source: draft-ietf-iri-3987bis/draft-ietf-iri-3987bis.xml @ 156

Last change on this file since 156 was 156, checked in by duerst@…, 7 years ago
  • removed domain name consideration from list of percent-encodings that cannot be eliminated (factual fix)
  • added consideration of query parts to URI->IRI procedure (non-escaping is now possible, but optional, see ticket 133)
  • minor wording changes
  • some paragraph reformatting by oXygen Author mode
  • Property svn:executable set to *
File size: 92.8 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 rfc3986 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3986.xml">
15<!ENTITY rfc5122 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.5122.xml">
16<!ENTITY rfc5890 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.5890.xml">
17<!ENTITY rfc5891 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.5891.xml">
18<!ENTITY rfc6055 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6055.xml">
19<!ENTITY DRAFT "draft-ietf-iri-3987bis-13">
20<!ENTITY YEAR "2012">
21]>
22<?rfc strict='yes'?>
23
24<?xml-stylesheet type='text/css' href='rfc2629.css' ?>
25<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
26<?rfc symrefs='yes'?>
27<?rfc sortrefs='yes'?>
28<?rfc iprnotified="no" ?>
29<?rfc toc='yes'?>
30<?rfc compact='yes'?>
31<?rfc subcompact='no'?>
32<rfc ipr="pre5378Trust200902" docName="&DRAFT;" category="std" xml:lang="en" obsoletes="3987">
33<front>
34<title abbrev="IRIs">Internationalized Resource Identifiers (IRIs)</title>
35
36<author initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst"
37  fullname="Martin J. Duerst (Note: Please write &quot;Duerst&quot; with u-umlaut wherever possible, for example as &quot;D&amp;#252;rst&quot; in XML and HTML.)">
38    <organization>Aoyama Gakuin University<ionly> (青山学院大学)</ionly> </organization>
39    <address>
40  <postal>
41  <street>5-10-1 Fuchinobe</street>
42  <street>Chuo-ku</street>
43  <city>Sagamihara</city>
44  <region>Kanagawa</region>
45  <code>252-5258</code>
46  <country>Japan</country>
47  </postal>
48  <phone>+81 42 759 6329</phone>
49  <facsimile>+81 42 759 6495</facsimile>
50  <email>duerst@it.aoyama.ac.jp</email>
51  <uri><aonly>http://www.sw.it.aoyama.ac.jp/D%C3%BCrst/ (Note: This is the percent-encoded form of an IRI)</aonly><ionly>http://www.sw.it.aoyama.ac.jp/Dürst/</ionly></uri>
52  </address>
53</author>
54 
55  <author initials="M.L." surname="Suignard" fullname="Michel Suignard">
56   <organization>Unicode Consortium</organization>
57   <address>
58   <postal>
59   <street></street>
60   <street>P.O. Box 391476</street>
61   <city>Mountain View</city>
62   <region>CA</region>
63   <code>94039-1476</code>
64   <country>U.S.A.</country>
65   </postal>
66   <phone>+1-650-693-3921</phone>
67   <email>michel@unicode.org</email>
68   <uri>http://www.suignard.com</uri>
69   </address>
70</author>
71<author initials="L." surname="Masinter" fullname="Larry Masinter">
72   <organization>Adobe</organization>
73   <address>
74   <postal>
75   <street>345 Park Ave</street>
76   <city>San Jose</city>
77   <region>CA</region>
78   <code>95110</code>
79   <country>U.S.A.</country>
80   </postal>
81   <phone>+1-408-536-3024</phone>
82   <email>masinter@adobe.com</email>
83   <uri>http://larry.masinter.net</uri>
84   </address>
85</author>
86
87  <date year="&YEAR;" />
88<area>Applications</area>
89<workgroup>Internationalized Resource Identifiers (iri)</workgroup>
90<keyword>IRI</keyword>
91<keyword>Internationalized Resource Identifier</keyword>
92<keyword>UTF-8</keyword>
93<keyword>URI</keyword>
94<keyword>IDN</keyword>
95<keyword>LEIRI</keyword>
96
97<abstract>
98<t>This document defines the Internationalized Resource Identifier
99(IRI) protocol element, as an extension of the Uniform Resource
100Identifier (URI).  An IRI is a sequence of characters from the
101Universal Character Set (Unicode/ISO 10646). Grammar and processing
102rules are given for IRIs and related syntactic forms.</t>
103
104<t>Defining IRI as a new protocol element (rather than updating or
105extending the definition of URI) allows independent orderly
106transitions: protocols and languages that use URIs must
107explicitly choose to allow IRIs.</t>
108
109<t>Guidelines are provided for the use and deployment of IRIs and
110related protocol elements when revising protocols, formats, and
111software components that currently deal only with URIs.</t>
112
113<t>This document is part of a set of documents intended to
114replace RFC 3987.</t>
115
116</abstract>
117  <note title='RFC Editor: Please remove the next paragraph before publication.'>
118    <t>This document, and several companion documents, are intended to obsolete RFC 3987.
119    For discussion and comments on these
120    drafts, please join the IETF IRI WG by subscribing to the mailing
121    list public-iri@w3.org, archives at http://lists.w3.org/archives/public/public-iri/.
122    For a list of open issues, please see
123    the issue tracker of the WG at http://trac.tools.ietf.org/wg/iri/trac/report/1.
124    For a list of individual edits, please see the change history at
125    http://trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis.</t>
126    <t>This document is available in (line-printer ready) plaintext ASCII and PDF.
127      It is also available in HTML from
128      <eref target="http://www.sw.it.aoyama.ac.jp/&YEAR;/pub/&DRAFT;.html"
129        >http://www.sw.it.aoyama.ac.jp/&YEAR;/pub/&DRAFT;.html</eref>,
130      and in UTF-8 plaintext from
131      <eref target="http://www.sw.it.aoyama.ac.jp/&YEAR;/pub/&DRAFT;.utf8.txt"
132        >http://www.sw.it.aoyama.ac.jp/&YEAR;/pub/&DRAFT;.utf8.txt</eref>.
133      While all these versions are identical in their technical content,
134      the HTML, PDF, and UTF-8 plaintext versions show non-Unicode characters directly.
135      This often makes it easier to understand examples, and readers are therefore advised
136      to consult these versions in preference or as a supplement to the ASCII version.</t>
137</note>
138</front>
139<middle>
140
141<section title="Introduction">
142
143<section title="Overview and Motivation" anchor="overview">
144
145<t>A Uniform Resource Identifier (URI) is defined in <xref
146target="RFC3986"/> as a sequence of characters chosen from a limited
147subset of the repertoire of US-ASCII <xref target="ASCII"/>
148characters.</t>
149
150<t>The characters in URIs are frequently used for representing words
151of natural languages.  This usage has many advantages: Such URIs are
152easier to memorize, easier to interpret, easier to transcribe, easier
153to create, and easier to guess. For most languages other than English,
154however, the natural script uses characters other than A - Z. For many
155people, handling Latin characters is as difficult as handling the
156characters of other scripts is for those who use only the Latin
157script. Many languages with non-Latin scripts are transcribed with
158Latin letters. These transcriptions are now often used in URIs, but
159they introduce additional difficulties.</t>
160
161<t>The infrastructure for the appropriate handling of characters from
162additional scripts is now widely deployed in operating system and
163application software. Software that can handle a wide variety of
164scripts and languages at the same time is increasingly common. Also,
165an increasing number of protocols and formats can carry a wide range of
166characters.</t>
167
168<t>URIs are composed out of a very limited repertoire of characters;
169this design choice was made to support global transcription (see <xref
170target="RFC3986"/> section 1.2.1.).  Reliable transition between a URI
171(as an abstract protocol element composed of a sequence of characters)
172and a presentation of that URI (written on a napkin, read out loud)
173and back is relatively straightforward, because of the limited
174repertoire of characters used.  IRIs are designed to satisfy a
175different set of use requirements; in particular, to allow IRIs to be
176written in ways that are more meaningful to their users, even at the
177expense of global transcribability. However, ensuring reliability of
178the transition between an IRI and its presentation and back is more
179difficult and complex when dealing with the larger set of Unicode
180characters.  For example, Unicode supports multiple ways of encoding
181complex combinations of characters and accents, with multiple
182character sequences that can result in the same presentation.</t>
183
184<t>This document defines the protocol element called Internationalized
185Resource Identifier (IRI), which allows applications of URIs to be
186extended to use resource identifiers that have a much wider repertoire
187of characters. It also provides corresponding "internationalized"
188versions of other constructs from <xref target="RFC3986"/>, such as
189URI references. The syntax of IRIs is defined in <xref
190target="syntax"/>.
191</t>
192
193<t>Within this document,
194               <xref target="IRIuse"/> discusses the use
195of IRIs in different situations.  <xref target="guidelines"/> gives
196additional informative guidelines.  <xref target="security"/>
197discusses IRI-specific security considerations.</t>
198
199<t>This specification is part of a collection of specifications
200intended to replace <xref target="RFC3987"/>.
201<xref target="Bidi"/> discusses the special case of
202bidirectional IRIs, IRIs using characters from scripts written
203right-to-left.
204<xref target="Equivalence"/> gives guidelines for applications wishing
205to determine if two IRIs are equivalent, as well as defining
206some equivalence methods.
207<xref target="RFC4395bis"/> updates the URI scheme registration
208guidelines and procedures to note that every URI scheme is also
209automatically an IRI scheme and to allow scheme definitions
210to be directly described in terms of Unicode characters.
211</t>
212
213</section> <!-- overview -->
214
215<section title="Applicability" anchor="Applicability">
216
217<t>IRIs are designed to allow protocols and software that deal with
218URIs to be updated to handle IRIs. Processing of
219IRIs is accomplished by extending the URI syntax while retaining (and
220not expanding) the set of "reserved" characters, such that the syntax
221for any URI scheme may be extended to allow non-ASCII
222characters. In addition, following parsing of an IRI, it is possible
223to construct a corresponding URI by first encoding characters outside
224of the allowed URI range and then reassembling the components.
