes'?>
33<?rfc subcompact='no'?>
[82]34<rfc ipr="pre5378Trust200902" docName="draft-ietf-iri-3987bis-09" category="std" xml:lang="en" obsoletes="3987">
36<title abbrev="IRIs">Internationalized Resource Identifiers (IRIs)</title>
38  <author initials="M.J." surname="Duerst" fullname='Martin Duerst'>
39    <!-- (Note: Please write "Duerst" with u-umlaut wherever
[21]40      possible, for example as "D&#252;rst" in XML and HTML) -->
[20]41  <organization abbrev="Aoyama Gakuin University">Aoyama Gakuin University</organization>
42  <address>
43  <postal>
44  <street>5-10-1 Fuchinobe</street>
45  <city>Sagamihara</city>
46  <region>Kanagawa</region>
47  <code>229-8558</code>
48  <country>Japan</country>
49  </postal>
50  <phone>+81 42 759 6329</phone>
51  <facsimile>+81 42 759 6495</facsimile>
52  <email></email>
53  <uri><!-- (Note: This is the percent-encoded form of an IRI)--></uri>
54  </address>
57<author initials="M.L." surname="Suignard" fullname="Michel Suignard">
58   <organization>Unicode Consortium</organization>
59   <address>
60   <postal>
61   <street></street>
62   <street>P.O. Box 391476</street>
63   <city>Mountain View</city>
64   <region>CA</region>
65   <code>94039-1476</code>
66   <country>U.S.A.</country>
67   </postal>
68   <phone>+1-650-693-3921</phone>
69   <email></email>
70   <uri></uri>
71   </address>
73<author initials="L." surname="Masinter" fullname="Larry Masinter">
74   <organization>Adobe</organization>
75   <address>
76   <postal>
77   <street>345 Park Ave</street>
78   <city>San Jose</city>
79   <region>CA</region>
80   <code>95110</code>
81   <country>U.S.A.</country>
82   </postal>
83   <phone>+1-408-536-3024</phone>
84   <email></email>
85   <uri></uri>
86   </address>
[70]89<date year="2011" />
91<workgroup>Internationalized Resource Identifiers (iri)</workgroup>
93<keyword>Internationalized Resource Identifier</keyword>
100<t>This document defines the Internationalized Resource Identifier
101(IRI) protocol element, as an extension of the Uniform Resource
102Identifier (URI).  An IRI is a sequence of characters from the
103Universal Character Set (Unicode/ISO 10646). Grammar and processing
104rules are given for IRIs and related syntactic forms.</t>
106<t>Defining IRI as new protocol element (rather than updating or
107extending the definition of URI) allows independent orderly
108transitions: other protocols and languages that use URIs must
109explicitly choose to allow IRIs.</t>
111<t>Guidelines are provided for the use and deployment of IRIs and
112related protocol elements when revising protocols, formats, and
113software components that currently deal only with URIs.</t>
[82]115<t>This document is part of a set of documents intended to
116replace RFC 3987.</t>
119  <note title='RFC Editor: Please remove the next paragraph before publication.'>
[71]120    <t>This (and several companion documents) are intended to obsolete RFC 3987,
121    and also move towards IETF Draft Standard.  For discussion and comments on these
122    drafts, please join the IETF IRI WG by subscribing to the mailing
123    list, archives at
124    For a list of open issues, please see
[40]125    the issue tracker of the WG at
126    For a list of individual edits, please see the change history at
132<section title="Introduction">
134<section title="Overview and Motivation" anchor="overview">
136<t>A Uniform Resource Identifier (URI) is defined in <xref
137target="RFC3986"/> as a sequence of characters chosen from a limited
138subset of the repertoire of US-ASCII <xref target="ASCII"/>
141<t>The characters in URIs are frequently used for representing words
142of natural languages.  This usage has many advantages: Such URIs are
143easier to memorize, easier to interpret, easier to transcribe, easier
144to create, and easier to guess. For most languages other than English,
145however, the natural script uses characters other than A - Z. For many
146people, handling Latin characters is as difficult as handling the
147characters of other scripts is for those who use only the Latin
148alphabet. Many languages with non-Latin scripts are transcribed with
149Latin letters. These transcriptions are now often used in URIs, but
150they introduce additional difficulties.</t>
152<t>The infrastructure for the appropriate handling of characters from
153additional scripts is now widely deployed in operating system and
154application software. Software that can handle a wide variety of
155scripts and languages at the same time is increasingly common. Also,
156an increasing number of protocols and formats can carry a wide range of
[82]159<t>URIs are composed out of a very limited repertoire of characters;
160this design choice was made to support global transcription(<xref
161target="RFC3986"/> section 1.2.1.).  Reliable transition between a URI
162(as an abstract protocol element composed of a sequence of characters)
163and a presentation of that URI (written on a napkin, read out loud)
164and back is relatively straightforward, because of the limited
165repertoire of characters used.  IRIs are designed to satisfy a
166different set of use requirements; in particular, to allow IRIs to be
167written in ways that are more meaningful to their users, even at the
168expense of global transcribability. However, ensuring reliability of
169the transition between an IRI and its presentation and back is more
170difficult and complex when dealing with the larger set of Unicode
171characters.  For example, Unicode supports multiple ways of encoding
172complex combinations of characters and accents, with multiple
173character sequences that can result in the same presentation.</t>
175<t>This document defines the protocol element called Internationalized
176Resource Identifier (IRI), which allow applications of URIs to be
177extended to use resource identifiers that have a much wider repertoire
178of characters. It also provides corresponding "internationalized"
179versions of other constructs from <xref target="RFC3986"/>, such as
180URI references. The syntax of IRIs is defined in <xref
[82]184<t>Within this document,
185               <xref target="IRIuse"/> discusses the use
[20]186of IRIs in different situations.  <xref target="guidelines"/> gives
187additional informative guidelines.  <xref target="security"/>
188discusses IRI-specific security considerations.</t>
[82]190<t>This specification is part of a collection of specifications
191intended to replace <xref target="RFC3987"/>.
[71]192<xref target="Bidi"/> discusses the special case of
193bidirectional IRIs using characters from scripts written
195<xref target="Equivalence"/> gives guidelines for applications wishing
196to determine if two IRIs are equivalent, as well as defining
197some equivalence methods.
198<xref target="RFC4395bis"/> updates the URI scheme registration
[82]199guidelines and procedures to note that every URI scheme is also
[71]200automatically an IRI scheme and to allow scheme definitions
201to be directly described in terms of Unicode characters.
[20]204</section> <!-- overview -->
206<section title="Applicability" anchor="Applicability">
208<t>IRIs are designed to allow protocols and software that deal with
[71]209URIs to be updated to handle IRIs. Processing of
[20]210IRIs is accomplished by extending the URI syntax while retaining (and
211not expanding) the set of "reserved" characters, such that the syntax
[70]212for any URI scheme may be extended to allow non-ASCII
[20]213characters. In addition, following parsing of an IRI, it is possible
214to construct a corresponding URI by first encoding characters outside
215of the allowed URI range and then reassembling the components.
218<t>Practical use of IRIs forms in place of URIs forms depends on the
219following conditions being met:</t>
221<t><list style="hanging">
223<t hangText="a.">A protocol or format element MUST be explicitly designated to be
224  able to carry IRIs. The intent is to avoid introducing IRIs into
225  contexts that are not defined to accept them.  For example, XML
226  schema <xref target="XMLSchema"/> has an explicit type "anyURI" that
227  includes IRIs and IRI references. Therefore, IRIs and IRI references
228  can be in attributes and elements of type "anyURI".  On the other
229  hand, in the <xref target="RFC2616"/> definition of HTTP/1.1, the
230  Request URI is defined as a URI, which means that direct use of IRIs
231  is not allowed in HTTP requests.</t>
233<t hangText="b.">The protocol or format carrying the IRIs MUST have a
234  mechanism to represent the wide range of characters used in IRIs,
235  either natively or by some protocol- or format-specific escaping
236  mechanism (for example, numeric character references in <xref
237  target="XML1"/>).</t>
239<t hangText="c.">The URI scheme definition, if it explicitly allows a
240  percent sign ("%") in any syntactic component, SHOULD define the
241  interpretation of sequences of percent-encoded octets (using "%XX"
242  hex octets) as octet from sequences of UTF-8 encoded strings; this
243  is recommended in the guidelines for registering new schemes, <xref
[24]244  target="RFC4395bis"/>.  For example, this is the practice for IMAP URLs
[20]245  <xref target="RFC2192"/>, POP URLs <xref target="RFC2384"/> and the
246  URN syntax <xref target="RFC2141"/>). Note that use of
247  percent-encoding may also be restricted in some situations, for
248  example, URI schemes that disallow percent-encoding might still be
249  used with a fragment identifier which is percent-encoded (e.g.,
250  <xref target="XPointer"/>). See <xref target="UTF8use"/> for further
251  discussion.</t>
254</section> <!-- applicability -->
256<section title="Definitions" anchor="sec-Definitions">
258<t>The following definitions are used in this document; they follow the
259terms in <xref target="RFC2130"/>, <xref target="RFC2277"/>, and
260<xref target="ISO10646"/>.</t>
261<t><list style="hanging">
263<t hangText="character:">A member of a set of elements used for the
264    organization, control, or representation of data. For example,
265    "LATIN CAPITAL LETTER A" names a character.</t>
267<t hangText="octet:">An ordered sequence of eight bits considered as a
268    unit.</t>
270<t hangText="character repertoire:">A set of characters (set in the
271    mathematical sense).</t>
273<t hangText="sequence of characters:">A sequence of characters (one
274    after another).</t>
276<t hangText="sequence of octets:">A sequence of octets (one after
277    another).</t>
279<t hangText="character encoding:">A method of representing a sequence
280    of characters as a sequence of octets (maybe with variants). Also,
281    a method of (unambiguously) converting a sequence of octets into a
282    sequence of characters.</t>
284<t hangText="charset:">The name of a parameter or attribute used to
285    identify a character encoding.</t>
287<t hangText="UCS:">Universal Character Set. The coded character set
288    defined by ISO/IEC 10646 <xref target="ISO10646"/> and the Unicode
[30]289    Standard <xref target="UNIV6"/>.</t>
291<t hangText="IRI reference:">Denotes the common usage of an
292    Internationalized Resource Identifier. An IRI reference may be
293    absolute or relative.  However, the "IRI" that results from such a
294    reference only includes absolute IRIs; any relative IRI references
295    are resolved to their absolute form.  Note that in <xref
296    target="RFC2396"/> URIs did not include fragment identifiers, but
297    in <xref target="RFC3986"/> fragment identifiers are part of
298    URIs.</t>
300<t hangText="LEIRI (Legacy Extended IRI) processing:">  This term was used in
301   various XML specifications to refer
302   to strings that, although not valid IRIs, were acceptable input to
303   the processing rules in <xref target="LEIRIspec" />.</t>
305<t hangText="running text:">Human text (paragraphs, sentences,
306   phrases) with syntax according to orthographic conventions of a
307   natural language, as opposed to syntax defined for ease of
308   processing by machines (e.g., markup, programming languages).</t>
