source: draft-ietf-iri-3987bis/draft-ietf-iri-3987bis.xml @ 111

Last change on this file since 111 was 111, checked in by duerst@…, 8 years ago

fixing codepoint number for CYRILLIC CAPITAL LETTER YA, not sure why this was wrong for such a long time

  • Property svn:executable set to *
File size: 88.4 KB
Line 
1<?xml version="1.0"?>
2<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
3<!ENTITY rfc2119 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml">
4<!ENTITY rfc2130 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2130.xml">
5<!ENTITY rfc2141 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2141.xml">
6<!ENTITY rfc2192 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2192.xml">
7<!ENTITY rfc2277 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2277.xml">
8<!ENTITY rfc2384 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2384.xml">
9<!ENTITY rfc2396 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2396.xml">
10<!ENTITY rfc2397 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2397.xml">
11<!ENTITY rfc2616 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2616.xml">
12<!ENTITY rfc2640 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2640.xml">
13<!ENTITY rfc3491 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3491.xml">
14<!ENTITY rfc3629 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3629.xml">
15<!ENTITY rfc3986 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3986.xml">
16<!ENTITY rfc3987 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3987.xml">
17<!ENTITY rfc5122 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.5122.xml">
18<!ENTITY rfc5890 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.5890.xml">
19<!ENTITY rfc5891 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.5891.xml">
20<!ENTITY rfc5892 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.5892.xml">
21<!ENTITY rfc6055 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6055.xml">
22<!ENTITY rfc6068 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6068.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-11" 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="2012" />
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>Defining IRI as a new protocol element (rather than updating or
107extending the definition of URI) allows independent orderly
108transitions: protocols and languages that use URIs must
109explicitly choose to allow IRIs.</t>
110
111<t>Guidelines are provided for the use and deployment of IRIs and
112related protocol elements when revising protocols, formats, and
113software components that currently deal only with URIs.</t>
114
115<t>This document is part of a set of documents intended to
116replace RFC 3987.</t>
117
118</abstract>
119  <note title='RFC Editor: Please remove the next paragraph before publication.'>
120    <t>This (and several companion documents) are intended to obsolete RFC 3987,
121    and also move towards IETF Draft Standard.  For discussion and comments on these
122    drafts, please join the IETF IRI WG by subscribing to the mailing
123    list public-iri@w3.org, archives at http://lists.w3.org/archives/public/public-iri/.
124    For a list of open issues, please see
125    the issue tracker of the WG at http://trac.tools.ietf.org/wg/iri/trac/report/1.
126    For a list of individual edits, please see the change history at
127    http://trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis.</t>
128</note>
129</front>
130<middle>
131
132<section title="Introduction">
133
134<section title="Overview and Motivation" anchor="overview">
135
136<t>A Uniform Resource Identifier (URI) is defined in <xref
137target="RFC3986"/> as a sequence of characters chosen from a limited
138subset of the repertoire of US-ASCII <xref target="ASCII"/>
139characters.</t>
140
141<t>The characters in URIs are frequently used for representing words
142of natural languages.  This usage has many advantages: Such URIs are
143easier to memorize, easier to interpret, easier to transcribe, easier
144to create, and easier to guess. For most languages other than English,
145however, the natural script uses characters other than A - Z. For many
146people, handling Latin characters is as difficult as handling the
147characters of other scripts is for those who use only the Latin
148script. Many languages with non-Latin scripts are transcribed with
149Latin letters. These transcriptions are now often used in URIs, but
150they introduce additional difficulties.</t>
151
152<t>The infrastructure for the appropriate handling of characters from
153additional scripts is now widely deployed in operating system and
154application software. Software that can handle a wide variety of
155scripts and languages at the same time is increasingly common. Also,
156an increasing number of protocols and formats can carry a wide range of
157characters.</t>
158
159<t>URIs are composed out of a very limited repertoire of characters;
160this design choice was made to support global transcription (see <xref
161target="RFC3986"/> section 1.2.1.).  Reliable transition between a URI
162(as an abstract protocol element composed of a sequence of characters)
163and a presentation of that URI (written on a napkin, read out loud)
164and back is relatively straightforward, because of the limited
165repertoire of characters used.  IRIs are designed to satisfy a
166different set of use requirements; in particular, to allow IRIs to be
167written in ways that are more meaningful to their users, even at the
168expense of global transcribability. However, ensuring reliability of
169the transition between an IRI and its presentation and back is more
170difficult and complex when dealing with the larger set of Unicode
171characters.  For example, Unicode supports multiple ways of encoding
172complex combinations of characters and accents, with multiple
173character sequences that can result in the same presentation.</t>
174
175<t>This document defines the protocol element called Internationalized
176Resource Identifier (IRI), which allows applications of URIs to be
177extended to use resource identifiers that have a much wider repertoire
178of characters. It also provides corresponding "internationalized"
179versions of other constructs from <xref target="RFC3986"/>, such as
180URI references. The syntax of IRIs is defined in <xref
181target="syntax"/>.
182</t>
183
184<t>Within this document,
185               <xref target="IRIuse"/> discusses the use
186of IRIs in different situations.  <xref target="guidelines"/> gives
187additional informative guidelines.  <xref target="security"/>
188discusses IRI-specific security considerations.</t>
189
190<t>This specification is part of a collection of specifications
191intended to replace <xref target="RFC3987"/>.
192<xref target="Bidi"/> discusses the special case of
193bidirectional IRIs, IRIs using characters from scripts written
194right-to-left.
195<xref target="Equivalence"/> gives guidelines for applications wishing
196to determine if two IRIs are equivalent, as well as defining
197some equivalence methods.
198<xref target="RFC4395bis"/> updates the URI scheme registration
199guidelines and procedures to note that every URI scheme is also
200automatically an IRI scheme and to allow scheme definitions
201to be directly described in terms of Unicode characters.
202</t>
203
204</section> <!-- overview -->
205
206<section title="Applicability" anchor="Applicability">
207
208<t>IRIs are designed to allow protocols and software that deal with
209URIs to be updated to handle IRIs. Processing of
210IRIs is accomplished by extending the URI syntax while retaining (and
211not expanding) the set of "reserved" characters, such that the syntax
212for any URI scheme may be extended to allow non-ASCII
213characters. In addition, following parsing of an IRI, it is possible
214to construct a corresponding URI by first encoding characters outside
215of the allowed URI range and then reassembling the components.
216</t>
217
218<t>Practical use of IRIs forms in place of URIs forms depends on the
219following conditions being met:</t>
220
221<t><list style="hanging">
222   
223<t hangText="a.">A protocol or format element MUST be explicitly designated to be
224  able to carry IRIs. The intent is to avoid introducing IRIs into
225  contexts that are not defined to accept them.  For example, XML
226  schema <xref target="XMLSchema"/> has an explicit type "anyURI" that
227  includes IRIs and IRI references. Therefore, IRIs and IRI references
228  can be used in attributes and elements of type "anyURI".  On the other
229  hand, in HTTP/1.1 (<xref target="RFC2616"/>) , the
230  Request URI is defined as a URI, which means that direct use of IRIs
231  is not allowed in HTTP requests.</t>
232
233<t hangText="b.">The protocol or format carrying the IRIs MUST have a
234  mechanism to represent the wide range of characters used in IRIs,
235  either natively or by some protocol- or format-specific escaping
236  mechanism (for example, numeric character references in <xref
237  target="XML1"/>).</t>
238
239<t hangText="c.">The URI scheme definition, if it explicitly allows a
240  percent sign ("%") in any syntactic component, SHOULD define the
241  interpretation of sequences of percent-encoded octets (using "%XX"
242  hex octets) as octets from sequences of UTF-8 encoded characters; this
243  is recommended in the guidelines for registering new schemes, <xref
244  target="RFC4395bis"/>.  For example, this is the practice for IMAP URLs
245  <xref target="RFC2192"/>, POP URLs <xref target="RFC2384"/> and the
246  URN syntax <xref target="RFC2141"/>). Note that use of
247  percent-encoding may also be restricted in some situations, for
248  example, URI schemes that disallow percent-encoding might still be
249  used with a fragment identifier which is percent-encoded (e.g.,
250  <xref target="XPointer"/>). See <xref target="UTF8use"/> for further
251  discussion.</t>
252</list></t>
253
254</section> <!-- applicability -->
255
256<section title="Definitions" anchor="sec-Definitions">
257 
258<t>The following definitions are used in this document; they follow the
259terms in <xref target="RFC2130"/>, <xref target="RFC2277"/>, and
260<xref target="ISO10646"/>.</t>
261<t><list style="hanging">
262   
263<t hangText="character:">A member of a set of elements used for the
264    organization, control, or representation of data. For example,
265    "LATIN CAPITAL LETTER A" names a character.</t>
266   
267<t hangText="octet:">An ordered sequence of eight bits considered as a
268    unit.</t>
269   
270<t hangText="character repertoire:">A set of characters (set in the
271    mathematical sense).</t>
272   
273<t hangText="sequence of characters:">A sequence of characters (one
274    after another).</t>
275   
276<t hangText="sequence of octets:">A sequence of octets (one after
277    another).</t>
278   
279<t hangText="character encoding:">A method of representing a sequence
280    of characters as a sequence of octets (maybe with variants). Also,
281    a method of (unambiguously) converting a sequence of octets into a
282    sequence of characters.</t>
283   
284<t hangText="charset:">The name of a parameter or attribute used to
285    identify a character encoding.</t>
286   
287<t hangText="UCS:">Universal Character Set. The coded character set
288    defined by ISO/IEC 10646 <xref target="ISO10646"/> and the Unicode
289    Standard <xref target="UNIV6"/>.</t>
290   
291<t hangText="IRI reference:">Denotes the common usage of an
292    Internationalized Resource Identifier. An IRI reference may be
293    absolute or relative.  However, the "IRI" that results from such a
294    reference only includes absolute IRIs; any relative IRI references
295    are resolved to their absolute form.  Note that in <xref
296    target="RFC2396"/> URIs did not include fragment identifiers, but
297    in <xref target="RFC3986"/> fragment identifiers are part of
298    URIs.</t>
299   
300<t hangText="LEIRI (Legacy Extended IRI):">  This term is used in
301   various XML specifications to refer
302   to strings that, although not valid IRIs, are acceptable input to
303   the processing rules in <xref target="LEIRIspec" />.</t>
304
305<t hangText="running text:">Human text (paragraphs, sentences,
306   phrases) with syntax according to orthographic conventions of a
307   natural language, as opposed to syntax defined for ease of
308   processing by machines (e.g., markup, programming languages).</t>
309   
310<t hangText="protocol element:">Any portion of a message that affects
311    processing of that message by the protocol in question.</t>
312   
313<t hangText="create (a URI or IRI):">With respect to URIs and IRIs,
314     the term is used for the initial creation. This may be the
315     initial creation of a resource with a certain identifier, or the
316     initial exposition of a resource under a particular
317     identifier.</t>
318   
319<t hangText="generate (a URI or IRI):">With respect to URIs and IRIs,
320     the term is used when the identifier is generated by derivation
321     from other information.</t>
322
323<t hangText="parsed URI component:">When a URI processor parses a URI
324   (following the generic syntax or a scheme-specific syntax, the result
325   is a set of parsed URI components, each of which has a type
326   (corresponding to the syntactic definition) and a sequence of URI
327   characters.  </t>
328
329<t hangText="parsed IRI component:">When an IRI processor parses
330   an IRI directly, following the general syntax or a scheme-specific
331   syntax, the result is a set of parsed IRI components, each of
332   which has a type (corresponding to the syntactic definition)
333   and a sequence of IRI characters. (This definition is analogous
334   to "parsed URI component".)</t>
335
336<t hangText="IRI scheme:">A URI scheme may also be known as
337   an "IRI scheme" if the scheme's syntax has been extended to
338   allow non-US-ASCII characters according to the rules in this
339   document.</t>
340
341</list></t>
342</section> <!-- definitions -->
343<section title="Notation" anchor="sec-Notation">
344     
345<t>RFCs and Internet Drafts currently do not allow any characters
346outside the US-ASCII repertoire. Therefore, this document uses various
347special notations for such characters in examples.</t>
348     
349<t>In text, characters outside US-ASCII are sometimes referenced by
350using a prefix of 'U+', followed by four to six hexadecimal
351digits.</t>
352
353<t>To represent characters outside US-ASCII in examples, this document
354uses 'XML Notation'.</t>
355
356<t>XML Notation uses a leading '&amp;#x', a trailing ';', and the
357hexadecimal number of the character in the UCS in between. For
358example, &amp;#x42F; stands for CYRILLIC CAPITAL LETTER YA. In this
359notation, an actual '&amp;' is denoted by '&amp;amp;'.</t>
360
361<t>To denote actual octets in examples (as opposed to percent-encoded
362octets), the two hex digits denoting the octet are enclosed in "&lt;"
363and "&gt;".  For example, the octet often denoted as 0xc9 is denoted
364here as &lt;c9&gt;.</t>
365
366<t> In this document, the key words "MUST", "MUST NOT", "REQUIRED",
367"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
368and "OPTIONAL" are to be interpreted as described in <xref
369target="RFC2119"/>.</t>
370
371</section> <!-- notation -->
372</section> <!-- introduction -->
373
374<section title="IRI Syntax" anchor="syntax">
375<t>This section defines the syntax of Internationalized Resource
376Identifiers (IRIs).</t>
377
378<t>As with URIs, an IRI is defined as a sequence of characters, not as
379a sequence of octets.
