source: draft-ietf-iri-3987bis/draft-ietf-iri-3987bis.xml @ 81

Last change on this file since 81 was 81, checked in by duerst@…, 8 years ago

removed superfluous whitespace after: ; non-zero-length segment without any colon ":"
(pointed out by Julian Reschke)

  • Property svn:executable set to *
File size: 86.6 KB
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1<?xml version="1.0"?>
2<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
3<!ENTITY rfc2045 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2045.xml">
4<!ENTITY rfc2119 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml">
5<!ENTITY rfc2130 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2130.xml">
6<!ENTITY rfc2141 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2141.xml">
7<!ENTITY rfc2192 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2192.xml">
8<!ENTITY rfc2277 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2277.xml">
9<!ENTITY rfc2368 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2368.xml">
10<!ENTITY rfc2384 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2384.xml">
11<!ENTITY rfc2396 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2396.xml">
12<!ENTITY rfc2397 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2397.xml">
13<!ENTITY rfc2616 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2616.xml">
14<!ENTITY rfc2640 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2640.xml">
15<!ENTITY rfc3491 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3491.xml">
16<!ENTITY rfc3629 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3629.xml">
17<!ENTITY rfc3986 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3986.xml">
18<!ENTITY rfc3987 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3987.xml">
19<!ENTITY rfc5890 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.5890.xml">
20<!ENTITY rfc5891 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.5891.xml">
21<!ENTITY rfc6055 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6055.xml">
22<!ENTITY rfc6082 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6082.xml">
23]>
24<?rfc strict='yes'?>
25
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'?>
34<rfc ipr="pre5378Trust200902" docName="draft-ietf-iri-3987bis-08" category="std" xml:lang="en" obsoletes="3987">
35<front>
36<title abbrev="IRIs">Internationalized Resource Identifiers (IRIs)</title>
37
38  <author initials="M.J." surname="Duerst" fullname='Martin Duerst'>
39    <!-- (Note: Please write "Duerst" with u-umlaut wherever
40      possible, for example as "D&#252;rst" in XML and HTML) -->
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>duerst@it.aoyama.ac.jp</email>
53  <uri>http://www.sw.it.aoyama.ac.jp/D%C3%BCrst/<!-- (Note: This is the percent-encoded form of an IRI)--></uri>
54  </address>
55</author>
56
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>michel@unicode.org</email>
70   <uri>http://www.suignard.com</uri>
71   </address>
72</author>
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>masinter@adobe.com</email>
85   <uri>http://larry.masinter.net</uri>
86   </address>
87</author>
88
89<date year="2011" />
90<area>Applications</area>
91<workgroup>Internationalized Resource Identifiers (iri)</workgroup>
92<keyword>IRI</keyword>
93<keyword>Internationalized Resource Identifier</keyword>
94<keyword>UTF-8</keyword>
95<keyword>URI</keyword>
96<keyword>IDN</keyword>
97<keyword>LEIRI</keyword>
98
99<abstract>
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>
105
106<t>In addition, this document provides named additional rule sets
107for processing otherwise invalid IRIs, in a way that supports
108other specifications that wish to mandate common behavior for
109'error' handling. In particular, rules used in some XML languages
110(LEIRI) and web applications are given.</t>
111
112<t>Defining IRI as new protocol element (rather than updating or
113extending the definition of URI) allows independent orderly
114transitions: other protocols and languages that use URIs must
115explicitly choose to allow IRIs.</t>
116
117<t>Guidelines are provided for the use and deployment of IRIs and
118related protocol elements when revising protocols, formats, and
119software components that currently deal only with URIs.</t>
120
121</abstract>
122  <note title='RFC Editor: Please remove the next paragraph before publication.'>
123    <t>This (and several companion documents) are intended to obsolete RFC 3987,
124    and also move towards IETF Draft Standard.  For discussion and comments on these
125    drafts, please join the IETF IRI WG by subscribing to the mailing
126    list public-iri@w3.org, archives at http://lists.w3.org/archives/public/public-iri/.
127    For a list of open issues, please see
128    the issue tracker of the WG at http://trac.tools.ietf.org/wg/iri/trac/report/1.
129    For a list of individual edits, please see the change history at
130    http://trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis.</t>
131</note>
132</front>
133<middle>
134
135<section title="Introduction">
136
137<section title="Overview and Motivation" anchor="overview">
138
139<t>A Uniform Resource Identifier (URI) is defined in <xref
140target="RFC3986"/> as a sequence of characters chosen from a limited
141subset of the repertoire of US-ASCII <xref target="ASCII"/>
142characters.</t>
143
144<t>The characters in URIs are frequently used for representing words
145of natural languages.  This usage has many advantages: Such URIs are
146easier to memorize, easier to interpret, easier to transcribe, easier
147to create, and easier to guess. For most languages other than English,
148however, the natural script uses characters other than A - Z. For many
149people, handling Latin characters is as difficult as handling the
150characters of other scripts is for those who use only the Latin
151alphabet. Many languages with non-Latin scripts are transcribed with
152Latin letters. These transcriptions are now often used in URIs, but
153they introduce additional difficulties.</t>
154
155<t>The infrastructure for the appropriate handling of characters from
156additional scripts is now widely deployed in operating system and
157application software. Software that can handle a wide variety of
158scripts and languages at the same time is increasingly common. Also,
159an increasing number of protocols and formats can carry a wide range of
160characters.</t>
161
162<t>URIs are used both as a protocol element (for transmission and
163processing by software) and also a presentation element (for display
164and handling by people who read, interpret, coin, or guess them). The
165transition between these roles is more difficult and complex when
166dealing with the larger set of characters than allowed for URIs in
167<xref target="RFC3986"/>. </t>
168
169<t>This document defines the protocol element called Internationalized
170Resource Identifier (IRI), which allow applications of URIs to be
171extended to use resource identifiers that have a much wider repertoire
172of characters. It also provides corresponding "internationalized"
173versions of other constructs from <xref target="RFC3986"/>, such as
174URI references. The syntax of IRIs is defined in <xref
175target="syntax"/>.
176</t>
177
178<t>Using characters outside of A - Z in IRIs adds a number of
179difficulties. <xref target="IRIuse"/> discusses the use
180of IRIs in different situations.  <xref target="guidelines"/> gives
181additional informative guidelines.  <xref target="security"/>
182discusses IRI-specific security considerations.</t>
183
184<t>
185<xref target="Bidi"/> discusses the special case of
186bidirectional IRIs using characters from scripts written
187right-to-left.
188<xref target="Equivalence"/> gives guidelines for applications wishing
189to determine if two IRIs are equivalent, as well as defining
190some equivalence methods.
191<xref target="RFC4395bis"/> updates the URI scheme registration
192guidelines and proceedures to note that every URI scheme is also
193automatically an IRI scheme and to allow scheme definitions
194to be directly described in terms of Unicode characters.
195</t>
196
197 <t>When originally defining IRIs, several design alternatives were considered.
198    Historically interested readers can find an overview in Appendix A of <xref target="RFC3987"/>.
199  For some additional background on the design of URIs and IRIs, please also see
200    <xref target="Gettys"/>.</t>
201
202</section> <!-- overview -->
203
204<section title="Applicability" anchor="Applicability">
205
206<t>IRIs are designed to allow protocols and software that deal with
207URIs to be updated to handle IRIs. Processing of
208IRIs is accomplished by extending the URI syntax while retaining (and
209not expanding) the set of "reserved" characters, such that the syntax
210for any URI scheme may be extended to allow non-ASCII
211characters. In addition, following parsing of an IRI, it is possible
212to construct a corresponding URI by first encoding characters outside
213of the allowed URI range and then reassembling the components.
214</t>
215
216<t>Practical use of IRIs forms in place of URIs forms depends on the
217following conditions being met:</t>
218
219<t><list style="hanging">
220   
221<t hangText="a.">A protocol or format element MUST be explicitly designated to be
222  able to carry IRIs. The intent is to avoid introducing IRIs into
223  contexts that are not defined to accept them.  For example, XML
224  schema <xref target="XMLSchema"/> has an explicit type "anyURI" that
225  includes IRIs and IRI references. Therefore, IRIs and IRI references
226  can be in attributes and elements of type "anyURI".  On the other
227  hand, in the <xref target="RFC2616"/> definition of HTTP/1.1, the
228  Request URI is defined as a URI, which means that direct use of IRIs
229  is not allowed in HTTP requests.</t>
230
231<t hangText="b.">The protocol or format carrying the IRIs MUST have a
232  mechanism to represent the wide range of characters used in IRIs,
233  either natively or by some protocol- or format-specific escaping
234  mechanism (for example, numeric character references in <xref
235  target="XML1"/>).</t>
236
237<t hangText="c.">The URI scheme definition, if it explicitly allows a
238  percent sign ("%") in any syntactic component, SHOULD define the
239  interpretation of sequences of percent-encoded octets (using "%XX"
240  hex octets) as octet from sequences of UTF-8 encoded strings; this
241  is recommended in the guidelines for registering new schemes, <xref
242  target="RFC4395bis"/>.  For example, this is the practice for IMAP URLs
243  <xref target="RFC2192"/>, POP URLs <xref target="RFC2384"/> and the
244  URN syntax <xref target="RFC2141"/>). Note that use of
245  percent-encoding may also be restricted in some situations, for
246  example, URI schemes that disallow percent-encoding might still be
247  used with a fragment identifier which is percent-encoded (e.g.,
248  <xref target="XPointer"/>). See <xref target="UTF8use"/> for further
249  discussion.</t>
250</list></t>
251
252</section> <!-- applicability -->
253
254<section title="Definitions" anchor="sec-Definitions">
255 
256<t>The following definitions are used in this document; they follow the
257terms in <xref target="RFC2130"/>, <xref target="RFC2277"/>, and
258<xref target="ISO10646"/>.</t>
259<t><list style="hanging">
260   
261<t hangText="character:">A member of a set of elements used for the
262    organization, control, or representation of data. For example,
263    "LATIN CAPITAL LETTER A" names a character.</t>
264   
265<t hangText="octet:">An ordered sequence of eight bits considered as a
266    unit.</t>
267   
268<t hangText="character repertoire:">A set of characters (set in the
269    mathematical sense).</t>
270   
271<t hangText="sequence of characters:">A sequence of characters (one
272    after another).</t>
273   
274<t hangText="sequence of octets:">A sequence of octets (one after
275    another).</t>
276   
277<t hangText="character encoding:">A method of representing a sequence
278    of characters as a sequence of octets (maybe with variants). Also,
279    a method of (unambiguously) converting a sequence of octets into a
280    sequence of characters.</t>
281   
282<t hangText="charset:">The name of a parameter or attribute used to
283    identify a character encoding.</t>
284   
285<t hangText="UCS:">Universal Character Set. The coded character set
286    defined by ISO/IEC 10646 <xref target="ISO10646"/> and the Unicode
287    Standard <xref target="UNIV6"/>.</t>
288   
289<t hangText="IRI reference:">Denotes the common usage of an
290    Internationalized Resource Identifier. An IRI reference may be
291    absolute or relative.  However, the "IRI" that results from such a
292    reference only includes absolute IRIs; any relative IRI references
293    are resolved to their absolute form.  Note that in <xref
294    target="RFC2396"/> URIs did not include fragment identifiers, but
295    in <xref target="RFC3986"/> fragment identifiers are part of
296    URIs.</t>
297   
298<t hangText="LEIRI (Legacy Extended IRI) processing:">  This term was used in
299   various XML specifications to refer