310<t hangText="protocol element:">Any portion of a message that affects
311    processing of that message by the protocol in question.</t>
313<t hangText="create (a URI or IRI):">With respect to URIs and IRIs,
314     the term is used for the initial creation. This may be the
315     initial creation of a resource with a certain identifier, or the
316     initial exposition of a resource under a particular
317     identifier.</t>
319<t hangText="generate (a URI or IRI):">With respect to URIs and IRIs,
320     the term is used when the identifier is generated by derivation
321     from other information.</t>
323<t hangText="parsed URI component:">When a URI processor parses a URI
324   (following the generic syntax or a scheme-specific syntax, the result
325   is a set of parsed URI components, each of which has a type
326   (corresponding to the syntactic definition) and a sequence of URI
327   characters.  </t>
329<t hangText="parsed IRI component:">When an IRI processor parses
330   an IRI directly, following the general syntax or a scheme-specific
331   syntax, the result is a set of parsed IRI components, each of
332   which has a type (corresponding to the syntactice definition)
333   and a sequence of IRI characters. (This definition is analogous
334   to "parsed URI component".)</t>
336<t hangText="IRI scheme:">A URI scheme may also be known as
337   an "IRI scheme" if the scheme's syntax has been extended to
338   allow non-US-ASCII characters according to the rules in this
339   document.</t>
342</section> <!-- definitions -->
343<section title="Notation" anchor="sec-Notation">
345<t>RFCs and Internet Drafts currently do not allow any characters
346outside the US-ASCII repertoire. Therefore, this document uses various
347special notations to denote such characters in examples.</t>
349<t>In text, characters outside US-ASCII are sometimes referenced by
350using a prefix of 'U+', followed by four to six hexadecimal
353<t>To represent characters outside US-ASCII in examples, this document
[71]354uses 'XML Notation'.</t>
356<t>XML Notation uses a leading '&amp;#x', a trailing ';', and the
357hexadecimal number of the character in the UCS in between. For
358example, &amp;#x44F; stands for CYRILLIC CAPITAL LETTER YA. In this
359notation, an actual '&amp;' is denoted by '&amp;amp;'.</t>
361<t>To denote actual octets in examples (as opposed to percent-encoded
362octets), the two hex digits denoting the octet are enclosed in "&lt;"
363and "&gt;".  For example, the octet often denoted as 0xc9 is denoted
364here as &lt;c9&gt;.</t>
366<t> In this document, the key words "MUST", "MUST NOT", "REQUIRED",
368and "OPTIONAL" are to be interpreted as described in <xref
371</section> <!-- notation -->
372</section> <!-- introduction -->
374<section title="IRI Syntax" anchor="syntax">
375<t>This section defines the syntax of Internationalized Resource
376Identifiers (IRIs).</t>
378<t>As with URIs, an IRI is defined as a sequence of characters, not as
[82]379a sequence of octets.
380This definition accommodates the fact that IRIs
[20]381may be written on paper or read over the radio as well as stored or
382transmitted digitally.  The same IRI might be represented as different
383sequences of octets in different protocols or documents if these
384protocols or documents use different character encodings (and/or
385transfer encodings).  Using the same character encoding as the
386containing protocol or document ensures that the characters in the IRI
387can be handled (e.g., searched, converted, displayed) in the same way
388as the rest of the protocol or document.</t>
390<section title="Summary of IRI Syntax" anchor="summary">
[70]392<t>The IRI syntax extends the URI syntax in <xref
393target="RFC3986"/> by extending the class of unreserved characters,
394primarily by adding the characters of the UCS (Universal Character Set, <xref
[20]395target="ISO10646"/>) beyond U+007F, subject to the limitations given
396in the syntax rules below and in <xref target="limitations"/>.</t>
398<t>The syntax and use of components and reserved characters is the
399same as that in <xref target="RFC3986"/>. Each "URI scheme" thus also
400functions as an "IRI scheme", in that scheme-specific parsing rules
401for URIs of a scheme are be extended to allow parsing of IRIs using
402the same parsing rules.</t>
404<t>All the operations defined in <xref target="RFC3986"/>, such as the
405resolution of relative references, can be applied to IRIs by
406IRI-processing software in exactly the same way as they are for URIs
407by URI-processing software.</t>
409<t>Characters outside the US-ASCII repertoire MUST NOT be reserved and
410therefore MUST NOT be used for syntactical purposes, such as to
411delimit components in newly defined schemes. For example, U+00A2, CENT
412SIGN, is not allowed as a delimiter in IRIs, because it is in the
413'iunreserved' category. This is similar to the fact that it is not
414possible to use '-' as a delimiter in URIs, because it is in the
415'unreserved' category.</t>
417</section> <!-- summary -->
418<section title="ABNF for IRI References and IRIs" anchor="abnf">
420<t>An ABNF definition for IRI references (which are the most general
421concept and the start of the grammar) and IRIs is given here. The
422syntax of this ABNF is described in <xref target="STD68"/>. Character
423numbers are taken from the UCS, without implying any actual binary
424encoding. Terminals in the ABNF are characters, not octets.</t>
426<t>The following grammar closely follows the URI grammar in <xref
427target="RFC3986"/>, except that the range of unreserved characters is
428expanded to include UCS characters, with the restriction that private
429UCS characters can occur only in query parts. The grammar is split
430into two parts: Rules that differ from <xref target="RFC3986"/>
431because of the above-mentioned expansion, and rules that are the same
432as those in <xref target="RFC3986"/>. For rules that are different
433than those in <xref target="RFC3986"/>, the names of the non-terminals
434have been changed as follows. If the non-terminal contains 'URI', this
[41]435has been changed to 'IRI'. Otherwise, an 'i' has been prefixed.
436The rule &lt;pct-form> has been introduced in order to be able to reference it from other parts of
437the document.</t>
440for line length measuring in artwork (max 72 chars, three chars at start):
441      1         2         3         4         5         6         7
445<preamble>The following rules are different from those in <xref target="RFC3986"/>:</preamble>
447IRI            = scheme ":" ihier-part [ "?" iquery ]
448                 [ "#" ifragment ]
450ihier-part     = "//" iauthority ipath-abempty
451               / ipath-absolute
452               / ipath-rootless
453               / ipath-empty
455IRI-reference  = IRI / irelative-ref
457absolute-IRI   = scheme ":" ihier-part [ "?" iquery ]
459irelative-ref  = irelative-part [ "?" iquery ] [ "#" ifragment ]
461irelative-part = "//" iauthority ipath-abempty
462               / ipath-absolute
463               / ipath-noscheme
464               / ipath-empty
466iauthority     = [ iuserinfo "@" ] ihost [ ":" port ]
467iuserinfo      = *( iunreserved / pct-form / sub-delims / ":" )
468ihost          = IP-literal / IPv4address / ireg-name
470pct-form       = pct-encoded
472ireg-name      = *( iunreserved / sub-delims )
474ipath          = ipath-abempty   ; begins with "/" or is empty
475               / ipath-absolute  ; begins with "/" but not "//"
476               / ipath-noscheme  ; begins with a non-colon segment
477               / ipath-rootless  ; begins with a segment
478               / ipath-empty     ; zero characters
480ipath-abempty  = *( path-sep isegment )
481ipath-absolute = path-sep [ isegment-nz *( path-sep isegment ) ]
482ipath-noscheme = isegment-nz-nc *( path-sep isegment )
483ipath-rootless = isegment-nz *( path-sep isegment )
484ipath-empty    = 0&lt;ipchar&gt;
485path-sep       = "/"
487isegment       = *ipchar
488isegment-nz    = 1*ipchar
489isegment-nz-nc = 1*( iunreserved / pct-form / sub-delims
490                     / "@" )
[81]491               ; non-zero-length segment without any colon ":"
493ipchar         = iunreserved / pct-form / sub-delims / ":"
494               / "@"
496iquery         = *( ipchar / iprivate / "/" / "?" )
[55]498ifragment      = *( ipchar / "/" / "?" )
500iunreserved    = ALPHA / DIGIT / "-" / "." / "_" / "~" / ucschar
502ucschar        = %xA0-D7FF / %xF900-FDCF / %xFDF0-FFEF
503               / %x10000-1FFFD / %x20000-2FFFD / %x30000-3FFFD
504               / %x40000-4FFFD / %x50000-5FFFD / %x60000-6FFFD
505               / %x70000-7FFFD / %x80000-8FFFD / %x90000-9FFFD
506               / %xA0000-AFFFD / %xB0000-BFFFD / %xC0000-CFFFD
507               / %xD0000-DFFFD / %xE1000-EFFFD
509iprivate       = %xE000-F8FF / %xE0000-E0FFF / %xF0000-FFFFD
510               / %x100000-10FFFD
514<t>Some productions are ambiguous. The "first-match-wins" (a.k.a. "greedy")
515algorithm applies. For details, see <xref target="RFC3986"/>.</t>
518<preamble>The following rules are the same as those in <xref target="RFC3986"/>:</preamble>
520scheme         = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
522port           = *DIGIT
524IP-literal     = "[" ( IPv6address / IPvFuture  ) "]"
526IPvFuture      = "v" 1*HEXDIG "." 1*( unreserved / sub-delims / ":" )
528IPv6address    =                            6( h16 ":" ) ls32
529               /                       "::" 5( h16 ":" ) ls32
530               / [               h16 ] "::" 4( h16 ":" ) ls32
531               / [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
532               / [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
533               / [ *3( h16 ":" ) h16 ] "::"    h16 ":"   ls32
534               / [ *4( h16 ":" ) h16 ] "::"              ls32
535               / [ *5( h16 ":" ) h16 ] "::"              h16
536               / [ *6( h16 ":" ) h16 ] "::"
538h16            = 1*4HEXDIG
539ls32           = ( h16 ":" h16 ) / IPv4address
541IPv4address    = dec-octet "." dec-octet "." dec-octet "." dec-octet
543dec-octet      = DIGIT                 ; 0-9
544               / %x31-39 DIGIT         ; 10-99
545               / "1" 2DIGIT            ; 100-199
546               / "2" %x30-34 DIGIT     ; 200-249
547               / "25" %x30-35          ; 250-255
549pct-encoded    = "%" HEXDIG HEXDIG
551unreserved     = ALPHA / DIGIT / "-" / "." / "_" / "~"
552reserved       = gen-delims / sub-delims
553gen-delims     = ":" / "/" / "?" / "#" / "[" / "]" / "@"
554sub-delims     = "!" / "$" / "&amp;" / "'" / "(" / ")"
555               / "*" / "+" / "," / ";" / "="
558<t>This syntax does not support IPv6 scoped addressing zone identifiers.</t>
560</section> <!-- abnf -->
562</section> <!-- syntax -->
564<section title="Processing IRIs and related protocol elements" anchor="processing">
566<t>IRIs are meant to replace URIs in identifying resources within new
567versions of protocols, formats, and software components that use a
568UCS-based character repertoire.  Protocols and components may use and
569process IRIs directly. However, there are still numerous systems and
570protocols which only accept URIs or components of parsed URIs; that is,
571they only accept sequences of characters within the subset of US-ASCII
572characters allowed in URIs. </t>
574<t>This section defines specific processing steps for IRI consumers
575which establish the relationship between the string given and the
576interpreted derivatives. These
577processing steps apply to both IRIs and IRI references (i.e., absolute
578or relative forms); for IRIs, some steps are scheme specific. </t>
580<section title="Converting to UCS" anchor="ucsconv"> 
582<t>Input that is already in a Unicode form (i.e., a sequence of Unicode
583 characters or an octet-stream representing a Unicode-based character
584 encoding such as UTF-8 or UTF-16) should be left as is and not
[70]585 normalized or changed.</t>
[22]587  <t>An IRI or IRI reference is a sequence of characters from the UCS.