380This definition accommodates the fact that IRIs
381may be written on paper or read over the radio as well as stored or
382transmitted digitally.  The same IRI might be represented as different
383sequences of octets in different protocols or documents if these
384protocols or documents use different character encodings (and/or
385transfer encodings).  Using the same character encoding as the
386containing protocol or document ensures that the characters in the IRI
387can be handled (e.g., searched, converted, displayed) in the same way
388as the rest of the protocol or document.</t>
389
390<section title="Summary of IRI Syntax" anchor="summary">
391
392<t>The IRI syntax extends the URI syntax in <xref
393target="RFC3986"/> by extending the class of unreserved characters,
394primarily by adding the characters of the UCS (Universal Character Set, <xref
395target="ISO10646"/>) beyond U+007F, subject to the limitations given
396in the syntax rules below and in <xref target="limitations"/>.</t>
397
398<t>The syntax and use of components and reserved characters is the
399same as that in <xref target="RFC3986"/>. Each URI scheme thus also
400functions as an IRI scheme, in that scheme-specific parsing rules
401for URIs of a scheme are extended to allow parsing of IRIs using
402the same parsing rules.</t>
403
404<t>All the operations defined in <xref target="RFC3986"/>, such as the
405resolution of relative references, can be applied to IRIs by
406IRI-processing software in exactly the same way as they are for URIs
407by URI-processing software.</t>
408
409<t>Characters outside the US-ASCII repertoire MUST NOT be reserved and
410therefore MUST NOT be used for syntactical purposes, such as to
411delimit components in newly defined schemes. For example, U+00A2, CENT
412SIGN, is not allowed as a delimiter in IRIs, because it is in the
413'iunreserved' category. This is similar to the fact that it is not
414possible to use '-' as a delimiter in URIs, because it is in the
415'unreserved' category.</t>
416
417</section> <!-- summary -->
418<section title="ABNF for IRI References and IRIs" anchor="abnf">
419
420<t>An ABNF definition for IRI references (which are the most general
421concept and the start of the grammar) and IRIs is given here. The
422syntax of this ABNF is described in <xref target="STD68"/>. Character
423numbers are taken from the UCS, without implying any actual binary
424encoding. Terminals in the ABNF are characters, not octets.</t>
425
426<t>The following grammar closely follows the URI grammar in <xref
427target="RFC3986"/>, except that the range of unreserved characters is
428expanded to include UCS characters, with the restriction that private
429UCS characters can occur only in query parts. The grammar is split
430into two parts: Rules that differ from <xref target="RFC3986"/>
431because of the above-mentioned expansion, and rules that are the same
432as those in <xref target="RFC3986"/>. For rules that are different
433than those in <xref target="RFC3986"/>, the names of the non-terminals
434have been changed as follows. If the non-terminal contains 'URI', this
435has been changed to 'IRI'. Otherwise, an 'i' has been prefixed.
436The rule &lt;pct-form> has been introduced in order to be able to reference it from other parts of
437the document.</t>
438
439<!--
440for line length measuring in artwork (max 72 chars, three chars at start):
441      1         2         3         4         5         6         7
442456789012345678901234567890123456789012345678901234567890123456789012
443-->
444<figure>
445<preamble>The following rules are different from those in <xref target="RFC3986"/>:</preamble>
446<artwork>
447IRI            = scheme ":" ihier-part [ "?" iquery ]
448                 [ "#" ifragment ]
449
450ihier-part     = "//" iauthority ipath-abempty
451               / ipath-absolute
452               / ipath-rootless
453               / ipath-empty
454
455IRI-reference  = IRI / irelative-ref
456
457absolute-IRI   = scheme ":" ihier-part [ "?" iquery ]
458
459irelative-ref  = irelative-part [ "?" iquery ] [ "#" ifragment ]
460
461irelative-part = "//" iauthority ipath-abempty
462               / ipath-absolute
463               / ipath-noscheme
464               / ipath-empty
465
466iauthority     = [ iuserinfo "@" ] ihost [ ":" port ]
467iuserinfo      = *( iunreserved / pct-form / sub-delims / ":" )
468ihost          = IP-literal / IPv4address / ireg-name
469
470pct-form       = pct-encoded
471
472ireg-name      = *( iunreserved / sub-delims )
473
474ipath          = ipath-abempty   ; begins with "/" or is empty
475               / ipath-absolute  ; begins with "/" but not "//"
476               / ipath-noscheme  ; begins with a non-colon segment
477               / ipath-rootless  ; begins with a segment
478               / ipath-empty     ; zero characters
479
480ipath-abempty  = *( path-sep isegment )
481ipath-absolute = path-sep [ isegment-nz *( path-sep isegment ) ]
482ipath-noscheme = isegment-nz-nc *( path-sep isegment )
483ipath-rootless = isegment-nz *( path-sep isegment )
484ipath-empty    = ""
485path-sep       = "/"
486
487isegment       = *ipchar
488isegment-nz    = 1*ipchar
489isegment-nz-nc = 1*( iunreserved / pct-form / sub-delims
490                     / "@" )
491               ; non-zero-length segment without any colon ":"
492
493ipchar         = iunreserved / pct-form / sub-delims / ":"
494               / "@"
495 
496iquery         = *( ipchar / iprivate / "/" / "?" )
497
498ifragment      = *( ipchar / "/" / "?" )
499
500iunreserved    = ALPHA / DIGIT / "-" / "." / "_" / "~" / ucschar
501
502ucschar        = %xA0-D7FF / %xF900-FDCF / %xFDF0-FFEF
503               / %x10000-1FFFD / %x20000-2FFFD / %x30000-3FFFD
504               / %x40000-4FFFD / %x50000-5FFFD / %x60000-6FFFD
505               / %x70000-7FFFD / %x80000-8FFFD / %x90000-9FFFD
506               / %xA0000-AFFFD / %xB0000-BFFFD / %xC0000-CFFFD
507               / %xD0000-DFFFD / %xE1000-EFFFD
508
509iprivate       = %xE000-F8FF / %xE0000-E0FFF / %xF0000-FFFFD
510               / %x100000-10FFFD
511</artwork>
512</figure>
513
514<t>Some productions are ambiguous. The "first-match-wins" (a.k.a. "greedy")
515algorithm applies. For details, see <xref target="RFC3986"/>.</t>
516
517<figure>
518<preamble>The following rules are the same as those in <xref target="RFC3986"/>:</preamble>
519<artwork>
520scheme         = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
521 
522port           = *DIGIT
523 
524IP-literal     = "[" ( IPv6address / IPvFuture  ) "]"
525 
526IPvFuture      = "v" 1*HEXDIG "." 1*( unreserved / sub-delims / ":" )
527 
528IPv6address    =                            6( h16 ":" ) ls32
529               /                       "::" 5( h16 ":" ) ls32
530               / [               h16 ] "::" 4( h16 ":" ) ls32
531               / [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
532               / [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
533               / [ *3( h16 ":" ) h16 ] "::"    h16 ":"   ls32
534               / [ *4( h16 ":" ) h16 ] "::"              ls32
535               / [ *5( h16 ":" ) h16 ] "::"              h16
536               / [ *6( h16 ":" ) h16 ] "::"
537               
538h16            = 1*4HEXDIG
539ls32           = ( h16 ":" h16 ) / IPv4address
540
541IPv4address    = dec-octet "." dec-octet "." dec-octet "." dec-octet
542
543dec-octet      = DIGIT                 ; 0-9
544               / %x31-39 DIGIT         ; 10-99
545               / "1" 2DIGIT            ; 100-199
546               / "2" %x30-34 DIGIT     ; 200-249
547               / "25" %x30-35          ; 250-255
548           
549pct-encoded    = "%" HEXDIG HEXDIG
550
551unreserved     = ALPHA / DIGIT / "-" / "." / "_" / "~"
552reserved       = gen-delims / sub-delims
553gen-delims     = ":" / "/" / "?" / "#" / "[" / "]" / "@"
554sub-delims     = "!" / "$" / "&amp;" / "'" / "(" / ")"
555               / "*" / "+" / "," / ";" / "="
556</artwork></figure>
557
558<t>This syntax does not support IPv6 scoped addressing zone identifiers.</t>
559
560</section> <!-- abnf -->
561
562</section> <!-- syntax -->
563
564<section title="Processing IRIs and related protocol elements" anchor="processing">
565
566<t>IRIs are meant to replace URIs in identifying resources within new
567versions of protocols, formats, and software components that use a
568UCS-based character repertoire.  Protocols and components may use and
569process IRIs directly. However, there are still numerous systems and
570protocols which only accept URIs or components of parsed URIs; that is,
571they only accept sequences of characters within the subset of US-ASCII
572characters allowed in URIs. </t>
573
574<t>This section defines specific processing steps for IRI consumers
575which establish the relationship between the string given and the
576interpreted derivatives. These
577processing steps apply to both IRIs and IRI references (i.e., absolute
578or relative forms); for IRIs, some steps are scheme specific. </t>
579
580<section title="Converting to UCS" anchor="ucsconv"> 
581 
582<t>Input that is already in a Unicode form (i.e., a sequence of Unicode
583 characters or an octet-stream representing a Unicode-based character
584 encoding such as UTF-8 or UTF-16) should be left as is and not
585 normalized or changed.</t>
586
587  <t>An IRI or IRI reference is a sequence of characters from the UCS.
