source: draft-ietf-iri-3987bis/draft-ietf-iri-3987bis.xml @ 161

Last change on this file since 161 was 161, checked in by duerst@…, 7 years ago

added a section about Processing of URIs/IRIs/URLs by Web Browsers

  • Property svn:executable set to *
File size: 92.5 KB
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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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448456789012345678901234567890123456789012345678901234567890123456789012
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>Domain Names can appear in parts of an IRI other
709than the ireg-name part.  It is the responsibility of scheme-specific
710implementations (if the Internationalized Domain Name is part of the
711scheme syntax) or of server-side implementations (if the
712Internationalized Domain Name is part of 'iquery') to apply the
713necessary conversions at the appropriate point. Example: Trying to
714validate the Web page at<vspace/>
715  <aonly>http://r&amp;#xE9;sum&amp;#xE9;.example.org</aonly><ionly>http://résumé.example.org</ionly>
716  would lead to an IRI of
717  <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,
718which would convert to a URI
719of<vspace/>http://validator.w3.org/check?uri=http%3A%2F%2Fr%C3%A9sum%C3%A9.<vspace/>example.org.
720The server-side implementation is responsible for making the
721necessary conversions to be able to retrieve the Web page.</t>
722 
723<t>In this process, characters allowed in URI
724references and existing percent-encoded sequences are not encoded further.
725(This mapping is similar to, but different from, the encoding applied
726when arbitrary content is included in some part of a URI.)
727
728For example, an IRI of
729<vspace/><aonly>"http://www.example.org/red%09ros&amp;#xE9;#red"
730  (in XML notation)</aonly><ionly>"http://www.example.org/red%09rosé#red"</ionly>
731  is converted to
732<vspace/>"http://www.example.org/red%09ros%C3%A9#red", not to
733something like
734<vspace/>"http%3A%2F%2Fwww.example.org%2Fred%2509ros%C3%A9%23red".</t>
735
736</section> <!-- additional -->
737</section> <!-- dnsmapping -->
738
739<section title="Mapping query components" anchor="querymapping">
740
741<t>For compatibility with existing deployed HTTP infrastructure, the following special case applies
742          for the schemes "http" and "https" when an IRI is found in a document whose charset is not
743          based on UCS (e.g., not UTF-8 or UTF-16). In such a case, the "query" component of an IRI
744          is mapped into a URI by using the document charset rather than UTF-8 as the binary
745          representation before pct-encoding. This mapping is not applied for any other schemes or
746          components.</t>
747
748</section> <!-- querymapping -->
749
750<section title="Mapping IRIs to URIs" anchor="mapping">
751
752<t>The mapping from an IRI to URI is accomplished by applying the
753mapping above (from IRI to URI components) and then reassembling a URI
754from the parsed URI components using the original punctuation that
755delimited the IRI components. </t>
756
757</section> <!-- mapping -->
758</section> <!-- processing -->
759
760<section title="Converting URIs to IRIs" anchor="URItoIRI">
761
762  <t>In some situations, for presentation and further processing, it is desirable to convert a URI
763        into an equivalent IRI without unnecessary percent encoding. Of course, every URI is already
764        an IRI in its own right without any conversion. This section gives one possible procedure
765        for converting a URI to an IRI.</t>
766
767<section title='Limitations'>
768<t>The conversion described in this section, if given a valid URI, will result in an IRI that maps
769        back to the URI used as an input for the conversion (except for potential case differences
770        in percent-encoding and for potential percent-encoded unreserved characters). However, the
771        IRI resulting from this conversion may differ from the original IRI (if there ever was
772        one).</t> 
773
774<t>URI-to-IRI conversion removes percent-encodings, but not all
775percent-encodings can be eliminated. There are several reasons for
776this:</t>
777
778<t><list style="hanging">
779
780<t hangText="1.">Some percent-encodings are necessary to distinguish
781    percent-encoded and unencoded uses of reserved characters.</t>
782
783<t hangText="2.">Some percent-encodings cannot be interpreted as sequences
784    of UTF-8 octets.<vspace blankLines="1"/>
785    (Note: The octet patterns of UTF-8 are highly regular.