300   to strings that, although not valid IRIs, were acceptable input to
301   the processing rules in <xref target="LEIRIspec" />.</t>
302
303<t hangText="running text:">Human text (paragraphs, sentences,
304   phrases) with syntax according to orthographic conventions of a
305   natural language, as opposed to syntax defined for ease of
306   processing by machines (e.g., markup, programming languages).</t>
307   
308<t hangText="protocol element:">Any portion of a message that affects
309    processing of that message by the protocol in question.</t>
310   
311<t hangText="presentation element:">A presentation form corresponding
312    to a protocol element; for example, using a wider range of
313    characters.</t>
314   
315<t hangText="create (a URI or IRI):">With respect to URIs and IRIs,
316     the term is used for the initial creation. This may be the
317     initial creation of a resource with a certain identifier, or the
318     initial exposition of a resource under a particular
319     identifier.</t>
320   
321<t hangText="generate (a URI or IRI):">With respect to URIs and IRIs,
322     the term is used when the identifier is generated by derivation
323     from other information.</t>
324
325<t hangText="parsed URI component:">When a URI processor parses a URI
326   (following the generic syntax or a scheme-specific syntax, the result
327   is a set of parsed URI components, each of which has a type
328   (corresponding to the syntactic definition) and a sequence of URI
329   characters.  </t>
330
331<t hangText="parsed IRI component:">When an IRI processor parses
332   an IRI directly, following the general syntax or a scheme-specific
333   syntax, the result is a set of parsed IRI components, each of
334   which has a type (corresponding to the syntactice definition)
335   and a sequence of IRI characters. (This definition is analogous
336   to "parsed URI component".)</t>
337
338<t hangText="IRI scheme:">A URI scheme may also be known as
339   an "IRI scheme" if the scheme's syntax has been extended to
340   allow non-US-ASCII characters according to the rules in this
341   document.</t>
342
343</list></t>
344</section> <!-- definitions -->
345<section title="Notation" anchor="sec-Notation">
346     
347<t>RFCs and Internet Drafts currently do not allow any characters
348outside the US-ASCII repertoire. Therefore, this document uses various
349special notations to denote such characters in examples.</t>
350     
351<t>In text, characters outside US-ASCII are sometimes referenced by
352using a prefix of 'U+', followed by four to six hexadecimal
353digits.</t>
354
355<t>To represent characters outside US-ASCII in examples, this document
356uses 'XML Notation'.</t>
357
358<t>XML Notation uses a leading '&amp;#x', a trailing ';', and the
359hexadecimal number of the character in the UCS in between. For
360example, &amp;#x44F; stands for CYRILLIC CAPITAL LETTER YA. In this
361notation, an actual '&amp;' is denoted by '&amp;amp;'.</t>
362
363<t>To denote actual octets in examples (as opposed to percent-encoded
364octets), the two hex digits denoting the octet are enclosed in "&lt;"
365and "&gt;".  For example, the octet often denoted as 0xc9 is denoted
366here as &lt;c9&gt;.</t>
367
368<t> In this document, the key words "MUST", "MUST NOT", "REQUIRED",
369"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
370and "OPTIONAL" are to be interpreted as described in <xref
371target="RFC2119"/>.</t>
372
373</section> <!-- notation -->
374</section> <!-- introduction -->
375
376<section title="IRI Syntax" anchor="syntax">
377<t>This section defines the syntax of Internationalized Resource
378Identifiers (IRIs).</t>
379
380<t>As with URIs, an IRI is defined as a sequence of characters, not as
381a sequence of octets. This definition accommodates the fact that IRIs
382may be written on paper or read over the radio as well as stored or
383transmitted digitally.  The same IRI might be represented as different
384sequences of octets in different protocols or documents if these
385protocols or documents use different character encodings (and/or
386transfer encodings).  Using the same character encoding as the
387containing protocol or document ensures that the characters in the IRI
388can be handled (e.g., searched, converted, displayed) in the same way
389as the rest of the protocol or document.</t>
390
391<section title="Summary of IRI Syntax" anchor="summary">
392
393<t>The IRI syntax extends the URI syntax in <xref
394target="RFC3986"/> by extending the class of unreserved characters,
395primarily by adding the characters of the UCS (Universal Character Set, <xref
396target="ISO10646"/>) beyond U+007F, subject to the limitations given
397in the syntax rules below and in <xref target="limitations"/>.</t>
398
399<t>The syntax and use of components and reserved characters is the
400same as that in <xref target="RFC3986"/>. Each "URI scheme" thus also
401functions as an "IRI scheme", in that scheme-specific parsing rules
402for URIs of a scheme are be extended to allow parsing of IRIs using
403the same parsing rules.</t>
404
405<t>All the operations defined in <xref target="RFC3986"/>, such as the
406resolution of relative references, can be applied to IRIs by
407IRI-processing software in exactly the same way as they are for URIs
408by URI-processing software.</t>
409
410<t>Characters outside the US-ASCII repertoire MUST NOT be reserved and
411therefore MUST NOT be used for syntactical purposes, such as to
412delimit components in newly defined schemes. For example, U+00A2, CENT
413SIGN, is not allowed as a delimiter in IRIs, because it is in the
414'iunreserved' category. This is similar to the fact that it is not
415possible to use '-' as a delimiter in URIs, because it is in the
416'unreserved' category.</t>
417
418</section> <!-- summary -->
419<section title="ABNF for IRI References and IRIs" anchor="abnf">
420
421<t>An ABNF definition for IRI references (which are the most general
422concept and the start of the grammar) and IRIs is given here. The
423syntax of this ABNF is described in <xref target="STD68"/>. Character
424numbers are taken from the UCS, without implying any actual binary
425encoding. Terminals in the ABNF are characters, not octets.</t>
426
427<t>The following grammar closely follows the URI grammar in <xref
428target="RFC3986"/>, except that the range of unreserved characters is
429expanded to include UCS characters, with the restriction that private
430UCS characters can occur only in query parts. The grammar is split
431into two parts: Rules that differ from <xref target="RFC3986"/>
432because of the above-mentioned expansion, and rules that are the same
433as those in <xref target="RFC3986"/>. For rules that are different
434than those in <xref target="RFC3986"/>, the names of the non-terminals
435have been changed as follows. If the non-terminal contains 'URI', this
436has been changed to 'IRI'. Otherwise, an 'i' has been prefixed.
437The rule &lt;pct-form> has been introduced in order to be able to reference it from other parts of
438the document.</t>
439
440<!--
441for line length measuring in artwork (max 72 chars, three chars at start):
442      1         2         3         4         5         6         7
443456789012345678901234567890123456789012345678901234567890123456789012
444-->
445<figure>
446<preamble>The following rules are different from those in <xref target="RFC3986"/>:</preamble>
447<artwork>
448IRI            = scheme ":" ihier-part [ "?" iquery ]
449                 [ "#" ifragment ]
450
451ihier-part     = "//" iauthority ipath-abempty
452               / ipath-absolute
453               / ipath-rootless
454               / ipath-empty
455
456IRI-reference  = IRI / irelative-ref
457
458absolute-IRI   = scheme ":" ihier-part [ "?" iquery ]
459
460irelative-ref  = irelative-part [ "?" iquery ] [ "#" ifragment ]
461
462irelative-part = "//" iauthority ipath-abempty
463               / ipath-absolute
464               / ipath-noscheme
465               / ipath-empty
466
467iauthority     = [ iuserinfo "@" ] ihost [ ":" port ]
468iuserinfo      = *( iunreserved / pct-form / sub-delims / ":" )
469ihost          = IP-literal / IPv4address / ireg-name
470
471pct-form       = pct-encoded
472
473ireg-name      = *( iunreserved / sub-delims )
474
475ipath          = ipath-abempty   ; begins with "/" or is empty
476               / ipath-absolute  ; begins with "/" but not "//"
477               / ipath-noscheme  ; begins with a non-colon segment
478               / ipath-rootless  ; begins with a segment
479               / ipath-empty     ; zero characters
480
481ipath-abempty  = *( path-sep isegment )
482ipath-absolute = path-sep [ isegment-nz *( path-sep isegment ) ]
483ipath-noscheme = isegment-nz-nc *( path-sep isegment )
484ipath-rootless = isegment-nz *( path-sep isegment )
485ipath-empty    = 0&lt;ipchar&gt;
486path-sep       = "/"
487
488isegment       = *ipchar
489isegment-nz    = 1*ipchar
490isegment-nz-nc = 1*( iunreserved / pct-form / sub-delims
491                     / "@" )
492               ; non-zero-length segment without any colon ":"
493
494ipchar         = iunreserved / pct-form / sub-delims / ":"
495               / "@"
496 
497iquery         = *( ipchar / iprivate / "/" / "?" )
498
499ifragment      = *( ipchar / "/" / "?" )
500
501iunreserved    = ALPHA / DIGIT / "-" / "." / "_" / "~" / ucschar
502
503ucschar        = %xA0-D7FF / %xF900-FDCF / %xFDF0-FFEF
504               / %x10000-1FFFD / %x20000-2FFFD / %x30000-3FFFD
505               / %x40000-4FFFD / %x50000-5FFFD / %x60000-6FFFD
506               / %x70000-7FFFD / %x80000-8FFFD / %x90000-9FFFD
507               / %xA0000-AFFFD / %xB0000-BFFFD / %xC0000-CFFFD
508               / %xD0000-DFFFD / %xE1000-EFFFD
509
510iprivate       = %xE000-F8FF / %xE0000-E0FFF / %xF0000-FFFFD
511               / %x100000-10FFFD
512</artwork>
513</figure>
514
515<t>Some productions are ambiguous. The "first-match-wins" (a.k.a. "greedy")
516algorithm applies. For details, see <xref target="RFC3986"/>.</t>
517
518<figure>
519<preamble>The following rules are the same as those in <xref target="RFC3986"/>:</preamble>
520<artwork>
521scheme         = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
522 
523port           = *DIGIT
524 
525IP-literal     = "[" ( IPv6address / IPvFuture  ) "]"
526 
527IPvFuture      = "v" 1*HEXDIG "." 1*( unreserved / sub-delims / ":" )
528 
529IPv6address    =                            6( h16 ":" ) ls32
530               /                       "::" 5( h16 ":" ) ls32
531               / [               h16 ] "::" 4( h16 ":" ) ls32
532               / [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
533               / [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
534               / [ *3( h16 ":" ) h16 ] "::"    h16 ":"   ls32
535               / [ *4( h16 ":" ) h16 ] "::"              ls32
536               / [ *5( h16 ":" ) h16 ] "::"              h16
537               / [ *6( h16 ":" ) h16 ] "::"
538               
539h16            = 1*4HEXDIG
540ls32           = ( h16 ":" h16 ) / IPv4address
541
542IPv4address    = dec-octet "." dec-octet "." dec-octet "." dec-octet
543
544dec-octet      = DIGIT                 ; 0-9
545               / %x31-39 DIGIT         ; 10-99
546               / "1" 2DIGIT            ; 100-199
547               / "2" %x30-34 DIGIT     ; 200-249
548               / "25" %x30-35          ; 250-255
549           
550pct-encoded    = "%" HEXDIG HEXDIG
551
552unreserved     = ALPHA / DIGIT / "-" / "." / "_" / "~"
553reserved       = gen-delims / sub-delims
554gen-delims     = ":" / "/" / "?" / "#" / "[" / "]" / "@"
555sub-delims     = "!" / "$" / "&amp;" / "'" / "(" / ")"
556               / "*" / "+" / "," / ";" / "="
557</artwork></figure>
558
559<t>This syntax does not support IPv6 scoped addressing zone identifiers.</t>
560
561</section> <!-- abnf -->
562
563</section> <!-- syntax -->
564
565<section title="Processing IRIs and related protocol elements" anchor="processing">
566
567<t>IRIs are meant to replace URIs in identifying resources within new
568versions of protocols, formats, and software components that use a
569UCS-based character repertoire.  Protocols and components may use and
570process IRIs directly. However, there are still numerous systems and
571protocols which only accept URIs or components of parsed URIs; that is,
572they only accept sequences of characters within the subset of US-ASCII
573characters allowed in URIs. </t>
574
575<t>This section defines specific processing steps for IRI consumers
576which establish the relationship between the string given and the
577interpreted derivatives. These
578processing steps apply to both IRIs and IRI references (i.e., absolute
579or relative forms); for IRIs, some steps are scheme specific. </t>
580
581<section title="Converting to UCS" anchor="ucsconv"> 
582 
583<t>Input that is already in a Unicode form (i.e., a sequence of Unicode
584 characters or an octet-stream representing a Unicode-based character
585 encoding such as UTF-8 or UTF-16) should be left as is and not
586 normalized or changed.</t>
587
588  <t>An IRI or IRI reference is a sequence of characters from the UCS.