588    For input from presentations (written on paper, read aloud)
589    or translation from other representations (a text stream using a legacy character
590    encoding), convert the input to Unicode.
591    Note that some character encodings or transcriptions can be converted
592    to or represented by more than one sequence of Unicode characters.
593
594    Ideally the resulting IRI would use a normalized form,
595    such as Unicode Normalization Form C <xref target="UTR15"/>,
596    since that ensures a stable, consistent representation
597    that is most likely to produce the intended results.
598    Previous versions of this specification required
599    normalization at this step. However, attempts to
600    require normalization in other protocols have met with
601    strong enough resistance that requiring normalization
602    here was considered impractical.
603    Implementers and users are cautioned that, while denormalized character sequences are valid,
604    they might be difficult for other users or processes to reproduce
605    and might lead to unexpected results.
606  <!-- raise on list:
607    It is recommended
608    that the processing of IRI components treat
609    strings with the same normalized forms as equivalent.
610   -->
611  </t>
612
613</section> <!-- ucsconv -->
614
615<section title="Parse the IRI into IRI components">
616
617<t>Parse the IRI, either as a relative reference (no scheme)
618or using scheme specific processing (according to the scheme
619given); the result is a set of parsed IRI components.</t>
620
621</section> <!-- parse -->
622
623<section title="General percent-encoding of IRI components" anchor="compmapping">
624   
625<t>Except as noted in the following subsections, IRI components are mapped
626to the equivalent URI components by percent-encoding those characters
627not allowed in URIs. Previous processing steps will have removed
628some characters, and the interpretation of reserved characters will
629have already been done (with the syntactic reserved characters outside
630of the IRI component). This mapping is defined for all sequences
631of Unicode characters, whether or not they are valid for the component
632in question. </t>
633   
634<t>For each character which is not allowed anywhere in a valid URI
635 apply the following steps. </t>
636<t><list style="hanging">
637
638<t hangText="Convert to UTF-8:">Convert the character to a sequence of
639  one or more octets using UTF-8 <xref target="RFC3629"/>.</t>
640
641<t hangText="Percent encode:">Convert each octet of this sequence to %HH,
642   where HH is the hexadecimal notation of the octet value. The
643   hexadecimal notation SHOULD use uppercase letters. (This is the
644   general URI percent-encoding mechanism in Section 2.1 of <xref
645   target="RFC3986"/>.)</t>
646   
647</list></t>
648
649<t>Note that the mapping is an identity transformation for parsed URI
650components of valid URIs, and is idempotent: applying the mapping a
651second time will not change anything.</t>
652</section> <!-- general conversion -->
653
654<section title="Mapping ireg-name" anchor="dnsmapping">
655  <t>The mapping from &lt;ireg-name> to a &lt;reg-name> requires a choice
656    between one of the two methods described below.</t>
657  <section title='Mapping using Percent-Encoding' anchor='dnspercent'>
658  <t>The ireg-name component SHOULD be converted
659    according to the general procedure for percent-encoding
660    of IRI components described in <xref target="compmapping"/>.</t>
661 
662  <t>For example, the IRI
663    <vspace/>"http://r&amp;#xE9;sum&amp;#xE9;.example.org"<vspace/> will be
664    converted to <vspace/>"http://r%C3%A9sum%C3%A9.example.org".</t>
665
666  <t>This conversion for ireg-name is in line with Section 3.2.2
667    of <xref target="RFC3986"/>, which does not mandate
668    a particular registered name lookup technology. For further background,
669    see <xref target="RFC6055"/> and <xref target="Gettys"/>.</t>
670</section> <!-- dnspercent -->
671<section title="Mapping using Punycode" anchor='dnspunycode'>
672  <t>In situations where it is certain that &lt;ireg-name> is intended
673    to be used as a domain name to be processed by Domain Name Lookup
674    (as per <xref target="RFC5891"/>), an alternative method MAY be
675    used, converting &lt;ireg-name> as follows:</t>
676
677  <t>If there are any sequences of &lt;pct-encoded&gt;, and their
678    corresponding octets all represent valid UTF-8
679    octet sequences, then convert these back to Unicode
680    character sequences. (If any &lt;pct-encoded&gt; sequences are not
681    valid UTF-8 octet sequences, then leave the entire field as is
682    without any change, since punycode encoding would not succeed.)</t>
683
684<t>Replace the ireg-name part of the IRI by the part converted using
685the Domain Name Lookup procedure (Subsections 5.3 to 5.5) of <xref target="RFC5891"/>.
686  on each dot-separated label, and by using U+002E
687(FULL STOP) as a label separator.
688This procedure may fail, but this would mean that the IRI cannot be resolved.
689In such cases, if the domain name conversion fails, then the
690entire IRI conversion fails. Processors that have no mechanism for
691signalling a failure MAY instead substitute an otherwise
692invalid host name, although such processing SHOULD be avoided.</t>
693
694<t>For example, the IRI
695<vspace/>"http://r&amp;#xE9;sum&amp;#xE9;.example.org"<vspace/> is
696converted to <vspace/>"http://xn--rsum-bad.example.org".</t>
697  <t>This conversion for ireg-name will be better able to deal with legacy
698    infrastructure that cannot handle percent-encoding in domain names.</t>
699</section> <!-- punicode -->
700  <section title="Additional Considerations">
701
702<t><list style="hanging"> 
703<t hangText="Note:">Domain Names may appear in parts of an IRI other
704than the ireg-name part.  It is the responsibility of scheme-specific
705implementations (if the Internationalized Domain Name is part of the
706scheme syntax) or of server-side implementations (if the
707Internationalized Domain Name is part of 'iquery') to apply the
708necessary conversions at the appropriate point. Example: Trying to
709validate the Web page at<vspace/>
710http://r&amp;#xE9;sum&amp;#xE9;.example.org would lead to an IRI of
711<vspace/>http://validator.w3.org/check?uri=http%3A%2F%2Fr&amp;#xE9;sum&amp;#xE9;.<vspace/>example.org,
712which would convert to a URI
713of<vspace/>http://validator.w3.org/check?uri=http%3A%2F%2Fr%C3%A9sum%C3%A9.<vspace/>example.org.
714The server-side implementation is responsible for making the
715necessary conversions to be able to retrieve the Web page.</t>
716
717<t hangText="Note:">In this process, characters allowed in URI
718references and existing percent-encoded sequences are not encoded further.
719(This mapping is similar to, but different from, the encoding applied
720when arbitrary content is included in some part of a URI.)
721
722For example, an IRI of
723<vspace/>"http://www.example.org/red%09ros&amp;#xE9;#red"
724(in XML notation) is converted to
725<vspace/>"http://www.example.org/red%09ros%C3%A9#red", not to
726something like
727<vspace/>"http%3A%2F%2Fwww.example.org%2Fred%2509ros%C3%A9%23red".</t>
728
729</list></t>
730</section> <!-- additional -->
731</section> <!-- dnsmapping -->
732
733<section title="Mapping query components" anchor="querymapping">
734
735<t>For compatibility with existing deployed HTTP infrastructure,
736the following special case applies for schemes "http" and "https"
737and IRIs whose origin has a document charset other than one which
738is UCS-based (e.g., UTF-8 or UTF-16). In such a case, the "query"
739component of an IRI is mapped into a URI by using the document
740charset rather than UTF-8 as the binary representation before
741pct-encoding. This mapping is not applied for any other scheme
742or component.</t>
743
744</section> <!-- querymapping -->
745
746<section title="Mapping IRIs to URIs" anchor="mapping">
747
748<t>The mapping from an IRI to URI is accomplished by applying the
749mapping above (from IRI to URI components) and then reassembling a URI
750from the parsed URI components using the original punctuation that
751delimited the IRI components. </t>
752
753</section> <!-- mapping -->
754</section> <!-- processing -->
755
756<section title="Converting URIs to IRIs" anchor="URItoIRI">
757
758  <t>In some situations, for presentation and further processing,
759it is desirable to convert a URI into an equivalent IRI
760without unnecessary percent encoding.
761Of course, every URI is already an IRI in its own right without any
762conversion. This section gives one possible procedure for URI to IRI mapping.</t>
763
764<t>
765The conversion described in this section, if given a valid URI, will
766result in an IRI that maps back to the URI used as an input for the
767conversion (except for potential case differences in percent-encoding
768and for potential percent-encoded unreserved characters).
769
770However, the IRI resulting from this conversion may differ
771from the original IRI (if there ever was one).</t> 
772
773<t>URI-to-IRI conversion removes percent-encodings, but not all
774percent-encodings can be eliminated. There are several reasons for
775this:</t>
776
777<t><list style="hanging">
778
779<t hangText="1.">Some percent-encodings are necessary to distinguish
780    percent-encoded and unencoded uses of reserved characters.</t>
781
782<t hangText="2.">Some percent-encodings cannot be interpreted as sequences
783    of UTF-8 octets.<vspace blankLines="1"/>
784    (Note: The octet patterns of UTF-8 are highly regular.
785    Therefore, there is a very high probability, but no guarantee,
786    that percent-encodings that can be interpreted as sequences of UTF-8
787    octets actually originated from UTF-8. For a detailed discussion,
788    see <xref target="Duerst97"/>.)</t>
789
790<t hangText="3.">The conversion may result in a character that is not
791    appropriate in an IRI. See <xref target="abnf"/>,
792      and <xref target="limitations"/> for further details.</t>
793
794<t hangText="4.">IRI to URI conversion has different rules for
795    dealing with domain names and query parameters.</t>
796
797</list></t>
798
799<t>Conversion from a URI to an IRI MAY be done by using the following
800steps:
801
802<list style="hanging">
803<t hangText="1.">Represent the URI as a sequence of octets in
804       US-ASCII.</t>
805
806<t hangText="2.">Convert all percent-encodings ("%" followed by two
807      hexadecimal digits) to the corresponding octets, except those
808      corresponding to "%", characters in "reserved", and characters
809      in US-ASCII not allowed in URIs.</t> 
810
811<t hangText="3.">Re-percent-encode any octet produced in step 2 that
812      is not part of a strictly legal UTF-8 octet sequence.</t>
813
814
815<t hangText="4.">Re-percent-encode all octets produced in step 3 that
816      in UTF-8 represent characters that are not appropriate according
817      to <xref target="abnf"/>  and <xref
818      target="limitations"/>.</t> 
819
820<t hangText="5.">Interpret the resulting octet sequence as a sequence
821      of characters encoded in UTF-8.</t>
822
823<t hangText="6.">URIs known to contain domain names in the reg-name
824      component SHOULD convert punycode-encoded domain name labels to
825      the corresponding characters using the ToUnicode procedure. </t>
826</list></t>
827
828<t>This procedure will convert as many percent-encoded characters as
829possible to characters in an IRI. Because there are some choices when
830step 4 is applied (see <xref target="limitations"/>), results may
831vary.</t>
832
833<t>Conversions from URIs to IRIs MUST NOT use any character
834encoding other than UTF-8 in steps 3 and 4, even if it might be
835possible to guess from the context that another character encoding
836than UTF-8 was used in the URI.  For example, the URI
837"http://www.example.org/r%E9sum%E9.html" might with some guessing be
838interpreted to contain two e-acute characters encoded as
839iso-8859-1. It must not be converted to an IRI containing these
840e-acute characters. Otherwise, in the future the IRI will be mapped to
841"http://www.example.org/r%C3%A9sum%C3%A9.html", which is a different
842URI from "http://www.example.org/r%E9sum%E9.html".</t>
843
844<section title="Examples">
845
846<t>This section shows various examples of converting URIs to IRIs.