786    Therefore, there is a very high probability, but no guarantee,
787    that percent-encodings that can be interpreted as sequences of UTF-8
788    octets actually originated from UTF-8. For a detailed discussion,
789    see <xref target="Duerst97"/>.)</t>
790
791<t hangText="3.">The conversion may result in a character that is not
792    appropriate in an IRI. See <xref target="abnf"/>,
793      and <xref target="limitations"/> for further details.</t>
794
795<t hangText="4.">As described in <xref target="querymapping"/>, IRI to URI conversion may work
796            somewhat differently for query components.</t>
797
798</list></t>
799</section>
800
801<section title="Conversion">
802<t>Conversion from a URI to an IRI MAY be done by using the following
803steps:
804
805<list style="hanging">
806<t hangText="1.">Represent the URI as a sequence of octets in
807       US-ASCII.</t>
808
809<t hangText="2.">Convert all percent-encodings ("%" followed by two
810      hexadecimal digits) to the corresponding octets, except those
811      corresponding to "%", characters in "reserved", and characters
812      in US-ASCII not allowed in URIs.</t> 
813
814<t hangText="3.">Re-percent-encode any octet produced in step 2 that
815      is not part of a strictly legal UTF-8 octet sequence.</t>
816
817
818<t hangText="4.">Re-percent-encode all octets produced in step 3 that
819      in UTF-8 represent characters that are not appropriate according
820      to <xref target="abnf"/>  and <xref
821      target="limitations"/>.</t>
822          <t hangText="5.">Optionally, re-percent-encode octets in the query component if the scheme
823            is one of those mentioned in <xref target="querymapping"/>.</t> 
824
825<t hangText="6.">Interpret the resulting octet sequence as a sequence of characters encoded in
826            UTF-8.</t>
827
828<t hangText="7.">URIs known to contain domain names in the reg-name component SHOULD convert
829            punycode-encoded domain name labels to the corresponding characters using the ToUnicode
830            procedure. </t>
831</list></t>
832
833<t>This procedure will convert as many percent-encoded characters as possible to characters in an
834        IRI. Because there are some choices in steps 4 (see also <xref target="limitations"/>) and
835        5, results may vary.</t>
836
837<t>Conversions from URIs to IRIs MUST NOT use any character
838encoding other than UTF-8 in steps 3 and 4, even if it might be
839possible to guess from the context that another character encoding
840than UTF-8 was used in the URI.  For example, the URI
841"http://www.example.org/r%E9sum%E9.html" might with some guessing be
842interpreted to contain two e-acute characters encoded as
843iso-8859-1. It must not be converted to an IRI containing these
844e-acute characters. Otherwise, in the future the IRI will be mapped to
845"http://www.example.org/r%C3%A9sum%C3%A9.html", which is a different
846URI from "http://www.example.org/r%E9sum%E9.html".</t>
847</section>
848
849<section title="Examples">
850
851<t>This section shows various examples of converting URIs to IRIs.
852Each example shows the result after each of the steps 1 through 6 is
853applied. XML Notation is used for the final result.  Octets are
854denoted by "&lt;" followed by two hexadecimal digits followed by
855"&gt;".</t>
856
857<t>The following example contains the sequence "%C3%BC", which is a
858strictly legal UTF-8 sequence, and which is converted into the actual
859character U+00FC, LATIN SMALL LETTER U WITH DIAERESIS (also known as
860u-umlaut).