589    For resource identifiers that are not already in a Unicode form
590    (as when written on paper, read aloud, or represented in a text stream
591    using a legacy character encoding), convert the IRI to Unicode.
592    Note that some character encodings or transcriptions can be converted
593    to or represented by more than one sequence of Unicode characters.
594
595    Ideally the resulting IRI would use a normalized form,
596    such as Unicode Normalization Form C <xref target="UTR15"/>,
597    since that ensures a stable, consistent representation
598    that is most likely to produce the intended results.
599    Implementers and users are cautioned that, while denormalized character sequences are valid,
600    they might be difficult for other users or processes to reproduce
601    and might lead to unexpected results.
602  </t>
603
604<t> In other cases (written on paper, read aloud, or otherwise
605 represented independent of any character encoding) represent the IRI
606 as a sequence of characters from the UCS normalized according to
607 Unicode Normalization Form C (NFC, <xref target="UTR15"/>).</t>
608</section> <!-- ucsconv -->
609
610<section title="Parse the IRI into IRI components">
611
612<t>Parse the IRI, either as a relative reference (no scheme)
613or using scheme specific processing (according to the scheme
614given); the result is a set of parsed IRI components.</t>
615
616</section> <!-- parse -->
617
618<section title="General percent-encoding of IRI components" anchor="compmapping">
619   
620<t>Except as noted in the following subsections, IRI components are mapped
621to the equivalent URI components by percent-encoding those characters
622not allowed in URIs. Previous processing steps will have removed
623some characters, and the interpretation of reserved characters will
624have already been done (with the syntactic reserved characters outside
625of the IRI component). This mapping is defined for all sequences
626of Unicode characters, whether or not they are valid for the component
627in question. </t>
628   
629<t>For each character which is not allowed anywhere in a valid URI
630 apply the following steps. </t>
631<t><list style="hanging">
632
633<t hangText="Convert to UTF-8">Convert the character to a sequence of
634  one or more octets using UTF-8 <xref target="RFC3629"/>.</t>
635
636<t hangText="Percent encode">Convert each octet of this sequence to %HH,
637   where HH is the hexadecimal notation of the octet value. The
638   hexadecimal notation SHOULD use uppercase letters. (This is the
639   general URI percent-encoding mechanism in Section 2.1 of <xref
640   target="RFC3986"/>.)</t>
641   
642</list></t>
643
644<t>Note that the mapping is an identity transformation for parsed URI
645components of valid URIs, and is idempotent: applying the mapping a
646second time will not change anything.</t>
647</section> <!-- general conversion -->
648
649<section title="Mapping ireg-name" anchor="dnsmapping">
650  <section title='Mapping using Percent-Encoding' anchor='dnspercent'>
651  <t>The ireg-name component SHOULD be converted
652    according to the general procedure for percent-encoding
653    of IRI components described in <xref target="compmapping"/>.</t>
654 
655  <t>For example, the IRI
656    <vspace/>"http://r&amp;#xE9;sum&amp;#xE9;.example.org"<vspace/> will be
657    converted to <vspace/>"http://r%C3%A9sum%C3%A9.example.org".</t>
658
659  <t>This conversion for ireg-name is in line with Section 3.2.2
660    of <xref target="RFC3986"/>, which does not mandate
661    a particular registered name lookup technology. For further background,
662    see <xref target="RFC6055"/> and <xref target="Gettys"/>.</t>
663</section> <!-- dnspercent -->
664<section title="Mapping using Punycode" anchor='dnspunycode'>
665  <t>The ireg-name component MAY also be converted as follows:</t>
666
667  <t>If there are any sequences of &lt;pct-encoded&gt;, and their
668    corresponding octets all represent valid UTF-8
669    octet sequences, then convert these back to Unicode
670    character sequences. (If any &lt;pct-encoded&gt; sequences are not
671    valid UTF-8 octet sequences, then leave the entire field as is
672    without any change, since punycode encoding would not succeed.)</t>
673
674<t>Replace the ireg-name part of the IRI by the part converted using
675the Domain Name Lookup procedure (Subsections 5.3 to 5.5) of <xref target="RFC5891"/>.
676  on each dot-separated label, and by using U+002E
677(FULL STOP) as a label separator.
678This procedure may fail, but this would mean that the IRI cannot be resolved.
679In such cases, if the domain name conversion fails, then the
680entire IRI conversion fails. Processors that have no mechanism for
681signalling a failure MAY instead substitute an otherwise
682invalid host name, although such processing SHOULD be avoided.</t>
683
684<t>For example, the IRI
685<vspace/>"http://r&amp;#xE9;sum&amp;#xE9;.example.org"<vspace/> MAY be
686converted to <vspace/>"http://xn--rsum-bad.example.org"<vspace/>.</t>
687  <t>This conversion for ireg-name will be better able to deal with legacy
688    infrastructure that cannot handle percent-encoding in domain names.</t>
689</section> <!-- punicode -->
690  <section title="Additional Considerations">
691
692<t><list style="hanging"> 
693<t hangText="Note:">Domain Names may appear in parts of an IRI other
694than the ireg-name part.  It is the responsibility of scheme-specific
695implementations (if the Internationalized Domain Name is part of the
696scheme syntax) or of server-side implementations (if the
697Internationalized Domain Name is part of 'iquery') to apply the
698necessary conversions at the appropriate point. Example: Trying to
699validate the Web page at<vspace/>
700http://r&amp;#xE9;sum&amp;#xE9;.example.org would lead to an IRI of
701<vspace/>http://validator.w3.org/check?uri=http%3A%2F%2Fr&amp;#xE9;sum&amp;#xE9;.<vspace/>example.org,
702which would convert to a URI
703of<vspace/>http://validator.w3.org/check?uri=http%3A%2F%2Fr%C3%A9sum%C3%A9.<vspace/>example.org.
704The server-side implementation is responsible for making the
705necessary conversions to be able to retrieve the Web page.</t>
706
707<t hangText="Note:">In this process, characters allowed in URI
708references and existing percent-encoded sequences are not encoded further.
709(This mapping is similar to, but different from, the encoding applied
710when arbitrary content is included in some part of a URI.)
711
712For example, an IRI of
713<vspace/>"http://www.example.org/red%09ros&amp;#xE9;#red"
714(in XML notation) is converted to
715<vspace/>"http://www.example.org/red%09ros%C3%A9#red", not to
716something like
717<vspace/>"http%3A%2F%2Fwww.example.org%2Fred%2509ros%C3%A9%23red".</t>
718
719</list></t>
720</section> <!-- additional -->
721</section> <!-- dnsmapping -->
722
723<section title="Mapping query components" anchor="querymapping">
724
725<t>For compatibility with existing deployed HTTP infrastructure,
726the following special case applies for schemes "http" and "https"
727and IRIs whose origin has a document charset other than one which
728is UCS-based (e.g., UTF-8 or UTF-16). In such a case, the "query"
729component of an IRI is mapped into a URI by using the document
730charset rather than UTF-8 as the binary representation before
731pct-encoding. This mapping is not applied for any other scheme
732or component.</t>
733
734</section> <!-- querymapping -->
735
736<section title="Mapping IRIs to URIs" anchor="mapping">
737
738<t>The mapping from an IRI to URI is accomplished by applying the
739mapping above (from IRI to URI components) and then reassembling a URI
740from the parsed URI components using the original punctuation that
741delimited the IRI components. </t>
742
743</section> <!-- mapping -->
744
745<section title="Converting URIs to IRIs" anchor="URItoIRI">
746
747  <t>In some situations, for presentation and further processing,
748it is desirable to convert a URI into an equivalent IRI
749without unnecessary percent encoding.
750Of course, every URI is already an IRI in its own right without any
751conversion. This section gives one possible procedure for URI to IRI mapping.</t>
752
753<t>
754The conversion described in this section, if given a valid URI, will
755result in an IRI that maps back to the URI used as an input for the
756conversion (except for potential case differences in percent-encoding
757and for potential percent-encoded unreserved characters).
758
759However, the IRI resulting from this conversion may differ
760from the original IRI (if there ever was one).</t> 
761
762<t>URI-to-IRI conversion removes percent-encodings, but not all
763percent-encodings can be eliminated. There are several reasons for
764this:</t>
765
766<t><list style="hanging">
767
768<t hangText="1.">Some percent-encodings are necessary to distinguish
769    percent-encoded and unencoded uses of reserved characters.</t>
770
771<t hangText="2.">Some percent-encodings cannot be interpreted as sequences
772    of UTF-8 octets.<vspace blankLines="1"/>
773    (Note: The octet patterns of UTF-8 are highly regular.