847Each example shows the result after each of the steps 1 through 6 is
848applied. XML Notation is used for the final result.  Octets are
849denoted by "&lt;" followed by two hexadecimal digits followed by
850"&gt;".</t>
851
852<t>The following example contains the sequence "%C3%BC", which is a
853strictly legal UTF-8 sequence, and which is converted into the actual
854character U+00FC, LATIN SMALL LETTER U WITH DIAERESIS (also known as
855u-umlaut).
856
857<list style="hanging">
858<t hangText="1.">http://www.example.org/D%C3%BCrst</t>
859<t hangText="2.">http://www.example.org/D&lt;c3&gt;&lt;bc&gt;rst</t>
860<t hangText="3.">http://www.example.org/D&lt;c3&gt;&lt;bc&gt;rst</t>
861<t hangText="4.">http://www.example.org/D&lt;c3&gt;&lt;bc&gt;rst</t>
862<t hangText="5.">http://www.example.org/D&amp;#xFC;rst</t>
863<t hangText="6.">http://www.example.org/D&amp;#xFC;rst</t>
864</list>
865</t>
866
867<t>The following example contains the sequence "%FC", which might
868represent U+00FC, LATIN SMALL LETTER U WITH DIAERESIS, in
869the<vspace/>iso-8859-1 character encoding.  (It might represent other
870characters in other character encodings. For example, the octet
871&lt;fc&gt; in iso-8859-5 represents U+045C, CYRILLIC SMALL LETTER
872KJE.)  Because &lt;fc&gt; is not part of a strictly legal UTF-8
873sequence, it is re-percent-encoded in step 3.
874
875
876<list style="hanging">
877<t hangText="1.">http://www.example.org/D%FCrst</t>
878<t hangText="2.">http://www.example.org/D&lt;fc&gt;rst</t>
879<t hangText="3.">http://www.example.org/D%FCrst</t>
880<t hangText="4.">http://www.example.org/D%FCrst</t>
881<t hangText="5.">http://www.example.org/D%FCrst</t>
882<t hangText="6.">http://www.example.org/D%FCrst</t>
883</list>
884</t>
885
886<t>The following example contains "%e2%80%ae", which is the percent-encoded<vspace/>UTF-8
887character encoding of U+202E, RIGHT-TO-LEFT OVERRIDE.
888The direct use of this character is forbiddin in an IRI. Therefore, the
889corresponding octets are re-percent-encoded in step 4. This example shows
890that the case (upper- or lowercase) of letters used in percent-encodings may not be preserved.
891The example also contains a punycode-encoded domain name label (xn--99zt52a),
892which is not converted.
893
894<list style="hanging">
895<t hangText="1.">http://xn--99zt52a.example.org/%e2%80%ae</t>
896<t hangText="2.">http://xn--99zt52a.example.org/&lt;e2&gt;&lt;80&gt;&lt;ae&gt;</t>
897<t hangText="3.">http://xn--99zt52a.example.org/&lt;e2&gt;&lt;80&gt;&lt;ae&gt;</t>
898<t hangText="4.">http://xn--99zt52a.example.org/%E2%80%AE</t>
899<t hangText="5.">http://xn--99zt52a.example.org/%E2%80%AE</t>
900<t hangText="6.">http://&amp;#x7D0D;&amp;#x8C46;.example.org/%E2%80%AE</t>
901</list></t>
902
903<t>Note that the label "xn--99zt52a" is converted to U+7D0D U+8C46
904(Japanese Natto). ((EDITOR NOTE: There is some inconsistency in this note.))</t>
905
906</section> <!-- examples -->
907</section> <!-- URItoIRI -->
908
909
910<section title="Use of IRIs" anchor="IRIuse">
911
912<section title="Limitations on UCS Characters Allowed in IRIs" anchor="limitations">
913
914<t>This section discusses limitations on characters and character
915sequences usable for IRIs beyond those given in <xref target="abnf"/>.
916The considerations in this section are
917relevant when IRIs are created and when URIs are converted to
918IRIs.</t>
919
920<t>
921
922<list style="hanging"><t hangText="a.">The repertoire of characters allowed
923    in each IRI component is limited by the definition of that component.
924    For example, the definition of the scheme component does not allow
925    characters beyond US-ASCII.
926    <vspace blankLines="1"/>
927    (Note: In accordance with URI practice, generic IRI
928    software cannot and should not check for such limitations.)</t>
929
930<t hangText="b.">The UCS contains many areas of characters for which
931    there are strong visual look-alikes. Because of the likelihood of
932    transcription errors, these also should be avoided. This includes
933    the full-width equivalents of Latin characters, half-width
934    Katakana characters for Japanese, and many others. It also
935    includes many look-alikes of "space", "delims", and "unwise",
936    characters excluded in <xref target="RFC3491"/>.</t>
937 
938<t hangText="c.">At the start of a component, the use of combining marks is strongly discouraged. As
939    an example, a COMBINING TILDE OVERLAY (U+0334) would be very confusing at the start of
940    a &lt;isegment>. Combined with the preceeding '/', it might look like a solidus
941    with combining tilde overlay, but IRI processing software will parse and process the
942    '/' separately.</t>
943<t hangText='d.'>The ZERO WIDTH NON-JOINER (U+200C) and ZERO WIDTH
944    JOINER (U+200D) are invisible in most contexts, but are crucial in
945    some very limited contexts. Appendix A of <xref target="RFC5892"/>
946    contains contextual restrictions for these and some other characters.
947    The use of these characters are strongly discouraged except
948    in the relevant contexts.</t>
949</list>
950</t>
951
952<t>Additional information is available from <xref target="UNIXML"/>.
953    <xref target="UNIXML"/> is written in the context of running text
954    rather than in that of identifiers. Nevertheless, it discusses
955    many of the categories of characters not appropriate for IRIs.</t>
956</section> <!-- limitations -->
957
958<section title="Software Interfaces and Protocols">
959
960<t>Although an IRI is defined as a sequence of characters, software
961interfaces for URIs typically function on sequences of octets or other
962kinds of code units. Thus, software interfaces and protocols MUST
963define which character encoding is used.</t>
964
965<t>Intermediate software interfaces between IRI-capable components and
966URI-only components MUST map the IRIs per <xref target="mapping"/>,
967when transferring from IRI-capable to URI-only components.
968
969This mapping SHOULD be applied as late as possible. It SHOULD NOT be
970applied between components that are known to be able to handle IRIs.</t>
971</section> <!-- software -->
972
973<section title="Format of URIs and IRIs in Documents and Protocols">
974
975<t>Document formats that transport URIs may have to be upgraded to allow
976the transport of IRIs. In cases where the document as a whole
977has a native character encoding, IRIs MUST also be encoded in this
978character encoding and converted accordingly by a parser or interpreter.
979
980IRI characters not expressible in the native character encoding SHOULD
981be escaped by using the escaping conventions of the document format if
982such conventions are available. Alternatively, they MAY be
983percent-encoded according to <xref target="mapping"/>. For example, in
984HTML or XML, numeric character references SHOULD be used. If a
985document as a whole has a native character encoding and that character
986encoding is not UTF-8, then IRIs MUST NOT be placed into the document
987in the UTF-8 character encoding.</t>
988
989<t>((UPDATE THIS NOTE)) Note: Some formats already accommodate IRIs,
990although they use different terminology. HTML 4.0 <xref
991target="HTML4"/> defines the conversion from IRIs to URIs as
992error-avoiding behavior. XML 1.0 <xref target="XML1"/>, XLink <xref
993target="XLink"/>, XML Schema <xref target="XMLSchema"/>, and
994specifications based upon them allow IRIs. Also, it is expected that
995all relevant new W3C formats and protocols will be required to handle
996IRIs <xref target="CharMod"/>.</t>
997
998</section> <!-- format -->
999
1000<section title="Use of UTF-8 for Encoding Original Characters" anchor="UTF8use">
1001
1002<t>This section discusses details and gives examples for point c) in
1003<xref target="Applicability"/>. To be able to use IRIs, the URI
1004corresponding to the IRI in question has to encode original characters
1005into octets by using UTF-8.  This can be specified for all URIs of a
1006URI scheme or can apply to individual URIs for schemes that do not
1007specify how to encode original characters.  It can apply to the whole
1008URI, or only to some part. For background information on encoding
1009characters into URIs, see also Section 2.5 of <xref
1010target="RFC3986"/>.</t>
1011
1012<t>For new URI schemes, using UTF-8 is recommended in <xref
1013target="RFC4395bis"/>.  Examples where UTF-8 is already used are the URN
1014syntax <xref target="RFC2141"/>, IMAP URLs <xref target="RFC2192"/>,
1015POP URLs <xref target="RFC2384"/>, XMPP URLs <xref target='RFC5122'/>,
1016and the 'mailto:' scheme <xref target='RFC6068'/>. On the other hand, because the
1017HTTP URI scheme does not specify how to encode original characters,
1018only some HTTP URLs can have corresponding but different IRIs.</t>
1019
1020<t>For example, for a document with a URI
1021of<vspace/>"http://www.example.org/r%C3%A9sum%C3%A9.html", it is
1022possible to construct a corresponding IRI (in XML notation, see <xref
1023target="sec-Notation"/>):
1024"http://www.example.org/r&amp;#xE9;sum&amp;#xE9;.html" ("&amp;#xE9;"
1025stands for the e-acute character, and "%C3%A9" is the UTF-8 encoded
1026and percent-encoded representation of that character). On the other
1027hand, for a document with a URI of
1028"http://www.example.org/r%E9sum%E9.html", the percent-encoded octets
1029cannot be converted to actual characters in an IRI, as the
1030percent-encoding is not based on UTF-8.</t>
1031
1032<t>For most URI schemes, there is no need to upgrade their scheme
1033definition in order for them to work with IRIs.  The main case where
1034upgrading makes sense is when a scheme definition, or a particular
1035component of a scheme, is strictly limited to the use of US-ASCII
1036characters with no provision to include non-ASCII characters/octets
1037via percent-encoding, or if a scheme definition currently uses highly
1038scheme-specific provisions for the encoding of non-ASCII characters.</t>
1039
1040<t>This specification updates the IANA registry of URI schemes to note
1041their applicability to IRIs, see <xref target="iana"/>.  All IRIs use
1042URI schemes, and all URIs with URI schemes can be used as IRIs, even
1043though in some cases only by using URIs directly as IRIs, without any
1044conversion.</t>
1045
1046<t>Scheme definitions can impose restrictions on the syntax of
1047scheme-specific URIs; i.e., URIs that are admissible under the generic
1048URI syntax <xref target="RFC3986"/> may not be admissible due to
1049narrower syntactic constraints imposed by a URI scheme
1050specification. URI scheme definitions cannot broaden the syntactic
1051restrictions of the generic URI syntax; otherwise, it would be
1052possible to generate URIs that satisfied the scheme-specific syntactic
1053constraints without satisfying the syntactic constraints of the
1054generic URI syntax. However, additional syntactic constraints imposed
1055by URI scheme specifications are applicable to IRI, as the
1056corresponding URI resulting from the mapping defined in <xref
1057target="mapping"/> MUST be a valid URI under the syntactic
1058restrictions of generic URI syntax and any narrower restrictions
1059imposed by the corresponding URI scheme specification.</t>
1060
1061<t>The requirement for the use of UTF-8 generally applies to all parts
1062of a URI.  However, it is possible that the capability of IRIs to
1063represent a wide range of characters directly is used just in some
1064parts of the IRI (or IRI reference). The other parts of the IRI may
1065only contain US-ASCII characters, or they may not be based on
1066UTF-8. They may be based on another character encoding, or they may
1067directly encode raw binary data (see also <xref
1068target="RFC2397"/>). </t>
1069
1070<t>For example, it is possible to have a URI reference
1071of<vspace/>"http://www.example.org/r%E9sum%E9.xml#r%C3%A9sum%C3%A9",
1072where the document name is encoded in iso-8859-1 based on server
1073settings, but where the fragment identifier is encoded in UTF-8 according
1074to <xref target="XPointer"/>. The IRI corresponding to the above
1075URI would be (in XML notation)<vspace/>"http://www.example.org/r%E9sum%E9.xml#r&amp;#xE9;sum&amp;#xE9;".</t>
1076
1077<t>Similar considerations apply to query parts. The functionality
1078of IRIs (namely, to be able to include non-ASCII characters) can
1079only be used if the query part is encoded in UTF-8.</t>
1080
1081</section> <!-- utf8 -->
1082
1083<section title="Relative IRI References">
1084<t>Processing of relative IRI references against a base is handled
1085straightforwardly; the algorithms of <xref target="RFC3986"/> can
1086be applied directly, treating the characters additionally allowed
1087in IRI references in the same way that unreserved characters are treated in URI
1088references.</t>
1089
1090</section> <!-- relative -->
1091</section> <!-- IRIuse -->
1092
1093  <section title="Legacy Extended IRIs (LEIRIs)">
1094    <t>In some cases, there have been formats which have used a protocol element
1095      which is a variant of the IRI definition; these variants have usually been
1096      somewhat less restricted in syntax. This section provides
1097      a definition and a name (Legacy Extended IRI or LEIRI) for one of these
1098      variants used widely in XML-based protocols. This variant has to be used with care;
1099      it requires further processing before being fully interchangeable as IRIs.