225</t>
226
227<t>Practical use of IRIs forms in place of URIs forms depends on the
228following conditions being met:</t>
229
230<t><list style="hanging">
231   
232<t hangText="a.">A protocol or format element MUST be explicitly designated to be
233  able to carry IRIs. The intent is to avoid introducing IRIs into
234  contexts that are not defined to accept them.  For example, XML
235  schema <xref target="XMLSchema"/> has an explicit type "anyURI" that
236  includes IRIs and IRI references. Therefore, IRIs and IRI references
237  can be used in attributes and elements of type "anyURI".  On the other
238  hand, in HTTP/1.1 (<xref target="RFC2616"/>) , the
239  Request URI is defined as a URI, which means that direct use of IRIs
240  is not allowed in HTTP requests.</t>
241
242<t hangText="b.">The protocol or format carrying the IRIs MUST have a
243  mechanism to represent the wide range of characters used in IRIs,
244  either natively or by some protocol- or format-specific escaping
245  mechanism (for example, numeric character references in <xref
246  target="XML1"/>).</t>
247
248<t hangText="c.">The URI scheme definition, if it explicitly allows a
249  percent sign ("%") in any syntactic component, SHOULD define the
250  interpretation of sequences of percent-encoded octets (using "%XX"
251  hex octets) as octets from sequences of UTF-8 encoded characters; this
252  is recommended in the guidelines for registering new schemes, <xref
253  target="RFC4395bis"/>.  For example, this is the practice for IMAP URLs
254  <xref target="RFC2192"/>, POP URLs <xref target="RFC2384"/> and the
255  URN syntax <xref target="RFC2141"/>). Note that use of
256  percent-encoding may also be restricted in some situations, for
257  example, URI schemes that disallow percent-encoding might still be
258  used with a fragment identifier which is percent-encoded (e.g.,
259  <xref target="XPointer"/>). See <xref target="UTF8use"/> for further
260  discussion.</t>
261</list></t>
262
263</section> <!-- applicability -->
264
265<section title="Definitions" anchor="sec-Definitions">
266 
267<t>The following definitions are used in this document; they follow the
268terms in <xref target="RFC2130"/>, <xref target="RFC2277"/>, and
269<xref target="ISO10646"/>.</t>
270<t><list style="hanging">
271   
272<t hangText="character:">A member of a set of elements used for the
273    organization, control, or representation of data. For example,
274    "LATIN CAPITAL LETTER A" names a character.</t>
275   
276<t hangText="octet:">An ordered sequence of eight bits considered as a
277    unit.</t>
278   
279<t hangText="character repertoire:">A set of characters (set in the
280    mathematical sense).</t>
281   
282<t hangText="sequence of characters:">A sequence of characters (one
283    after another).</t>
284   
285<t hangText="sequence of octets:">A sequence of octets (one after
286    another).</t>
287   
288<t hangText="character encoding:">A method of representing a sequence
289    of characters as a sequence of octets (maybe with variants). Also,
290    a method of (unambiguously) converting a sequence of octets into a
291    sequence of characters.</t>
292   
293<t hangText="charset:">The name of a parameter or attribute used to
294    identify a character encoding.</t>
295   
296<t hangText="UCS:">Universal Character Set. The coded character set
297    defined by ISO/IEC 10646 <xref target="ISO10646"/> and the Unicode
298    Standard <xref target="UNIV6"/>.</t>
299   
300<t hangText="IRI reference:">Denotes the common usage of an
301    Internationalized Resource Identifier. An IRI reference may be
302    absolute or relative.  However, the "IRI" that results from such a
303    reference only includes absolute IRIs; any relative IRI references
304    are resolved to their absolute form.  Note that in <xref
305    target="RFC2396"/> URIs did not include fragment identifiers, but
306    in <xref target="RFC3986"/> fragment identifiers are part of
307    URIs.</t>
308   
309<t hangText="LEIRI (Legacy Extended IRI):">  This term is used in
310   various XML specifications to refer
311   to strings that, although not valid IRIs, are acceptable input to
312   the processing rules in <xref target="LEIRIspec" />.</t>
313
314<t hangText="protocol element:">Any portion of a message that affects
315    processing of that message by the protocol in question.</t>
316   
317<t hangText="create (a URI or IRI):">With respect to URIs and IRIs,
318     the term is used for the initial creation. This may be the
319     initial creation of a resource with a certain identifier, or the
320     initial exposition of a resource under a particular
321     identifier.</t>
322   
323<t hangText="generate (a URI or IRI):">With respect to URIs and IRIs,
324     the term is used when the identifier is generated by derivation
325     from other information.</t>
326
327<t hangText="parsed URI component:">When a URI processor parses a URI
328   (following the generic syntax or a scheme-specific syntax, the result
329   is a set of parsed URI components, each of which has a type
330   (corresponding to the syntactic definition) and a sequence of URI
331   characters.  </t>
332
333<t hangText="parsed IRI component:">When an IRI processor parses
334   an IRI directly, following the general syntax or a scheme-specific
335   syntax, the result is a set of parsed IRI components, each of
336   which has a type (corresponding to the syntactic definition)
337   and a sequence of IRI characters. (This definition is analogous
338   to "parsed URI component".)</t>
339
340<t hangText="IRI scheme:">A URI scheme may also be known as
341   an "IRI scheme" if the scheme's syntax has been extended to
342   allow non-US-ASCII characters according to the rules in this
343   document.</t>
344
345</list></t>
346</section> <!-- definitions -->
347<section title="Notation" anchor="sec-Notation">
348     
349<t>RFCs and Internet Drafts currently do not allow any characters
350outside the US-ASCII repertoire. Therefore, this document uses various
351special notations for such characters in examples.</t>
352     
353<t>In text, characters outside US-ASCII are sometimes referenced by
354using a prefix of 'U+', followed by four to six hexadecimal
355digits.</t>
356
357  <t>To represent characters outside US-ASCII in a document format
358    that is limited to US-ASCII, this document
359    uses 'XML Notation'.
360    XML Notation uses a leading '&amp;#x', a trailing ';', and the
361hexadecimal number of the character in the UCS in between. For
362example, &amp;#x42F; stands for CYRILLIC CAPITAL LETTER YA<ionly> (Я)</ionly>.
363In this notation, an actual '&amp;' is denoted by '&amp;amp;'.
364This notation is only used in the ASCII version(s) of this document,
365because in the other versions, non-ASCII characters are used directly.</t>
366
367<t>To denote actual octets in examples (as opposed to percent-encoded
368octets), the two hex digits denoting the octet are enclosed in "&lt;"
369and "&gt;".  For example, the octet often denoted as 0xc9 is denoted
370here as &lt;c9&gt;.</t>
371
372<t> In this document, the key words "MUST", "MUST NOT", "REQUIRED",
373"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
374and "OPTIONAL" are to be interpreted as described in <xref
375target="RFC2119"/>.</t>
376
377</section> <!-- notation -->
378</section> <!-- introduction -->
379
380<section title="IRI Syntax" anchor="syntax">
381<t>This section defines the syntax of Internationalized Resource
382Identifiers (IRIs).</t>
383
384<t>As with URIs, an IRI is defined as a sequence of characters, not as
385a sequence of octets.
386This definition accommodates the fact that IRIs
387may be written on paper or read over the radio as well as stored or
388transmitted digitally.  The same IRI might be represented as different
389sequences of octets in different protocols or documents if these
390protocols or documents use different character encodings (and/or
391transfer encodings).  Using the same character encoding as the
392containing protocol or document ensures that the characters in the IRI
393can be handled (e.g., searched, converted, displayed) in the same way
394as the rest of the protocol or document.</t>
395
396<section title="Summary of IRI Syntax" anchor="summary">
397
398<t>The IRI syntax extends the URI syntax in <xref
399target="RFC3986"/> by extending the class of unreserved characters,
400primarily by adding the characters of the UCS (Universal Character Set, <xref
401target="ISO10646"/>) beyond U+007F, subject to the limitations given
402in the syntax rules below and in <xref target="limitations"/>.</t>
403
404<t>The syntax and use of components and reserved characters is the
405same as that in <xref target="RFC3986"/>. Each URI scheme thus also
406functions as an IRI scheme, in that scheme-specific parsing rules
407for URIs of a scheme are extended to allow parsing of IRIs using
408the same parsing rules.</t>
409
410<t>All the operations defined in <xref target="RFC3986"/>, such as the
411resolution of relative references, can be applied to IRIs by
412IRI-processing software in exactly the same way as they are for URIs
413by URI-processing software.</t>
414
415<t>Characters outside the US-ASCII repertoire MUST NOT be reserved and
416therefore MUST NOT be used for syntactical purposes, such as to
417delimit components in newly defined schemes. For example, U+00A2, CENT
418SIGN, is not allowed as a delimiter in IRIs, because it is in the
419'iunreserved' category. This is similar to the fact that it is not
420possible to use '-' as a delimiter in URIs, because it is in the
421'unreserved' category.</t>
422
423</section> <!-- summary -->
424<section title="ABNF for IRI References and IRIs" anchor="abnf">
425
426<t>An ABNF definition for IRI references (which are the most general
427concept and the start of the grammar) and IRIs is given here. The
428syntax of this ABNF is described in <xref target="STD68"/>. Character
429numbers are taken from the UCS, without implying any actual binary
430encoding. Terminals in the ABNF are characters, not octets.</t>
431
432<t>The following grammar closely follows the URI grammar in <xref
433target="RFC3986"/>, except that the range of unreserved characters is
434expanded to include UCS characters, with the restriction that private
435UCS characters can occur only in query parts. The grammar is split
436into two parts: Rules that differ from <xref target="RFC3986"/>
437because of the above-mentioned expansion, and rules that are the same
438as those in <xref target="RFC3986"/>. For rules that are different
439than those in <xref target="RFC3986"/>, the names of the non-terminals
440have been changed as follows. If the non-terminal contains 'URI', this
441has been changed to 'IRI'. Otherwise, an 'i' has been prefixed.
442The rule &lt;pct-form> has been introduced in order to be able to reference it from other parts of
443the document.</t>
444
445<!--
446for line length measuring in artwork (max 72 chars, three chars at start):
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449-->
450<figure>
451<preamble>The following rules are different from those in <xref target="RFC3986"/>:</preamble>
452<artwork>
453IRI            = scheme ":" ihier-part [ "?" iquery ]
454                 [ "#" ifragment ]
455
456ihier-part     = "//" iauthority ipath-abempty
457               / ipath-absolute
458               / ipath-rootless
459               / ipath-empty
460
461IRI-reference  = IRI / irelative-ref
462
463absolute-IRI   = scheme ":" ihier-part [ "?" iquery ]
464
465irelative-ref  = irelative-part [ "?" iquery ] [ "#" ifragment ]
466
467irelative-part = "//" iauthority ipath-abempty
468               / ipath-absolute
469               / ipath-noscheme
470               / ipath-empty
471
472iauthority     = [ iuserinfo "@" ] ihost [ ":" port ]
473iuserinfo      = *( iunreserved / pct-form / sub-delims / ":" )
474ihost          = IP-literal / IPv4address / ireg-name
475
476pct-form       = pct-encoded
477
478ireg-name      = *( iunreserved / sub-delims )
479
480ipath          = ipath-abempty   ; begins with "/" or is empty
481               / ipath-absolute  ; begins with "/" but not "//"
482               / ipath-noscheme  ; begins with a non-colon segment
483               / ipath-rootless  ; begins with a segment
484               / ipath-empty     ; zero characters
485
486ipath-abempty  = *( path-sep isegment )
487ipath-absolute = path-sep [ isegment-nz *( path-sep isegment ) ]
488ipath-noscheme = isegment-nz-nc *( path-sep isegment )
489ipath-rootless = isegment-nz *( path-sep isegment )
490ipath-empty    = ""
491path-sep       = "/"
492
493isegment       = *ipchar
494isegment-nz    = 1*ipchar
495isegment-nz-nc = 1*( iunreserved / pct-form / sub-delims
496                     / "@" )
497               ; non-zero-length segment without any colon ":"
498
499ipchar         = iunreserved / pct-form / sub-delims / ":"
500               / "@"
501 
502iquery         = *( ipchar / iprivate / "/" / "?" )
503
504ifragment      = *( ipchar / "/" / "?" )
505
506iunreserved    = ALPHA / DIGIT / "-" / "." / "_" / "~" / ucschar
507
508ucschar        = %xA0-D7FF / %xF900-FDCF / %xFDF0-FFEF
509               / %x10000-1FFFD / %x20000-2FFFD / %x30000-3FFFD
510               / %x40000-4FFFD / %x50000-5FFFD / %x60000-6FFFD
511               / %x70000-7FFFD / %x80000-8FFFD / %x90000-9FFFD
512               / %xA0000-AFFFD / %xB0000-BFFFD / %xC0000-CFFFD
513               / %xD0000-DFFFD / %xE1000-EFFFD
514
515iprivate       = %xE000-F8FF / %xE0000-E0FFF / %xF0000-FFFFD
516               / %x100000-10FFFD
517</artwork>
518</figure>
519
520<t>Some productions are ambiguous. The "first-match-wins" (a.k.a. "greedy")
521algorithm applies. For details, see <xref target="RFC3986"/>.</t>
522
523<figure>
524<preamble>The following rules are the same as those in <xref target="RFC3986"/>:</preamble>
525<artwork>
526scheme         = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
527 
528port           = *DIGIT
529 
530IP-literal     = "[" ( IPv6address / IPvFuture  ) "]"
531 
532IPvFuture      = "v" 1*HEXDIG "." 1*( unreserved / sub-delims / ":" )
533 
534IPv6address    =                            6( h16 ":" ) ls32
535               /                       "::" 5( h16 ":" ) ls32
536               / [               h16 ] "::" 4( h16 ":" ) ls32
537               / [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
538               / [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
539               / [ *3( h16 ":" ) h16 ] "::"    h16 ":"   ls32
540               / [ *4( h16 ":" ) h16 ] "::"              ls32
541               / [ *5( h16 ":" ) h16 ] "::"              h16
542               / [ *6( h16 ":" ) h16 ] "::"
543               
544h16            = 1*4HEXDIG
545ls32           = ( h16 ":" h16 ) / IPv4address
546
547IPv4address    = dec-octet "." dec-octet "." dec-octet "." dec-octet
548
549dec-octet      = DIGIT                 ; 0-9
550               / %x31-39 DIGIT         ; 10-99
551               / "1" 2DIGIT            ; 100-199
552               / "2" %x30-34 DIGIT     ; 200-249
553               / "25" %x30-35          ; 250-255
554           
555pct-encoded    = "%" HEXDIG HEXDIG
556
557unreserved     = ALPHA / DIGIT / "-" / "." / "_" / "~"
558reserved       = gen-delims / sub-delims
559gen-delims     = ":" / "/" / "?" / "#" / "[" / "]" / "@"
560sub-delims     = "!" / "$" / "&amp;" / "'" / "(" / ")"
561               / "*" / "+" / "," / ";" / "="
562</artwork></figure>
563
564<t>This syntax does not support IPv6 scoped addressing zone identifiers.</t>
565
566</section> <!-- abnf -->
567
568</section> <!-- syntax -->
569
570<section title="Processing IRIs and related protocol elements" anchor="processing">
571
572<t>IRIs are meant to replace URIs in identifying resources within new
573versions of protocols, formats, and software components that use a
574UCS-based character repertoire.  Protocols and components may use and
575process IRIs directly. However, there are still numerous systems and
576protocols which only accept URIs or components of parsed URIs; that is,
577they only accept sequences of characters within the subset of US-ASCII
578characters allowed in URIs. </t>
579
580<t>This section defines specific processing steps for IRI consumers
581which establish the relationship between the string given and the
582interpreted derivatives. These
583processing steps apply to both IRIs and IRI references (i.e., absolute
584or relative forms); for IRIs, some steps are scheme specific. </t>
585
586<section title="Converting to UCS" anchor="ucsconv"> 
587 
588<t>Input that is already in a Unicode form (i.e., a sequence of Unicode
589 characters or an octet-stream representing a Unicode-based character
590 encoding such as UTF-8 or UTF-16) should be left as is and not
591 normalized or changed.</t>
592
593  <t>An IRI or IRI reference is a sequence of characters from the UCS.