774    Therefore, there is a very high probability, but no guarantee,
775    that percent-encodings that can be interpreted as sequences of UTF-8
776    octets actually originated from UTF-8. For a detailed discussion,
777    see <xref target="Duerst97"/>.)</t>
778
779<t hangText="3.">The conversion may result in a character that is not
780    appropriate in an IRI. See <xref target="abnf"/>,
781      and <xref target="limitations"/> for further details.</t>
782
783<t hangText="4.">IRI to URI conversion has different rules for
784    dealing with domain names and query parameters.</t>
785
786</list></t>
787
788<t>Conversion from a URI to an IRI MAY be done by using the following
789steps:
790
791<list style="hanging">
792<t hangText="1.">Represent the URI as a sequence of octets in
793       US-ASCII.</t>
794
795<t hangText="2.">Convert all percent-encodings ("%" followed by two
796      hexadecimal digits) to the corresponding octets, except those
797      corresponding to "%", characters in "reserved", and characters
798      in US-ASCII not allowed in URIs.</t> 
799
800<t hangText="3.">Re-percent-encode any octet produced in step 2 that
801      is not part of a strictly legal UTF-8 octet sequence.</t>
802
803
804<t hangText="4.">Re-percent-encode all octets produced in step 3 that
805      in UTF-8 represent characters that are not appropriate according
806      to <xref target="abnf"/>  and <xref
807      target="limitations"/>.</t> 
808
809<t hangText="5.">Interpret the resulting octet sequence as a sequence
810      of characters encoded in UTF-8.</t>
811
812<t hangText="6.">URIs known to contain domain names in the reg-name
813      component SHOULD convert punycode-encoded domain name labels to
814      the corresponding characters using the ToUnicode procedure. </t>
815</list></t>
816
817<t>This procedure will convert as many percent-encoded characters as
818possible to characters in an IRI. Because there are some choices when
819step 4 is applied (see <xref target="limitations"/>), results may
820vary.</t>
821
822<t>Conversions from URIs to IRIs MUST NOT use any character
823encoding other than UTF-8 in steps 3 and 4, even if it might be
824possible to guess from the context that another character encoding
825than UTF-8 was used in the URI.  For example, the URI
826"http://www.example.org/r%E9sum%E9.html" might with some guessing be
827interpreted to contain two e-acute characters encoded as
828iso-8859-1. It must not be converted to an IRI containing these
829e-acute characters. Otherwise, in the future the IRI will be mapped to
830"http://www.example.org/r%C3%A9sum%C3%A9.html", which is a different
831URI from "http://www.example.org/r%E9sum%E9.html".</t>
832
833<section title="Examples">
834
835<t>This section shows various examples of converting URIs to IRIs.
836Each example shows the result after each of the steps 1 through 6 is
837applied. XML Notation is used for the final result.  Octets are
838denoted by "&lt;" followed by two hexadecimal digits followed by
839"&gt;".</t>
840
841<t>The following example contains the sequence "%C3%BC", which is a
842strictly legal UTF-8 sequence, and which is converted into the actual
843character U+00FC, LATIN SMALL LETTER U WITH DIAERESIS (also known as
844u-umlaut).
845
846<list style="hanging">
847<t hangText="1.">http://www.example.org/D%C3%BCrst</t>
848<t hangText="2.">http://www.example.org/D&lt;c3&gt;&lt;bc&gt;rst</t>
849<t hangText="3.">http://www.example.org/D&lt;c3&gt;&lt;bc&gt;rst</t>
850<t hangText="4.">http://www.example.org/D&lt;c3&gt;&lt;bc&gt;rst</t>
851<t hangText="5.">http://www.example.org/D&amp;#xFC;rst</t>
852<t hangText="6.">http://www.example.org/D&amp;#xFC;rst</t>
853</list>
854</t>
855
856<t>The following example contains the sequence "%FC", which might
857represent U+00FC, LATIN SMALL LETTER U WITH DIAERESIS, in
858the<vspace/>iso-8859-1 character encoding.  (It might represent other
859characters in other character encodings. For example, the octet
860&lt;fc&gt; in iso-8859-5 represents U+045C, CYRILLIC SMALL LETTER
861KJE.)  Because &lt;fc&gt; is not part of a strictly legal UTF-8
862sequence, it is re-percent-encoded in step 3.
863
864
865<list style="hanging">
866<t hangText="1.">http://www.example.org/D%FCrst</t>
867<t hangText="2.">http://www.example.org/D&lt;fc&gt;rst</t>
868<t hangText="3.">http://www.example.org/D%FCrst</t>
869<t hangText="4.">http://www.example.org/D%FCrst</t>
870<t hangText="5.">http://www.example.org/D%FCrst</t>
871<t hangText="6.">http://www.example.org/D%FCrst</t>
872</list>
873</t>
874
875<t>The following example contains "%e2%80%ae", which is the percent-encoded<vspace/>UTF-8
876character encoding of U+202E, RIGHT-TO-LEFT OVERRIDE.
877The direct use of this character is forbiddin in an IRI. Therefore, the
878corresponding octets are re-percent-encoded in step 4. This example shows
879that the case (upper- or lowercase) of letters used in percent-encodings may not be preserved.
880The example also contains a punycode-encoded domain name label (xn--99zt52a),
881which is not converted.
882
883<list style="hanging">
884<t hangText="1.">http://xn--99zt52a.example.org/%e2%80%ae</t>
885<t hangText="2.">http://xn--99zt52a.example.org/&lt;e2&gt;&lt;80&gt;&lt;ae&gt;</t>
886<t hangText="3.">http://xn--99zt52a.example.org/&lt;e2&gt;&lt;80&gt;&lt;ae&gt;</t>
887<t hangText="4.">http://xn--99zt52a.example.org/%E2%80%AE</t>
888<t hangText="5.">http://xn--99zt52a.example.org/%E2%80%AE</t>
889<t hangText="6.">http://&amp;#x7D0D;&amp;#x8C46;.example.org/%E2%80%AE</t>
890</list></t>
891
892<t>Note that the label "xn--99zt52a" is converted to U+7D0D U+8C46
893(Japanese Natto). ((EDITOR NOTE: There is some inconsistency in this note.))</t>
894
895</section> <!-- examples -->
896</section> <!-- URItoIRI -->
897</section> <!-- processing -->
898
899
900<section title="Use of IRIs" anchor="IRIuse">
901
902<section title="Limitations on UCS Characters Allowed in IRIs" anchor="limitations">
903
904<t>This section discusses limitations on characters and character
905sequences usable for IRIs beyond those given in <xref target="abnf"/>.
906The considerations in this section are
907relevant when IRIs are created and when URIs are converted to
908IRIs.</t>
909
910<t>
911
912<list style="hanging"><t hangText="a.">The repertoire of characters allowed
913    in each IRI component is limited by the definition of that component.
914    For example, the definition of the scheme component does not allow
915    characters beyond US-ASCII.
916    <vspace blankLines="1"/>
917    (Note: In accordance with URI practice, generic IRI
918    software cannot and should not check for such limitations.)</t>
919
920<t hangText="b.">The UCS contains many areas of characters for which
921    there are strong visual look-alikes. Because of the likelihood of
922    transcription errors, these also should be avoided. This includes
923    the full-width equivalents of Latin characters, half-width
924    Katakana characters for Japanese, and many others. It also
925    includes many look-alikes of "space", "delims", and "unwise",
926    characters excluded in <xref target="RFC3491"/>.</t>
927   
928</list>
929</t>
930
931<t>Additional information is available from <xref target="UNIXML"/>.
932    <xref target="UNIXML"/> is written in the context of running text
933    rather than in that of identifiers. Nevertheless, it discusses
934    many of the categories of characters not appropriate for IRIs.</t>
935</section> <!-- limitations -->
936
937<section title="Software Interfaces and Protocols">
938
939<t>Although an IRI is defined as a sequence of characters, software
940interfaces for URIs typically function on sequences of octets or other
941kinds of code units. Thus, software interfaces and protocols MUST
942define which character encoding is used.</t>
943
944<t>Intermediate software interfaces between IRI-capable components and
945URI-only components MUST map the IRIs per <xref target="mapping"/>,
946when transferring from IRI-capable to URI-only components.
947
948This mapping SHOULD be applied as late as possible. It SHOULD NOT be
949applied between components that are known to be able to handle IRIs.</t>
950</section> <!-- software -->
951
952<section title="Format of URIs and IRIs in Documents and Protocols">
953
954<t>Document formats that transport URIs may have to be upgraded to allow
955the transport of IRIs. In cases where the document as a whole
956has a native character encoding, IRIs MUST also be encoded in this
957character encoding and converted accordingly by a parser or interpreter.
958
959IRI characters not expressible in the native character encoding SHOULD
960be escaped by using the escaping conventions of the document format if
961such conventions are available. Alternatively, they MAY be
962percent-encoded according to <xref target="mapping"/>. For example, in
963HTML or XML, numeric character references SHOULD be used. If a
964document as a whole has a native character encoding and that character
965encoding is not UTF-8, then IRIs MUST NOT be placed into the document
966in the UTF-8 character encoding.</t>
967
968<t>((UPDATE THIS NOTE)) Note: Some formats already accommodate IRIs,
969although they use different terminology. HTML 4.0 <xref
970target="HTML4"/> defines the conversion from IRIs to URIs as
971error-avoiding behavior. XML 1.0 <xref target="XML1"/>, XLink <xref
972target="XLink"/>, XML Schema <xref target="XMLSchema"/>, and
973specifications based upon them allow IRIs. Also, it is expected that
974all relevant new W3C formats and protocols will be required to handle
975IRIs <xref target="CharMod"/>.</t>
976
977</section> <!-- format -->
978
979<section title="Use of UTF-8 for Encoding Original Characters" anchor="UTF8use">
980
981<t>This section discusses details and gives examples for point c) in
982<xref target="Applicability"/>. To be able to use IRIs, the URI
983corresponding to the IRI in question has to encode original characters
984into octets by using UTF-8.  This can be specified for all URIs of a
985URI scheme or can apply to individual URIs for schemes that do not
986specify how to encode original characters.  It can apply to the whole
987URI, or only to some part. For background information on encoding
988characters into URIs, see also Section 2.5 of <xref
989target="RFC3986"/>.</t>
990
991<t>For new URI schemes, using UTF-8 is recommended in <xref
992target="RFC4395bis"/>.  Examples where UTF-8 is already used are the URN
993syntax <xref target="RFC2141"/>, IMAP URLs <xref target="RFC2192"/>,
994and POP URLs <xref target="RFC2384"/>.  On the other hand, because the
995HTTP URI scheme does not specify how to encode original characters,
996only some HTTP URLs can have corresponding but different IRIs.</t>
997
998<t>For example, for a document with a URI
999of<vspace/>"http://www.example.org/r%C3%A9sum%C3%A9.html", it is
1000possible to construct a corresponding IRI (in XML notation, see <xref
1001target="sec-Notation"/>):
1002"http://www.example.org/r&amp;#xE9;sum&amp;#xE9;.html" ("&amp;#xE9;"
1003stands for the e-acute character, and "%C3%A9" is the UTF-8 encoded
1004and percent-encoded representation of that character). On the other
1005hand, for a document with a URI of
1006"http://www.example.org/r%E9sum%E9.html", the percent-encoding octets
1007cannot be converted to actual characters in an IRI, as the
1008percent-encoding is not based on UTF-8.</t>
1009
1010<t>For most URI schemes, there is no need to upgrade their scheme
1011definition in order for them to work with IRIs.  The main case where
1012upgrading makes sense is when a scheme definition, or a particular
1013component of a scheme, is strictly limited to the use of US-ASCII
1014characters with no provision to include non-ASCII characters/octets
1015via percent-encoding, or if a scheme definition currently uses highly
1016scheme-specific provisions for the encoding of non-ASCII characters.