1100
1101      New protocols and formats SHOULD NOT use Legacy Extended IRIs.
1102      Even where Legacy Extended IRIs are allowed, only IRIs fully conforming
1103      to the syntax definition in <xref target="abnf"></xref> SHOULD be created,
1104      generated, and used. The provisions in this section also apply to
1105      Legacy Extended IRI references.</t>
1106   
1107    <section title="Legacy Extended IRI Syntax">
1108      <figure>
1109
1110        <preamble>This section defines Legacy Extended IRIs (LEIRIs).  The syntax of
1111   Legacy Extended IRIs is the same as that for &lt;IRI-reference&gt;, except
1112   that the ucschar production is replaced by the leiri-ucschar
1113   production:
1114
1115</preamble>
1116        <artwork>
1117leiri-ucschar  = " " / "&lt;" / "&gt;" / '"' / "{" / "}" / "|"
1118               / "\" / "^" / "`" / %x0-1F / %x7F-D7FF
1119               / %xE000-FFFD / %x10000-10FFFF
1120        </artwork>
1121        <postamble>The restriction on bidirectional formatting characters in <xref target="Bidi"></xref> is lifted.
1122        The iprivate production becomes redundant.</postamble>
1123      </figure>
1124
1125      <t>Likewise, the syntax for Legacy Extended IRI references
1126      (LEIRI references) is the same as that for IRI references with
1127      the above replacement of ucschar with leiri-ucschar.</t>
1128
1129     </section>
1130    <section title="Conversion of Legacy Extended IRIs to IRIs" anchor="LEIRIspec">
1131      <t>To convert a Legacy Extended IRI (reference) to
1132      an IRI (reference), each character allowed in a Legacy Extended IRI (reference)
1133      but not allowed in an IRI (reference) (see <xref target="notAllowed"></xref>)  MUST be percent-encoded
1134      by applying the steps in <xref target="compmapping"></xref>.</t>
1135    </section>
1136     
1137    <section title="Characters Allowed in Legacy Extended IRIs but not in IRIs" anchor="notAllowed">
1138      <t>This section provides a list of the groups of characters and code points
1139        that are allowed in Legacy Extedend IRIs, but are not allowed in IRIs
1140        or are allowed in IRIs only in the query part. For each group of characters,
1141        advice on the usage of these characters is also given, concentrating on the
1142        reasons for why not to use them.</t>
1143      <t>
1144        <list>
1145          <t>Space (U+0020): Some formats and applications use space as a delimiter,
1146            e.g., for items in a list. Appendix C of <xref target="RFC3986"></xref>
1147            also mentions that white space may have to be added when displaying
1148            or printing long URIs; the same applies to long IRIs.
1149            Spaces might disappear, or a single Legacy Extended IRI
1150            might incorrectly be interpreted as two or more separate ones.</t>
1151     
1152          <t>Delimiters "&lt;" (U+003C), "&gt;" (U+003E), and '"' (U+0022):
1153            Appendix C of <xref target="RFC3986"></xref> suggests the use of
1154            double-quotes ("http://example.com/") and angle brackets
1155        (&lt;http://example.com/&gt;) as delimiters for URIs in plain text.
1156        These conventions are often used, and also apply to IRIs.
1157        Legacy Extended IRIs using these characters might be cut off at the wrong place.</t>
1158     
1159          <t>Unwise characters "\" (U+005C),
1160          "^" (U+005E), "`" (U+0060), "{" (U+007B), "|" (U+007C), and "}" (U+007D):
1161          These characters originally were excluded from URIs because
1162          the respective codepoints are assigned to different graphic characters
1163          in some 7-bit or 8-bit encoding. Despite the move to Unicode,
1164          some of these characters are still occasionally displayed differently
1165          on some systems, e.g., U+005C as a Japanese Yen symbol.
1166     
1167          Also, the fact that these characters are not used in URIs or IRIs
1168          has encouraged their use outside URIs or IRIs in contexts that may
1169          include URIs or IRIs. In case a Legacy Extended IRI with such a character
1170          is used in such a context, the Legacy Extended IRI will be interpreted piecemeal.</t>
1171     
1172          <t>The controls (C0 controls, DEL, and C1 controls, #x0  - #x1F  #x7F - #x9F):
1173            There is no way to transmit these characters reliably except potentially
1174            in electronic form. Even when in electronic form, some software components
1175            might silently filter out some of these characters,
1176            or may stop processing alltogether when encountering some of them.
1177            These characters may affect text display in subtle, unnoticable ways
1178            or in drastic, global, and irreversible ways depending
1179            on the hardware and software involved.
1180            The use of some of these characters may allow malicious users
1181            to manipulate the display of a Legacy Extended IRI and its context.</t>
1182          <t>Bidi formatting characters (U+200E, U+200F, U+202A-202E):
1183            These characters affect the display ordering of characters.
1184            Displayed Legacy Extended IRIs containing these characters
1185            cannot be converted back to electronic form (logical order) unambiguously.
1186            These characters may allow malicious users to manipulate
1187            the display of a Legacy Extended IRI and its context.</t>
1188          <t>Specials (U+FFF0-FFFD): These code points provide functionality
1189            beyond that useful in a Legacy Extended IRI, for example byte order identification,
1190            annotation, and replacements for unknown characters and objects.
1191            Their use and interpretation in a Legacy Extended IRI
1192            serves no purpose and may lead to confusing display variations.</t>
1193          <t>Private use code points (U+E000-F8FF, U+F0000-FFFFD, U+100000-10FFFD):
1194            Display and interpretation of these code points is by definition
1195            undefined without private agreement. Therefore, these code points
1196            are not suited for use on the Internet. They are not interoperable and may have
1197            unpredictable effects.</t>
1198          <t>Tags (U+E0000-E0FFF): These characters provide a way to language tag in Unicode plain text.