[82]588    For input from presentations (written on paper, read aloud)
589    or translation from other representations (a text stream using a legacy character
590    encoding), convert the input to Unicode.
[22]591    Note that some character encodings or transcriptions can be converted
592    to or represented by more than one sequence of Unicode characters.
[22]594    Ideally the resulting IRI would use a normalized form,
[70]595    such as Unicode Normalization Form C <xref target="UTR15"/>,
[22]596    since that ensures a stable, consistent representation
597    that is most likely to produce the intended results.
[82]598    Previous versions of this specification required
599    normalization at this step. However, attempts to
600    require normalization in other protocols have met with
601    strong enough resistance that requiring normalization
602    here was considered impractical.
[22]603    Implementers and users are cautioned that, while denormalized character sequences are valid,
604    they might be difficult for other users or processes to reproduce
605    and might lead to unexpected results.
[82]606  <!-- raise on list:
607    It is recommended
608    that the processing of IRI components treat
609    strings with the same normalized forms as equivalent.
610   -->
[22]611  </t>
[20]613</section> <!-- ucsconv -->
615<section title="Parse the IRI into IRI components">
617<t>Parse the IRI, either as a relative reference (no scheme)
618or using scheme specific processing (according to the scheme
[58]619given); the result is a set of parsed IRI components.</t>
621</section> <!-- parse -->
623<section title="General percent-encoding of IRI components" anchor="compmapping">
[60]625<t>Except as noted in the following subsections, IRI components are mapped
626to the equivalent URI components by percent-encoding those characters
[20]627not allowed in URIs. Previous processing steps will have removed
628some characters, and the interpretation of reserved characters will
629have already been done (with the syntactic reserved characters outside
630of the IRI component). This mapping is defined for all sequences
631of Unicode characters, whether or not they are valid for the component
632in question. </t>
[70]634<t>For each character which is not allowed anywhere in a valid URI
635 apply the following steps. </t>
[20]636<t><list style="hanging">
638<t hangText="Convert to UTF-8">Convert the character to a sequence of
639  one or more octets using UTF-8 <xref target="RFC3629"/>.</t>
641<t hangText="Percent encode">Convert each octet of this sequence to %HH,
642   where HH is the hexadecimal notation of the octet value. The
643   hexadecimal notation SHOULD use uppercase letters. (This is the
644   general URI percent-encoding mechanism in Section 2.1 of <xref
645   target="RFC3986"/>.)</t>
649<t>Note that the mapping is an identity transformation for parsed URI
650components of valid URIs, and is idempotent: applying the mapping a
651second time will not change anything.</t>
652</section> <!-- general conversion -->
654<section title="Mapping ireg-name" anchor="dnsmapping">
[65]655  <section title='Mapping using Percent-Encoding' anchor='dnspercent'>
[61]656  <t>The ireg-name component SHOULD be converted
657    according to the general procedure for percent-encoding
[62]658    of IRI components described in <xref target="compmapping"/>.</t>
660  <t>For example, the IRI
661    <vspace/>"http://r&amp;#xE9;sum&amp;#xE9;"<vspace/> will be
[63]662    converted to <vspace/>"".</t>
[64]664  <t>This conversion for ireg-name is in line with Section 3.2.2
665    of <xref target="RFC3986"/>, which does not mandate
666    a particular registered name lookup technology. For further background,
667    see <xref target="RFC6055"/> and <xref target="Gettys"/>.</t>
[71]668</section> <!-- dnspercent -->
[66]669<section title="Mapping using Punycode" anchor='dnspunycode'>
[61]670  <t>The ireg-name component MAY also be converted as follows:</t>
[77]672  <t>If there are any sequences of &lt;pct-encoded&gt;, and their
673    corresponding octets all represent valid UTF-8
674    octet sequences, then convert these back to Unicode
675    character sequences. (If any &lt;pct-encoded&gt; sequences are not
676    valid UTF-8 octet sequences, then leave the entire field as is
677    without any change, since punycode encoding would not succeed.)</t>
[20]679<t>Replace the ireg-name part of the IRI by the part converted using
[63]680the Domain Name Lookup procedure (Subsections 5.3 to 5.5) of <xref target="RFC5891"/>.
681  on each dot-separated label, and by using U+002E
682(FULL STOP) as a label separator.
683This procedure may fail, but this would mean that the IRI cannot be resolved.
[20]684In such cases, if the domain name conversion fails, then the
685entire IRI conversion fails. Processors that have no mechanism for
686signalling a failure MAY instead substitute an otherwise
[63]687invalid host name, although such processing SHOULD be avoided.</t>
689<t>For example, the IRI
690<vspace/>"http://r&amp;#xE9;sum&amp;#xE9;"<vspace/> MAY be
[61]691converted to <vspace/>""<vspace/>.</t>
[66]692  <t>This conversion for ireg-name will be better able to deal with legacy
693    infrastructure that cannot handle percent-encoding in domain names.</t>
[71]694</section> <!-- punicode -->
[65]695  <section title="Additional Considerations">
[20]697<t><list style="hanging"> 
698<t hangText="Note:">Domain Names may appear in parts of an IRI other
699than the ireg-name part.  It is the responsibility of scheme-specific
700implementations (if the Internationalized Domain Name is part of the
701scheme syntax) or of server-side implementations (if the
702Internationalized Domain Name is part of 'iquery') to apply the
703necessary conversions at the appropriate point. Example: Trying to
704validate the Web page at<vspace/>
705http://r&amp;#xE9;sum&amp;#xE9; would lead to an IRI of
707which would convert to a URI
709The server-side implementation is responsible for making the
710necessary conversions to be able to retrieve the Web page.</t>
712<t hangText="Note:">In this process, characters allowed in URI
713references and existing percent-encoded sequences are not encoded further.
714(This mapping is similar to, but different from, the encoding applied
715when arbitrary content is included in some part of a URI.)
717For example, an IRI of
719(in XML notation) is converted to
720<vspace/>"", not to
721something like
[71]725</section> <!-- additional -->
[20]726</section> <!-- dnsmapping -->
728<section title="Mapping query components" anchor="querymapping">
[71]730<t>For compatibility with existing deployed HTTP infrastructure,
[20]731the following special case applies for schemes "http" and "https"
732and IRIs whose origin has a document charset other than one which
733is UCS-based (e.g., UTF-8 or UTF-16). In such a case, the "query"
734component of an IRI is mapped into a URI by using the document
735charset rather than UTF-8 as the binary representation before
736pct-encoding. This mapping is not applied for any other scheme
737or component.</t>
739</section> <!-- querymapping -->
741<section title="Mapping IRIs to URIs" anchor="mapping">
[71]743<t>The mapping from an IRI to URI is accomplished by applying the
[20]744mapping above (from IRI to URI components) and then reassembling a URI
745from the parsed URI components using the original punctuation that
746delimited the IRI components. </t>
748</section> <!-- mapping -->
750<section title="Converting URIs to IRIs" anchor="URItoIRI">
[76]752  <t>In some situations, for presentation and further processing,
753it is desirable to convert a URI into an equivalent IRI
754without unnecessary percent encoding.
755Of course, every URI is already an IRI in its own right without any
756conversion. This section gives one possible procedure for URI to IRI mapping.</t>
759The conversion described in this section, if given a valid URI, will
760result in an IRI that maps back to the URI used as an input for the
761conversion (except for potential case differences in percent-encoding
762and for potential percent-encoded unreserved characters).
764However, the IRI resulting from this conversion may differ
765from the original IRI (if there ever was one).</t> 
767<t>URI-to-IRI conversion removes percent-encodings, but not all
768percent-encodings can be eliminated. There are several reasons for
771<t><list style="hanging">
773<t hangText="1.">Some percent-encodings are necessary to distinguish
774    percent-encoded and unencoded uses of reserved characters.</t>
776<t hangText="2.">Some percent-encodings cannot be interpreted as sequences
777    of UTF-8 octets.<vspace blankLines="1"/>
778    (Note: The octet patterns of UTF-8 are highly regular.