1017An example of this is the mailto: scheme <xref target="RFC2368"/>.</t>
1018
1019<t>This specification updates the IANA registry of URI schemes to note
1020their applicability to IRIs, see <xref target="iana"/>.  All IRIs use
1021URI schemes, and all URIs with URI schemes can be used as IRIs, even
1022though in some cases only by using URIs directly as IRIs, without any
1023conversion.</t>
1024
1025<t>Scheme definitions can impose restrictions on the syntax of
1026scheme-specific URIs; i.e., URIs that are admissible under the generic
1027URI syntax <xref target="RFC3986"/> may not be admissible due to
1028narrower syntactic constraints imposed by a URI scheme
1029specification. URI scheme definitions cannot broaden the syntactic
1030restrictions of the generic URI syntax; otherwise, it would be
1031possible to generate URIs that satisfied the scheme-specific syntactic
1032constraints without satisfying the syntactic constraints of the
1033generic URI syntax. However, additional syntactic constraints imposed
1034by URI scheme specifications are applicable to IRI, as the
1035corresponding URI resulting from the mapping defined in <xref
1036target="mapping"/> MUST be a valid URI under the syntactic
1037restrictions of generic URI syntax and any narrower restrictions
1038imposed by the corresponding URI scheme specification.</t>
1039
1040<t>The requirement for the use of UTF-8 generally applies to all parts
1041of a URI.  However, it is possible that the capability of IRIs to
1042represent a wide range of characters directly is used just in some
1043parts of the IRI (or IRI reference). The other parts of the IRI may
1044only contain US-ASCII characters, or they may not be based on
1045UTF-8. They may be based on another character encoding, or they may
1046directly encode raw binary data (see also <xref
1047target="RFC2397"/>). </t>
1048
1049<t>For example, it is possible to have a URI reference
1050of<vspace/>"http://www.example.org/r%E9sum%E9.xml#r%C3%A9sum%C3%A9",
1051where the document name is encoded in iso-8859-1 based on server
1052settings, but where the fragment identifier is encoded in UTF-8 according
1053to <xref target="XPointer"/>. The IRI corresponding to the above
1054URI would be (in XML notation)<vspace/>"http://www.example.org/r%E9sum%E9.xml#r&amp;#xE9;sum&amp;#xE9;".</t>
1055
1056<t>Similar considerations apply to query parts. The functionality
1057of IRIs (namely, to be able to include non-ASCII characters) can
1058only be used if the query part is encoded in UTF-8.</t>
1059
1060</section> <!-- utf8 -->
1061
1062<section title="Relative IRI References">
1063<t>Processing of relative IRI references against a base is handled
1064straightforwardly; the algorithms of <xref target="RFC3986"/> can
1065be applied directly, treating the characters additionally allowed
1066in IRI references in the same way that unreserved characters are in URI
1067references.</t>
1068
1069</section> <!-- relative -->
1070</section> <!-- IRIuse -->
1071
1072<section title="Liberal Handling of Otherwise Invalid IRIs" anchor="LEIRIHREF">
1073
1074<t>
1075Some technical specifications and widely-deployed software have
1076allowed additional variations and extensions of IRIs to be used in
1077syntactic components. </t>
1078<t>Future technical specifications SHOULD NOT allow conforming
1079producers to produce, or conforming content to contain, such forms,
1080as they are not interoperable with other IRI consuming software.</t>
1081
1082<section title="LEIRI Processing"  anchor="LEIRIspec">
1083  <t>This section defines Legacy Extended IRIs (LEIRIs).
1084    The syntax of Legacy Extended IRIs is the same as that for &lt;IRI-reference>,
1085    except that the ucschar production is replaced by the leiri-ucschar production:</t>
1086<figure>
1087
1088<artwork>
1089  leiri-ucschar  = " " / "&lt;" / "&gt;" / DQUOTE / "{" / "}" / "|"
1090                   / "\" / "^" / "`" / %x0-1F / %x7F-D7FF
1091                   / %xE000-FFFD / %x10000-10FFFF
1092</artwork>
1093
1094<postamble>
1095  Among other extensions, processors based on this specification also
1096  did not enforce the restriction on bidirectional formatting
1097  characters in <xref target="Bidi"></xref>, and the iprivate
1098  production becomes redundant.</postamble>
1099</figure>
1100
1101<t>To convert a string allowed as a LEIRI to an IRI, each character
1102allowed in leiri-ucschar but not in ucschar must be percent-encoded
1103using <xref target="compmapping"/>.</t>
1104</section> <!-- leiriproc -->
1105</section> <!-- LEIRIHREF -->
1106
1107  <section title="Characters Disallowed or Not Recommended in IRIs" anchor="notAllowed">
1108
1109<t>This section provides a list of the groups of characters and code
1110points that are allowed in some contexts but are not allowed in IRIs or are
1111allowed in IRIs only in the query part. For each group of characters,
1112advice on the usage of these characters is also given, concentrating
1113on the reasons for why they are excluded from IRI use.</t>
1114
1115<t>
1116
1117<list><t>Space (U+0020): Some formats and applications use space as a
1118delimiter, e.g. for items in a list. Appendix C of <xref
1119target="RFC3986"></xref> also mentions that white space may have to be
1120added when displaying or printing long URIs; the same applies to long
1121IRIs. This means that spaces can disappear, or can make the what is
1122intended as a single IRI or IRI reference to be treated as two or more
1123separate IRIs.</t>
1124
1125<t>Delimiters "&lt;" (U+003C), "&gt;" (U+003E), and '"' (U+0022):
1126Appendix C of <xref target="RFC3986"></xref> suggests the use of
1127double-quotes ("http://example.com/") and angle brackets
1128(&lt;http://example.com/&gt;) as delimiters for URIs in plain
1129text. These conventions are often used, and also apply to IRIs.  Using
1130these characters in strings intended to be IRIs would result in the
1131IRIs being cut off at the wrong place.</t>
1132
1133<t>Unwise characters "\" (U+005C), "^" (U+005E), "`"
1134(U+0060), "{" (U+007B), "|" (U+007C), and "}" (U+007D): These
1135characters originally have been excluded from URIs because the
1136respective codepoints are assigned to different graphic characters in
1137some 7-bit or 8-bit encoding. Despite the move to Unicode, some of
1138these characters are still occasionally displayed differently on some
1139systems, e.g. U+005C may appear as a Japanese Yen symbol on some
1140systems. Also, the fact that these characters are not used in URIs or
1141IRIs has encouraged their use outside URIs or IRIs in contexts that
1142may include URIs or IRIs. If a string with such a character were used
1143as an IRI in such a context, it would likely be interpreted
1144piecemeal.</t>
1145
1146<t>The controls (C0 controls, DEL, and C1 controls, #x0 - #x1F #x7F -
1147#x9F): There is generally no way to transmit these characters reliably
1148as text outside of a charset encoding.  Even when in encoded form,
1149many software components silently filter out some of these characters,
1150or may stop processing alltogether when encountering some of
1151them. These characters may affect text display in subtle, unnoticable
1152ways or in drastic, global, and irreversible ways depending on the
1153hardware and software involved. The use of some of these characters
1154would allow malicious users to manipulate the display of an IRI and
1155its context in many situations.</t>
1156
1157<t>Bidi formatting characters (U+200E, U+200F, U+202A-202E): These
1158characters affect the display ordering of characters. If IRIs were
1159allowed to contain these characters and the resulting visual display
1160transcribed. they could not be converted back to electronic form
1161(logical order) unambiguously. These characters, if allowed in IRIs,
1162might allow malicious users to manipulate the display of IRI and its
1163context.</t>
1164
1165<t>Specials (U+FFF0-FFFD): These code points provide functionality
1166beyond that useful in an IRI, for example byte order identification,
1167annotation, and replacements for unknown characters and objects. Their
1168use and interpretation in an IRI would serve no purpose and might lead
1169to confusing display variations.</t>
1170
1171<t>Private use code points (U+E000-F8FF, U+F0000-FFFFD,
1172U+100000-10FFFD): Display and interpretation of these code points is
1173by definition undefined without private agreement. In any case, these
1174code points are not suited for use on the Internet. They are not
1175interoperable and may have unpredictable effects.</t>
1176
1177<t>Tags (U+E0000-E0FFF): These characters were intended to provide
1178  a way to language tag in Unicode plain text. They are now deprecated <xref target="RFC6082" />.
1179  In any case, they would not be appropriate for IRIs because
1180language information in identifiers cannot reliably be input,
1181transmitted (e.g. on a visual medium such as paper), or
1182recognized.</t>
1183
1184<t>Non-characters (U+FDD0-FDEF, U+1FFFE-1FFFF, U+2FFFE-2FFFF,
1185U+3FFFE-3FFFF, U+4FFFE-4FFFF, U+5FFFE-5FFFF, U+6FFFE-6FFFF,
1186U+7FFFE-7FFFF, U+8FFFE-8FFFF, U+9FFFE-9FFFF, U+AFFFE-AFFFF,
1187U+BFFFE-BFFFF, U+CFFFE-CFFFF, U+DFFFE-DFFFF, U+EFFFE-EFFFF,
1188U+FFFFE-FFFFF, U+10FFFE-10FFFF): These code points are defined as
1189non-characters. Applications may use some of them internally, but are
1190not prepared to interchange them.</t>
1191
1192</list></t>
1193
1194<t>LEIRI preprocessing disallowed some code points and
1195code units:
1196
1197<list><t>Surrogate code units (D800-DFFF): These do not represent
1198Unicode codepoints.</t></list></t>
1199</section> <!-- notallowed -->
1200
1201<section title="URI/IRI Processing Guidelines (Informative)" anchor="guidelines">
1202
1203<t>This informative section provides guidelines for supporting IRIs in
1204the same software components and operations that currently process
1205URIs: Software interfaces that handle URIs, software that allows users
1206to enter URIs, software that creates or generates URIs, software that
1207displays URIs, formats and protocols that transport URIs, and software
1208that interprets URIs. These may all require modification before
1209functioning properly with IRIs. The considerations in this section
1210also apply to URI references and IRI references.</t>
1211
1212<section title="URI/IRI Software Interfaces">
1213<t>Software interfaces that handle URIs, such as URI-handling APIs and
1214protocols transferring URIs, need interfaces and protocol elements
1215that are designed to carry IRIs.</t>
1216
1217<t>In case the current handling in an API or protocol is based on
1218US-ASCII, UTF-8 is recommended as the character encoding for IRIs, as
1219it is compatible with US-ASCII, is in accordance with the
1220recommendations of <xref target="RFC2277"/>, and makes converting to
1221URIs easy. In any case, the API or protocol definition must clearly
1222define the character encoding to be used.</t>
1223
1224<t>The transfer from URI-only to IRI-capable components requires no
1225mapping, although the conversion described in <xref
1226target="URItoIRI"/> above may be performed. It is preferable not to
1227perform this inverse conversion unless it is certain this can be done
1228correctly.</t>
1229</section><!-- software interfaces -->
1230
1231<section title="URI/IRI Entry">
1232
1233<t>Some components allow users to enter URIs into the system
1234by typing or dictation, for example. This software must be updated to allow
1235for IRI entry.</t>
1236
1237<t>A person viewing a visual representation of an IRI (as a sequence
1238of glyphs, in some order, in some visual display) or hearing an IRI
1239will use an entry method for characters in the user's language to
1240input the IRI. Depending on the script and the input method used, this
1241may be a more or less complicated process.</t>
1242
1243<t>The process of IRI entry must ensure, as much as possible, that the
1244restrictions defined in <xref target="abnf"/> are met. This may be
1245done by choosing appropriate input methods or variants/settings
1246thereof, by appropriately converting the characters being input, by
1247eliminating characters that cannot be converted, and/or by issuing a
1248warning or error message to the user.</t>
1249
1250<t>As an example of variant settings, input method editors for East
1251Asian Languages usually allow the input of Latin letters and related
1252characters in full-width or half-width versions. For IRI input, the
1253input method editor should be set so that it produces half-width Latin
1254letters and punctuation and full-width Katakana.</t>
1255
1256<t>An input field primarily or solely used for the input of URIs/IRIs
1257might allow the user to view an IRI as it is mapped to a URI.  Places
1258where the input of IRIs is frequent may provide the possibility for
1259viewing an IRI as mapped to a URI. This will help users when some of
1260the software they use does not yet accept IRIs.</t>
1261
1262<t>An IRI input component interfacing to components that handle URIs,
1263but not IRIs, must map the IRI to a URI before passing it to these
1264components.</t>
1265
1266<t>For the input of IRIs with right-to-left characters, please see
1267<xref target="Bidi"></xref>.</t>
1268</section><!-- entry -->
1269
1270<section title="URI/IRI Transfer between Applications">
1271
1272<t>Many applications (for example, mail user agents) try to detect
1273URIs appearing in plain text. For this, they use some heuristics based
1274on URI syntax. They then allow the user to click on such URIs and
1275retrieve the corresponding resource in an appropriate (usually
1276scheme-dependent) application.</t>
1277
1278<t>Such applications would need to be upgraded, in order to use the
1279IRI syntax as a base for heuristics. In particular, a non-ASCII
1280character should not be taken as the indication of the end of an IRI.