1199            They are not appropriate for Legacy Extended IRIs because language information
1200            in identifiers cannot reliably be input, transmitted
1201            (e.g., on a visual medium such as paper), or recognized.</t>
1202          <t>Non-characters (U+FDD0-FDEF, U+1FFFE-1FFFF, U+2FFFE-2FFFF, U+3FFFE-3FFFF,
1203            U+4FFFE-4FFFF, U+5FFFE-5FFFF, U+6FFFE-6FFFF, U+7FFFE-7FFFF, U+8FFFE-8FFFF,
1204            U+9FFFE-9FFFF, U+AFFFE-AFFFF, U+BFFFE-BFFFF, U+CFFFE-CFFFF, U+DFFFE-DFFFF,
1205            U+EFFFE-EFFFF, U+FFFFE-FFFFF, U+10FFFE-10FFFF):
1206            These code points are defined as non-characters. Applications may use
1207            some of them internally, but are not prepared to interchange them.</t>
1208        </list>
1209      </t>
1210      <t>For reference, we here also list the code points and code units
1211        not even allowed in Legacy Extended IRIs:
1212        <list>
1213         
1214          <t>Surrogate code units (D800-DFFF):
1215          These do not represent Unicode codepoints.</t>
1216           <t>Non-characters (U+FFFE-FFFF): These are not allowed in XML nor LEIRIs.</t>
1217     
1218        </list>
1219      </t>
1220    </section>
1221  </section>
1222 
1223<section title="URI/IRI Processing Guidelines (Informative)" anchor="guidelines">
1224
1225<t>This informative section provides guidelines for supporting IRIs in
1226the same software components and operations that currently process
1227URIs: Software interfaces that handle URIs, software that allows users
1228to enter URIs, software that creates or generates URIs, software that
1229displays URIs, formats and protocols that transport URIs, and software
1230that interprets URIs. These may all require modification before
1231functioning properly with IRIs. The considerations in this section
1232also apply to URI references and IRI references.</t>
1233
1234<section title="URI/IRI Software Interfaces">
1235<t>Software interfaces that handle URIs, such as URI-handling APIs and
1236protocols transferring URIs, need interfaces and protocol elements
1237that are designed to carry IRIs.</t>
1238
1239<t>In case the current handling in an API or protocol is based on
1240US-ASCII, UTF-8 is recommended as the character encoding for IRIs, as
1241it is compatible with US-ASCII, is in accordance with the
1242recommendations of <xref target="RFC2277"/>, and makes converting to
1243URIs easy. In any case, the API or protocol definition must clearly
1244define the character encoding to be used.</t>
1245
1246<t>The transfer from URI-only to IRI-capable components requires no
1247mapping, although the conversion described in <xref
1248target="URItoIRI"/> above may be performed. It is preferable not to
1249perform this inverse conversion unless it is certain this can be done
1250correctly.</t>
1251</section><!-- software interfaces -->
1252
1253<section title="URI/IRI Entry">
1254
1255<t>Some components allow users to enter URIs into the system
1256by typing or dictation, for example. This software must be updated to allow
1257for IRI entry.</t>
1258
1259<t>A person viewing a visual presentation of an IRI (as a sequence
1260of glyphs, in some order, in some visual display)
1261will use an entry method for characters in the user's language to
1262input the IRI. Depending on the script and the input method used, this
1263may be a more or less complicated process.</t>
1264
1265<t>The process of IRI entry must ensure, as much as possible, that the
1266restrictions defined in <xref target="abnf"/> are met. This may be
1267done by choosing appropriate input methods or variants/settings
1268thereof, by appropriately converting the characters being input, by
1269eliminating characters that cannot be converted, and/or by issuing a
1270warning or error message to the user.</t>
1271
1272<t>As an example of variant settings, input method editors for East
1273Asian Languages usually allow the input of Latin letters and related
1274characters in full-width or half-width versions. For IRI input, the
1275input method editor should be set so that it produces half-width Latin
1276letters and punctuation and full-width Katakana.</t>
1277
1278<t>An input field primarily or solely used for the input of URIs/IRIs
1279might allow the user to view an IRI as it is mapped to a URI.  Places
1280where the input of IRIs is frequent may provide the possibility for
1281viewing an IRI as mapped to a URI. This will help users when some of
1282the software they use does not yet accept IRIs.</t>
1283
1284<t>An IRI input component interfacing to components that handle URIs,
1285but not IRIs, must map the IRI to a URI before passing it to these
1286components.</t>
1287
1288<t>For the input of IRIs with right-to-left characters, please see
1289<xref target="Bidi"></xref>.</t>
1290</section><!-- entry -->
1291
1292<section title="URI/IRI Transfer between Applications">
1293
1294<t>Many applications (for example, mail user agents) try to detect
1295URIs appearing in plain text. For this, they use some heuristics based
1296on URI syntax. They then allow the user to click on such URIs and
1297retrieve the corresponding resource in an appropriate (usually
1298scheme-dependent) application.</t>
1299
1300<t>Such applications would need to be upgraded, in order to use the
1301IRI syntax as a base for heuristics. In particular, a non-ASCII
1302character should not be taken as the indication of the end of an IRI.
1303Such applications also would need to make sure that they correctly
1304convert the detected IRI from the character encoding of the document
1305or application where the IRI appears, to the character encoding used
1306by the system-wide IRI invocation mechanism, or to a URI (according to
1307<xref target="mapping"/>) if the system-wide invocation mechanism only
1308accepts URIs.</t>
1309
1310<t>The clipboard is another frequently used way to transfer URIs and
1311IRIs from one application to another. On most platforms, the clipboard
1312is able to store and transfer text in many languages and scripts.
1313Correctly used, the clipboard transfers characters, not octets, which
1314will do the right thing with IRIs.</t>
1315</section><!-- transfer -->
1316
1317<section title="URI/IRI Generation">
1318
1319<t>Systems that offer resources through the Internet, where those
1320resources have logical names, sometimes automatically generate URIs
1321for the resources they offer. For example, some HTTP servers can
1322generate a directory listing for a file directory and then respond to
1323the generated URIs with the files.</t>
1324
1325<t>Many legacy character encodings are in use in various file systems.
1326Many currently deployed systems do not transform the local character
1327representation of the underlying system before generating URIs.</t>
1328
1329<t>For maximum interoperability, systems that generate resource
1330identifiers should make the appropriate transformations. For example,
1331if a file system contains a file named
1332"r&amp;#xE9;sum&amp;#xE9;.html", a server should expose this as
1333"r%C3%A9sum%C3%A9.html" in a URI, which allows use of
1334"r&amp;#xE9;sum&amp;#xE9;.html" in an IRI, even if locally the file
1335name is kept in a character encoding other than UTF-8.
1336</t>
1337
1338<t>This recommendation particularly applies to HTTP servers. For FTP
1339servers, similar considerations apply; see <xref target="RFC2640"/>.</t>
1340</section><!-- generation -->
1341
1342<section title="URI/IRI Selection" anchor="selection">
1343<t>In some cases, resource owners and publishers have control over the
1344IRIs used to identify their resources. This control is mostly
1345executed by controlling the resource names, such as file names,
1346directly.</t>
1347
1348<t>In these cases, it is recommended to avoid choosing IRIs that are
1349easily confused. For example, for US-ASCII, the lower-case ell ("l") is
1350easily confused with the digit one ("1"), and the upper-case oh ("O") is
1351easily confused with the digit zero ("0"). Publishers should avoid
1352confusing users with "br0ken" or "1ame" identifiers.</t>
1353
1354<t>Outside the US-ASCII repertoire, there are many more opportunities for
1355confusion; a complete set of guidelines is too lengthy to include
1356here. As long as names are limited to characters from a single script,
1357native writers of a given script or language will know best when
1358ambiguities can appear, and how they can be avoided. What may look
1359ambiguous to a stranger may be completely obvious to the average
1360native user. On the other hand, in some cases, the UCS contains
1361variants for compatibility reasons; for example, for typographic purposes.
1362These should be avoided wherever possible. Although there may be exceptions,
1363newly created resource names should generally be in NFKC
1364<xref target="UTR15"></xref> (which means that they are also in NFC).</t>
1365
1366<t>As an example, the UCS contains the "fi" ligature at U+FB01
1367for compatibility reasons.
1368Wherever possible, IRIs should use the two letters "f" and "i" rather
1369than the "fi" ligature. An example where the latter may be used is
1370in the query part of an IRI for an explicit search for a word written
1371containing the "fi" ligature.</t>
1372
1373<t>In certain cases, there is a chance that characters from different
1374scripts look the same. The best known example is the similarity of the
1375Latin "A", the Greek "Alpha", and the Cyrillic "A". To avoid such
1376cases, IRIs should only be created where all the characters in a
1377single component are used together in a given language. This usually
1378means that all of these characters will be from the same script, but
1379there are languages that mix characters from different scripts (such
1380as Japanese).  This is similar to the heuristics used to distinguish
1381between letters and numbers in the examples above. Also, for Latin,
1382Greek, and Cyrillic, using lowercase letters results in fewer
1383ambiguities than using uppercase letters would.</t>
1384</section><!-- selection -->
1385
1386<section title="Display of URIs/IRIs" anchor="display">
1387<t>
1388In situations where the rendering software is not expected to display
1389non-ASCII parts of the IRI correctly using the available layout and font
1390resources, these parts should be percent-encoded before being displayed.</t>
1391
1392<t>For display of Bidi IRIs, please see <xref target="Bidi"/>.</t>
1393</section> <!-- display -->
1394
1395<section title="Interpretation of URIs and IRIs">
1396<t>Software that interprets IRIs as the names of local resources should
1397accept IRIs in multiple forms and convert and match them with the
1398appropriate local resource names.</t>
1399
1400<t>First, multiple representations include both IRIs in the native
1401character encoding of the protocol and also their URI counterparts.</t>
1402
1403<t>Second, it may include URIs constructed based on character
1404encodings other than UTF-8. These URIs may be produced by user agents that do
1405not conform to this specification and that use legacy character encodings to
1406convert non-ASCII characters to URIs. Whether this is necessary, and what
1407character encodings to cover, depends on a number of factors, such as
1408the legacy character encodings used locally and the distribution of
1409various versions of user agents. For example, software for Japanese
1410may accept URIs in Shift_JIS and/or EUC-JP in addition to UTF-8.</t>
1411
1412<t>Third, it may include additional mappings to be more user-friendly
1413and robust against transmission errors. These would be similar to how
1414some servers currently treat URIs as case insensitive or perform
1415additional matching to account for spelling errors. For characters
1416beyond the US-ASCII repertoire, this may, for example, include
1417ignoring the accents on received IRIs or resource names. Please note
1418that such mappings, including case mappings, are language
1419dependent.</t>
1420
1421<t>It can be difficult to identify a resource unambiguously if too
1422many mappings are taken into consideration. However, percent-encoded
1423and not percent-encoded parts of IRIs can always be clearly distinguished.
1424Also, the regularity of UTF-8 (see <xref target="Duerst97"/>) makes the
1425potential for collisions lower than it may seem at first.</t>
1426</section> <!-- interpretation -->
1427
1428<section title="Upgrading Strategy">
1429<t>Where this recommendation places further constraints on software
1430for which many instances are already deployed, it is important to
1431introduce upgrades carefully and to be aware of the various
1432interdependencies.</t>
1433
1434<t>If IRIs cannot be interpreted correctly, they should not be created,
1435generated, or transported. This suggests that upgrading URI interpreting
1436software to accept IRIs should have highest priority.</t>
1437
1438<t>On the other hand, a single IRI is interpreted only by a single or
1439very few interpreters that are known in advance, although it may be
1440entered and transported very widely.</t>
1441
1442<t>Therefore, IRIs benefit most from a broad upgrade of software to be
1443able to enter and transport IRIs. However, before an
1444individual IRI is published, care should be taken to upgrade the corresponding
1445interpreting software in order to cover the forms expected to be
1446received by various versions of entry and transport software.</t>
1447
1448<t>The upgrade of generating software to generate IRIs instead of using a
1449local character encoding should happen only after the service is upgraded
1450to accept IRIs. Similarly, IRIs should only be generated when the service
1451accepts IRIs and the intervening infrastructure and protocol is known
1452to transport them safely.</t>
1453
1454<t>Software converting from URIs to IRIs for display should be upgraded
1455only after upgraded entry software has been widely deployed to the
1456population that will see the displayed result.</t>
1457
1458
1459<t>Where there is a free choice of character encodings, it is often
1460possible to reduce the effort and dependencies for upgrading to IRIs
1461by using UTF-8 rather than another encoding. For example, when a new
1462file-based Web server is set up, using UTF-8 as the character encoding
1463for file names will make the transition to IRIs easier. Likewise, when
1464a new Web form is set up using UTF-8 as the character encoding of the
1465form page, the returned query URIs will use UTF-8 as the character
1466encoding (unless the user, for whatever reason, changes the character
1467encoding) and will therefore be compatible with IRIs.</t>
1468
1469
1470<t>These recommendations, when taken together, will allow for the
1471extension from URIs to IRIs in order to handle characters other than
1472US-ASCII while minimizing interoperability problems. For
1473considerations regarding the upgrade of URI scheme definitions, see
1474<xref target="UTF8use"/>.</t>
1475
1476</section> <!-- upgrading -->
1477</section> <!-- guidelines -->
1478
1479<section title="IANA Considerations" anchor="iana">
1480
1481<t>NOTE: THIS SECTION NEEDS REVIEW AGAINST HAPPIANA WORK.</t>
1482
1483<t>RFC Editor and IANA note: Please Replace RFC XXXX with the
1484number of this document when it issues as an RFC, and RFC YYYY
1485with the number of the RFC issued for draft-ietf-iri-rfc3987bis. </t>
1486
1487<t>IANA maintains a registry of "URI schemes".  This document attempts
1488to make it clear from the registry that a "URI scheme" also serves an
1489"IRI scheme", and makes several changes to the registry. </t>
1490
1491<t>The description of the registry should be changed: "RFC 4395
1492defined an IANA-maintained registry of URI Schemes. RFC XXXX updates
1493this registry to make it clear that the registered values also serve
1494as IRI schemes, as defined in RFC YYYY." </t>
1495
1496<t>The registry includes schemes marked as Permanent or Provisional.