594    For input from presentations (written on paper, read aloud)
595    or translation from other representations (a text stream using a legacy character
596    encoding), convert the input to Unicode.
597    Note that some character encodings or transcriptions can be converted
598    to or represented by more than one sequence of Unicode characters.
599
600    Ideally the resulting IRI would use a normalized form,
601    such as Unicode Normalization Form C <xref target="UTR15"/>,
602    since that ensures a stable, consistent representation
603    that is most likely to produce the intended results.
604    Previous versions of this specification required
605    normalization at this step. However, attempts to
606    require normalization in other protocols have met with
607    strong enough resistance that requiring normalization
608    here was considered impractical.
609    Implementers and users are cautioned that, while denormalized character sequences are valid,
610    they might be difficult for other users or processes to reproduce
611    and might lead to unexpected results.
612  <!-- raise on list:
613    It is recommended
614    that the processing of IRI components treat
615    strings with the same normalized forms as equivalent.
616   -->
617  </t>
618
619</section> <!-- ucsconv -->
620
621<section title="Parse the IRI into IRI components">
622
623<t>Parse the IRI, either as a relative reference (no scheme)
624or using scheme specific processing (according to the scheme
625given); the result is a set of parsed IRI components.</t>
626
627</section> <!-- parse -->
628
629<section title="General percent-encoding of IRI components" anchor="compmapping">
630   
631<t>Except as noted in the following subsections, IRI components are mapped
632to the equivalent URI components by percent-encoding those characters
633not allowed in URIs. Previous processing steps will have removed
634some characters, and the interpretation of reserved characters will
635have already been done (with the syntactic reserved characters outside
636of the IRI component). This mapping is defined for all sequences
637of Unicode characters, whether or not they are valid for the component
638in question. </t>
639   
640<t>For each character which is not allowed anywhere in a valid URI
641 apply the following steps. </t>
642<t><list style="hanging">
643
644<t hangText="Convert to UTF-8:">Convert the character to a sequence of
645  one or more octets using UTF-8 <xref target="STD63"/>.</t>
646
647<t hangText="Percent encode:">Convert each octet of this sequence to %HH,
648   where HH is the hexadecimal notation of the octet value. The
649   hexadecimal notation SHOULD use uppercase letters. (This is the
650   general URI percent-encoding mechanism in Section 2.1 of <xref
651   target="RFC3986"/>.)</t>
652   
653</list></t>
654
655<t>Note that the mapping is an identity transformation for parsed URI
656components of valid URIs, and is idempotent: applying the mapping a
657second time will not change anything.</t>
658</section> <!-- general conversion -->
659
660<section title="Mapping ireg-name" anchor="dnsmapping">
661  <t>The mapping from &lt;ireg-name> to a &lt;reg-name> requires a choice
662    between one of the two methods described below.</t>
663  <section title='Mapping using Percent-Encoding' anchor='dnspercent'>
664  <t>The ireg-name component SHOULD be converted
665    according to the general procedure for percent-encoding
666    of IRI components described in <xref target="compmapping"/>.</t>
667 
668  <t>For example, the IRI
669    <vspace/><aonly>"http://r&amp;#xE9;sum&amp;#xE9;.example.org"</aonly><ionly>"http://résumé.example.org"</ionly><vspace/> will be
670    converted to <vspace/>"http://r%C3%A9sum%C3%A9.example.org".</t>
671
672  <t>This conversion for ireg-name is in line with Section 3.2.2
673    of <xref target="RFC3986"/>, which does not mandate
674    a particular registered name lookup technology. For further background,
675    see <xref target="RFC6055"/> and <xref target="Gettys"/>.</t>
676</section> <!-- dnspercent -->
677<section title="Mapping using Punycode" anchor='dnspunycode'>
678  <t>In situations where it is certain that &lt;ireg-name> is intended
679    to be used as a domain name to be processed by Domain Name Lookup
680    (as per <xref target="RFC5891"/>), an alternative method MAY be
681    used, converting &lt;ireg-name> as follows:</t>
682
683  <t>If there are any sequences of &lt;pct-encoded&gt;, and their
684    corresponding octets all represent valid UTF-8
685    octet sequences, then convert these back to Unicode
686    character sequences. (If any &lt;pct-encoded&gt; sequences are not
687    valid UTF-8 octet sequences, then leave the entire field as is
688    without any change, since punycode encoding would not succeed.)</t>
689
690<t>Replace the ireg-name part of the IRI by the part converted using
691the Domain Name Lookup procedure (Subsections 5.3 to 5.5) of <xref target="RFC5891"/>.
692  on each dot-separated label, and by using U+002E
693(FULL STOP) as a label separator.
694This procedure may fail, but this would mean that the IRI cannot be resolved.
695In such cases, if the domain name conversion fails, then the
696entire IRI conversion fails. Processors that have no mechanism for
697signalling a failure MAY instead substitute an otherwise
698invalid host name, although such processing SHOULD be avoided.</t>
699
700<t>For example, the IRI
701  <vspace/><aonly>"http://r&amp;#xE9;sum&amp;#xE9;.example.org"</aonly><ionly>"http://résumé.example.org"</ionly><vspace/> is
702converted to <vspace/>"http://xn--rsum-bad.example.org".</t>
703  <t>This conversion for ireg-name will be better able to deal with legacy
704    infrastructure that cannot handle percent-encoding in domain names.</t>
705</section> <!-- punicode -->
706  <section title="Additional Considerations">
707
708<t><list style="hanging"> 
709<t hangText="Note:">Domain Names may appear in parts of an IRI other
710than the ireg-name part.  It is the responsibility of scheme-specific
711implementations (if the Internationalized Domain Name is part of the
712scheme syntax) or of server-side implementations (if the
713Internationalized Domain Name is part of 'iquery') to apply the
714necessary conversions at the appropriate point. Example: Trying to
715validate the Web page at<vspace/>
716  <aonly>http://r&amp;#xE9;sum&amp;#xE9;.example.org</aonly><ionly>http://résumé.example.org</ionly>
717  would lead to an IRI of
718  <vspace/>http://validator.w3.org/check?uri=http%3A%2F%2F<aonly>r&amp;#xE9;sum&amp;#xE9;</aonly><ionly>résumé</ionly><vspace/>.example.org,
719which would convert to a URI
720of<vspace/>http://validator.w3.org/check?uri=http%3A%2F%2Fr%C3%A9sum%C3%A9.<vspace/>example.org.
721The server-side implementation is responsible for making the
722necessary conversions to be able to retrieve the Web page.</t>
723 
724<t hangText="Note:">In this process, characters allowed in URI
725references and existing percent-encoded sequences are not encoded further.
726(This mapping is similar to, but different from, the encoding applied
727when arbitrary content is included in some part of a URI.)
728
729For example, an IRI of
730<vspace/><aonly>"http://www.example.org/red%09ros&amp;#xE9;#red"
731  (in XML notation)</aonly><ionly>"http://www.example.org/red%09rosé#red"</ionly>
732  is converted to
733<vspace/>"http://www.example.org/red%09ros%C3%A9#red", not to
734something like
735<vspace/>"http%3A%2F%2Fwww.example.org%2Fred%2509ros%C3%A9%23red".</t>
736
737</list></t>
738</section> <!-- additional -->
739</section> <!-- dnsmapping -->
740
741<section title="Mapping query components" anchor="querymapping">
742
743<t>For compatibility with existing deployed HTTP infrastructure, the following special case applies
744          for the schemes "http" and "https" when an IRI is found in a document whose charset is not
745          based on UCS (e.g., not UTF-8 or UTF-16). In such a case, the "query" component of an IRI
746          is mapped into a URI by using the document charset rather than UTF-8 as the binary
747          representation before pct-encoding. This mapping is not applied for any other schemes or
748          components.</t>
749
750</section> <!-- querymapping -->
751
752<section title="Mapping IRIs to URIs" anchor="mapping">
753
754<t>The mapping from an IRI to URI is accomplished by applying the
755mapping above (from IRI to URI components) and then reassembling a URI
756from the parsed URI components using the original punctuation that
757delimited the IRI components. </t>
758
759</section> <!-- mapping -->
760</section> <!-- processing -->
761
762<section title="Converting URIs to IRIs" anchor="URItoIRI">
763
764  <t>In some situations, for presentation and further processing, it is desirable to convert a URI
765        into an equivalent IRI without unnecessary percent encoding. Of course, every URI is already
766        an IRI in its own right without any conversion. This section gives one possible procedure
767        for converting a URI to an IRI.</t>
768
769<t>The conversion described in this section, if given a valid URI, will result in an IRI that maps
770        back to the URI used as an input for the conversion (except for potential case differences
771        in percent-encoding and for potential percent-encoded unreserved characters). However, the
772        IRI resulting from this conversion may differ from the original IRI (if there ever was
773        one).</t> 
774
775<t>URI-to-IRI conversion removes percent-encodings, but not all
776percent-encodings can be eliminated. There are several reasons for
777this:</t>
778
779<t><list style="hanging">
780
781<t hangText="1.">Some percent-encodings are necessary to distinguish
782    percent-encoded and unencoded uses of reserved characters.</t>
783
784<t hangText="2.">Some percent-encodings cannot be interpreted as sequences
785    of UTF-8 octets.<vspace blankLines="1"/>
786    (Note: The octet patterns of UTF-8 are highly regular.