861
862<list style="hanging">
863<t hangText="1.">http://www.example.org/D%C3%BCrst</t>
864<t hangText="2.">http://www.example.org/D&lt;c3&gt;&lt;bc&gt;rst</t>
865<t hangText="3.">http://www.example.org/D&lt;c3&gt;&lt;bc&gt;rst</t>
866<t hangText="4.">http://www.example.org/D&lt;c3&gt;&lt;bc&gt;rst</t>
867  <t hangText="5."><aonly>http://www.example.org/D&amp;#xFC;rst</aonly><ionly>http://www.example.org/Dürst</ionly></t>
868  <t hangText="6."><aonly>http://www.example.org/D&amp;#xFC;rst</aonly><ionly>http://www.example.org/Dürst</ionly></t>
869</list>
870</t>
871
872<t>The following example contains the sequence "%FC", which might
873represent U+00FC, LATIN SMALL LETTER U WITH DIAERESIS, in
874the<vspace/>iso-8859-1 character encoding.  (It might represent other
875characters in other character encodings. For example, the octet
876&lt;fc&gt; in iso-8859-5 represents U+045C, CYRILLIC SMALL LETTER
877KJE.)  Because &lt;fc&gt; is not part of a strictly legal UTF-8
878sequence, it is re-percent-encoded in step 3.
879
880
881<list style="hanging">
882<t hangText="1.">http://www.example.org/D%FCrst</t>
883<t hangText="2.">http://www.example.org/D&lt;fc&gt;rst</t>
884<t hangText="3.">http://www.example.org/D%FCrst</t>
885<t hangText="4.">http://www.example.org/D%FCrst</t>
886<t hangText="5.">http://www.example.org/D%FCrst</t>
887<t hangText="6.">http://www.example.org/D%FCrst</t>
888</list>
889</t>
890
891<t>The following example contains "%e2%80%ae", which is the percent-encoded<vspace/>UTF-8
892character encoding of U+202E, RIGHT-TO-LEFT OVERRIDE.
893The direct use of this character is forbidden in an IRI. Therefore, the
894corresponding octets are re-percent-encoded in step 4. This example shows
895that the case (upper- or lowercase) of letters used in percent-encodings may not be preserved.
896The example also contains a punycode-encoded domain name label (xn--99zt52a),
897which is not converted.
898
899<list style="hanging">
900<t hangText="1.">http://xn--99zt52a.example.org/%e2%80%ae</t>
901<t hangText="2.">http://xn--99zt52a.example.org/&lt;e2&gt;&lt;80&gt;&lt;ae&gt;</t>
902<t hangText="3.">http://xn--99zt52a.example.org/&lt;e2&gt;&lt;80&gt;&lt;ae&gt;</t>
903<t hangText="4.">http://xn--99zt52a.example.org/%E2%80%AE</t>
904<t hangText="5.">http://xn--99zt52a.example.org/%E2%80%AE</t>
905  <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>
906</list></t>
907
908<t>Note that the label "xn--99zt52a" is converted to U+7D0D U+8C46
909(Japanese Natto<ionly>, 納豆</ionly>). ((EDITOR NOTE: There is some inconsistency in this note.))</t>
910
911</section> <!-- examples -->
912</section> <!-- URItoIRI -->
913
914
915<section title="Use of IRIs" anchor="IRIuse">
916
917<section title="Limitations on UCS Characters Allowed in IRIs" anchor="limitations">
918
919<t>This section discusses limitations on characters and character
920sequences usable for IRIs beyond those given in <xref target="abnf"/>.
921The considerations in this section are
922relevant when IRIs are created and when URIs are converted to
923IRIs.</t>
924
925<t>
926
927<list style="hanging"><t hangText="a.">The repertoire of characters allowed
928    in each IRI component is limited by the definition of that component.
929    For example, the definition of the scheme component does not allow
930    characters beyond US-ASCII.