1497Previously, this was accomplished by having two sections, "Permanent"
1498and "Provisional". However, in order to allow other status
1499("Historical", and possibly a Proposed status for proposals which have
1500been received but not accepted), the registry should be changed so
1501that the status is indicated in a separate "Status" column, whose
1502values may be "Permanent", "Provisional" or "Historical".
1503Changes in status as well as updates to the entire registration
1504may be accomplished by requests and expert review.
1505</t>
1506
1507
1508</section> <!-- IANA -->
1509   
1510<section title="Security Considerations" anchor="security">
1511<t>The security considerations discussed in <xref target="RFC3986"/>
1512also apply to IRIs. In addition, the following issues require
1513particular care for IRIs.</t>
1514<t>Incorrect encoding or decoding can lead to security problems.
1515For example, some UTF-8 decoders do not check against overlong
1516byte sequences. See <xref target='UTR36'/> Section 3 for details.</t>
1517
1518  <t>There are serious difficulties with relying on a human to verify that a
1519    an IRI (whether presented visually or aurally)
1520    is the same as another IRI or is the one intended.
1521    These problems exist with ASCII-only URIs (bl00mberg.com vs. bloomberg.com)
1522    but are strongly exacerbated when using the much larger character repertoire of Unicode.
1523    For details, see Section 2 of <xref target='UTR36'/>.
1524    Using administrative and technical means to reduce the availability
1525    of such exploits is possible, but they are difficult to eliminate altogether.
1526    User agents SHOULD NOT rely on visual or perceptual comparison or verification of IRIs
1527    as a means of validating or assuring safety, correctness or appropriateness of an IRI.
1528    Other means of presenting users with the validity, safety, or appropriateness
1529    of visited sites are being developed in the browser community
1530    as an alternative means of avoiding these difficulties.</t>
1531
1532<t>Besides the large character repertoire of Unicode, reasons for
1533  confusion include different forms of normalization and different normalization
1534  expectations, use of percent-encoding with various legacy encodings,
1535  and bidirectionality issues. See also <xref target="Bidi"/>.</t>
1536
1537<t>Confusion can occur in various IRI components, such as the
1538domain name part or the path part, or between IRI components. For considerations specific
1539to the domain name part, see <xref target="RFC5890"/>. For considerations specific to
1540particular protocols or schemes, see the security sections of the relevant specifications
1541and registration templates.
1542Administrators of sites that allow independent
1543users to create resources in the same sub area have to be careful.
1544Details are discussed in <xref target="selection"/>.</t>
1545
1546  <t>The characters additionally allowed in Legacy Extended IRIs
1547    introduce additional security issues. For details, see <xref target='notAllowed'/>.</t>
1548</section><!-- security -->
1549
1550<section title="Acknowledgements">
1551<t>This document was derived from <xref target="RFC3987"/>; the acknowledgments from
1552that specification still apply.</t>
1553<t>In addition, this document was influenced by contributions from (in no particular order)
1554  Norman Walsh, Richard Tobin,
1555  Henry S. Thomson, John Cowan, Paul Grosso, the XML Core Working Group of the W3C,
1556  Chris Lilley, Bjoern Hoehrmann,
1557Felix Sasaki, Jeremy Carroll, Frank Ellermann, Michael Everson, Cary Karp, Matitiahu Allouche,
1558Richard Ishida, Addison Phillips, Jonathan Rosenne, Najib Tounsi, Debbie Garside, Mark Davis, Sarmad
1559Hussain, Ted Hardie, Konrad Lanz, Thomas Roessler, Lisa Dusseault, Julian Reschke, Giovanni
1560Campagna, Anne van Kesteren, Mark Nottingham, Erik van der Poel, Marcin Hanclik, Marcos Caceres, Roy
1561Fielding, Greg Wilkins, Pieter Hintjens, Daniel R. Tobias, Marko Martin, Maciej Stanchowiak, Wil
1562Tan, Yui Naruse, Michael A. Puls II, Dave Thaler, Tom Petch, John Klensin, Shawn Steele, Peter
1563Saint-Andre, Geoffrey Sneddon, Chris Weber, Alex Melnikov, Slim Amamou, S. Moonesamy, Tim Berners-Lee, Yaron
1564Goland, Sam Ruby, Adam Barth, Abdulrahman I. ALGhadir, Aharon Lanin, Thomas Milo, Murray Sargent,
1565Marc Blanchet, and Mykyta Yevstifeyev.</t>
1566</section> <!-- Acknowledgements -->
1567
1568<section title="Main Changes Since RFC 3987">
1569  <t>This section describes the main changes since <xref target="RFC3987"></xref>.</t>
1570  <section title="Split out Bidi, processing guidelines, comparison sections">
1571    <t>Move some components (comparison, bidi, processing) into separate documents.</t>
1572  </section>
1573  <section title="Major restructuring of IRI processing model" anchor="forkChanges">
1574    <t>Major restructuring of IRI processing model to make scheme-specific translation
1575      necessary to handle IDNA requirements and for consistency with web implementations. </t>
1576    <t>Starting with IRI, you want one of:
1577      <list style="hanging">
1578        <t hangText="a"> IRI components (IRI parsed into UTF8 pieces)</t>
1579        <t hangText="b"> URI components (URI parsed into ASCII pieces, encoded correctly) </t>
1580        <t hangText="c"> whole URI  (for passing on to some other system that wants whole URIs) </t>
1581      </list></t>
1582   
1583    <section title="OLD WAY">
1584      <t><list style="numbers">
1585       
1586        <t>Pct-encoding on the whole thing to a URI.
1587          (c1) If you want a (maybe broken) whole URI, you might
1588          stop here.</t>
1589       
1590        <t>Parsing the URI into URI components.
1591          (b1) If you want (maybe broken) URI components, stop here.</t>
1592       
1593        <t> Decode the components (undoing the pct-encoding).
1594          (a) if you want IRI components, stop here.</t>
1595       
1596        <t> reencode:  Either using a different encoding some components
1597          (for domain names, and query components in web pages, which
1598          depends on the component, scheme and context), and otherwise
1599          using pct-encoding.
1600          (b2) if you want (good) URI components, stop here.</t>
1601       
1602        <t> reassemble the reencoded components.
1603          (c2) if you want a (*good*) whole URI stop here.</t>
1604      </list>
1605       
1606      </t>
1607     
1608    </section>
1609   
1610    <section title="NEW WAY">
1611      <t>
1612        <list style="numbers">
1613         
1614          <t> Parse the IRI into IRI components using the generic syntax.
1615            (a) if you want IRI components, stop here.</t>
1616         
1617          <t> Encode each components, using pct-encoding, IDN encoding, or
1618            special query part encoding depending on the component
1619            scheme or context. (b) If you want URI components, stop here.</t>
1620          <t> reassemble the a whole URI from URI components.
1621            (c) if you want a whole URI stop here.</t>
1622        </list></t>
1623    </section>
1624    <section title="Extension of Syntax">
1625      <t>Added the tag range (U+E0000-E0FFF) to the iprivate production.
1626        Some IRIs generated with the new syntax may fail to pass very strict checks
1627        relying on the old syntax. But characters in this range should be extremely infrequent
1628        anyway.</t>
1629    </section>
1630    <section title="More to be added"><t>TODO: There are more main changes that need to be
1631      documented in this section.</t></section>
1632</section>
1633
1634<section title="Change Log">
1635
1636<t>Note to RFC Editor: Please completely remove this section before publication.</t>
1637
1638<section title='Changes after draft-ietf-iri-3987bis-01'>
1639    <t>Changes from draft-ietf-iri-3987bis-01 onwards are available as changesets
1640      in the IETF tools subversion repository at
1641      http://trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis/draft-ietf-iri-3987bis.xml.</t>
1642</section>
1643 
1644<section title='Changes from draft-duerst-iri-bis-07 to draft-ietf-iri-3987bis-00'>
1645     <t>Changed draft name, date, last paragraph of abstract, and titles in change log, and added this section
1646     in moving from draft-duerst-iri-bis-07 (personal submission) to draft-ietf-iri-3987bis-00 (WG document).</t>
1647</section>
1648
1649<section title="Changes from -06 to -07 of draft-duerst-iri-bis">
1650  <t>Major restructuring of the processing model, see <xref target="forkChanges"></xref>.</t>
1651</section>
1652</section>
1653
1654<section title='Changes from -00 to -01'><t><list style="symbols">
1655  <t>Removed 'mailto:' before mail addresses of authors.</t>
1656  <t>Added "&lt;to be done&gt;" as right side of 'href-strip' rule. Fixed '|' to '/' for
1657    alternatives.</t>
1658</list></t>
1659</section>
1660
1661<section title="Changes from -05 to -06 of draft-duerst-iri-bis-00"><t><list style="symbols">
1662<t>Add HyperText Reference, change abstract, acks and references for it</t>
1663<t>Add Masinter back as another editor.</t>
1664<t>Masinter integrates HRef material from HTML5 spec.</t>
1665<t>Rewrite introduction sections to modernize.</t>
1666</list></t>
1667</section>
1668
1669<section title="Changes from -04 to -05 of draft-duerst-iri-bis">
1670  <t><list style="symbols">
1671    <t>Updated references.</t>
1672    <t>Changed IPR text to pre5378Trust200902.</t></list></t>
1673</section>
1674
1675<section title="Changes from -03 to -04 of draft-duerst-iri-bis">
1676  <t><list style="symbols">
1677    <t>Added explicit abbreviation for LEIRIs.</t>
1678    <t>Mentioned LEIRI references.</t>
1679    <t>Completed text in LEIRI section about tag characters and about specials.</t></list></t>
1680</section>
1681
1682<section title="Changes from -02 to -03 of draft-duerst-iri-bis">
1683  <t><list style="symbols">
1684    <t>Updated some references.</t>
1685    <t>Updated Michel Suginard's coordinates.</t></list></t>
1686</section>
1687
1688<section title="Changes from -01 to -02 of draft-duerst-iri-bis">
1689  <t><list style="symbols">
1690    <t>Added tag range to iprivate (issue private-include-tags-115).</t>
1691    <t>Added Specials (U+FFF0-FFFD) to Legacy Extended IRIs.</t></list></t>
1692</section>
1693<section title="Changes from -00 to -01 of draft-duerst-iri-bis">
1694  <t><list style="symbols">
1695    <t>Changed from "IRIs with Spaces/Controls" to "Legacy Extended IRI"
1696      based on input from the W3C XML Core WG.