787    Therefore, there is a very high probability, but no guarantee,
788    that percent-encodings that can be interpreted as sequences of UTF-8
789    octets actually originated from UTF-8. For a detailed discussion,
790    see <xref target="Duerst97"/>.)</t>
791
792<t hangText="3.">The conversion may result in a character that is not
793    appropriate in an IRI. See <xref target="abnf"/>,
794      and <xref target="limitations"/> for further details.</t>
795
796<t hangText="4.">As described in <xref target="querymapping"/>, IRI to URI conversion may work
797            somewhat differently for query components.</t>
798
799</list></t>
800
801<t>Conversion from a URI to an IRI MAY be done by using the following
802steps:
803
804<list style="hanging">
805<t hangText="1.">Represent the URI as a sequence of octets in
806       US-ASCII.</t>
807
808<t hangText="2.">Convert all percent-encodings ("%" followed by two
809      hexadecimal digits) to the corresponding octets, except those
810      corresponding to "%", characters in "reserved", and characters
811      in US-ASCII not allowed in URIs.</t> 
812
813<t hangText="3.">Re-percent-encode any octet produced in step 2 that
814      is not part of a strictly legal UTF-8 octet sequence.</t>
815
816
817<t hangText="4.">Re-percent-encode all octets produced in step 3 that
818      in UTF-8 represent characters that are not appropriate according
819      to <xref target="abnf"/>  and <xref
820      target="limitations"/>.</t>
821          <t hangText="5.">Optionally, re-percent-encode octets in the query component if the scheme
822            is one of those mentioned in <xref target="querymapping"/>.</t> 
823
824<t hangText="6.">Interpret the resulting octet sequence as a sequence of characters encoded in
825            UTF-8.</t>
826
827<t hangText="7.">URIs known to contain domain names in the reg-name component SHOULD convert
828            punycode-encoded domain name labels to the corresponding characters using the ToUnicode
829            procedure. </t>
830</list></t>
831
832<t>This procedure will convert as many percent-encoded characters as possible to characters in an
833        IRI. Because there are some choices in steps 4 (see also <xref target="limitations"/>) and
834        5, results may vary.</t>
835
836<t>Conversions from URIs to IRIs MUST NOT use any character
837encoding other than UTF-8 in steps 3 and 4, even if it might be
838possible to guess from the context that another character encoding
839than UTF-8 was used in the URI.  For example, the URI
840"http://www.example.org/r%E9sum%E9.html" might with some guessing be
841interpreted to contain two e-acute characters encoded as
842iso-8859-1. It must not be converted to an IRI containing these
843e-acute characters. Otherwise, in the future the IRI will be mapped to
844"http://www.example.org/r%C3%A9sum%C3%A9.html", which is a different
845URI from "http://www.example.org/r%E9sum%E9.html".</t>
846
847<section title="Examples">
848
849<t>This section shows various examples of converting URIs to IRIs.
850Each example shows the result after each of the steps 1 through 6 is
851applied. XML Notation is used for the final result.  Octets are
852denoted by "&lt;" followed by two hexadecimal digits followed by
853"&gt;".</t>
854
855<t>The following example contains the sequence "%C3%BC", which is a
856strictly legal UTF-8 sequence, and which is converted into the actual
857character U+00FC, LATIN SMALL LETTER U WITH DIAERESIS (also known as
858u-umlaut).
859
860<list style="hanging">
861<t hangText="1.">http://www.example.org/D%C3%BCrst</t>
862<t hangText="2.">http://www.example.org/D&lt;c3&gt;&lt;bc&gt;rst</t>
863<t hangText="3.">http://www.example.org/D&lt;c3&gt;&lt;bc&gt;rst</t>
864<t hangText="4.">http://www.example.org/D&lt;c3&gt;&lt;bc&gt;rst</t>
865  <t hangText="5."><aonly>http://www.example.org/D&amp;#xFC;rst</aonly><ionly>http://www.example.org/Dürst</ionly></t>
866  <t hangText="6."><aonly>http://www.example.org/D&amp;#xFC;rst</aonly><ionly>http://www.example.org/Dürst</ionly></t>
867</list>
868</t>
869
870<t>The following example contains the sequence "%FC", which might
871represent U+00FC, LATIN SMALL LETTER U WITH DIAERESIS, in
872the<vspace/>iso-8859-1 character encoding.  (It might represent other
873characters in other character encodings. For example, the octet
874&lt;fc&gt; in iso-8859-5 represents U+045C, CYRILLIC SMALL LETTER
875KJE.)  Because &lt;fc&gt; is not part of a strictly legal UTF-8
876sequence, it is re-percent-encoded in step 3.
877
878
879<list style="hanging">
880<t hangText="1.">http://www.example.org/D%FCrst</t>
881<t hangText="2.">http://www.example.org/D&lt;fc&gt;rst</t>
882<t hangText="3.">http://www.example.org/D%FCrst</t>
883<t hangText="4.">http://www.example.org/D%FCrst</t>
884<t hangText="5.">http://www.example.org/D%FCrst</t>
885<t hangText="6.">http://www.example.org/D%FCrst</t>
886</list>
887</t>
888
889<t>The following example contains "%e2%80%ae", which is the percent-encoded<vspace/>UTF-8
890character encoding of U+202E, RIGHT-TO-LEFT OVERRIDE.
891The direct use of this character is forbidden in an IRI. Therefore, the
892corresponding octets are re-percent-encoded in step 4. This example shows
893that the case (upper- or lowercase) of letters used in percent-encodings may not be preserved.
894The example also contains a punycode-encoded domain name label (xn--99zt52a),
895which is not converted.
896
897<list style="hanging">
898<t hangText="1.">http://xn--99zt52a.example.org/%e2%80%ae</t>
899<t hangText="2.">http://xn--99zt52a.example.org/&lt;e2&gt;&lt;80&gt;&lt;ae&gt;</t>
900<t hangText="3.">http://xn--99zt52a.example.org/&lt;e2&gt;&lt;80&gt;&lt;ae&gt;</t>
901<t hangText="4.">http://xn--99zt52a.example.org/%E2%80%AE</t>
902<t hangText="5.">http://xn--99zt52a.example.org/%E2%80%AE</t>
903  <t hangText="6."><aonly>http://&amp;#x7D0D;&amp;#x8C46;.example.org/%E2%80%AE</aonly><ionly>http://納豆.example.org/%E2%80%AE</ionly></t>
904</list></t>
905
906<t>Note that the label "xn--99zt52a" is converted to U+7D0D U+8C46
907(Japanese Natto<ionly>, 納豆</ionly>). ((EDITOR NOTE: There is some inconsistency in this note.))</t>
908
909</section> <!-- examples -->
910</section> <!-- URItoIRI -->
911
912
913<section title="Use of IRIs" anchor="IRIuse">
914
915<section title="Limitations on UCS Characters Allowed in IRIs" anchor="limitations">
916
917<t>This section discusses limitations on characters and character
918sequences usable for IRIs beyond those given in <xref target="abnf"/>.
919The considerations in this section are
920relevant when IRIs are created and when URIs are converted to
921IRIs.</t>
922
923<t>
924
925<list style="hanging"><t hangText="a.">The repertoire of characters allowed
926    in each IRI component is limited by the definition of that component.
927    For example, the definition of the scheme component does not allow
928    characters beyond US-ASCII.
929    <vspace blankLines="1"/>
930    (Note: In accordance with URI practice, generic IRI
931    software cannot and should not check for such limitations.)</t>
932
933<t hangText="b.">The UCS contains many areas of characters for which
934    there are strong visual look-alikes. Because of the likelihood of
935    transcription errors, these also should be avoided. This includes
936    the full-width equivalents of Latin characters, half-width
937    Katakana characters for Japanese, and many others. It also
938    includes many look-alikes of "space", "delims", and "unwise",
939    characters excluded in <xref target="RFC3491"/>.</t>
940 
941<t hangText="c.">At the start of a component, the use of combining marks is strongly discouraged. As
942    an example, a COMBINING TILDE OVERLAY (U+0334) would be very confusing at the start of
943    a &lt;isegment>. Combined with the preceeding '/', it might look like a solidus
944    with combining tilde overlay, but IRI processing software will parse and process the
945    '/' separately.</t>
946<t hangText='d.'>The ZERO WIDTH NON-JOINER (U+200C) and ZERO WIDTH
947    JOINER (U+200D) are invisible in most contexts, but are crucial in
948    some very limited contexts. Appendix A of <xref target="RFC5892"/>
949    contains contextual restrictions for these and some other characters.
950    The use of these characters are strongly discouraged except
951    in the relevant contexts.</t>
952</list>
953</t>
954
955<t>Additional information is available from <xref target="UNIXML"/>.
956    <xref target="UNIXML"/> is written in the context of general purpose text
957    rather than in that of identifiers. Nevertheless, it discusses
958    many of the categories of characters not appropriate for IRIs.</t>
959</section> <!-- limitations -->
960
961<section title="Software Interfaces and Protocols">
962
963<t>Although an IRI is defined as a sequence of characters, software
964interfaces for URIs typically function on sequences of octets or other
965kinds of code units. Thus, software interfaces and protocols MUST
966define which character encoding is used.</t>
967
968<t>Intermediate software interfaces between IRI-capable components and
969URI-only components MUST map the IRIs per <xref target="mapping"/>,
970when transferring from IRI-capable to URI-only components.
971
972This mapping SHOULD be applied as late as possible. It SHOULD NOT be
973applied between components that are known to be able to handle IRIs.</t>
974</section> <!-- software -->
975
976<section title="Format of URIs and IRIs in Documents and Protocols">
977
978<t>Document formats that transport URIs may have to be upgraded to allow
979the transport of IRIs. In cases where the document as a whole
980has a native character encoding, IRIs MUST also be encoded in this
981character encoding and converted accordingly by a parser or interpreter.