931    <vspace blankLines="1"/>
932    (Note: In accordance with URI practice, generic IRI
933    software cannot and should not check for such limitations.)</t>
934
935<t hangText="b.">The UCS contains many areas of characters for which
936    there are strong visual look-alikes. Because of the likelihood of
937    transcription errors, these also should be avoided. This includes
938    the full-width equivalents of Latin characters, half-width
939    Katakana characters for Japanese, and many others. It also
940    includes many look-alikes of "space", "delims", and "unwise",
941    characters excluded in <xref target="RFC3491"/>.</t>
942 
943<t hangText="c.">At the start of a component, the use of combining marks is strongly discouraged. As
944    an example, a COMBINING TILDE OVERLAY (U+0334) would be very confusing at the start of
945    a &lt;isegment>. Combined with the preceeding '/', it might look like a solidus
946    with combining tilde overlay, but IRI processing software will parse and process the
947    '/' separately.</t>
948<t hangText='d.'>The ZERO WIDTH NON-JOINER (U+200C) and ZERO WIDTH
949    JOINER (U+200D) are invisible in most contexts, but are crucial in
950    some very limited contexts. Appendix A of <xref target="RFC5892"/>
951    contains contextual restrictions for these and some other characters.
952    The use of these characters are strongly discouraged except
953    in the relevant contexts.</t>
954</list>
955</t>
956
957<t>Additional information is available from <xref target="UNIXML"/>.
958    <xref target="UNIXML"/> is written in the context of general purpose text
959    rather than in that of identifiers. Nevertheless, it discusses
960    many of the categories of characters not appropriate for IRIs.</t>
961</section> <!-- limitations -->
962
963<section title="Software Interfaces and Protocols">
964
965<t>Although an IRI is defined as a sequence of characters, software
966interfaces for URIs typically function on sequences of octets or other
967kinds of code units. Thus, software interfaces and protocols MUST
968define which character encoding is used.</t>
969
970<t>Intermediate software interfaces between IRI-capable components and
971URI-only components MUST map the IRIs per <xref target="mapping"/>,
972when transferring from IRI-capable to URI-only components.
973
974This mapping SHOULD be applied as late as possible. It SHOULD NOT be
975applied between components that are known to be able to handle IRIs.</t>
976</section> <!-- software -->
977
978<section title="Format of URIs and IRIs in Documents and Protocols">
979
980<t>Document formats that transport URIs may have to be upgraded to allow
981the transport of IRIs. In cases where the document as a whole
982has a native character encoding, IRIs MUST also be encoded in this
983character encoding and converted accordingly by a parser or interpreter.
984
985IRI characters not expressible in the native character encoding SHOULD
986be escaped by using the escaping conventions of the document format if
987such conventions are available. Alternatively, they MAY be
988percent-encoded according to <xref target="mapping"/>. For example, in
989HTML or XML, numeric character references SHOULD be used. If a
990document as a whole has a native character encoding and that character
991encoding is not UTF-8, then IRIs MUST NOT be placed into the document
992in the UTF-8 character encoding.</t>
993
994<t>((UPDATE THIS NOTE)) Note: Some formats already accommodate IRIs,
995although they use different terminology. HTML 4.0 <xref
996target="HTML4"/> defines the conversion from IRIs to URIs as
997error-avoiding behavior. XML 1.0 <xref target="XML1"/>, XLink <xref
998target="XLink"/>, XML Schema <xref target="XMLSchema"/>, and
999specifications based upon them allow IRIs. Also, it is expected that
1000all relevant new W3C formats and protocols will be required to handle
1001IRIs <xref target="CharMod"/>.</t>
1002
1003</section> <!-- format -->
1004
1005<section title="Use of UTF-8 for Encoding Original Characters" anchor="UTF8use">
1006
1007<t>This section discusses details and gives examples for point c) in
1008<xref target="Applicability"/>. To be able to use IRIs, the URI
1009corresponding to the IRI in question has to encode original characters
1010into octets by using UTF-8.  This can be specified for all URIs of a
1011URI scheme or can apply to individual URIs for schemes that do not
1012specify how to encode original characters.  It can apply to the whole
1013URI, or only to some part. For background information on encoding
1014characters into URIs, see also Section 2.5 of <xref
1015target="RFC3986"/>.</t>
1016
1017<t>For new URI/IRI schemes, using UTF-8 is recommended in <xref
1018target="RFC4395bis"/>.  Examples where UTF-8 is already used are the URN
1019syntax <xref target="RFC2141"/>, IMAP URLs <xref target="RFC2192"/>,