1697      Moved the relevant subsections to the back and promoted them to a section.</t>
1698    <t>Added some text re. Legacy Extended IRIs to the security section.</t>
1699    <t>Added a IANA Consideration Section.</t>
1700    <t>Added this Change Log Section.</t>
1701    <t>Added a section about "IRIs with Spaces/Controls" (converting from a Note in RFC 3987).</t></list></t>
1702</section> <!-- -00 to -01 -->
1703<section title="Changes from RFC 3987 to -00 of draft-duerst-iri-bis">
1704  <t><list>
1705    <t>Fixed errata (see http://www.rfc-editor.org/cgi-bin/errataSearch.pl?rfc=3987).</t></list></t>
1706</section> <!-- from 3987 -->
1707</section>
1708</middle>
1709
1710<back>
1711<references title="Normative References">
1712
1713<reference anchor="ASCII">
1714<front>
1715<title>Coded Character Set -- 7-bit American Standard Code for Information
1716Interchange</title>
1717<author>
1718<organization>American National Standards Institute</organization>
1719</author>
1720<date year="1986"/>
1721</front>
1722<seriesInfo name="ANSI" value="X3.4"/>
1723</reference>
1724
1725  <reference anchor="ISO10646" target='http://standards.iso.org/ittf/PubliclyAvailableStandards/c051273_ISO_IEC_10646_2011(E).zip'>
1726<front>
1727<title>ISO/IEC 10646:2011: Information Technology -
1728Universal Multiple-Octet Coded Character Set (UCS)</title>
1729<author>
1730<organization>International Organization for Standardization</organization>
1731</author>
1732<date month="March" year="20011"/>
1733</front>
1734<seriesInfo name="ISO" value="Standard 10646"/>
1735</reference>
1736
1737&rfc2119;
1738&rfc3491;
1739&rfc3629;
1740&rfc3986;
1741
1742<reference anchor="STD68">
1743<front>
1744<title abbrev="ABNF">Augmented BNF for Syntax Specifications: ABNF</title>
1745<author initials="D." surname="Crocker" fullname="Dave Crocker"><organization/></author>
1746<author initials="P." surname="Overell" fullname="Paul Overell"><organization/></author>
1747<date month="January" year="2008"/></front>
1748<seriesInfo name="STD" value="68"/><seriesInfo name="RFC" value="5234"/>
1749</reference>
1750 
1751&rfc5890;
1752&rfc5891;
1753&rfc5892;
1754
1755<reference anchor="UNIV6">
1756<front>
1757<title>The Unicode Standard, Version 6.0.0 (Mountain View, CA, The Unicode Consortium, 2011, ISBN 978-1-936213-01-6)</title>
1758<author><organization>The Unicode Consortium</organization></author>
1759<date year="2010" month="October"/>
1760</front>
1761</reference>
1762
1763<reference anchor="UTR15" target="http://www.unicode.org/unicode/reports/tr15/tr15-23.html">
1764<front>
1765<title>Unicode Normalization Forms</title>
1766<author initials="M." surname="Davis" fullname="Mark Davis"><organization/></author>
1767<author initials="M.J." surname="Duerst" fullname="Martin Duerst"><organization/></author>
1768<date year="2008" month="March"/>
1769</front>
1770<seriesInfo name="Unicode Standard Annex" value="#15"/>
1771</reference>
1772
1773</references>
1774
1775<references title="Informative References">
1776
1777  <reference anchor='CharMod' target='http://www.w3.org/TR/2004/CR-charmod-resid/'>
1778    <front>
1779      <title>Character Model for the World Wide Web 1.0: Resource Identifiers</title>
1780      <author fullname='Martin J. Duerst' surname='Duerst' initials='M. J.'/>
1781      <author fullname='Francois Yergeau' surname='Yergeau' initials='F.'/>
1782      <author fullname='Richard Ishida' surname='Ishida' initials='R. '/>
1783      <author fullname='Misha Wolf' surname='Wolf' initials='M. '/>
1784      <author fullname='Tex Texin' surname='Texin' initials='T. '/>
1785      <date year='2004' month='November' day='22'/>
1786    </front>
1787    <seriesInfo name='W3C Candidate Recommendation' value='CR-charmod-resid-20041122'/>
1788  </reference>
1789
1790<reference anchor="Duerst97" target="http://www.ifi.unizh.ch/mml/mduerst/papers/PDF/IUC11-UTF-8.pdf">
1791<front>
1792<title>The Properties and Promises of UTF-8</title>
1793<author initials="M.J." surname="Duerst" fullname="Martin Duerst"><organization/></author>
1794<date year="1997" month="September"/>
1795</front>
1796<seriesInfo name="Proc. 11th International Unicode Conference, San Jose" value=""/>
1797</reference>
1798
1799<reference anchor="Gettys" target="http://www.w3.org/DesignIssues/ModelConsequences">
1800<front>
1801<title>URI Model Consequences</title>
1802<author initials="J." surname="Gettys" fullname="Jim Gettys"><organization/></author>
1803<date month="" year=""/>
1804</front>
1805</reference>
1806
1807<reference anchor='HTML4' target='http://www.w3.org/TR/1999/REC-html401'>
1808<front>
1809<title>HTML 4.01 Specification</title>
1810<author fullname='David Raggett' surname='Raggett' initials='D. '/>
1811<author fullname='Arnaud Le Hors' surname='Le Hors' initials='A. '/>
1812<author fullname='Ian Jacobs' surname='Jacobs' initials='I. '/>
1813<date year='1999' month='December' day='24'/>
1814</front>
1815<seriesInfo name='W3C Recommendation' value='REC-html401-19991224'/>
1816</reference>
1817&rfc2130;
1818&rfc2141;
1819&rfc2192;
1820&rfc2277;
1821&rfc2384;
1822&rfc2396;
1823&rfc2397;
1824&rfc2616;
1825&rfc2640;
1826&rfc3987;
1827&rfc5122;
1828&rfc6055;
1829&rfc6068;
1830
1831<reference anchor='Bidi'>
1832  <front>
1833    <title>Guidelines for Internationalized Resource Identifiers with Bi-directional Characters (Bidi IRIs)</title>
1834    <author initials="M." surname="Duerst"/>
1835    <author initials='L.' surname='Masinter' />
1836    <author initials='A.' surname='Allawi' />
1837    <date year="2012" month="March" day="9" />
1838  </front>
1839  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-bidi-guidelines-02"/>
1840</reference>
1841
1842<reference anchor='Equivalence'>
1843  <front>
1844    <title>Equivalence and Canonicalization of Internationalized Resource Identifiers (IRIs)</title>
1845    <author initials='L.' surname='Masinter' />
1846    <author initials="M." surname="Duerst"/>
1847    <date year="2012" month="March" day="2" />
1848  </front>
1849  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-comparison-01"/>
1850</reference>
1851
1852<reference anchor='RFC4395bis'>
1853  <front>
1854    <title>Guidelines and Registration Procedures for New URI/IRI Schemes</title>
1855    <author initials='T.' surname='Hansen' fullname="Tony Hansen"><organization/></author>
1856    <author initials='T.' surname='Hardie' fullname="Ted Hardie"><organization/></author>
1857    <author initials='L.' surname='Masinter' fullname="Larry Masinter"><organization/></author>
1858    <date year='2011' month='December'/>
1859    <workgroup>IRI</workgroup>
1860  </front>
1861  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-4395bis-irireg-04"/>
1862</reference>
1863 
1864 
1865<reference anchor="UNIXML" target="http://www.w3.org/TR/unicode-xml/">
1866<front>
1867<title>Unicode in XML and other Markup Languages</title>
1868<author initials="M.J." surname="Duerst" fullname="Martin Duerst"><organization/></author>
1869<author initials="A." surname="Freytag" fullname="Asmus Freytag"><organization/></author>
1870<date year="2003" month="June" day="18"/>
1871</front>
1872<seriesInfo name="Unicode Technical Report" value="#20"/>
1873<seriesInfo name="World Wide Web Consortium" value="Note"/>
1874</reference>
1875 
1876<reference anchor="UTR36" target="http://unicode.org/reports/tr36/">
1877<front>
1878<title>Unicode Security Considerations</title>
1879<author initials="M." surname="Davis" fullname="Mark Davis"><organization/></author>
1880<author initials="M." surname="Suignard" fullname="Michel Suignard"><organization/></author>
1881<date year="2010" month="August" day="4"/>
1882</front>
1883<seriesInfo name="Unicode Technical Report" value="#36"/>
1884</reference>
1885
1886<reference anchor='XLink' target='http://www.w3.org/TR/xlink11/#link-locators'>
1887<front>
1888<title>XML Linking Language (XLink) Version 1.1</title>
1889<author fullname='Steve DeRose' surname='DeRose' initials='S. '/>
1890<author fullname='Eve Maler' surname='Maler' initials='E. '/>
1891<author fullname='David Orchard' surname='Orchard' initials='D. '/>
1892<author fullname='Norman Walsh' surname='Walsh' initials='N. '/>
1893<date year='2010' month='May' day='06'/>
1894</front>
1895<seriesInfo name='W3C Recommendation' value='REC-xlink11-20100506'/>
1896</reference>
1897 
1898<reference anchor='XML1' target='http://www.w3.org/TR/2008/REC-xml/'>
1899<front>
1900<title>Extensible Markup Language (XML) 1.0 (Fifth Edition)</title>
1901<author fullname='Tim Bray' surname='Bray' initials='T. '/>
1902<author fullname='Jean Paoli' surname='Paoli' initials='J. '/>
1903<author fullname='C. M. Sperberg-McQueen' surname='Sperberg-McQueen' initials='C. M. '/>
1904<author fullname='Eve Maler' surname='Maler' initials='E. '/>
1905<author fullname='Francois Yergeau' surname='Yergeau' initials='F.'/>
1906<date year='2008' month='November' day='26'/>
1907</front>
1908<seriesInfo name='W3C Recommendation' value='REC-xml-20081126'/>
1909</reference>
1910 
1911<reference anchor="XMLSchema" target="http://www.w3.org/TR/xmlschema-2/#anyURI">
1912<front>
1913<title>XML Schema Part 2: Datatypes Second Edition</title>
1914<author fullname='Paul V. Biron' surname='Biron' initials='P. V. '/>
1915<author fullname='Ashok Malhotra' surname='Malhotra' initials='A. '/>
1916<date year='2004' month='October' day='28'/>
1917</front>
1918<seriesInfo name='W3C Recommendation' value='REC-xmlschema-2-20041028'/>
1919</reference>
1920 
1921<reference anchor="XPointer" target="http://www.w3.org/TR/xptr-framework/#escaping">
1922<front>
1923<title>XPointer Framework</title>
1924<author fullname='Paul Grosso' surname='Grosso' initials='P. '/>
1925<author fullname='Eve Maler' surname='Maler' initials='E. '/>
1926<author fullname='Jonathan Marsh' surname='Marsh' initials='J. '/>
1927<author fullname='Norman Walsh' surname='Walsh' initials='N. '/>
1928<date year='2003' month='March' day='25'/>
1929</front>
1930<seriesInfo name='W3C Recommendation' value='REC-xptr-framework-20030325'/>
1931</reference>
1932
1933</references>
1934
1935</back>
1936</rfc>
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