982
983IRI characters not expressible in the native character encoding SHOULD
984be escaped by using the escaping conventions of the document format if
985such conventions are available. Alternatively, they MAY be
986percent-encoded according to <xref target="mapping"/>. For example, in
987HTML or XML, numeric character references SHOULD be used. If a
988document as a whole has a native character encoding and that character
989encoding is not UTF-8, then IRIs MUST NOT be placed into the document
990in the UTF-8 character encoding.</t>
991
992<t>((UPDATE THIS NOTE)) Note: Some formats already accommodate IRIs,
993although they use different terminology. HTML 4.0 <xref
994target="HTML4"/> defines the conversion from IRIs to URIs as
995error-avoiding behavior. XML 1.0 <xref target="XML1"/>, XLink <xref
996target="XLink"/>, XML Schema <xref target="XMLSchema"/>, and
997specifications based upon them allow IRIs. Also, it is expected that
998all relevant new W3C formats and protocols will be required to handle
999IRIs <xref target="CharMod"/>.</t>
1000
1001</section> <!-- format -->
1002
1003<section title="Use of UTF-8 for Encoding Original Characters" anchor="UTF8use">
1004
1005<t>This section discusses details and gives examples for point c) in
1006<xref target="Applicability"/>. To be able to use IRIs, the URI
1007corresponding to the IRI in question has to encode original characters
1008into octets by using UTF-8.  This can be specified for all URIs of a
1009URI scheme or can apply to individual URIs for schemes that do not
1010specify how to encode original characters.  It can apply to the whole
1011URI, or only to some part. For background information on encoding
1012characters into URIs, see also Section 2.5 of <xref
1013target="RFC3986"/>.</t>
1014
1015<t>For new URI schemes, using UTF-8 is recommended in <xref
1016target="RFC4395bis"/>.  Examples where UTF-8 is already used are the URN
1017syntax <xref target="RFC2141"/>, IMAP URLs <xref target="RFC2192"/>,
1018POP URLs <xref target="RFC2384"/>, XMPP URLs <xref target='RFC5122'/>,
1019and the 'mailto:' scheme <xref target='RFC6068'/>. On the other hand, because the
1020HTTP URI scheme does not specify how to encode original characters,
1021only some HTTP URLs can have corresponding but different IRIs.</t>
1022
1023<t>For example, for a document with a URI
1024of<vspace/>"http://www.example.org/r%C3%A9sum%C3%A9.html", it is
1025possible to construct a corresponding IRI
1026  <aonly>(in XML notation, see <xref target="sec-Notation"/>):
1027    "http://www.example.org/r&amp;#xE9;sum&amp;#xE9;.html"
1028    ("&amp;#xE9;" stands for the e-acute character, and "%C3%A9" is the UTF-8 encoded
1029    and percent-encoded representation of that character).</aonly>
1030  <ionly>: "http://www.example.org/résumé.html"
1031    ("é" is the e-acute character, and "%C3%A9" is the UTF-8 encoded
1032    and percent-encoded representation of that character).</ionly>
1033  On the other hand, for a document with a URI of
1034"http://www.example.org/r%E9sum%E9.html", the percent-encoded octets
1035cannot be converted to actual characters in an IRI, as the
1036percent-encoding is not based on UTF-8.</t>
1037
1038<t>For most URI schemes, there is no need to upgrade their scheme
1039definition in order for them to work with IRIs.  The main case where
1040upgrading makes sense is when a scheme definition, or a particular
1041component of a scheme, is strictly limited to the use of US-ASCII
1042characters with no provision to include non-ASCII characters/octets
1043via percent-encoding, or if a scheme definition currently uses highly
1044scheme-specific provisions for the encoding of non-ASCII characters.</t>
1045
1046<t>This specification updates the IANA registry of URI schemes to note
1047their applicability to IRIs, see <xref target="iana"/>.  All IRIs use
1048URI schemes, and all URIs with URI schemes can be used as IRIs, even
1049though in some cases only by using URIs directly as IRIs, without any
1050conversion.</t>
1051
1052<t>Scheme definitions can impose restrictions on the syntax of
1053scheme-specific URIs; i.e., URIs that are admissible under the generic
1054URI syntax <xref target="RFC3986"/> may not be admissible due to
1055narrower syntactic constraints imposed by a URI scheme
1056specification. URI scheme definitions cannot broaden the syntactic
1057restrictions of the generic URI syntax; otherwise, it would be
1058possible to generate URIs that satisfied the scheme-specific syntactic
1059constraints without satisfying the syntactic constraints of the
1060generic URI syntax. However, additional syntactic constraints imposed
1061by URI scheme specifications are applicable to IRI, as the
1062corresponding URI resulting from the mapping defined in <xref
1063target="mapping"/> MUST be a valid URI under the syntactic
1064restrictions of generic URI syntax and any narrower restrictions
1065imposed by the corresponding URI scheme specification.</t>
1066
1067<t>The requirement for the use of UTF-8 generally applies to all parts
1068of a URI.  However, it is possible that the capability of IRIs to
1069represent a wide range of characters directly is used just in some
1070parts of the IRI (or IRI reference). The other parts of the IRI may
1071only contain US-ASCII characters, or they may not be based on
1072UTF-8. They may be based on another character encoding, or they may
1073directly encode raw binary data (see also <xref
1074target="RFC2397"/>). </t>
1075
1076<t>For example, it is possible to have a URI reference
1077of<vspace/>"http://www.example.org/r%E9sum%E9.xml#r%C3%A9sum%C3%A9",
1078where the document name is encoded in iso-8859-1 based on server
1079settings, but where the fragment identifier is encoded in UTF-8 according
1080to <xref target="XPointer"/>. The IRI corresponding to the above URI would be
1081  <aonly>(in XML notation)<vspace/>"http://www.example.org/r%E9sum%E9.xml#r&amp;#xE9;sum&amp;#xE9;".</aonly>
1082  <ionly><vspace/>"http://www.example.org/r%E9sum%E9.xml#résumé".</ionly>
1083</t>
1084
1085<t>Similar considerations apply to query parts. The functionality
1086of IRIs (namely, to be able to include non-ASCII characters) can
1087only be used if the query part is encoded in UTF-8.</t>
1088
1089</section> <!-- utf8 -->
1090
1091<section title="Relative IRI References">
1092<t>Processing of relative IRI references against a base is handled
1093straightforwardly; the algorithms of <xref target="RFC3986"/> can
1094be applied directly, treating the characters additionally allowed
1095in IRI references in the same way that unreserved characters are treated in URI
1096references.</t>
1097
1098</section> <!-- relative -->
1099</section> <!-- IRIuse -->
1100
1101  <section title="Legacy Extended IRIs (LEIRIs)">
1102    <t>In some cases, there have been formats which have used a protocol element
1103      which is a variant of the IRI definition; these variants have usually been
1104      somewhat less restricted in syntax. This section provides
1105      a definition and a name (Legacy Extended IRI or LEIRI) for one of these
1106      variants used widely in XML-based protocols. This variant has to be used with care;
1107      it requires further processing before being fully interchangeable as IRIs.
1108
1109      New protocols and formats SHOULD NOT use Legacy Extended IRIs.
1110      Even where Legacy Extended IRIs are allowed, only IRIs fully conforming
1111      to the syntax definition in <xref target="abnf"></xref> SHOULD be created,
1112      generated, and used. The provisions in this section also apply to
1113      Legacy Extended IRI references.</t>
1114   
1115    <section title="Legacy Extended IRI Syntax">
1116      <figure>
1117
1118        <preamble>This section defines Legacy Extended IRIs (LEIRIs).  The syntax of
1119   Legacy Extended IRIs is the same as that for &lt;IRI-reference&gt;, except
1120   that the ucschar production is replaced by the leiri-ucschar
1121   production:
1122
1123</preamble>
1124        <artwork>
1125leiri-ucschar  = " " / "&lt;" / "&gt;" / '"' / "{" / "}" / "|"
1126               / "\" / "^" / "`" / %x0-1F / %x7F-D7FF
1127               / %xE000-FFFD / %x10000-10FFFF
1128        </artwork>
1129        <postamble>The restriction on bidirectional formatting characters in <xref target="Bidi"></xref> is lifted.
1130        The iprivate production becomes redundant.</postamble>
1131      </figure>
1132
1133      <t>Likewise, the syntax for Legacy Extended IRI references
1134      (LEIRI references) is the same as that for IRI references with
1135      the above replacement of ucschar with leiri-ucschar.</t>
1136
1137     </section>
1138    <section title="Conversion of Legacy Extended IRIs to IRIs" anchor="LEIRIspec">
1139      <t>To convert a Legacy Extended IRI (reference) to
1140      an IRI (reference), each character allowed in a Legacy Extended IRI (reference)
1141      but not allowed in an IRI (reference) (see <xref target="notAllowed"></xref>)  MUST be percent-encoded
1142      by applying the steps in <xref target="compmapping"></xref>.</t>
1143    </section>
1144     
1145    <section title="Characters Allowed in Legacy Extended IRIs but not in IRIs" anchor="notAllowed">
1146      <t>This section provides a list of the groups of characters and code points
1147        that are allowed in Legacy Extedend IRIs, but are not allowed in IRIs
1148        or are allowed in IRIs only in the query part. For each group of characters,
1149        advice on the usage of these characters is also given, concentrating on the
1150        reasons for why not to use them.</t>
1151      <t>
1152        <list>
1153          <t>Space (U+0020): Some formats and applications use space as a delimiter,
1154            e.g., for items in a list. Appendix C of <xref target="RFC3986"></xref>
1155            also mentions that white space may have to be added when displaying
1156            or printing long URIs; the same applies to long IRIs.
1157            Spaces might disappear, or a single Legacy Extended IRI
1158            might incorrectly be interpreted as two or more separate ones.</t>
1159     
1160          <t>Delimiters "&lt;" (U+003C), "&gt;" (U+003E), and '"' (U+0022):
1161            Appendix C of <xref target="RFC3986"></xref> suggests the use of
1162            double-quotes ("http://example.com/") and angle brackets
1163        (&lt;http://example.com/&gt;) as delimiters for URIs in plain text.
1164        These conventions are often used, and also apply to IRIs.
1165        Legacy Extended IRIs using these characters might be cut off at the wrong place.</t>
1166     
1167          <t>Unwise characters "\" (U+005C),
1168          "^" (U+005E), "`" (U+0060), "{" (U+007B), "|" (U+007C), and "}" (U+007D):
1169          These characters originally were excluded from URIs because
1170          the respective codepoints are assigned to different graphic characters
1171          in some 7-bit or 8-bit encoding. Despite the move to Unicode,
1172          some of these characters are still occasionally displayed differently
1173          on some systems, e.g., U+005C as a Japanese Yen symbol.
1174     
1175          Also, the fact that these characters are not used in URIs or IRIs
1176          has encouraged their use outside URIs or IRIs in contexts that may
1177          include URIs or IRIs. In case a Legacy Extended IRI with such a character
1178          is used in such a context, the Legacy Extended IRI will be interpreted piecemeal.</t>
1179     
1180          <t>The controls (C0 controls, DEL, and C1 controls, #x0  - #x1F  #x7F - #x9F):
1181            There is no way to transmit these characters reliably except potentially
1182            in electronic form. Even when in electronic form, some software components
1183            might silently filter out some of these characters,
1184            or may stop processing alltogether when encountering some of them.
1185            These characters may affect text display in subtle, unnoticable ways
1186            or in drastic, global, and irreversible ways depending
1187            on the hardware and software involved.
1188            The use of some of these characters may allow malicious users
1189            to manipulate the display of a Legacy Extended IRI and its context.</t>
1190          <t>Bidi formatting characters (U+200E, U+200F, U+202A-202E):
1191            These characters affect the display ordering of characters.
1192            Displayed Legacy Extended IRIs containing these characters
1193            cannot be converted back to electronic form (logical order) unambiguously.
1194            These characters may allow malicious users to manipulate
1195            the display of a Legacy Extended IRI and its context.</t>
1196          <t>Specials (U+FFF0-FFFD): These code points provide functionality
1197            beyond that useful in a Legacy Extended IRI, for example byte order identification,
1198            annotation, and replacements for unknown characters and objects.
1199            Their use and interpretation in a Legacy Extended IRI
1200            serves no purpose and may lead to confusing display variations.</t>
1201          <t>Private use code points (U+E000-F8FF, U+F0000-FFFFD, U+100000-10FFFD):
1202            Display and interpretation of these code points is by definition
1203            undefined without private agreement. Therefore, these code points
1204            are not suited for use on the Internet. They are not interoperable and may have
1205            unpredictable effects.</t>
1206          <t>Tags (U+E0000-E0FFF): These characters provide a way to language tag in Unicode plain text.