779    Therefore, there is a very high probability, but no guarantee,
780    that percent-encodings that can be interpreted as sequences of UTF-8
781    octets actually originated from UTF-8. For a detailed discussion,
782    see <xref target="Duerst97"/>.)</t>
784<t hangText="3.">The conversion may result in a character that is not
[71]785    appropriate in an IRI. See <xref target="abnf"/>,
[20]786      and <xref target="limitations"/> for further details.</t>
788<t hangText="4.">IRI to URI conversion has different rules for
789    dealing with domain names and query parameters.</t>
793<t>Conversion from a URI to an IRI MAY be done by using the following
796<list style="hanging">
797<t hangText="1.">Represent the URI as a sequence of octets in
798       US-ASCII.</t>
800<t hangText="2.">Convert all percent-encodings ("%" followed by two
801      hexadecimal digits) to the corresponding octets, except those
802      corresponding to "%", characters in "reserved", and characters
803      in US-ASCII not allowed in URIs.</t> 
805<t hangText="3.">Re-percent-encode any octet produced in step 2 that
806      is not part of a strictly legal UTF-8 octet sequence.</t>
809<t hangText="4.">Re-percent-encode all octets produced in step 3 that
810      in UTF-8 represent characters that are not appropriate according
[71]811      to <xref target="abnf"/>  and <xref
[20]812      target="limitations"/>.</t> 
814<t hangText="5.">Interpret the resulting octet sequence as a sequence
815      of characters encoded in UTF-8.</t>
817<t hangText="6.">URIs known to contain domain names in the reg-name
818      component SHOULD convert punycode-encoded domain name labels to
819      the corresponding characters using the ToUnicode procedure. </t>
822<t>This procedure will convert as many percent-encoded characters as
823possible to characters in an IRI. Because there are some choices when
824step 4 is applied (see <xref target="limitations"/>), results may
827<t>Conversions from URIs to IRIs MUST NOT use any character
828encoding other than UTF-8 in steps 3 and 4, even if it might be
829possible to guess from the context that another character encoding
830than UTF-8 was used in the URI.  For example, the URI
831"" might with some guessing be
832interpreted to contain two e-acute characters encoded as
833iso-8859-1. It must not be converted to an IRI containing these
834e-acute characters. Otherwise, in the future the IRI will be mapped to
835"", which is a different
836URI from "".</t>
838<section title="Examples">
840<t>This section shows various examples of converting URIs to IRIs.
841Each example shows the result after each of the steps 1 through 6 is
842applied. XML Notation is used for the final result.  Octets are
843denoted by "&lt;" followed by two hexadecimal digits followed by
846<t>The following example contains the sequence "%C3%BC", which is a
847strictly legal UTF-8 sequence, and which is converted into the actual
848character U+00FC, LATIN SMALL LETTER U WITH DIAERESIS (also known as
851<list style="hanging">
852<t hangText="1."></t>
853<t hangText="2.">;c3&gt;&lt;bc&gt;rst</t>
854<t hangText="3.">;c3&gt;&lt;bc&gt;rst</t>
855<t hangText="4.">;c3&gt;&lt;bc&gt;rst</t>
856<t hangText="5.">;#xFC;rst</t>
857<t hangText="6.">;#xFC;rst</t>
861<t>The following example contains the sequence "%FC", which might
863the<vspace/>iso-8859-1 character encoding.  (It might represent other
864characters in other character encodings. For example, the octet
865&lt;fc&gt; in iso-8859-5 represents U+045C, CYRILLIC SMALL LETTER
866KJE.)  Because &lt;fc&gt; is not part of a strictly legal UTF-8
867sequence, it is re-percent-encoded in step 3.
870<list style="hanging">
871<t hangText="1."></t>
872<t hangText="2.">;fc&gt;rst</t>
873<t hangText="3."></t>
874<t hangText="4."></t>
875<t hangText="5."></t>
876<t hangText="6."></t>
880<t>The following example contains "%e2%80%ae", which is the percent-encoded<vspace/>UTF-8
[71]881character encoding of U+202E, RIGHT-TO-LEFT OVERRIDE.
882The direct use of this character is forbiddin in an IRI. Therefore, the
[20]883corresponding octets are re-percent-encoded in step 4. This example shows
884that the case (upper- or lowercase) of letters used in percent-encodings may not be preserved.
885The example also contains a punycode-encoded domain name label (xn--99zt52a),
886which is not converted.
888<list style="hanging">
889<t hangText="1."></t>
890<t hangText="2.">;e2&gt;&lt;80&gt;&lt;ae&gt;</t>
891<t hangText="3.">;e2&gt;&lt;80&gt;&lt;ae&gt;</t>
892<t hangText="4."></t>
893<t hangText="5."></t>
894<t hangText="6.">http://&amp;#x7D0D;&amp;#x8C46;</t>
897<t>Note that the label "xn--99zt52a" is converted to U+7D0D U+8C46
898(Japanese Natto). ((EDITOR NOTE: There is some inconsistency in this note.))</t>
900</section> <!-- examples -->
901</section> <!-- URItoIRI -->
902</section> <!-- processing -->
905<section title="Use of IRIs" anchor="IRIuse">
907<section title="Limitations on UCS Characters Allowed in IRIs" anchor="limitations">
909<t>This section discusses limitations on characters and character
[71]910sequences usable for IRIs beyond those given in <xref target="abnf"/>.
911The considerations in this section are
[20]912relevant when IRIs are created and when URIs are converted to
917<list style="hanging"><t hangText="a.">The repertoire of characters allowed
918    in each IRI component is limited by the definition of that component.
919    For example, the definition of the scheme component does not allow
920    characters beyond US-ASCII.
921    <vspace blankLines="1"/>
922    (Note: In accordance with URI practice, generic IRI
923    software cannot and should not check for such limitations.)</t>
925<t hangText="b.">The UCS contains many areas of characters for which
926    there are strong visual look-alikes. Because of the likelihood of
927    transcription errors, these also should be avoided. This includes
928    the full-width equivalents of Latin characters, half-width
929    Katakana characters for Japanese, and many others. It also
930    includes many look-alikes of "space", "delims", and "unwise",
931    characters excluded in <xref target="RFC3491"/>.</t>
936<t>Additional information is available from <xref target="UNIXML"/>.
937    <xref target="UNIXML"/> is written in the context of running text
938    rather than in that of identifiers. Nevertheless, it discusses
939    many of the categories of characters not appropriate for IRIs.</t>
940</section> <!-- limitations -->
942<section title="Software Interfaces and Protocols">
944<t>Although an IRI is defined as a sequence of characters, software
945interfaces for URIs typically function on sequences of octets or other
946kinds of code units. Thus, software interfaces and protocols MUST
947define which character encoding is used.</t>
949<t>Intermediate software interfaces between IRI-capable components and
950URI-only components MUST map the IRIs per <xref target="mapping"/>,
951when transferring from IRI-capable to URI-only components.
953This mapping SHOULD be applied as late as possible. It SHOULD NOT be
954applied between components that are known to be able to handle IRIs.</t>
955</section> <!-- software -->
957<section title="Format of URIs and IRIs in Documents and Protocols">
959<t>Document formats that transport URIs may have to be upgraded to allow
960the transport of IRIs. In cases where the document as a whole
961has a native character encoding, IRIs MUST also be encoded in this
962character encoding and converted accordingly by a parser or interpreter.
964IRI characters not expressible in the native character encoding SHOULD
965be escaped by using the escaping conventions of the document format if
966such conventions are available. Alternatively, they MAY be
967percent-encoded according to <xref target="mapping"/>. For example, in
968HTML or XML, numeric character references SHOULD be used. If a
969document as a whole has a native character encoding and that character
970encoding is not UTF-8, then IRIs MUST NOT be placed into the document
971in the UTF-8 character encoding.</t>
973<t>((UPDATE THIS NOTE)) Note: Some formats already accommodate IRIs,
974although they use different terminology. HTML 4.0 <xref
975target="HTML4"/> defines the conversion from IRIs to URIs as
976error-avoiding behavior. XML 1.0 <xref target="XML1"/>, XLink <xref
977target="XLink"/>, XML Schema <xref target="XMLSchema"/>, and
978specifications based upon them allow IRIs. Also, it is expected that
979all relevant new W3C formats and protocols will be required to handle
980IRIs <xref target="CharMod"/>.</t>
982</section> <!-- format -->
984<section title="Use of UTF-8 for Encoding Original Characters" anchor="UTF8use">
986<t>This section discusses details and gives examples for point c) in
987<xref target="Applicability"/>. To be able to use IRIs, the URI
988corresponding to the IRI in question has to encode original characters
989into octets by using UTF-8.  This can be specified for all URIs of a
990URI scheme or can apply to individual URIs for schemes that do not
991specify how to encode original characters.  It can apply to the whole
992URI, or only to some part. For background information on encoding
993characters into URIs, see also Section 2.5 of <xref
996<t>For new URI schemes, using UTF-8 is recommended in <xref
[24]997target="RFC4395bis"/>.  Examples where UTF-8 is already used are the URN
[20]998syntax <xref target="RFC2141"/>, IMAP URLs <xref target="RFC2192"/>,
999and POP URLs <xref target="RFC2384"/>.  On the other hand, because the
1000HTTP URI scheme does not specify how to encode original characters,
1001only some HTTP URLs can have corresponding but different IRIs.</t>
1003<t>For example, for a document with a URI
1004of<vspace/>"", it is
1005possible to construct a corresponding IRI (in XML notation, see <xref
1007";#xE9;sum&amp;#xE9;.html" ("&amp;#xE9;"
1008stands for the e-acute character, and "%C3%A9" is the UTF-8 encoded
1009and percent-encoded representation of that character). On the other
1010hand, for a document with a URI of
1011"", the percent-encoding octets
1012cannot be converted to actual characters in an IRI, as the
1013percent-encoding is not based on UTF-8.</t>
1015<t>For most URI schemes, there is no need to upgrade their scheme
1016definition in order for them to work with IRIs.  The main case where
1017upgrading makes sense is when a scheme definition, or a particular
1018component of a scheme, is strictly limited to the use of US-ASCII
1019characters with no provision to include non-ASCII characters/octets
1020via percent-encoding, or if a scheme definition currently uses highly
1021scheme-specific provisions for the encoding of non-ASCII characters.