1281Such applications also would need to make sure that they correctly
1282convert the detected IRI from the character encoding of the document
1283or application where the IRI appears, to the character encoding used
1284by the system-wide IRI invocation mechanism, or to a URI (according to
1285<xref target="mapping"/>) if the system-wide invocation mechanism only
1286accepts URIs.</t>
1287
1288<t>The clipboard is another frequently used way to transfer URIs and
1289IRIs from one application to another. On most platforms, the clipboard
1290is able to store and transfer text in many languages and scripts.
1291Correctly used, the clipboard transfers characters, not octets, which
1292will do the right thing with IRIs.</t>
1293</section><!-- transfer -->
1294
1295<section title="URI/IRI Generation">
1296
1297<t>Systems that offer resources through the Internet, where those
1298resources have logical names, sometimes automatically generate URIs
1299for the resources they offer. For example, some HTTP servers can
1300generate a directory listing for a file directory and then respond to
1301the generated URIs with the files.</t>
1302
1303<t>Many legacy character encodings are in use in various file systems.
1304Many currently deployed systems do not transform the local character
1305representation of the underlying system before generating URIs.</t>
1306
1307<t>For maximum interoperability, systems that generate resource
1308identifiers should make the appropriate transformations. For example,
1309if a file system contains a file named
1310"r&amp;#xE9;sum&amp;#xE9;.html", a server should expose this as
1311"r%C3%A9sum%C3%A9.html" in a URI, which allows use of
1312"r&amp;#xE9;sum&amp;#xE9;.html" in an IRI, even if locally the file
1313name is kept in a character encoding other than UTF-8.
1314</t>
1315
1316<t>This recommendation particularly applies to HTTP servers. For FTP
1317servers, similar considerations apply; see <xref target="RFC2640"/>.</t>
1318</section><!-- generation -->
1319
1320<section title="URI/IRI Selection" anchor="selection">
1321<t>In some cases, resource owners and publishers have control over the
1322IRIs used to identify their resources. This control is mostly
1323executed by controlling the resource names, such as file names,
1324directly.</t>
1325
1326<t>In these cases, it is recommended to avoid choosing IRIs that are
1327easily confused. For example, for US-ASCII, the lower-case ell ("l") is
1328easily confused with the digit one ("1"), and the upper-case oh ("O") is
1329easily confused with the digit zero ("0"). Publishers should avoid
1330confusing users with "br0ken" or "1ame" identifiers.</t>
1331
1332<t>Outside the US-ASCII repertoire, there are many more opportunities for
1333confusion; a complete set of guidelines is too lengthy to include
1334here. As long as names are limited to characters from a single script,
1335native writers of a given script or language will know best when
1336ambiguities can appear, and how they can be avoided. What may look
1337ambiguous to a stranger may be completely obvious to the average
1338native user. On the other hand, in some cases, the UCS contains
1339variants for compatibility reasons; for example, for typographic purposes.
1340These should be avoided wherever possible. Although there may be exceptions,
1341newly created resource names should generally be in NFKC
1342<xref target="UTR15"></xref> (which means that they are also in NFC).</t>
1343
1344<t>As an example, the UCS contains the "fi" ligature at U+FB01
1345for compatibility reasons.
1346Wherever possible, IRIs should use the two letters "f" and "i" rather
1347than the "fi" ligature. An example where the latter may be used is
1348in the query part of an IRI for an explicit search for a word written
1349containing the "fi" ligature.</t>
1350
1351<t>In certain cases, there is a chance that characters from different
1352scripts look the same. The best known example is the similarity of the
1353Latin "A", the Greek "Alpha", and the Cyrillic "A". To avoid such
1354cases, IRIs should only be created where all the characters in a
1355single component are used together in a given language. This usually
1356means that all of these characters will be from the same script, but
1357there are languages that mix characters from different scripts (such
1358as Japanese).  This is similar to the heuristics used to distinguish
1359between letters and numbers in the examples above. Also, for Latin,
1360Greek, and Cyrillic, using lowercase letters results in fewer
1361ambiguities than using uppercase letters would.</t>
1362</section><!-- selection -->
1363
1364<section title="Display of URIs/IRIs" anchor="display">
1365<t>
1366In situations where the rendering software is not expected to display
1367non-ASCII parts of the IRI correctly using the available layout and font
1368resources, these parts should be percent-encoded before being displayed.</t>
1369
1370<t>For display of Bidi IRIs, please see <xref target="Bidi"/>.</t>
1371</section> <!-- display -->
1372
1373<section title="Interpretation of URIs and IRIs">
1374<t>Software that interprets IRIs as the names of local resources should
1375accept IRIs in multiple forms and convert and match them with the
1376appropriate local resource names.</t>
1377
1378<t>First, multiple representations include both IRIs in the native
1379character encoding of the protocol and also their URI counterparts.</t>
1380
1381<t>Second, it may include URIs constructed based on character
1382encodings other than UTF-8. These URIs may be produced by user agents that do
1383not conform to this specification and that use legacy character encodings to
1384convert non-ASCII characters to URIs. Whether this is necessary, and what
1385character encodings to cover, depends on a number of factors, such as
1386the legacy character encodings used locally and the distribution of
1387various versions of user agents. For example, software for Japanese
1388may accept URIs in Shift_JIS and/or EUC-JP in addition to UTF-8.</t>
1389
1390<t>Third, it may include additional mappings to be more user-friendly
1391and robust against transmission errors. These would be similar to how
1392some servers currently treat URIs as case insensitive or perform
1393additional matching to account for spelling errors. For characters
1394beyond the US-ASCII repertoire, this may, for example, include
1395ignoring the accents on received IRIs or resource names. Please note
1396that such mappings, including case mappings, are language
1397dependent.</t>
1398
1399<t>It can be difficult to identify a resource unambiguously if too
1400many mappings are taken into consideration. However, percent-encoded
1401and not percent-encoded parts of IRIs can always be clearly distinguished.
1402Also, the regularity of UTF-8 (see <xref target="Duerst97"/>) makes the
1403potential for collisions lower than it may seem at first.</t>
1404</section> <!-- interpretation -->
1405
1406<section title="Upgrading Strategy">
1407<t>Where this recommendation places further constraints on software
1408for which many instances are already deployed, it is important to
1409introduce upgrades carefully and to be aware of the various
1410interdependencies.</t>
1411
1412<t>If IRIs cannot be interpreted correctly, they should not be created,
1413generated, or transported. This suggests that upgrading URI interpreting
1414software to accept IRIs should have highest priority.</t>
1415
1416<t>On the other hand, a single IRI is interpreted only by a single or
1417very few interpreters that are known in advance, although it may be
1418entered and transported very widely.</t>
1419
1420<t>Therefore, IRIs benefit most from a broad upgrade of software to be
1421able to enter and transport IRIs. However, before an
1422individual IRI is published, care should be taken to upgrade the corresponding
1423interpreting software in order to cover the forms expected to be
1424received by various versions of entry and transport software.</t>
1425
1426<t>The upgrade of generating software to generate IRIs instead of using a
1427local character encoding should happen only after the service is upgraded
1428to accept IRIs. Similarly, IRIs should only be generated when the service
1429accepts IRIs and the intervening infrastructure and protocol is known
1430to transport them safely.</t>
1431
1432<t>Software converting from URIs to IRIs for display should be upgraded
1433only after upgraded entry software has been widely deployed to the
1434population that will see the displayed result.</t>
1435
1436
1437<t>Where there is a free choice of character encodings, it is often
1438possible to reduce the effort and dependencies for upgrading to IRIs
1439by using UTF-8 rather than another encoding. For example, when a new
1440file-based Web server is set up, using UTF-8 as the character encoding
1441for file names will make the transition to IRIs easier. Likewise, when
1442a new Web form is set up using UTF-8 as the character encoding of the
1443form page, the returned query URIs will use UTF-8 as the character
1444encoding (unless the user, for whatever reason, changes the character
1445encoding) and will therefore be compatible with IRIs.</t>
1446
1447
1448<t>These recommendations, when taken together, will allow for the
1449extension from URIs to IRIs in order to handle characters other than
1450US-ASCII while minimizing interoperability problems. For
1451considerations regarding the upgrade of URI scheme definitions, see
1452<xref target="UTF8use"/>.</t>
1453
1454</section> <!-- upgrading -->
1455</section> <!-- guidelines -->
1456
1457<section title="IANA Considerations" anchor="iana">
1458
1459<t>RFC Editor and IANA note: Please Replace RFC XXXX with the
1460number of this document when it issues as an RFC. </t>
1461
1462<t>IANA maintains a registry of "URI schemes". A "URI scheme" also
1463serves an "IRI scheme". </t>
1464
1465<t>To clarify that the URI scheme registration process also applies to
1466IRIs, change the description of the "URI schemes" registry
1467header to say "[RFC4395] defines an IANA-maintained registry of URI
1468Schemes. These registries include the Permanent and Provisional URI
1469Schemes.  RFC XXXX updates this registry to designate that schemes may
1470also indicate their usability as IRI schemes.</t>
1471
1472<t> Update "per RFC 4395" to "per RFC 4395 and RFC XXXX".
1473</t>
1474
1475</section> <!-- IANA -->
1476   
1477<section title="Security Considerations" anchor="security">
1478<t>The security considerations discussed in <xref target="RFC3986"/>
1479also apply to IRIs. In addition, the following issues require
1480particular care for IRIs.</t>
1481<t>Incorrect encoding or decoding can lead to security problems.