1207            They are not appropriate for Legacy Extended IRIs because language information
1208            in identifiers cannot reliably be input, transmitted
1209            (e.g., on a visual medium such as paper), or recognized.</t>
1210          <t>Non-characters (U+FDD0-FDEF, U+1FFFE-1FFFF, U+2FFFE-2FFFF, U+3FFFE-3FFFF,
1211            U+4FFFE-4FFFF, U+5FFFE-5FFFF, U+6FFFE-6FFFF, U+7FFFE-7FFFF, U+8FFFE-8FFFF,
1212            U+9FFFE-9FFFF, U+AFFFE-AFFFF, U+BFFFE-BFFFF, U+CFFFE-CFFFF, U+DFFFE-DFFFF,
1213            U+EFFFE-EFFFF, U+FFFFE-FFFFF, U+10FFFE-10FFFF):
1214            These code points are defined as non-characters. Applications may use
1215            some of them internally, but are not prepared to interchange them.</t>
1216        </list>
1217      </t>
1218      <t>For reference, we here also list the code points and code units
1219        not even allowed in Legacy Extended IRIs:
1220        <list>
1221         
1222          <t>Surrogate code units (D800-DFFF):
1223          These do not represent Unicode codepoints.</t>
1224           <t>Non-characters (U+FFFE-FFFF): These are not allowed in XML nor LEIRIs.</t>
1225     
1226        </list>
1227      </t>
1228    </section>
1229  </section>
1230 
1231<section title="URI/IRI Processing Guidelines (Informative)" anchor="guidelines">
1232
1233<t>This informative section provides guidelines for supporting IRIs in
1234the same software components and operations that currently process
1235URIs: Software interfaces that handle URIs, software that allows users
1236to enter URIs, software that creates or generates URIs, software that
1237displays URIs, formats and protocols that transport URIs, and software
1238that interprets URIs. These may all require modification before
1239functioning properly with IRIs. The considerations in this section
1240also apply to URI references and IRI references.</t>
1241
1242<section title="URI/IRI Software Interfaces">
1243<t>Software interfaces that handle URIs, such as URI-handling APIs and
1244protocols transferring URIs, need interfaces and protocol elements
1245that are designed to carry IRIs.</t>
1246
1247<t>In case the current handling in an API or protocol is based on
1248US-ASCII, UTF-8 is recommended as the character encoding for IRIs, as
1249it is compatible with US-ASCII, is in accordance with the
1250recommendations of <xref target="RFC2277"/>, and makes converting to
1251URIs easy. In any case, the API or protocol definition must clearly
1252define the character encoding to be used.</t>
1253
1254<t>The transfer from URI-only to IRI-capable components requires no
1255mapping, although the conversion described in <xref
1256target="URItoIRI"/> above may be performed. It is preferable not to
1257perform this inverse conversion unless it is certain this can be done
1258correctly.</t>
1259</section><!-- software interfaces -->
1260
1261<section title="URI/IRI Entry">
1262
1263<t>Some components allow users to enter URIs into the system
1264by typing or dictation, for example. This software must be updated to allow
1265for IRI entry.</t>
1266
1267<t>A person viewing a visual presentation of an IRI (as a sequence
1268of glyphs, in some order, in some visual display)
1269will use an entry method for characters in the user's language to
1270input the IRI. Depending on the script and the input method used, this
1271may be a more or less complicated process.</t>
1272
1273<t>The process of IRI entry must ensure, as much as possible, that the
1274restrictions defined in <xref target="abnf"/> are met. This may be
1275done by choosing appropriate input methods or variants/settings
1276thereof, by appropriately converting the characters being input, by
1277eliminating characters that cannot be converted, and/or by issuing a
1278warning or error message to the user.</t>
1279
1280<t>As an example of variant settings, input method editors for East
1281Asian Languages usually allow the input of Latin letters and related
1282characters in full-width or half-width versions. For IRI input, the
1283input method editor should be set so that it produces half-width Latin
1284letters and punctuation and full-width Katakana.</t>
1285
1286<t>An input field primarily or solely used for the input of URIs/IRIs
1287might allow the user to view an IRI as it is mapped to a URI.  Places
1288where the input of IRIs is frequent may provide the possibility for
1289viewing an IRI as mapped to a URI. This will help users when some of
1290the software they use does not yet accept IRIs.</t>
1291
1292<t>An IRI input component interfacing to components that handle URIs,
1293but not IRIs, must map the IRI to a URI before passing it to these
1294components.</t>
1295
1296<t>For the input of IRIs with right-to-left characters, please see
1297<xref target="Bidi"></xref>.</t>
1298</section><!-- entry -->
1299
1300<section title="URI/IRI Transfer between Applications">
1301
1302<t>Many applications (for example, mail user agents) try to detect
1303URIs appearing in plain text. For this, they use some heuristics based
1304on URI syntax. They then allow the user to click on such URIs and
1305retrieve the corresponding resource in an appropriate (usually
1306scheme-dependent) application.</t>
1307
1308<t>Such applications would need to be upgraded, in order to use the
1309IRI syntax as a base for heuristics. In particular, a non-ASCII
1310character should not be taken as the indication of the end of an IRI.
1311Such applications also would need to make sure that they correctly
1312convert the detected IRI from the character encoding of the document
1313or application where the IRI appears, to the character encoding used
1314by the system-wide IRI invocation mechanism, or to a URI (according to
1315<xref target="mapping"/>) if the system-wide invocation mechanism only
1316accepts URIs.</t>
1317
1318<t>The clipboard is another frequently used way to transfer URIs and
1319IRIs from one application to another. On most platforms, the clipboard
1320is able to store and transfer text in many languages and scripts.
1321Correctly used, the clipboard transfers characters, not octets, which
1322will do the right thing with IRIs.</t>
1323</section><!-- transfer -->
1324
1325<section title="URI/IRI Generation">
1326
1327<t>Systems that offer resources through the Internet, where those
1328resources have logical names, sometimes automatically generate URIs
1329for the resources they offer. For example, some HTTP servers can
1330generate a directory listing for a file directory and then respond to
1331the generated URIs with the files.</t>
1332
1333<t>Many legacy character encodings are in use in various file systems.
1334Many currently deployed systems do not transform the local character
1335representation of the underlying system before generating URIs.</t>
1336
1337<t>For maximum interoperability, systems that generate resource
1338identifiers should make the appropriate transformations. For example,
1339if a file system contains a file named
1340  <aonly>"r&amp;#xE9;sum&amp;#xE9;.html"</aonly><ionly>"résumé.html"</ionly>,
1341  a server should expose this as
1342"r%C3%A9sum%C3%A9.html" in a URI, which allows use of
1343  <aonly>"r&amp;#xE9;sum&amp;#xE9;.html"</aonly><ionly>"résumé.html"</ionly>
1344  in an IRI, even if locally the file
1345name is kept in a character encoding other than UTF-8.
1346</t>
1347
1348<t>This recommendation particularly applies to HTTP servers. For FTP
1349servers, similar considerations apply; see <xref target="RFC2640"/>.</t>
1350</section><!-- generation -->
1351
1352<section title="URI/IRI Selection" anchor="selection">
1353<t>In some cases, resource owners and publishers have control over the
1354IRIs used to identify their resources. This control is mostly
1355executed by controlling the resource names, such as file names,
1356directly.</t>
1357
1358<t>In these cases, it is recommended to avoid choosing IRIs that are
1359easily confused. For example, for US-ASCII, the lower-case ell ("l") is
1360easily confused with the digit one ("1"), and the upper-case oh ("O") is
1361easily confused with the digit zero ("0"). Publishers should avoid
1362confusing users with "br0ken" or "1ame" identifiers.</t>
1363
1364<t>Outside the US-ASCII repertoire, there are many more opportunities for
1365confusion; a complete set of guidelines is too lengthy to include
1366here. As long as names are limited to characters from a single script,
1367native writers of a given script or language will know best when
1368ambiguities can appear, and how they can be avoided. What may look
1369ambiguous to a stranger may be completely obvious to the average
1370native user. On the other hand, in some cases, the UCS contains
1371variants for compatibility reasons; for example, for typographic purposes.
1372These should be avoided wherever possible. Although there may be exceptions,
1373newly created resource names should generally be in NFKC
1374<xref target="UTR15"></xref> (which means that they are also in NFC).</t>
1375
1376<t>As an example, the UCS contains the "fi" ligature at U+FB01
1377for compatibility reasons.
1378Wherever possible, IRIs should use the two letters "f" and "i" rather
1379than the "fi" ligature. An example where the latter may be used is
1380in the query part of an IRI for an explicit search for a word written
1381containing the "fi" ligature.</t>
1382
1383<t>In certain cases, there is a chance that characters from different
1384scripts look the same. The best known example is the similarity of the
1385Latin "A", the Greek "Alpha", and the Cyrillic "A". To avoid such
1386cases, IRIs should only be created where all the characters in a
1387single component are used together in a given language. This usually
1388means that all of these characters will be from the same script, but
1389there are languages that mix characters from different scripts (such
1390as Japanese).  This is similar to the heuristics used to distinguish
1391between letters and numbers in the examples above. Also, for Latin,
1392Greek, and Cyrillic, using lowercase letters results in fewer
1393ambiguities than using uppercase letters would.</t>
1394</section><!-- selection -->
1395
1396<section title="Display of URIs/IRIs" anchor="display">
1397<t>
1398In situations where the rendering software is not expected to display
1399non-ASCII parts of the IRI correctly using the available layout and font
1400resources, these parts should be percent-encoded before being displayed.</t>
1401
1402<t>For display of Bidi IRIs, please see <xref target="Bidi"/>.</t>
1403</section> <!-- display -->
1404
1405<section title="Interpretation of URIs and IRIs">
1406<t>Software that interprets IRIs as the names of local resources should
1407accept IRIs in multiple forms and convert and match them with the
1408appropriate local resource names.</t>
1409
1410<t>First, multiple representations include both IRIs in the native
1411character encoding of the protocol and also their URI counterparts.</t>
1412
1413<t>Second, it may include URIs constructed based on character
1414encodings other than UTF-8. These URIs may be produced by user agents that do
1415not conform to this specification and that use legacy character encodings to
1416convert non-ASCII characters to URIs. Whether this is necessary, and what
1417character encodings to cover, depends on a number of factors, such as
1418the legacy character encodings used locally and the distribution of
1419various versions of user agents. For example, software for Japanese
1420may accept URIs in Shift_JIS and/or EUC-JP in addition to UTF-8.</t>
1421
1422<t>Third, it may include additional mappings to be more user-friendly
1423and robust against transmission errors. These would be similar to how
1424some servers currently treat URIs as case insensitive or perform
1425additional matching to account for spelling errors. For characters
1426beyond the US-ASCII repertoire, this may, for example, include
1427ignoring the accents on received IRIs or resource names. Please note
1428that such mappings, including case mappings, are language
1429dependent.</t>
1430
1431<t>It can be difficult to identify a resource unambiguously if too
1432many mappings are taken into consideration. However, percent-encoded
1433and not percent-encoded parts of IRIs can always be clearly distinguished.
1434Also, the regularity of UTF-8 (see <xref target="Duerst97"/>) makes the
1435potential for collisions lower than it may seem at first.</t>
1436</section> <!-- interpretation -->
1437
1438<section title="Upgrading Strategy">
1439<t>Where this recommendation places further constraints on software
1440for which many instances are already deployed, it is important to
1441introduce upgrades carefully and to be aware of the various
1442interdependencies.</t>
1443
1444<t>If IRIs cannot be interpreted correctly, they should not be created,
1445generated, or transported. This suggests that upgrading URI interpreting
1446software to accept IRIs should have highest priority.</t>
1447
1448<t>On the other hand, a single IRI is interpreted only by a single or
1449very few interpreters that are known in advance, although it may be
1450entered and transported very widely.</t>
1451
1452<t>Therefore, IRIs benefit most from a broad upgrade of software to be
1453able to enter and transport IRIs. However, before an
1454individual IRI is published, care should be taken to upgrade the corresponding
1455interpreting software in order to cover the forms expected to be
1456received by various versions of entry and transport software.</t>
1457
1458<t>The upgrade of generating software to generate IRIs instead of using a
1459local character encoding should happen only after the service is upgraded
1460to accept IRIs. Similarly, IRIs should only be generated when the service
1461accepts IRIs and the intervening infrastructure and protocol is known
1462to transport them safely.</t>
1463
1464<t>Software converting from URIs to IRIs for display should be upgraded
1465only after upgraded entry software has been widely deployed to the
1466population that will see the displayed result.</t>
1467
1468
1469<t>Where there is a free choice of character encodings, it is often
1470possible to reduce the effort and dependencies for upgrading to IRIs
1471by using UTF-8 rather than another encoding. For example, when a new
1472file-based Web server is set up, using UTF-8 as the character encoding
1473for file names will make the transition to IRIs easier. Likewise, when
1474a new Web form is set up using UTF-8 as the character encoding of the
1475form page, the returned query URIs will use UTF-8 as the character
1476encoding (unless the user, for whatever reason, changes the character
1477encoding) and will therefore be compatible with IRIs.</t>
1478
1479
1480<t>These recommendations, when taken together, will allow for the
1481extension from URIs to IRIs in order to handle characters other than
1482US-ASCII while minimizing interoperability problems. For
1483considerations regarding the upgrade of URI scheme definitions, see
1484<xref target="UTF8use"/>.</t>
1485
1486</section> <!-- upgrading -->
1487</section> <!-- guidelines -->
1488
1489<section title="IANA Considerations" anchor="iana">
1490
1491<t>NOTE: THIS SECTION NEEDS REVIEW AGAINST HAPPIANA WORK.</t>
1492
1493<t>RFC Editor and IANA note: Please Replace RFC XXXX with the
1494number of this document when it issues as an RFC, and RFC YYYY
1495with the number of the RFC issued for draft-ietf-iri-rfc3987bis. </t>
1496
1497<t>IANA maintains a registry of "URI schemes".  This document attempts
1498to make it clear from the registry that a "URI scheme" also serves an
1499"IRI scheme", and makes several changes to the registry. </t>
1500
1501<t>The description of the registry should be changed: "RFC 4395
1502defined an IANA-maintained registry of URI Schemes. RFC XXXX updates
1503this registry to make it clear that the registered values also serve
1504as IRI schemes, as defined in RFC YYYY." </t>
1505
1506<t>The registry includes schemes marked as Permanent or Provisional.