1022An example of this is the mailto: scheme <xref target="RFC2368"/>.</t>
1024<t>This specification updates the IANA registry of URI schemes to note
1025their applicability to IRIs, see <xref target="iana"/>.  All IRIs use
1026URI schemes, and all URIs with URI schemes can be used as IRIs, even
1027though in some cases only by using URIs directly as IRIs, without any
1030<t>Scheme definitions can impose restrictions on the syntax of
1031scheme-specific URIs; i.e., URIs that are admissible under the generic
1032URI syntax <xref target="RFC3986"/> may not be admissible due to
1033narrower syntactic constraints imposed by a URI scheme
1034specification. URI scheme definitions cannot broaden the syntactic
1035restrictions of the generic URI syntax; otherwise, it would be
1036possible to generate URIs that satisfied the scheme-specific syntactic
1037constraints without satisfying the syntactic constraints of the
1038generic URI syntax. However, additional syntactic constraints imposed
1039by URI scheme specifications are applicable to IRI, as the
1040corresponding URI resulting from the mapping defined in <xref
1041target="mapping"/> MUST be a valid URI under the syntactic
1042restrictions of generic URI syntax and any narrower restrictions
1043imposed by the corresponding URI scheme specification.</t>
1045<t>The requirement for the use of UTF-8 generally applies to all parts
1046of a URI.  However, it is possible that the capability of IRIs to
1047represent a wide range of characters directly is used just in some
1048parts of the IRI (or IRI reference). The other parts of the IRI may
1049only contain US-ASCII characters, or they may not be based on
1050UTF-8. They may be based on another character encoding, or they may
1051directly encode raw binary data (see also <xref
1052target="RFC2397"/>). </t>
1054<t>For example, it is possible to have a URI reference
1056where the document name is encoded in iso-8859-1 based on server
1057settings, but where the fragment identifier is encoded in UTF-8 according
1058to <xref target="XPointer"/>. The IRI corresponding to the above
1059URI would be (in XML notation)<vspace/>";#xE9;sum&amp;#xE9;".</t>
1061<t>Similar considerations apply to query parts. The functionality
1062of IRIs (namely, to be able to include non-ASCII characters) can
1063only be used if the query part is encoded in UTF-8.</t>
1065</section> <!-- utf8 -->
1067<section title="Relative IRI References">
1068<t>Processing of relative IRI references against a base is handled
1069straightforwardly; the algorithms of <xref target="RFC3986"/> can
1070be applied directly, treating the characters additionally allowed
1071in IRI references in the same way that unreserved characters are in URI
1074</section> <!-- relative -->
1075</section> <!-- IRIuse -->
[39]1077<section title="Liberal Handling of Otherwise Invalid IRIs" anchor="LEIRIHREF">
[20]1080Some technical specifications and widely-deployed software have
1081allowed additional variations and extensions of IRIs to be used in
[71]1082syntactic components. </t>
[20]1083<t>Future technical specifications SHOULD NOT allow conforming
1084producers to produce, or conforming content to contain, such forms,
1085as they are not interoperable with other IRI consuming software.</t>
[39]1087<section title="LEIRI Processing"  anchor="LEIRIspec">
[20]1088  <t>This section defines Legacy Extended IRIs (LEIRIs).
[36]1089    The syntax of Legacy Extended IRIs is the same as that for &lt;IRI-reference>,
[20]1090    except that the ucschar production is replaced by the leiri-ucschar production:</t>
[79]1094  leiri-ucschar  = " " / "&lt;" / "&gt;" / DQUOTE / "{" / "}" / "|"
[20]1095                   / "\" / "^" / "`" / %x0-1F / %x7F-D7FF
1096                   / %xE000-FFFD / %x10000-10FFFF
1100  Among other extensions, processors based on this specification also
1101  did not enforce the restriction on bidirectional formatting
[71]1102  characters in <xref target="Bidi"></xref>, and the iprivate
[20]1103  production becomes redundant.</postamble>
1106<t>To convert a string allowed as a LEIRI to an IRI, each character
1107allowed in leiri-ucschar but not in ucschar must be percent-encoded
1108using <xref target="compmapping"/>.</t>
1109</section> <!-- leiriproc -->
[71]1110</section> <!-- LEIRIHREF -->
[74]1112  <section title="Characters Disallowed or Not Recommended in IRIs" anchor="notAllowed">
1114<t>This section provides a list of the groups of characters and code
[71]1115points that are allowed in some contexts but are not allowed in IRIs or are
[20]1116allowed in IRIs only in the query part. For each group of characters,
1117advice on the usage of these characters is also given, concentrating
1118on the reasons for why they are excluded from IRI use.</t>
1122<list><t>Space (U+0020): Some formats and applications use space as a
1123delimiter, e.g. for items in a list. Appendix C of <xref
1124target="RFC3986"></xref> also mentions that white space may have to be
1125added when displaying or printing long URIs; the same applies to long
1126IRIs. This means that spaces can disappear, or can make the what is
1127intended as a single IRI or IRI reference to be treated as two or more
1128separate IRIs.</t>
1130<t>Delimiters "&lt;" (U+003C), "&gt;" (U+003E), and '"' (U+0022):
1131Appendix C of <xref target="RFC3986"></xref> suggests the use of
1132double-quotes ("") and angle brackets
1133(&lt;;) as delimiters for URIs in plain
1134text. These conventions are often used, and also apply to IRIs.  Using
1135these characters in strings intended to be IRIs would result in the
1136IRIs being cut off at the wrong place.</t>
1138<t>Unwise characters "\" (U+005C), "^" (U+005E), "`"
1139(U+0060), "{" (U+007B), "|" (U+007C), and "}" (U+007D): These
1140characters originally have been excluded from URIs because the
1141respective codepoints are assigned to different graphic characters in
1142some 7-bit or 8-bit encoding. Despite the move to Unicode, some of
1143these characters are still occasionally displayed differently on some
1144systems, e.g. U+005C may appear as a Japanese Yen symbol on some
1145systems. Also, the fact that these characters are not used in URIs or
1146IRIs has encouraged their use outside URIs or IRIs in contexts that
1147may include URIs or IRIs. If a string with such a character were used
1148as an IRI in such a context, it would likely be interpreted
1151<t>The controls (C0 controls, DEL, and C1 controls, #x0 - #x1F #x7F -
1152#x9F): There is generally no way to transmit these characters reliably
1153as text outside of a charset encoding.  Even when in encoded form,
1154many software components silently filter out some of these characters,
1155or may stop processing alltogether when encountering some of
1156them. These characters may affect text display in subtle, unnoticable
1157ways or in drastic, global, and irreversible ways depending on the
1158hardware and software involved. The use of some of these characters
1159would allow malicious users to manipulate the display of an IRI and
1160its context in many situations.</t>
1162<t>Bidi formatting characters (U+200E, U+200F, U+202A-202E): These
1163characters affect the display ordering of characters. If IRIs were
1164allowed to contain these characters and the resulting visual display
1165transcribed. they could not be converted back to electronic form
1166(logical order) unambiguously. These characters, if allowed in IRIs,
1167might allow malicious users to manipulate the display of IRI and its
1170<t>Specials (U+FFF0-FFFD): These code points provide functionality
1171beyond that useful in an IRI, for example byte order identification,
1172annotation, and replacements for unknown characters and objects. Their
1173use and interpretation in an IRI would serve no purpose and might lead
1174to confusing display variations.</t>
1176<t>Private use code points (U+E000-F8FF, U+F0000-FFFFD,
1177U+100000-10FFFD): Display and interpretation of these code points is
[72]1178by definition undefined without private agreement. In any case, these
[20]1179code points are not suited for use on the Internet. They are not
1180interoperable and may have unpredictable effects.</t>
[72]1182<t>Tags (U+E0000-E0FFF): These characters were intended to provide
1183  a way to language tag in Unicode plain text. They are now deprecated <xref target="RFC6082" />.
1184  In any case, they would not be appropriate for IRIs because
[20]1185language information in identifiers cannot reliably be input,
1186transmitted (e.g. on a visual medium such as paper), or
1189<t>Non-characters (U+FDD0-FDEF, U+1FFFE-1FFFF, U+2FFFE-2FFFF,
1193U+FFFFE-FFFFF, U+10FFFE-10FFFF): These code points are defined as
1194non-characters. Applications may use some of them internally, but are
1195not prepared to interchange them.</t>
1199<t>LEIRI preprocessing disallowed some code points and
1200code units:
1202<list><t>Surrogate code units (D800-DFFF): These do not represent
1203Unicode codepoints.</t></list></t>
1204</section> <!-- notallowed -->
[20]1206<section title="URI/IRI Processing Guidelines (Informative)" anchor="guidelines">
1208<t>This informative section provides guidelines for supporting IRIs in
1209the same software components and operations that currently process
1210URIs: Software interfaces that handle URIs, software that allows users
1211to enter URIs, software that creates or generates URIs, software that
1212displays URIs, formats and protocols that transport URIs, and software
1213that interprets URIs. These may all require modification before
1214functioning properly with IRIs. The considerations in this section
1215also apply to URI references and IRI references.</t>
1217<section title="URI/IRI Software Interfaces">
1218<t>Software interfaces that handle URIs, such as URI-handling APIs and
1219protocols transferring URIs, need interfaces and protocol elements
1220that are designed to carry IRIs.</t>
1222<t>In case the current handling in an API or protocol is based on
1223US-ASCII, UTF-8 is recommended as the character encoding for IRIs, as
1224it is compatible with US-ASCII, is in accordance with the
1225recommendations of <xref target="RFC2277"/>, and makes converting to
1226URIs easy. In any case, the API or protocol definition must clearly
1227define the character encoding to be used.</t>
1229<t>The transfer from URI-only to IRI-capable components requires no
1230mapping, although the conversion described in <xref
1231target="URItoIRI"/> above may be performed. It is preferable not to
1232perform this inverse conversion unless it is certain this can be done
[71]1234</section><!-- software interfaces -->
1236<section title="URI/IRI Entry">
1238<t>Some components allow users to enter URIs into the system
1239by typing or dictation, for example. This software must be updated to allow
1240for IRI entry.</t>
[82]1242<t>A person viewing a visual presentation of an IRI (as a sequence
1243of glyphs, in some order, in some visual display)
[20]1244will use an entry method for characters in the user's language to
1245input the IRI. Depending on the script and the input method used, this
1246may be a more or less complicated process.</t>
1248<t>The process of IRI entry must ensure, as much as possible, that the
1249restrictions defined in <xref target="abnf"/> are met. This may be
1250done by choosing appropriate input methods or variants/settings
1251thereof, by appropriately converting the characters being input, by
1252eliminating characters that cannot be converted, and/or by issuing a
1253warning or error message to the user.</t>
1255<t>As an example of variant settings, input method editors for East
1256Asian Languages usually allow the input of Latin letters and related
1257characters in full-width or half-width versions. For IRI input, the
1258input method editor should be set so that it produces half-width Latin
1259letters and punctuation and full-width Katakana.</t>
1261<t>An input field primarily or solely used for the input of URIs/IRIs
1262might allow the user to view an IRI as it is mapped to a URI.  Places
1263where the input of IRIs is frequent may provide the possibility for
1264viewing an IRI as mapped to a URI. This will help users when some of
1265the software they use does not yet accept IRIs.</t>
1267<t>An IRI input component interfacing to components that handle URIs,
1268but not IRIs, must map the IRI to a URI before passing it to these
1271<t>For the input of IRIs with right-to-left characters, please see
[71]1272<xref target="Bidi"></xref>.</t>
1273</section><!-- entry -->
1275<section title="URI/IRI Transfer between Applications">
1277<t>Many applications (for example, mail user agents) try to detect
1278URIs appearing in plain text. For this, they use some heuristics based
1279on URI syntax. They then allow the user to click on such URIs and
1280retrieve the corresponding resource in an appropriate (usually
1281scheme-dependent) application.</t>
1283<t>Such applications would need to be upgraded, in order to use the
1284IRI syntax as a base for heuristics. In particular, a non-ASCII
1285character should not be taken as the indication of the end of an IRI.