1482For example, some UTF-8 decoders do not check against overlong
1483byte sequences. See <xref target='UTR36'/> Section 3 for details.</t>
1484
1485  <t>There are serious difficulties with relying on a human to verify that a
1486    an IRI (whether presented visually or aurally)
1487    is the same as another IRI or is the one intended.
1488    These problems exist with ASCII-only URIs (bl00mberg.com vs. bloomberg.com)
1489    but are strongly exacerbated when using the much larger character repertoire of Unicode.
1490    For details, see Section 2 of <xref target='UTR36'/>.
1491    Using administrative and technical means to reduce the availability
1492    of such exploits is possible, but they are difficult to eliminate altogether.
1493    User agents SHOULD NOT rely on visual or perceptual comparison or verification of IRIs
1494    as a means of validating or assuring safety, correctness or appropriateness of an IRI.
1495    Other means of presenting users with the validity, safety, or appropriateness
1496    of visited sites are being developed in the browser community
1497    as an alternative means of avoiding these difficulties.</t>
1498
1499<t>Besides the large character repertoire of Unicode, reasons for
1500  confusion include different forms of normalization and different normalization
1501  expectations, use of percent-encoding with various legacy encodings,
1502  and bidirectionality issues. See also <xref target="Bidi"/>.</t>
1503
1504<t>Confusion can occur in various IRI components, such as the
1505domain name part or the path part, or between IRI components. For considerations specific
1506to the domain name part, see <xref target="RFC5890"/>. For considerations specific to
1507particular protocols or schemes, see the security sections of the relevant specifications
1508and registration templates.
1509Administrators of sites that allow independent
1510users to create resources in the same sub area have to be careful.
1511Details are discussed in <xref target="selection"/>.</t>
1512
1513  <t>The characters additionally allowed in Legacy Extended IRIs
1514    introduce additional security issues. For details, see <xref target='notAllowed'/>.</t>
1515</section><!-- security -->
1516
1517<section title="Acknowledgements">
1518<t>This document was derived from <xref target="RFC3987"/>; the acknowledgments from
1519that specification still apply.</t>
1520<t>In addition, this document was influenced by contributions from (in no particular order)Norman Walsh, Richard Tobin,
1521  Henry S. Thomson, John Cowan, Paul Grosso, the XML Core Working Group of the W3C,
1522 Chris
1523  Lilley, Bjoern Hoehrmann,
1524Felix Sasaki, Jeremy Carroll, Frank Ellermann, Michael Everson, Cary Karp, Matitiahu Allouche,
1525Richard Ishida, Addison Phillips, Jonathan Rosenne, Najib Tounsi, Debbie Garside, Mark Davis, Sarmad
1526Hussain, Ted Hardie, Konrad Lanz, Thomas Roessler, Lisa Dusseault, Julian Reschke, Giovanni
1527Campagna, Anne van Kesteren, Mark Nottingham, Erik van der Poel, Marcin Hanclik, Marcos Caceres, Roy
1528Fielding, Greg Wilkins, Pieter Hintjens, Daniel R. Tobias, Marko Martin, Maciej Stanchowiak, Wil
1529Tan, Yui Naruse, Michael A. Puls II, Dave Thaler, Tom Petch, John Klensin, Shawn Steele, Peter
1530Saint-Andre, Geoffrey Sneddon, Chris Weber, Alex Melnikov, Slim Amamou, S. Moonesamy, Tim Berners-Lee, Yaron
1531Goland, Sam Ruby, Adam Barth, Abdulrahman I. ALGhadir, Aharon Lanin, Thomas Milo, Murray Sargent,
1532Marc Blanchet, and Mykyta Yevstifeyev.</t>
1533</section> <!-- Acknowledgements -->
1534
1535<section title="Main Changes Since RFC 3987">
1536  <t>This section describes the main changes since <xref target="RFC3987"></xref>.</t>
1537  <section title="Split out Bidi, processing guidelines, comparison sections">
1538    <t>Move some components (comparison, bidi, processing) into separate documents.</t>
1539  </section>
1540  <section title="Major restructuring of IRI processing model" anchor="forkChanges">
1541    <t>Major restructuring of IRI processing model to make scheme-specific translation
1542      necessary to handle IDNA requirements and for consistency with web implementations. </t>
1543    <t>Starting with IRI, you want one of:
1544      <list style="hanging">
1545        <t hangText="a"> IRI components (IRI parsed into UTF8 pieces)</t>
1546        <t hangText="b"> URI components (URI parsed into ASCII pieces, encoded correctly) </t>
1547        <t hangText="c"> whole URI  (for passing on to some other system that wants whole URIs) </t>
1548      </list></t>
1549   
1550    <section title="OLD WAY">
1551      <t><list style="numbers">
1552       
1553        <t>Pct-encoding on the whole thing to a URI.
1554          (c1) If you want a (maybe broken) whole URI, you might
1555          stop here.</t>
1556       
1557        <t>Parsing the URI into URI components.
1558          (b1) If you want (maybe broken) URI components, stop here.</t>
1559       
1560        <t> Decode the components (undoing the pct-encoding).
1561          (a) if you want IRI components, stop here.</t>
1562       
1563        <t> reencode:  Either using a different encoding some components
1564          (for domain names, and query components in web pages, which
1565          depends on the component, scheme and context), and otherwise
1566          using pct-encoding.
1567          (b2) if you want (good) URI components, stop here.</t>
1568       
1569        <t> reassemble the reencoded components.
1570          (c2) if you want a (*good*) whole URI stop here.</t>
1571      </list>
1572       
1573      </t>
1574     
1575    </section>
1576   
1577    <section title="NEW WAY">
1578      <t>
1579        <list style="numbers">
1580         
1581          <t> Parse the IRI into IRI components using the generic syntax.
1582            (a) if you want IRI components, stop here.</t>
1583         
1584          <t> Encode each components, using pct-encoding, IDN encoding, or
1585            special query part encoding depending on the component
1586            scheme or context. (b) If you want URI components, stop here.</t>
1587          <t> reassemble the a whole URI from URI components.
1588            (c) if you want a whole URI stop here.</t>
1589        </list></t>
1590    </section>
1591    <section title="Extension of Syntax">
1592      <t>Added the tag range (U+E0000-E0FFF) to the iprivate production.
1593        Some IRIs generated with the new syntax may fail to pass very strict checks
1594        relying on the old syntax. But characters in this range should be extremely infrequent
1595        anyway.</t>
1596    </section>
1597    <section title="More to be added"><t>TODO: There are more main changes that need to be
1598      documented in this section.</t></section>
1599</section>
1600
1601<section title="Change Log">
1602
1603<t>Note to RFC Editor: Please completely remove this section before publication.</t>
1604
1605<section title='Changes after draft-ietf-iri-3987bis-01'>
1606    <t>Changes from draft-ietf-iri-3987bis-01 onwards are available as changesets
1607      in the IETF tools subversion repository at
1608      http://trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis/draft-ietf-iri-3987bis.xml.</t>
1609</section>
1610 
1611<section title='Changes from draft-duerst-iri-bis-07 to draft-ietf-iri-3987bis-00'>
1612     <t>Changed draft name, date, last paragraph of abstract, and titles in change log, and added this section
1613     in moving from draft-duerst-iri-bis-07 (personal submission) to draft-ietf-iri-3987bis-00 (WG document).</t>
1614</section>
1615
1616<section title="Changes from -06 to -07 of draft-duerst-iri-bis">
1617  <t>Major restructuring of the processing model, see <xref target="forkChanges"></xref>.</t>
1618</section>
1619</section>
1620
1621<section title='Changes from -00 to -01'><t><list style="symbols">
1622  <t>Removed 'mailto:' before mail addresses of authors.</t>
1623  <t>Added "&lt;to be done&gt;" as right side of 'href-strip' rule. Fixed '|' to '/' for
1624    alternatives.</t>
1625</list></t>
1626</section>
1627
1628<section title="Changes from -05 to -06 of draft-duerst-iri-bis-00"><t><list style="symbols">
1629<t>Add HyperText Reference, change abstract, acks and references for it</t>
1630<t>Add Masinter back as another editor.</t>
1631<t>Masinter integrates HRef material from HTML5 spec.</t>
1632<t>Rewrite introduction sections to modernize.</t>
1633</list></t>
1634</section>
1635
1636<section title="Changes from -04 to -05 of draft-duerst-iri-bis">
1637  <t><list style="symbols">
1638    <t>Updated references.</t>
1639    <t>Changed IPR text to pre5378Trust200902.</t></list></t>
1640</section>
1641
1642<section title="Changes from -03 to -04 of draft-duerst-iri-bis">
1643  <t><list style="symbols">
1644    <t>Added explicit abbreviation for LEIRIs.</t>
1645    <t>Mentioned LEIRI references.</t>
1646    <t>Completed text in LEIRI section about tag characters and about specials.</t></list></t>
1647</section>
1648
1649<section title="Changes from -02 to -03 of draft-duerst-iri-bis">
1650  <t><list style="symbols">
1651    <t>Updated some references.</t>
1652    <t>Updated Michel Suginard's coordinates.</t></list></t>
1653</section>
1654
1655<section title="Changes from -01 to -02 of draft-duerst-iri-bis">
1656  <t><list style="symbols">
1657    <t>Added tag range to iprivate (issue private-include-tags-115).</t>
1658    <t>Added Specials (U+FFF0-FFFD) to Legacy Extended IRIs.</t></list></t>
1659</section>
1660<section title="Changes from -00 to -01 of draft-duerst-iri-bis">
1661  <t><list style="symbols">
1662    <t>Changed from "IRIs with Spaces/Controls" to "Legacy Extended IRI"
1663      based on input from the W3C XML Core WG.