1507Previously, this was accomplished by having two sections, "Permanent"
1508and "Provisional". However, in order to allow other status
1509("Historical", and possibly a Proposed status for proposals which have
1510been received but not accepted), the registry should be changed so
1511that the status is indicated in a separate "Status" column, whose
1512values may be "Permanent", "Provisional" or "Historical".
1513Changes in status as well as updates to the entire registration
1514may be accomplished by requests and expert review.
1515</t>
1516
1517
1518</section> <!-- IANA -->
1519   
1520<section title="Security Considerations" anchor="security">
1521<t>The security considerations discussed in <xref target="RFC3986"/>
1522also apply to IRIs. In addition, the following issues require
1523particular care for IRIs.</t>
1524<t>Incorrect encoding or decoding can lead to security problems.
1525For example, some UTF-8 decoders do not check against overlong
1526byte sequences. See <xref target='UTR36'/> Section 3 for details.</t>
1527
1528  <t>There are serious difficulties with relying on a human to verify that a
1529    an IRI (whether presented visually or aurally)
1530    is the same as another IRI or is the one intended.
1531    These problems exist with ASCII-only URIs (bl00mberg.com vs. bloomberg.com)
1532    but are strongly exacerbated when using the much larger character repertoire of Unicode.
1533    For details, see Section 2 of <xref target='UTR36'/>.
1534    Using administrative and technical means to reduce the availability
1535    of such exploits is possible, but they are difficult to eliminate altogether.
1536    User agents SHOULD NOT rely on visual or perceptual comparison or verification of IRIs
1537    as a means of validating or assuring safety, correctness or appropriateness of an IRI.
1538    Other means of presenting users with the validity, safety, or appropriateness
1539    of visited sites are being developed in the browser community
1540    as an alternative means of avoiding these difficulties.</t>
1541
1542<t>Besides the large character repertoire of Unicode, reasons for
1543  confusion include different forms of normalization and different normalization
1544  expectations, use of percent-encoding with various legacy encodings,
1545  and bidirectionality issues. See also <xref target="Bidi"/>.</t>
1546
1547<t>Confusion can occur in various IRI components, such as the
1548domain name part or the path part, or between IRI components. For considerations specific
1549to the domain name part, see <xref target="RFC5890"/>. For considerations specific to
1550particular protocols or schemes, see the security sections of the relevant specifications
1551and registration templates.
1552Administrators of sites that allow independent
1553users to create resources in the same sub area have to be careful.
1554Details are discussed in <xref target="selection"/>.</t>
1555
1556  <t>The characters additionally allowed in Legacy Extended IRIs
1557    introduce additional security issues. For details, see <xref target='notAllowed'/>.</t>
1558</section><!-- security -->
1559
1560<section title="Acknowledgements">
1561<t>This document was derived from <xref target="RFC3987"/>; the acknowledgments from
1562that specification still apply.</t>
1563<t>In addition, this document was influenced by contributions from (in no particular order)
1564  Norman Walsh, Richard Tobin,
1565  Henry S. Thomson, John Cowan, Paul Grosso, the XML Core Working Group of the W3C,
1566  Chris Lilley, <aonly>Bjoern Hoehrmann</aonly><ionly>Björn Höhrmann</ionly>,
1567Felix Sasaki, Jeremy Carroll, Frank Ellermann, Michael Everson, Cary Karp, Matitiahu Allouche,
1568Richard Ishida, Addison Phillips, Jonathan Rosenne, Najib Tounsi, Debbie Garside, Mark Davis,
1569Sarmad Hussain, Ted Hardie, Konrad Lanz, Thomas Roessler, Lisa Dusseault, Julian Reschke,
1570Giovanni Campagna, Anne van Kesteren, Mark Nottingham, Erik van der Poel, Marcin Hanclik, Marcos Caceres,
1571Roy Fielding, Greg Wilkins, Pieter Hintjens, Daniel R. Tobias, Marko Martin, Maciej Stanchowiak,
1572Wil Tan, Yui Naruse<ionly> (成瀬ゆい)</ionly>, Michael A. Puls II, Dave Thaler, Tom Petch, John Klensin, Shawn Steele,
1573Peter Saint-Andre, Geoffrey Sneddon, Chris Weber, Alex Melnikov, Slim Amamou, S. Moonesamy, Tim Berners-Lee,
1574Yaron Goland, Sam Ruby, Adam Barth, Abdulrahman I. ALGhadir, Aharon Lanin, Thomas Milo, Murray Sargent,
1575Marc Blanchet, and Mykyta Yevstifeyev.</t>
1576</section> <!-- Acknowledgements -->
1577
1578<section title="Main Changes Since RFC 3987">
1579  <t>This section describes the main changes since <xref target="RFC3987"></xref>.</t>
1580  <section title="Split out Bidi, processing guidelines, comparison sections">
1581    <t>Move some components (comparison, bidi, processing) into separate documents.</t>
1582  </section>
1583  <section title="Major restructuring of IRI processing model" anchor="forkChanges">
1584    <t>Major restructuring of IRI processing model to make scheme-specific translation
1585      necessary to handle IDNA requirements and for consistency with web implementations. </t>
1586    <t>Starting with IRI, you want one of:
1587      <list style="hanging">
1588        <t hangText="a"> IRI components (IRI parsed into UTF8 pieces)</t>
1589        <t hangText="b"> URI components (URI parsed into ASCII pieces, encoded correctly) </t>
1590        <t hangText="c"> whole URI  (for passing on to some other system that wants whole URIs) </t>
1591      </list></t>
1592   
1593    <section title="OLD WAY">
1594      <t><list style="numbers">
1595       
1596        <t>Pct-encoding on the whole thing to a URI.
1597          (c1) If you want a (maybe broken) whole URI, you might
1598          stop here.</t>
1599       
1600        <t>Parsing the URI into URI components.
1601          (b1) If you want (maybe broken) URI components, stop here.</t>
1602       
1603        <t> Decode the components (undoing the pct-encoding).
1604          (a) if you want IRI components, stop here.</t>
1605       
1606        <t> reencode:  Either using a different encoding some components
1607          (for domain names, and query components in web pages, which
1608          depends on the component, scheme and context), and otherwise
1609          using pct-encoding.
1610          (b2) if you want (good) URI components, stop here.</t>
1611       
1612        <t> reassemble the reencoded components.
1613          (c2) if you want a (*good*) whole URI stop here.</t>
1614      </list>
1615       
1616      </t>
1617     
1618    </section>
1619   
1620    <section title="NEW WAY">
1621      <t>
1622        <list style="numbers">
1623         
1624          <t> Parse the IRI into IRI components using the generic syntax.
1625            (a) if you want IRI components, stop here.</t>
1626         
1627          <t> Encode each components, using pct-encoding, IDN encoding, or
1628            special query part encoding depending on the component
1629            scheme or context. (b) If you want URI components, stop here.</t>
1630          <t> reassemble the a whole URI from URI components.
1631            (c) if you want a whole URI stop here.</t>
1632        </list></t>
1633    </section>
1634    <section title="Extension of Syntax">
1635      <t>Added the tag range (U+E0000-E0FFF) to the iprivate production.
1636        Some IRIs generated with the new syntax may fail to pass very strict checks
1637        relying on the old syntax. But characters in this range should be extremely infrequent
1638        anyway.</t>
1639    </section>
1640    <section title="More to be added"><t>TODO: There are more main changes that need to be
1641      documented in this section.</t></section>
1642</section>
1643
1644<section title="Change Log">
1645
1646<t>Note to RFC Editor: Please completely remove this section before publication.</t>
1647
1648<section title='Changes after draft-ietf-iri-3987bis-01'>
1649    <t>Changes from draft-ietf-iri-3987bis-01 onwards are available as changesets
1650      in the IETF tools subversion repository at
1651      http://trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis/draft-ietf-iri-3987bis.xml.</t>
1652</section>
1653 
1654<section title='Changes from draft-duerst-iri-bis-07 to draft-ietf-iri-3987bis-00'>
1655     <t>Changed draft name, date, last paragraph of abstract, and titles in change log, and added this section
1656     in moving from draft-duerst-iri-bis-07 (personal submission) to draft-ietf-iri-3987bis-00 (WG document).</t>
1657</section>
1658
1659<section title="Changes from -06 to -07 of draft-duerst-iri-bis">
1660  <t>Major restructuring of the processing model, see <xref target="forkChanges"></xref>.</t>
1661</section>
1662</section>
1663
1664<section title='Changes from -00 to -01'><t><list style="symbols">
1665  <t>Removed 'mailto:' before mail addresses of authors.</t>
1666  <t>Added "&lt;to be done&gt;" as right side of 'href-strip' rule. Fixed '|' to '/' for
1667    alternatives.</t>
1668</list></t>
1669</section>
1670
1671<section title="Changes from -05 to -06 of draft-duerst-iri-bis-00"><t><list style="symbols">
1672<t>Add HyperText Reference, change abstract, acks and references for it</t>
1673<t>Add Masinter back as another editor.</t>
1674<t>Masinter integrates HRef material from HTML5 spec.</t>
1675<t>Rewrite introduction sections to modernize.</t>
1676</list></t>
1677</section>
1678
1679<section title="Changes from -04 to -05 of draft-duerst-iri-bis">
1680  <t><list style="symbols">
1681    <t>Updated references.</t>
1682    <t>Changed IPR text to pre5378Trust200902.</t></list></t>
1683</section>
1684
1685<section title="Changes from -03 to -04 of draft-duerst-iri-bis">
1686  <t><list style="symbols">
1687    <t>Added explicit abbreviation for LEIRIs.</t>
1688    <t>Mentioned LEIRI references.</t>
1689    <t>Completed text in LEIRI section about tag characters and about specials.</t></list></t>
1690</section>
1691
1692<section title="Changes from -02 to -03 of draft-duerst-iri-bis">
1693  <t><list style="symbols">
1694    <t>Updated some references.</t>
1695    <t>Updated Michel Suginard's coordinates.</t></list></t>
1696</section>
1697
1698<section title="Changes from -01 to -02 of draft-duerst-iri-bis">
1699  <t><list style="symbols">
1700    <t>Added tag range to iprivate (issue private-include-tags-115).</t>
1701    <t>Added Specials (U+FFF0-FFFD) to Legacy Extended IRIs.</t></list></t>
1702</section>
1703<section title="Changes from -00 to -01 of draft-duerst-iri-bis">
1704  <t><list style="symbols">
1705    <t>Changed from "IRIs with Spaces/Controls" to "Legacy Extended IRI"
1706      based on input from the W3C XML Core WG.