1286Such applications also would need to make sure that they correctly
1287convert the detected IRI from the character encoding of the document
1288or application where the IRI appears, to the character encoding used
1289by the system-wide IRI invocation mechanism, or to a URI (according to
1290<xref target="mapping"/>) if the system-wide invocation mechanism only
1291accepts URIs.</t>
1293<t>The clipboard is another frequently used way to transfer URIs and
1294IRIs from one application to another. On most platforms, the clipboard
1295is able to store and transfer text in many languages and scripts.
1296Correctly used, the clipboard transfers characters, not octets, which
1297will do the right thing with IRIs.</t>
[71]1298</section><!-- transfer -->
1300<section title="URI/IRI Generation">
1302<t>Systems that offer resources through the Internet, where those
1303resources have logical names, sometimes automatically generate URIs
1304for the resources they offer. For example, some HTTP servers can
1305generate a directory listing for a file directory and then respond to
1306the generated URIs with the files.</t>
1308<t>Many legacy character encodings are in use in various file systems.
1309Many currently deployed systems do not transform the local character
1310representation of the underlying system before generating URIs.</t>
1312<t>For maximum interoperability, systems that generate resource
1313identifiers should make the appropriate transformations. For example,
1314if a file system contains a file named
1315"r&amp;#xE9;sum&amp;#xE9;.html", a server should expose this as
1316"r%C3%A9sum%C3%A9.html" in a URI, which allows use of
1317"r&amp;#xE9;sum&amp;#xE9;.html" in an IRI, even if locally the file
1318name is kept in a character encoding other than UTF-8.
1321<t>This recommendation particularly applies to HTTP servers. For FTP
1322servers, similar considerations apply; see <xref target="RFC2640"/>.</t>
[71]1323</section><!-- generation -->
1325<section title="URI/IRI Selection" anchor="selection">
1326<t>In some cases, resource owners and publishers have control over the
1327IRIs used to identify their resources. This control is mostly
1328executed by controlling the resource names, such as file names,
1331<t>In these cases, it is recommended to avoid choosing IRIs that are
1332easily confused. For example, for US-ASCII, the lower-case ell ("l") is
1333easily confused with the digit one ("1"), and the upper-case oh ("O") is
1334easily confused with the digit zero ("0"). Publishers should avoid
1335confusing users with "br0ken" or "1ame" identifiers.</t>
1337<t>Outside the US-ASCII repertoire, there are many more opportunities for
1338confusion; a complete set of guidelines is too lengthy to include
1339here. As long as names are limited to characters from a single script,
1340native writers of a given script or language will know best when
1341ambiguities can appear, and how they can be avoided. What may look
1342ambiguous to a stranger may be completely obvious to the average
1343native user. On the other hand, in some cases, the UCS contains
1344variants for compatibility reasons; for example, for typographic purposes.
1345These should be avoided wherever possible. Although there may be exceptions,
1346newly created resource names should generally be in NFKC
1347<xref target="UTR15"></xref> (which means that they are also in NFC).</t>
1349<t>As an example, the UCS contains the "fi" ligature at U+FB01
1350for compatibility reasons.
1351Wherever possible, IRIs should use the two letters "f" and "i" rather
1352than the "fi" ligature. An example where the latter may be used is
1353in the query part of an IRI for an explicit search for a word written
1354containing the "fi" ligature.</t>
1356<t>In certain cases, there is a chance that characters from different
1357scripts look the same. The best known example is the similarity of the
1358Latin "A", the Greek "Alpha", and the Cyrillic "A". To avoid such
1359cases, IRIs should only be created where all the characters in a
1360single component are used together in a given language. This usually
1361means that all of these characters will be from the same script, but
1362there are languages that mix characters from different scripts (such
1363as Japanese).  This is similar to the heuristics used to distinguish
1364between letters and numbers in the examples above. Also, for Latin,
1365Greek, and Cyrillic, using lowercase letters results in fewer
1366ambiguities than using uppercase letters would.</t>
[71]1367</section><!-- selection -->
1369<section title="Display of URIs/IRIs" anchor="display">
1371In situations where the rendering software is not expected to display
1372non-ASCII parts of the IRI correctly using the available layout and font
1373resources, these parts should be percent-encoded before being displayed.</t>
[71]1375<t>For display of Bidi IRIs, please see <xref target="Bidi"/>.</t>
1376</section> <!-- display -->
1378<section title="Interpretation of URIs and IRIs">
1379<t>Software that interprets IRIs as the names of local resources should
1380accept IRIs in multiple forms and convert and match them with the
1381appropriate local resource names.</t>
1383<t>First, multiple representations include both IRIs in the native
1384character encoding of the protocol and also their URI counterparts.</t>
1386<t>Second, it may include URIs constructed based on character
1387encodings other than UTF-8. These URIs may be produced by user agents that do
1388not conform to this specification and that use legacy character encodings to
1389convert non-ASCII characters to URIs. Whether this is necessary, and what
1390character encodings to cover, depends on a number of factors, such as
1391the legacy character encodings used locally and the distribution of
1392various versions of user agents. For example, software for Japanese
1393may accept URIs in Shift_JIS and/or EUC-JP in addition to UTF-8.</t>
1395<t>Third, it may include additional mappings to be more user-friendly
1396and robust against transmission errors. These would be similar to how
1397some servers currently treat URIs as case insensitive or perform
1398additional matching to account for spelling errors. For characters
1399beyond the US-ASCII repertoire, this may, for example, include
1400ignoring the accents on received IRIs or resource names. Please note
1401that such mappings, including case mappings, are language
1404<t>It can be difficult to identify a resource unambiguously if too
1405many mappings are taken into consideration. However, percent-encoded
1406and not percent-encoded parts of IRIs can always be clearly distinguished.
1407Also, the regularity of UTF-8 (see <xref target="Duerst97"/>) makes the
1408potential for collisions lower than it may seem at first.</t>
[71]1409</section> <!-- interpretation -->
1411<section title="Upgrading Strategy">
1412<t>Where this recommendation places further constraints on software
1413for which many instances are already deployed, it is important to
1414introduce upgrades carefully and to be aware of the various
1417<t>If IRIs cannot be interpreted correctly, they should not be created,
1418generated, or transported. This suggests that upgrading URI interpreting
1419software to accept IRIs should have highest priority.</t>
1421<t>On the other hand, a single IRI is interpreted only by a single or
1422very few interpreters that are known in advance, although it may be
1423entered and transported very widely.</t>
1425<t>Therefore, IRIs benefit most from a broad upgrade of software to be
1426able to enter and transport IRIs. However, before an
1427individual IRI is published, care should be taken to upgrade the corresponding
1428interpreting software in order to cover the forms expected to be
1429received by various versions of entry and transport software.</t>
1431<t>The upgrade of generating software to generate IRIs instead of using a
1432local character encoding should happen only after the service is upgraded
1433to accept IRIs. Similarly, IRIs should only be generated when the service
1434accepts IRIs and the intervening infrastructure and protocol is known
1435to transport them safely.</t>
1437<t>Software converting from URIs to IRIs for display should be upgraded
1438only after upgraded entry software has been widely deployed to the
1439population that will see the displayed result.</t>
1442<t>Where there is a free choice of character encodings, it is often
1443possible to reduce the effort and dependencies for upgrading to IRIs
1444by using UTF-8 rather than another encoding. For example, when a new
1445file-based Web server is set up, using UTF-8 as the character encoding
1446for file names will make the transition to IRIs easier. Likewise, when
1447a new Web form is set up using UTF-8 as the character encoding of the
1448form page, the returned query URIs will use UTF-8 as the character
1449encoding (unless the user, for whatever reason, changes the character
1450encoding) and will therefore be compatible with IRIs.</t>
1453<t>These recommendations, when taken together, will allow for the
1454extension from URIs to IRIs in order to handle characters other than
1455US-ASCII while minimizing interoperability problems. For
1456considerations regarding the upgrade of URI scheme definitions, see
1457<xref target="UTF8use"/>.</t>
[71]1459</section> <!-- upgrading -->
[20]1460</section> <!-- guidelines -->
1462<section title="IANA Considerations" anchor="iana">
1464<t>RFC Editor and IANA note: Please Replace RFC XXXX with the
1465number of this document when it issues as an RFC. </t>
1467<t>IANA maintains a registry of "URI schemes". A "URI scheme" also
1468serves an "IRI scheme". </t>
1470<t>To clarify that the URI scheme registration process also applies to
1471IRIs, change the description of the "URI schemes" registry
1472header to say "[RFC4395] defines an IANA-maintained registry of URI
1473Schemes. These registries include the Permanent and Provisional URI
1474Schemes.  RFC XXXX updates this registry to designate that schemes may
1475also indicate their usability as IRI schemes.</t>
1477<t> Update "per RFC 4395" to "per RFC 4395 and RFC XXXX".