1020POP URLs <xref target="RFC2384"/>, XMPP URLs <xref target='RFC5122'/>,
1021and the 'mailto:' scheme <xref target='RFC6068'/>. On the other hand, because the
1022HTTP URI scheme does not specify how to encode original characters,
1023only some HTTP URLs can have corresponding but different IRIs.</t>
1024
1025<t>For example, for a document with a URI
1026of<vspace/>"http://www.example.org/r%C3%A9sum%C3%A9.html", it is
1027possible to construct a corresponding IRI
1028  <aonly>(in XML notation, see <xref target="sec-Notation"/>):
1029    "http://www.example.org/r&amp;#xE9;sum&amp;#xE9;.html"
1030    ("&amp;#xE9;" stands for the e-acute character, and "%C3%A9" is the UTF-8 encoded
1031    and percent-encoded representation of that character).</aonly>
1032  <ionly>: "http://www.example.org/résumé.html"
1033    ("é" is the e-acute character, and "%C3%A9" is the UTF-8 encoded
1034    and percent-encoded representation of that character).</ionly>
1035  On the other hand, for a document with a URI of
1036"http://www.example.org/r%E9sum%E9.html", the percent-encoded octets
1037cannot be converted to actual characters in an IRI, as the
1038percent-encoding is not based on UTF-8.</t>
1039
1040<t>For most URI schemes, there is no need to upgrade their scheme
1041definition in order for them to work with IRIs.  The main case where
1042upgrading makes sense is when a scheme definition, or a particular
1043component of a scheme, is strictly limited to the use of US-ASCII
1044characters with no provision to include non-ASCII characters/octets
1045via percent-encoding, or if a scheme definition currently uses highly
1046scheme-specific provisions for the encoding of non-ASCII characters.</t>
1047
1048<t>Scheme definitions can impose restrictions on the syntax of
1049scheme-specific URIs; i.e., URIs that are admissible under the generic
1050URI syntax <xref target="RFC3986"/> may not be admissible due to
1051narrower syntactic constraints imposed by a URI scheme
1052specification. URI scheme definitions cannot broaden the syntactic
1053restrictions of the generic URI syntax; otherwise, it would be
1054possible to generate URIs that satisfied the scheme-specific syntactic
1055constraints without satisfying the syntactic constraints of the
1056generic URI syntax. However, additional syntactic constraints imposed
1057by URI scheme specifications are applicable to IRI, as the
1058corresponding URI resulting from the mapping defined in <xref
1059target="mapping"/> MUST be a valid URI under the syntactic
1060restrictions of generic URI syntax and any narrower restrictions
1061imposed by the corresponding URI scheme specification.</t>
1062
1063<t>The requirement for the use of UTF-8 generally applies to all parts
1064of a URI.  However, it is possible that the capability of IRIs to
1065represent a wide range of characters directly is used just in some
1066parts of the IRI (or IRI reference). The other parts of the IRI may
1067only contain US-ASCII characters, or they may not be based on
1068UTF-8. They may be based on another character encoding, or they may
1069directly encode raw binary data (see also <xref
1070target="RFC2397"/>). </t>
1071
1072<t>For example, it is possible to have a URI reference
1073of<vspace/>"http://www.example.org/r%E9sum%E9.xml#r%C3%A9sum%C3%A9",
1074where the document name is encoded in iso-8859-1 based on server
1075settings, but where the fragment identifier is encoded in UTF-8 according
1076to <xref target="XPointer"/>. The IRI corresponding to the above URI would be
1077  <aonly>(in XML notation)<vspace/>"http://www.example.org/r%E9sum%E9.xml#r&amp;#xE9;sum&amp;#xE9;".</aonly>
1078  <ionly><vspace/>"http://www.example.org/r%E9sum%E9.xml#résumé".</ionly>
1079</t>
1080
1081<t>Similar considerations apply to query parts. The functionality
1082of IRIs (namely, to be able to include non-ASCII characters) can
1083only be used if the query part is encoded in UTF-8.</t>
1084
1085</section> <!-- utf8 -->
1086
1087<section title="Relative IRI References">
1088<t>Processing of relative IRI references against a base is handled
1089straightforwardly; the algorithms of <xref target="RFC3986"/> can
1090be applied directly, treating the characters additionally allowed
1091in IRI references in the same way that unreserved characters are treated in URI
1092references.</t>
1093
1094</section> <!-- relative -->
1095</section> <!-- IRIuse -->
1096
1097  <section title="Legacy Extended IRIs (LEIRIs)">
1098    <t>In some cases, there have been formats which have used a protocol element
1099      which is a variant of the IRI definition; these variants have usually been
1100      somewhat less restricted in syntax. This section provides
1101      a definition and a name (Legacy Extended IRI or LEIRI) for one of these
1102      variants used widely in XML-based protocols. This variant has to be used with care;
1103      it requires further processing before being fully interchangeable as IRIs.