1707      Moved the relevant subsections to the back and promoted them to a section.</t>
1708    <t>Added some text re. Legacy Extended IRIs to the security section.</t>
1709    <t>Added a IANA Consideration Section.</t>
1710    <t>Added this Change Log Section.</t>
1711    <t>Added a section about "IRIs with Spaces/Controls" (converting from a Note in RFC 3987).</t></list></t>
1712</section> <!-- -00 to -01 -->
1713<section title="Changes from RFC 3987 to -00 of draft-duerst-iri-bis">
1714  <t><list>
1715    <t>Fixed errata (see http://www.rfc-editor.org/cgi-bin/errataSearch.pl?rfc=3987).</t></list></t>
1716</section> <!-- from 3987 -->
1717</section>
1718</middle>
1719
1720<back>
1721<references title="Normative References">
1722
1723<reference anchor="ASCII">
1724<front>
1725<title>Coded Character Set -- 7-bit American Standard Code for Information
1726Interchange</title>
1727<author>
1728<organization>American National Standards Institute</organization>
1729</author>
1730<date year="1986"/>
1731</front>
1732<seriesInfo name="ANSI" value="X3.4"/>
1733</reference>
1734
1735  <reference anchor="ISO10646" target='http://standards.iso.org/ittf/PubliclyAvailableStandards/c051273_ISO_IEC_10646_2011(E).zip'>
1736<front>
1737<title>ISO/IEC 10646:2011: Information Technology -
1738Universal Multiple-Octet Coded Character Set (UCS)</title>
1739<author>
1740<organization>International Organization for Standardization</organization>
1741</author>
1742<date month="March" year="20011"/>
1743</front>
1744<seriesInfo name="ISO" value="Standard 10646"/>
1745</reference>
1746
1747&rfc2119;
1748&rfc3491;
1749
1750  <reference anchor="STD63">
1751    <front>
1752      <title abbrev="UTF-8">UTF-8, a transformation format of ISO 10646</title>
1753      <author initials="F." surname="Yergeau" ifullname="François Yergeau" fullname="Francois Yergeau"></author>
1754      <date month="November" year="2003"/>
1755    </front>
1756    <seriesInfo name="STD" value="63"/>
1757    <seriesInfo name="RFC" value="3629"/>
1758   
1759  </reference>
1760 
1761&rfc3986;
1762
1763<reference anchor="STD68">
1764<front>
1765<title abbrev="ABNF">Augmented BNF for Syntax Specifications: ABNF</title>
1766<author initials="D." surname="Crocker" fullname="Dave Crocker"><organization/></author>
1767<author initials="P." surname="Overell" fullname="Paul Overell"><organization/></author>
1768<date month="January" year="2008"/></front>
1769<seriesInfo name="STD" value="68"/><seriesInfo name="RFC" value="5234"/>
1770</reference>
1771 
1772&rfc5890;
1773&rfc5891;
1774
1775  <reference anchor="RFC5892">
1776    <front>
1777      <title>The Unicode Code Points and Internationalized Domain Names for Applications (IDNA)</title>
1778      <author initials="P." surname="Faltstrom" isurname="Fältström" fullname="P. Faltstrom" ifullname="P. Fältström">
1779        <organization/>
1780      </author>
1781      <date year="2010" month="August"/>
1782    </front>
1783    <seriesInfo name="RFC" value="5892"/>
1784    <format type="TXT" octets="187370" target="http://www.rfc-editor.org/rfc/rfc5892.txt"/>
1785  </reference>
1786
1787  <reference anchor="UNIV6">
1788    <front>
1789      <title>The Unicode Standard, Version 6.2.0 (Mountain View, CA, The
1790        Unicode Consortium, 2012, ISBN 978-1-936213-07-8)</title>
1791      <author>
1792        <organization>The Unicode Consortium</organization>
1793      </author>
1794      <date year="2012" month="October"/>
1795    </front>
1796  </reference>
1797 
1798<reference anchor="UTR15" target="http://www.unicode.org/unicode/reports/tr15/tr15-23.html">
1799<front>
1800<title>Unicode Normalization Forms</title>
1801<author initials="M." surname="Davis" fullname="Mark Davis"><organization/></author>
1802  <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"><organization/></author>
1803<date year="2008" month="March"/>
1804</front>
1805<seriesInfo name="Unicode Standard Annex" value="#15"/>
1806</reference>
1807
1808</references>
1809
1810<references title="Informative References">
1811
1812  <reference anchor='CharMod' target='http://www.w3.org/TR/2004/CR-charmod-resid/'>
1813    <front>
1814      <title>Character Model for the World Wide Web 1.0: Resource Identifiers</title>
1815      <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
1816      <author initials="F." surname="Yergeau" ifullname="François Yergeau" fullname="Francois Yergeau"></author>
1817      <author fullname='Richard Ishida' surname='Ishida' initials='R. '/>
1818      <author fullname='Misha Wolf' surname='Wolf' initials='M. '/>
1819      <author fullname='Tex Texin' surname='Texin' initials='T. '/>
1820      <date year='2004' month='November' day='22'/>
1821    </front>
1822    <seriesInfo name='W3C Candidate Recommendation' value='CR-charmod-resid-20041122'/>
1823  </reference>
1824
1825  <reference anchor="Duerst97" target="http://www.sw.it.aoyama.ac.jp/2012/pub/IUC11-UTF-8.pdf">
1826<front>
1827<title>The Properties and Promises of UTF-8</title>
1828  <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"></author>
1829<date year="1997" month="September"/>
1830</front>
1831<seriesInfo name="Proc. 11th International Unicode Conference, San Jose" value=""/>
1832</reference>
1833
1834<reference anchor="Gettys" target="http://www.w3.org/DesignIssues/ModelConsequences">
1835<front>
1836<title>URI Model Consequences</title>
1837<author initials="J." surname="Gettys" fullname="Jim Gettys"><organization/></author>
1838<date month="" year=""/>
1839</front>
1840</reference>
1841
1842<reference anchor='HTML4' target='http://www.w3.org/TR/1999/REC-html401'>
1843<front>
1844<title>HTML 4.01 Specification</title>
1845<author fullname='David Raggett' surname='Raggett' initials='D. '/>
1846<author fullname='Arnaud Le Hors' surname='Le Hors' initials='A. '/>
1847<author fullname='Ian Jacobs' surname='Jacobs' initials='I. '/>
1848<date year='1999' month='December' day='24'/>
1849</front>
1850<seriesInfo name='W3C Recommendation' value='REC-html401-19991224'/>
1851</reference>
1852&rfc2130;
1853&rfc2141;
1854&rfc2192;
1855&rfc2277;
1856&rfc2384;
1857&rfc2396;
1858&rfc2397;
1859&rfc2616;
1860&rfc2640;
1861
1862  <reference anchor="RFC3987">
1863    <front>
1864      <title>Internationalized Resource Identifiers (IRIs)</title>
1865      <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
1866      <author initials="M." surname="Suignard" fullname="M. Suignard">
1867        <organization/>
1868      </author>
1869      <date year="2005" month="January"/>
1870    </front>
1871    <seriesInfo name="RFC" value="3987"/>
1872    <format type="TXT" octets="111190" target="http://www.rfc-editor.org/rfc/rfc3987.txt"/>
1873  </reference>
1874
1875&rfc5122;
1876&rfc6055;
1877
1878  <reference anchor="RFC6068">
1879    <front>
1880      <title>
1881        The 'mailto' URI Scheme
1882      </title>
1883      <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
1884      <author initials="L." surname="Masinter" fullname="L. Masinter">
1885        <organization/>
1886      </author>
1887      <author initials="J." surname="Zawinski" fullname="J. Zawinski">
1888        <organization/>
1889      </author>
1890      <date year="2010" month="October"/>
1891    </front>
1892    <seriesInfo name="RFC" value="6068"/>
1893    <format type="TXT" octets="36683" target="http://www.rfc-editor.org/rfc/rfc6068.txt"/>
1894  </reference>
1895
1896<reference anchor='Bidi'>
1897  <front>
1898    <title>Guidelines for Internationalized Resource Identifiers with Bi-directional Characters (Bidi IRIs)</title>
1899    <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
1900    <author initials='L.' surname='Masinter' />
1901    <author initials="A." isurname="Allawi (عادل علاوي)" surname="Allawi"
1902      ifullname="عادل علاوي" fullname="Adil Allawi"/>    <date year="2012" month="March" day="9" />
1903  </front>
1904  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-bidi-guidelines-02"/>
1905</reference>
1906
1907<reference anchor='Equivalence'>
1908  <front>
1909    <title>Equivalence and Canonicalization of Internationalized Resource Identifiers (IRIs)</title>
1910    <author initials='L.' surname='Masinter' />
1911    <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
1912    <date year="2012" month="March" day="2" />
1913  </front>
1914  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-comparison-01"/>
1915</reference>
1916
1917<reference anchor='RFC4395bis'>
1918  <front>
1919    <title>Guidelines and Registration Procedures for New URI/IRI Schemes</title>
1920    <author initials='T.' surname='Hansen' fullname="Tony Hansen"><organization/></author>
1921    <author initials='T.' surname='Hardie' fullname="Ted Hardie"><organization/></author>
1922    <author initials='L.' surname='Masinter' fullname="Larry Masinter"><organization/></author>
1923    <date year='2011' month='December'/>
1924    <workgroup>IRI</workgroup>
1925  </front>
1926  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-4395bis-irireg-04"/>
1927</reference>
1928 
1929 
1930<reference anchor="UNIXML" target="http://www.w3.org/TR/unicode-xml/">
1931<front>
1932<title>Unicode in XML and other Markup Languages</title>
1933  <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"><organization/></author>
1934<author initials="A." surname="Freytag" fullname="Asmus Freytag"><organization/></author>
1935<date year="2003" month="June" day="18"/>
1936</front>
1937<seriesInfo name="Unicode Technical Report" value="#20"/>
1938<seriesInfo name="World Wide Web Consortium" value="Note"/>
1939</reference>
1940 
1941<reference anchor="UTR36" target="http://unicode.org/reports/tr36/">
1942<front>
1943<title>Unicode Security Considerations</title>
1944<author initials="M." surname="Davis" fullname="Mark Davis"><organization/></author>
1945<author initials="M." surname="Suignard" fullname="Michel Suignard"><organization/></author>
1946<date year="2010" month="August" day="4"/>
1947</front>
1948<seriesInfo name="Unicode Technical Report" value="#36"/>
1949</reference>
1950
1951<reference anchor='XLink' target='http://www.w3.org/TR/xlink11/#link-locators'>
1952<front>
1953<title>XML Linking Language (XLink) Version 1.1</title>
1954<author fullname='Steve DeRose' surname='DeRose' initials='S. '/>
1955<author fullname='Eve Maler' surname='Maler' initials='E. '/>
1956<author fullname='David Orchard' surname='Orchard' initials='D. '/>
1957<author fullname='Norman Walsh' surname='Walsh' initials='N. '/>
1958<date year='2010' month='May' day='06'/>
1959</front>
1960<seriesInfo name='W3C Recommendation' value='REC-xlink11-20100506'/>
1961</reference>
1962 
1963<reference anchor='XML1' target='http://www.w3.org/TR/2008/REC-xml/'>
1964<front>
1965<title>Extensible Markup Language (XML) 1.0 (Fifth Edition)</title>
1966<author fullname='Tim Bray' surname='Bray' initials='T. '/>
1967<author fullname='Jean Paoli' surname='Paoli' initials='J. '/>
1968<author fullname='C. M. Sperberg-McQueen' surname='Sperberg-McQueen' initials='C. M. '/>
1969<author fullname='Eve Maler' surname='Maler' initials='E. '/>
1970<author initials="F." surname="Yergeau" ifullname="François Yergeau" fullname="Francois Yergeau"/>
1971<date year='2008' month='November' day='26'/>
1972</front>
1973<seriesInfo name='W3C Recommendation' value='REC-xml-20081126'/>
1974</reference>
1975 
1976<reference anchor="XMLSchema" target="http://www.w3.org/TR/xmlschema-2/#anyURI">
1977<front>
1978<title>XML Schema Part 2: Datatypes Second Edition</title>
1979<author fullname='Paul V. Biron' surname='Biron' initials='P. V. '/>
1980<author fullname='Ashok Malhotra' surname='Malhotra' initials='A. '/>
1981<date year='2004' month='October' day='28'/>
1982</front>
1983<seriesInfo name='W3C Recommendation' value='REC-xmlschema-2-20041028'/>
1984</reference>
1985 
1986<reference anchor="XPointer" target="http://www.w3.org/TR/xptr-framework/#escaping">
1987<front>
1988<title>XPointer Framework</title>
1989<author fullname='Paul Grosso' surname='Grosso' initials='P. '/>
1990<author fullname='Eve Maler' surname='Maler' initials='E. '/>
1991<author fullname='Jonathan Marsh' surname='Marsh' initials='J. '/>
1992<author fullname='Norman Walsh' surname='Walsh' initials='N. '/>
1993<date year='2003' month='March' day='25'/>
1994</front>
1995<seriesInfo name='W3C Recommendation' value='REC-xptr-framework-20030325'/>
1996</reference>
1997
1998</references>
1999
2000</back>
2001</rfc>
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