1480</section> <!-- IANA -->
1482<section title="Security Considerations" anchor="security">
1483<t>The security considerations discussed in <xref target="RFC3986"/>
1484also apply to IRIs. In addition, the following issues require
1485particular care for IRIs.</t>
1486<t>Incorrect encoding or decoding can lead to security problems.
[42]1487For example, some UTF-8 decoders do not check against overlong
1488byte sequences. See <xref target='UTR36'/> Section 3 for details.</t>
[45]1490  <t>There are serious difficulties with relying on a human to verify that a
1491    an IRI (whether presented visually or aurally)
1492    is the same as another IRI or is the one intended.
1493    These problems exist with ASCII-only URIs ( vs.
1494    but are strongly exacerbated when using the much larger character repertoire of Unicode.
1495    For details, see Section 2 of <xref target='UTR36'/>.
[46]1496    Using administrative and technical means to reduce the availability
1497    of such exploits is possible, but they are difficult to eliminate altogether.
1498    User agents SHOULD NOT rely on visual or perceptual comparison or verification of IRIs
[47]1499    as a means of validating or assuring safety, correctness or appropriateness of an IRI.
1500    Other means of presenting users with the validity, safety, or appropriateness
1501    of visited sites are being developed in the browser community
1502    as an alternative means of avoiding these difficulties.</t>
[48]1504<t>Besides the large character repertoire of Unicode, reasons for
1505  confusion include different forms of normalization and different normalization
1506  expectations, use of percent-encoding with various legacy encodings,
[71]1507  and bidirectionality issues. See also <xref target="Bidi"/>.</t>
[52]1509<t>Confusion can occur in various IRI components, such as the
1510domain name part or the path part, or between IRI components. For considerations specific
1511to the domain name part, see <xref target="RFC5890"/>. For considerations specific to
1512particular protocols or schemes, see the security sections of the relevant specifications
1513and registration templates.
1514Administrators of sites that allow independent
1515users to create resources in the same sub area have to be careful.
1516Details are discussed in <xref target="selection"/>.</t>
[44]1518  <t>The characters additionally allowed in Legacy Extended IRIs
[56]1519    introduce additional security issues. For details, see <xref target='notAllowed'/>.</t>
[20]1520</section><!-- security -->
1522<section title="Acknowledgements">
[34]1523<t>This document was derived from <xref target="RFC3987"/>; the acknowledgments from
1524that specification still apply.</t>
[71]1525<t>In addition, this document was influenced by contributions from (in no particular order)Norman Walsh, Richard Tobin,
1526  Henry S. Thomson, John Cowan, Paul Grosso, the XML Core Working Group of the W3C,
1527 Chris
[34]1528  Lilley, Bjoern Hoehrmann,
1529Felix Sasaki, Jeremy Carroll, Frank Ellermann, Michael Everson, Cary Karp, Matitiahu Allouche,
1530Richard Ishida, Addison Phillips, Jonathan Rosenne, Najib Tounsi, Debbie Garside, Mark Davis, Sarmad
1531Hussain, Ted Hardie, Konrad Lanz, Thomas Roessler, Lisa Dusseault, Julian Reschke, Giovanni
1532Campagna, Anne van Kesteren, Mark Nottingham, Erik van der Poel, Marcin Hanclik, Marcos Caceres, Roy
1533Fielding, Greg Wilkins, Pieter Hintjens, Daniel R. Tobias, Marko Martin, Maciej Stanchowiak, Wil
[68]1534Tan, Yui Naruse, Michael A. Puls II, Dave Thaler, Tom Petch, John Klensin, Shawn Steele, Peter
[69]1535Saint-Andre, Geoffrey Sneddon, Chris Weber, Alex Melnikov, Slim Amamou, S. Moonesamy, Tim Berners-Lee, Yaron
[34]1536Goland, Sam Ruby, Adam Barth, Abdulrahman I. ALGhadir, Aharon Lanin, Thomas Milo, Murray Sargent,
1537Marc Blanchet, and Mykyta Yevstifeyev.</t>
[71]1538</section> <!-- Acknowledgements -->
[28]1540<section title="Main Changes Since RFC 3987">
1541  <t>This section describes the main changes since <xref target="RFC3987"></xref>.</t>
[71]1542  <section title="Split out Bidi, processing guidelines, comparison sections">
1543    <t>Move some components (comparison, bidi, processing) into separate documents.</t>
1544  </section>
[28]1545  <section title="Major restructuring of IRI processing model" anchor="forkChanges">
[31]1546    <t>Major restructuring of IRI processing model to make scheme-specific translation
1547      necessary to handle IDNA requirements and for consistency with web implementations. </t>
[28]1548    <t>Starting with IRI, you want one of:
1549      <list style="hanging">
1550        <t hangText="a"> IRI components (IRI parsed into UTF8 pieces)</t>
1551        <t hangText="b"> URI components (URI parsed into ASCII pieces, encoded correctly) </t>
1552        <t hangText="c"> whole URI  (for passing on to some other system that wants whole URIs) </t>
1553      </list></t>
1555    <section title="OLD WAY">
1556      <t><list style="numbers">
1558        <t>Pct-encoding on the whole thing to a URI.
1559          (c1) If you want a (maybe broken) whole URI, you might
1560          stop here.</t>
1562        <t>Parsing the URI into URI components.
1563          (b1) If you want (maybe broken) URI components, stop here.</t>
1565        <t> Decode the components (undoing the pct-encoding).
1566          (a) if you want IRI components, stop here.</t>
1568        <t> reencode:  Either using a different encoding some components
1569          (for domain names, and query components in web pages, which
1570          depends on the component, scheme and context), and otherwise
1571          using pct-encoding.
1572          (b2) if you want (good) URI components, stop here.</t>
1574        <t> reassemble the reencoded components.
1575          (c2) if you want a (*good*) whole URI stop here.</t>
1576      </list>
1578      </t>
1580    </section>
1582    <section title="NEW WAY">
1583      <t>
1584        <list style="numbers">
1586          <t> Parse the IRI into IRI components using the generic syntax.
1587            (a) if you want IRI components, stop here.</t>
1589          <t> Encode each components, using pct-encoding, IDN encoding, or
1590            special query part encoding depending on the component
1591            scheme or context. (b) If you want URI components, stop here.</t>
1592          <t> reassemble the a whole URI from URI components.
1593            (c) if you want a whole URI stop here.</t>
1594        </list></t>
1595    </section>
1596    <section title="Extension of Syntax">
1597      <t>Added the tag range (U+E0000-E0FFF) to the iprivate production.
1598        Some IRIs generated with the new syntax may fail to pass very strict checks
1599        relying on the old syntax. But characters in this range should be extremely infrequent
1600        anyway.</t>
1601    </section>
1602    <section title="More to be added"><t>TODO: There are more main changes that need to be
1603      documented in this section.</t></section>
1606<section title="Change Log">
1608<t>Note to RFC Editor: Please completely remove this section before publication.</t>
[28]1610<section title='Changes after draft-ietf-iri-3987bis-01'>
1611    <t>Changes from draft-ietf-iri-3987bis-01 onwards are available as changesets
1612      in the IETF tools subversion repository at
[20]1616<section title='Changes from draft-duerst-iri-bis-07 to draft-ietf-iri-3987bis-00'>
1617     <t>Changed draft name, date, last paragraph of abstract, and titles in change log, and added this section
1618     in moving from draft-duerst-iri-bis-07 (personal submission) to draft-ietf-iri-3987bis-00 (WG document).</t>
[28]1621<section title="Changes from -06 to -07 of draft-duerst-iri-bis">
1622  <t>Major restructuring of the processing model, see <xref target="forkChanges"></xref>.</t>
1626<section title='Changes from -00 to -01'><t><list style="symbols">
1627  <t>Removed 'mailto:' before mail addresses of authors.</t>
1628  <t>Added "&lt;to be done&gt;" as right side of 'href-strip' rule. Fixed '|' to '/' for
1629    alternatives.</t>
1633<section title="Changes from -05 to -06 of draft-duerst-iri-bis-00"><t><list style="symbols">
1634<t>Add HyperText Reference, change abstract, acks and references for it</t>
1635<t>Add Masinter back as another editor.</t>
1636<t>Masinter integrates HRef material from HTML5 spec.</t>
1637<t>Rewrite introduction sections to modernize.</t>
[31]1641<section title="Changes from -04 to -05 of draft-duerst-iri-bis">
1642  <t><list style="symbols">
1643    <t>Updated references.</t>
1644    <t>Changed IPR text to pre5378Trust200902.</t></list></t>
[31]1647<section title="Changes from -03 to -04 of draft-duerst-iri-bis">
1648  <t><list style="symbols">
1649    <t>Added explicit abbreviation for LEIRIs.</t>
1650    <t>Mentioned LEIRI references.</t>
1651    <t>Completed text in LEIRI section about tag characters and about specials.</t></list></t>
[31]1654<section title="Changes from -02 to -03 of draft-duerst-iri-bis">
1655  <t><list style="symbols">
1656    <t>Updated some references.</t>
1657    <t>Updated Michel Suginard's coordinates.</t></list></t>
[31]1660<section title="Changes from -01 to -02 of draft-duerst-iri-bis">
1661  <t><list style="symbols">
1662    <t>Added tag range to iprivate (issue private-include-tags-115).</t>
1663    <t>Added Specials (U+FFF0-FFFD) to Legacy Extended IRIs.</t></list></t>
[31]1665<section title="Changes from -00 to -01 of draft-duerst-iri-bis">
1666  <t><list style="symbols">
1667    <t>Changed from "IRIs with Spaces/Controls" to "Legacy Extended IRI"
1668      based on input from the W3C XML Core WG.