1104
1105      New protocols and formats SHOULD NOT use Legacy Extended IRIs.
1106      Even where Legacy Extended IRIs are allowed, only IRIs fully conforming
1107      to the syntax definition in <xref target="abnf"></xref> SHOULD be created,
1108      generated, and used. The provisions in this section also apply to
1109      Legacy Extended IRI references.</t>
1110   
1111    <section title="Legacy Extended IRI Syntax">
1112      <figure>
1113
1114        <preamble>This section defines Legacy Extended IRIs (LEIRIs).  The syntax of
1115   Legacy Extended IRIs is the same as that for &lt;IRI-reference&gt;, except
1116   that the ucschar production is replaced by the leiri-ucschar
1117   production:
1118
1119</preamble>
1120        <artwork>
1121leiri-ucschar  = " " / "&lt;" / "&gt;" / '"' / "{" / "}" / "|"
1122               / "\" / "^" / "`" / %x0-1F / %x7F-D7FF
1123               / %xE000-FFFD / %x10000-10FFFF
1124        </artwork>
1125        <postamble>The restriction on bidirectional formatting characters in <xref target="Bidi"></xref> is lifted.
1126        The iprivate production becomes redundant.</postamble>
1127      </figure>
1128
1129      <t>Likewise, the syntax for Legacy Extended IRI references
1130      (LEIRI references) is the same as that for IRI references with
1131      the above replacement of ucschar with leiri-ucschar.</t>
1132
1133     </section>
1134    <section title="Conversion of Legacy Extended IRIs to IRIs" anchor="LEIRIspec">
1135      <t>To convert a Legacy Extended IRI (reference) to
1136      an IRI (reference), each character allowed in a Legacy Extended IRI (reference)
1137      but not allowed in an IRI (reference) (see <xref target="notAllowed"></xref>)  MUST be percent-encoded
1138      by applying the steps in <xref target="compmapping"></xref>.</t>
1139    </section>
1140     
1141    <section title="Characters Allowed in Legacy Extended IRIs but not in IRIs" anchor="notAllowed">
1142      <t>This section provides a list of the groups of characters and code points
1143        that are allowed in Legacy Extedend IRIs, but are not allowed in IRIs
1144        or are allowed in IRIs only in the query part. For each group of characters,
1145        advice on the usage of these characters is also given, concentrating on the
1146        reasons for why not to use them.</t>
1147      <t>
1148        <list>
1149          <t>Space (U+0020): Some formats and applications use space as a delimiter,
1150            e.g., for items in a list. Appendix C of <xref target="RFC3986"></xref>
1151            also mentions that white space may have to be added when displaying
1152            or printing long URIs; the same applies to long IRIs.
1153            Spaces might disappear, or a single Legacy Extended IRI
1154            might incorrectly be interpreted as two or more separate ones.</t>
1155     
1156          <t>Delimiters "&lt;" (U+003C), "&gt;" (U+003E), and '"' (U+0022):
1157            Appendix C of <xref target="RFC3986"></xref> suggests the use of
1158            double-quotes ("http://example.com/") and angle brackets
1159        (&lt;http://example.com/&gt;) as delimiters for URIs in plain text.