1664      Moved the relevant subsections to the back and promoted them to a section.</t>
1665    <t>Added some text re. Legacy Extended IRIs to the security section.</t>
1666    <t>Added a IANA Consideration Section.</t>
1667    <t>Added this Change Log Section.</t>
1668    <t>Added a section about "IRIs with Spaces/Controls" (converting from a Note in RFC 3987).</t></list></t>
1669</section> <!-- -00 to -01 -->
1670<section title="Changes from RFC 3987 to -00 of draft-duerst-iri-bis">
1671  <t><list>
1672    <t>Fixed errata (see http://www.rfc-editor.org/cgi-bin/errataSearch.pl?rfc=3987).</t></list></t>
1673</section> <!-- from 3987 -->
1674</section>
1675</middle>
1676
1677<back>
1678<references title="Normative References">
1679
1680<reference anchor="ASCII">
1681<front>
1682<title>Coded Character Set -- 7-bit American Standard Code for Information
1683Interchange</title>
1684<author>
1685<organization>American National Standards Institute</organization>
1686</author>
1687<date year="1986"/>
1688</front>
1689<seriesInfo name="ANSI" value="X3.4"/>
1690</reference>
1691
1692  <reference anchor="ISO10646" target='http://standards.iso.org/ittf/PubliclyAvailableStandards/c051273_ISO_IEC_10646_2011(E).zip'>
1693<front>
1694<title>ISO/IEC 10646:2011: Information Technology -
1695Universal Multiple-Octet Coded Character Set (UCS)</title>
1696<author>
1697<organization>International Organization for Standardization</organization>
1698</author>
1699<date month="March" year="20011"/>
1700</front>
1701<seriesInfo name="ISO" value="Standard 10646"/>
1702</reference>
1703
1704&rfc2119;
1705&rfc3491;
1706&rfc3629;
1707&rfc3986;
1708
1709<reference anchor="STD68">
1710<front>
1711<title abbrev="ABNF">Augmented BNF for Syntax Specifications: ABNF</title>
1712<author initials="D." surname="Crocker" fullname="Dave Crocker"><organization/></author>
1713<author initials="P." surname="Overell" fullname="Paul Overell"><organization/></author>
1714<date month="January" year="2008"/></front>
1715<seriesInfo name="STD" value="68"/><seriesInfo name="RFC" value="5234"/>
1716</reference>
1717 
1718&rfc5890;
1719&rfc5891;
1720
1721<reference anchor="UNIV6">
1722<front>
1723<title>The Unicode Standard, Version 6.0.0 (Mountain View, CA, The Unicode Consortium, 2011, ISBN 978-1-936213-01-6)</title>
1724<author><organization>The Unicode Consortium</organization></author>
1725<date year="2010" month="October"/>
1726</front>
1727</reference>
1728
1729<reference anchor="UTR15" target="http://www.unicode.org/unicode/reports/tr15/tr15-23.html">
1730<front>
1731<title>Unicode Normalization Forms</title>
1732<author initials="M." surname="Davis" fullname="Mark Davis"><organization/></author>
1733<author initials="M.J." surname="Duerst" fullname="Martin Duerst"><organization/></author>
1734<date year="2008" month="March"/>
1735</front>
1736<seriesInfo name="Unicode Standard Annex" value="#15"/>
1737</reference>
1738
1739</references>
1740
1741<references title="Informative References">
1742
1743<reference anchor="CharMod" target="http://www.w3.org/TR/charmod-resid">
1744<front>
1745<title>Character Model for the World Wide Web: Resource Identifiers</title>
1746<author initials="M." surname="Duerst" fullname="Martin Duerst"><organization/></author>
1747<author initials="F." surname="Yergeau" fullname="Francois Yergeau"><organization/></author>
1748<author initials="R." surname="Ishida" fullname="Richard Ishida"><organization/></author>
1749<author initials="M." surname="Wolf" fullname="Misha Wolf"><organization/></author>
1750<author initials="T." surname="Texin" fullname="Tex Texin"><organization/></author>
1751<date year="2004" month="November" day="25"/>
1752</front>
1753<seriesInfo name="World Wide Web Consortium" value="Candidate Recommendation"/>
1754</reference>
1755
1756<reference anchor="Duerst97" target="http://www.ifi.unizh.ch/mml/mduerst/papers/PDF/IUC11-UTF-8.pdf">
1757<front>
1758<title>The Properties and Promises of UTF-8</title>
1759<author initials="M.J." surname="Duerst" fullname="Martin Duerst"><organization/></author>
1760<date year="1997" month="September"/>
1761</front>
1762<seriesInfo name="Proc. 11th International Unicode Conference, San Jose" value=""/>
1763</reference>
1764
1765<reference anchor="Gettys" target="http://www.w3.org/DesignIssues/ModelConsequences">
1766<front>
1767<title>URI Model Consequences</title>
1768<author initials="J." surname="Gettys" fullname="Jim Gettys"><organization/></author>
1769<date month="" year=""/>
1770</front>
1771</reference>
1772
1773<reference anchor="HTML4" target="http://www.w3.org/TR/html401/appendix/notes.html#h-B.2">
1774<front>
1775<title>HTML 4.01 Specification</title>
1776<author initials="D." surname="Raggett" fullname="Dave Raggett"><organization/></author>
1777<author initials="A." surname="Le Hors" fullname="Arnaud Le Hors"><organization/></author>
1778<author initials="I." surname="Jacobs" fullname="Ian Jacobs"><organization/></author>
1779<date year="1999" month="December" day="24"/>
1780</front>
1781<seriesInfo name="World Wide Web Consortium" value="Recommendation"/>
1782</reference>
1783
1784<reference anchor="LEIRI" target="http://www.w3.org/TR/leiri/">
1785<front>
1786<title>Legacy extended IRIs for XML resource identification</title>
1787<author initials="H." surname="Thompson" fullname="Henry Thompson"><organization/></author>
1788<author initials="R." surname="Tobin"    fullname="Richard Tobin"><organization/></author>
1789<author initials="N." surname="Walsh" fullname="Norman Walsh"><organization/></author>
1790  <date year="2008" month="November" day="3"/>
1791
1792</front>
1793<seriesInfo name="World Wide Web Consortium" value="Note"/>
1794</reference>
1795
1796
1797&rfc2045;
1798&rfc2130;
1799&rfc2141;
1800&rfc2192;
1801&rfc2277;
1802&rfc2368;
1803&rfc2384;
1804&rfc2396;
1805&rfc2397;
1806&rfc2616;
1807&rfc2640;
1808&rfc3987;
1809&rfc6055;
1810&rfc6082;
1811
1812<reference anchor='Bidi'>
1813  <front>
1814    <title>Guidelines for Internationalized Resource Identifiers with Bi-directional Characters (Bidi IRIs)</title>
1815    <author initials="M." surname="Duerst"/>
1816    <author initials='L.' surname='Masinter' />
1817    <date year="2011" month="August" day="14" />
1818  </front>
1819  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-bidi-guidelines-00"/>
1820</reference>
1821
1822<reference anchor='Equivalence'>
1823  <front>
1824    <title>Equivalence and Canonicalization of Internationalized Resource Identifiers (IRIs)</title>
1825    <author initials='L.' surname='Masinter' />
1826    <author initials="M." surname="Duerst"/>
1827    <date year="2011" month="August" day="13" />
1828  </front>
1829  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-comparison-00"/>
1830</reference>
1831
1832<reference anchor='RFC4395bis'>
1833  <front>
1834    <title>Guidelines and Registration Procedures for New URI/IRI Schemes</title>
1835    <author initials='T.' surname='Hansen' fullname="Tony Hansen"><organization/></author>
1836    <author initials='T.' surname='Hardie' fullname="Ted Hardie"><organization/></author>
1837    <author initials='L.' surname='Masinter' fullname="Larry Masinter"><organization/></author>
1838    <date year="2011" month='July' day="29"/>
1839    <workgroup>IRI</workgroup>
1840  </front>
1841  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-4395bis-irireg-03"/>
1842</reference>
1843 
1844 
1845<reference anchor="UNIXML" target="http://www.w3.org/TR/unicode-xml/">
1846<front>
1847<title>Unicode in XML and other Markup Languages</title>
1848<author initials="M.J." surname="Duerst" fullname="Martin Duerst"><organization/></author>
1849<author initials="A." surname="Freytag" fullname="Asmus Freytag"><organization/></author>
1850<date year="2003" month="June" day="18"/>
1851</front>
1852<seriesInfo name="Unicode Technical Report" value="#20"/>
1853<seriesInfo name="World Wide Web Consortium" value="Note"/>
1854</reference>
1855 
1856<reference anchor="UTR36" target="http://unicode.org/reports/tr36/">
1857<front>
1858<title>Unicode Security Considerations</title>
1859<author initials="M." surname="Davis" fullname="Mark Davis"><organization/></author>
1860<author initials="M." surname="Suignard" fullname="Michel Suignard"><organization/></author>
1861<date year="2010" month="August" day="4"/>
1862</front>
1863<seriesInfo name="Unicode Technical Report" value="#36"/>
1864</reference>
1865
1866<reference anchor="XLink" target="http://www.w3.org/TR/xlink/#link-locators">
1867<front>
1868<title>XML Linking Language (XLink) Version 1.0</title>
1869<author initials="S." surname="DeRose" fullname="Steve DeRose"><organization/></author>
1870<author initials="E." surname="Maler" fullname="Eve Maler"><organization/></author>
1871<author initials="D." surname="Orchard" fullname="David Orchard"><organization/></author>
1872<date year="2001" month="June" day="27"/>
1873</front>
1874  <seriesInfo name="World Wide Web Consortium" value="REC-xlink-20010627"/>
1875</reference>
1876
1877<reference anchor="XML1" target="http://www.w3.org/TR/REC-xml">
1878  <front>
1879    <title>Extensible Markup Language (XML) 1.0 (Forth Edition)</title>
1880    <author initials="T." surname="Bray" fullname="Tim Bray"><organization/></author>
1881    <author initials="J." surname="Paoli" fullname="Jean Paoli"><organization/></author>
1882    <author initials="C.M." surname="Sperberg-McQueen" fullname="C. M. Sperberg-McQueen">
1883      <organization/></author>
1884    <author initials="E." surname="Maler" fullname="Eve Maler"><organization/></author>
1885    <author initials="F." surname="Yergeau" fullname="Francois Yergeau"><organization/></author>
1886    <date day="16" month="August" year="2006"/>
1887  </front>
1888  <seriesInfo name="World Wide Web Consortium" value="REC-xml-20081126"/>
1889</reference>
1890
1891<reference anchor="XMLNamespace" target="http://www.w3.org/TR/REC-xml-names">
1892  <front>
1893    <title>Namespaces in XML (Second Edition)</title>
1894    <author initials="T." surname="Bray" fullname="Tim Bray"><organization/></author>
1895    <author initials="D." surname="Hollander" fullname="Dave Hollander"><organization/></author>
1896    <author initials="A." surname="Layman" fullname="Andrew Layman"><organization/></author>
1897    <author initials="R." surname="Tobin" fullname="Richard Tobin"><organization></organization></author>
1898    <date day="16" month="August" year="2006"/>
1899  </front>
1900  <seriesInfo name="World Wide Web Consortium" value="REC-xml-names-20091208"/>
1901</reference>
1902
1903<reference anchor="XMLSchema" target="http://www.w3.org/TR/xmlschema-2/#anyURI">
1904<front>
1905<title>XML Schema Part 2: Datatypes</title>
1906<author initials="P." surname="Biron" fullname="Paul Biron"><organization/></author>
1907<author initials="A." surname="Malhotra" fullname="Ashok Malhotra"><organization/></author>
1908<date year="2001" month="May" day="2"/>
1909</front>
1910  <seriesInfo name="World Wide Web Consortium" value="REC-xmlschema-2-20041028"/>
1911</reference>
1912
1913<reference anchor="XPointer" target="http://www.w3.org/TR/xptr-framework/#escaping">
1914<front>
1915<title>XPointer Framework</title>
1916<author initials="P." surname="Grosso" fullname="Paul Grosso"><organization/></author>
1917<author initials="E." surname="Maler" fullname="Eve Maler"><organization/></author>
1918<author initials="J." surname="Marsh" fullname="Jonathan Marsh"><organization/></author>
1919<author initials="N." surname="Walsh" fullname="Norman Walsh"><organization/></author>
1920<date year="2003" month="March" day="25"/>
1921</front>
1922  <seriesInfo name="World Wide Web Consortium" value="REC-xptr-framework-20030325"/>
1923</reference>
1924
1925</references>
1926
1927</back>
1928</rfc>
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