1669      Moved the relevant subsections to the back and promoted them to a section.</t>
1670    <t>Added some text re. Legacy Extended IRIs to the security section.</t>
1671    <t>Added a IANA Consideration Section.</t>
1672    <t>Added this Change Log Section.</t>
1673    <t>Added a section about "IRIs with Spaces/Controls" (converting from a Note in RFC 3987).</t></list></t>
[71]1674</section> <!-- -00 to -01 -->
[31]1675<section title="Changes from RFC 3987 to -00 of draft-duerst-iri-bis">
1676  <t><list>
1677    <t>Fixed errata (see</t></list></t>
[71]1678</section> <!-- from 3987 -->
1683<references title="Normative References">
1685<reference anchor="ASCII">
1687<title>Coded Character Set -- 7-bit American Standard Code for Information
1690<organization>American National Standards Institute</organization>
1692<date year="1986"/>
1694<seriesInfo name="ANSI" value="X3.4"/>
[73]1697  <reference anchor="ISO10646" target=''>
[73]1699<title>ISO/IEC 10646:2011: Information Technology -
[20]1700Universal Multiple-Octet Coded Character Set (UCS)</title>
1702<organization>International Organization for Standardization</organization>
[73]1704<date month="March" year="20011"/>
1706<seriesInfo name="ISO" value="Standard 10646"/>
1714<reference anchor="STD68">
1716<title abbrev="ABNF">Augmented BNF for Syntax Specifications: ABNF</title>
1717<author initials="D." surname="Crocker" fullname="Dave Crocker"><organization/></author>
1718<author initials="P." surname="Overell" fullname="Paul Overell"><organization/></author>
1719<date month="January" year="2008"/></front>
1720<seriesInfo name="STD" value="68"/><seriesInfo name="RFC" value="5234"/>
[30]1726<reference anchor="UNIV6">
[30]1728<title>The Unicode Standard, Version 6.0.0 (Mountain View, CA, The Unicode Consortium, 2011, ISBN 978-1-936213-01-6)</title>
[20]1729<author><organization>The Unicode Consortium</organization></author>
[30]1730<date year="2010" month="October"/>
1734<reference anchor="UTR15" target="">
1736<title>Unicode Normalization Forms</title>
1737<author initials="M." surname="Davis" fullname="Mark Davis"><organization/></author>
1738<author initials="M.J." surname="Duerst" fullname="Martin Duerst"><organization/></author>
1739<date year="2008" month="March"/>
1741<seriesInfo name="Unicode Standard Annex" value="#15"/>
1746<references title="Informative References">
1748<reference anchor="CharMod" target="">
1750<title>Character Model for the World Wide Web: Resource Identifiers</title>
1751<author initials="M." surname="Duerst" fullname="Martin Duerst"><organization/></author>
1752<author initials="F." surname="Yergeau" fullname="Francois Yergeau"><organization/></author>
1753<author initials="R." surname="Ishida" fullname="Richard Ishida"><organization/></author>
1754<author initials="M." surname="Wolf" fullname="Misha Wolf"><organization/></author>
1755<author initials="T." surname="Texin" fullname="Tex Texin"><organization/></author>
1756<date year="2004" month="November" day="25"/>
1758<seriesInfo name="World Wide Web Consortium" value="Candidate Recommendation"/>
1761<reference anchor="Duerst97" target="">
1763<title>The Properties and Promises of UTF-8</title>
1764<author initials="M.J." surname="Duerst" fullname="Martin Duerst"><organization/></author>
1765<date year="1997" month="September"/>
1767<seriesInfo name="Proc. 11th International Unicode Conference, San Jose" value=""/>
1770<reference anchor="Gettys" target="">
1772<title>URI Model Consequences</title>
1773<author initials="J." surname="Gettys" fullname="Jim Gettys"><organization/></author>
1774<date month="" year=""/>
1778<reference anchor="HTML4" target="">
1780<title>HTML 4.01 Specification</title>
1781<author initials="D." surname="Raggett" fullname="Dave Raggett"><organization/></author>
1782<author initials="A." surname="Le Hors" fullname="Arnaud Le Hors"><organization/></author>
1783<author initials="I." surname="Jacobs" fullname="Ian Jacobs"><organization/></author>
1784<date year="1999" month="December" day="24"/>
1786<seriesInfo name="World Wide Web Consortium" value="Recommendation"/>
1789<reference anchor="LEIRI" target="">
1791<title>Legacy extended IRIs for XML resource identification</title>
1792<author initials="H." surname="Thompson" fullname="Henry Thompson"><organization/></author>
1793<author initials="R." surname="Tobin"    fullname="Richard Tobin"><organization/></author>
1794<author initials="N." surname="Walsh" fullname="Norman Walsh"><organization/></author>
1795  <date year="2008" month="November" day="3"/>
1798<seriesInfo name="World Wide Web Consortium" value="Note"/>
1817<reference anchor='Bidi'>
1818  <front>
1819    <title>Guidelines for Internationalized Resource Identifiers with Bi-directional Characters (Bidi IRIs)</title>
1820    <author initials="M." surname="Duerst"/>
1821    <author initials='L.' surname='Masinter' />
1822    <date year="2011" month="August" day="14" />
1823  </front>
1824  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-bidi-guidelines-00"/>
1827<reference anchor='Equivalence'>
1828  <front>
1829    <title>Equivalence and Canonicalization of Internationalized Resource Identifiers (IRIs)</title>
1830    <author initials='L.' surname='Masinter' />
1831    <author initials="M." surname="Duerst"/>
1832    <date year="2011" month="August" day="13" />
1833  </front>
1834  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-comparison-00"/>
[24]1837<reference anchor='RFC4395bis'>
1838  <front>
1839    <title>Guidelines and Registration Procedures for New URI/IRI Schemes</title>
1840    <author initials='T.' surname='Hansen' fullname="Tony Hansen"><organization/></author>
1841    <author initials='T.' surname='Hardie' fullname="Ted Hardie"><organization/></author>
1842    <author initials='L.' surname='Masinter' fullname="Larry Masinter"><organization/></author>
[71]1843    <date year="2011" month='July' day="29"/>
[24]1844    <workgroup>IRI</workgroup>
1845  </front>
[71]1846  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-4395bis-irireg-03"/>
[20]1850<reference anchor="UNIXML" target="">
1852<title>Unicode in XML and other Markup Languages</title>
1853<author initials="M.J." surname="Duerst" fullname="Martin Duerst"><organization/></author>
1854<author initials="A." surname="Freytag" fullname="Asmus Freytag"><organization/></author>
1855<date year="2003" month="June" day="18"/>
1857<seriesInfo name="Unicode Technical Report" value="#20"/>
1858<seriesInfo name="World Wide Web Consortium" value="Note"/>
1861<reference anchor="UTR36" target="">
1863<title>Unicode Security Considerations</title>
1864<author initials="M." surname="Davis" fullname="Mark Davis"><organization/></author>
1865<author initials="M." surname="Suignard" fullname="Michel Suignard"><organization/></author>
1866<date year="2010" month="August" day="4"/>
1868<seriesInfo name="Unicode Technical Report" value="#36"/>
1871<reference anchor="XLink" target="">
1873<title>XML Linking Language (XLink) Version 1.0</title>
1874<author initials="S." surname="DeRose" fullname="Steve DeRose"><organization/></author>
1875<author initials="E." surname="Maler" fullname="Eve Maler"><organization/></author>
1876<author initials="D." surname="Orchard" fullname="David Orchard"><organization/></author>
1877<date year="2001" month="June" day="27"/>
[80]1879  <seriesInfo name="World Wide Web Consortium" value="REC-xlink-20010627"/>
1882<reference anchor="XML1" target="">
1883  <front>
1884    <title>Extensible Markup Language (XML) 1.0 (Forth Edition)</title>
1885    <author initials="T." surname="Bray" fullname="Tim Bray"><organization/></author>
1886    <author initials="J." surname="Paoli" fullname="Jean Paoli"><organization/></author>
1887    <author initials="C.M." surname="Sperberg-McQueen" fullname="C. M. Sperberg-McQueen">
1888      <organization/></author>
1889    <author initials="E." surname="Maler" fullname="Eve Maler"><organization/></author>
1890    <author initials="F." surname="Yergeau" fullname="Francois Yergeau"><organization/></author>
1891    <date day="16" month="August" year="2006"/>
1892  </front>
[80]1893  <seriesInfo name="World Wide Web Consortium" value="REC-xml-20081126"/>
1896<reference anchor="XMLNamespace" target="">
1897  <front>
1898    <title>Namespaces in XML (Second Edition)</title>
1899    <author initials="T." surname="Bray" fullname="Tim Bray"><organization/></author>
1900    <author initials="D." surname="Hollander" fullname="Dave Hollander"><organization/></author>
1901    <author initials="A." surname="Layman" fullname="Andrew Layman"><organization/></author>
[31]1902    <author initials="R." surname="Tobin" fullname="Richard Tobin"><organization></organization></author>
1903    <date day="16" month="August" year="2006"/>
[20]1904  </front>
[80]1905  <seriesInfo name="World Wide Web Consortium" value="REC-xml-names-20091208"/>
1908<reference anchor="XMLSchema" target="">
1910<title>XML Schema Part 2: Datatypes</title>
1911<author initials="P." surname="Biron" fullname="Paul Biron"><organization/></author>
1912<author initials="A." surname="Malhotra" fullname="Ashok Malhotra"><organization/></author>
1913<date year="2001" month="May" day="2"/>
[80]1915  <seriesInfo name="World Wide Web Consortium" value="REC-xmlschema-2-20041028"/>
1918<reference anchor="XPointer" target="">
1920<title>XPointer Framework</title>
1921<author initials="P." surname="Grosso" fullname="Paul Grosso"><organization/></author>
1922<author initials="E." surname="Maler" fullname="Eve Maler"><organization/></author>
1923<author initials="J." surname="Marsh" fullname="Jonathan Marsh"><organization/></author>
1924<author initials="N." surname="Walsh" fullname="Norman Walsh"><organization/></author>
1925<date year="2003" month="March" day="25"/>
[80]1927  <seriesInfo name="World Wide Web Consortium" value="REC-xptr-framework-20030325"/>
Note: See TracBrowser for help on using the repository browser.