1160        These conventions are often used, and also apply to IRIs.
1161        Legacy Extended IRIs using these characters might be cut off at the wrong place.</t>
1162     
1163          <t>Unwise characters "\" (U+005C),
1164          "^" (U+005E), "`" (U+0060), "{" (U+007B), "|" (U+007C), and "}" (U+007D):
1165          These characters originally were excluded from URIs because
1166          the respective codepoints are assigned to different graphic characters
1167          in some 7-bit or 8-bit encoding. Despite the move to Unicode,
1168          some of these characters are still occasionally displayed differently
1169          on some systems, e.g., U+005C as a Japanese Yen symbol.
1170     
1171          Also, the fact that these characters are not used in URIs or IRIs
1172          has encouraged their use outside URIs or IRIs in contexts that may
1173          include URIs or IRIs. In case a Legacy Extended IRI with such a character
1174          is used in such a context, the Legacy Extended IRI will be interpreted piecemeal.</t>
1175     
1176          <t>The controls (C0 controls, DEL, and C1 controls, #x0  - #x1F  #x7F - #x9F):
1177            There is no way to transmit these characters reliably except potentially
1178            in electronic form. Even when in electronic form, some software components
1179            might silently filter out some of these characters,
1180            or may stop processing alltogether when encountering some of them.
1181            These characters may affect text display in subtle, unnoticable ways
1182            or in drastic, global, and irreversible ways depending
1183            on the hardware and software involved.
1184            The use of some of these characters may allow malicious users
1185            to manipulate the display of a Legacy Extended IRI and its context.</t>
1186          <t>Bidi formatting characters (U+200E, U+200F, U+202A-202E):
1187            These characters affect the display ordering of characters.
1188            Displayed Legacy Extended IRIs containing these characters
1189            cannot be converted back to electronic form (logical order) unambiguously.
1190            These characters may allow malicious users to manipulate
1191            the display of a Legacy Extended IRI and its context.</t>
1192          <t>Specials (U+FFF0-FFFD): These code points provide functionality
1193            beyond that useful in a Legacy Extended IRI, for example byte order identification,
1194            annotation, and replacements for unknown characters and objects.
1195            Their use and interpretation in a Legacy Extended IRI
1196            serves no purpose and may lead to confusing display variations.</t>
1197          <t>Private use code points (U+E000-F8FF, U+F0000-FFFFD, U+100000-10FFFD):
1198            Display and interpretation of these code points is by definition
1199            undefined without private agreement. Therefore, these code points
1200            are not suited for use on the Internet. They are not interoperable and may have
1201            unpredictable effects.</t>
1202          <t>Tags (U+E0000-E0FFF): These characters provide a way to language tag in Unicode plain text.
1203            They are not appropriate for Legacy Extended IRIs because language information
1204            in identifiers cannot reliably be input, transmitted
1205            (e.g., on a visual medium such as paper), or recognized.</t>
1206          <t>Non-characters (U+FDD0-FDEF, U+1FFFE-1FFFF, U+2FFFE-2FFFF, U+3FFFE-3FFFF,
1207            U+4FFFE-4FFFF, U+5FFFE-5FFFF, U+6FFFE-6FFFF, U+7FFFE-7FFFF, U+8FFFE-8FFFF,
1208            U+9FFFE-9FFFF, U+AFFFE-AFFFF, U+BFFFE-BFFFF, U+CFFFE-CFFFF, U+DFFFE-DFFFF,
1209            U+EFFFE-EFFFF, U+FFFFE-FFFFF, U+10FFFE-10FFFF):
1210            These code points are defined as non-characters. Applications may use
1211            some of them internally, but are not prepared to interchange them.</t>
1212        </list>
1213      </t>
1214      <t>For reference, we here also list the code points and code units
1215        not even allowed in Legacy Extended IRIs:
1216        <list>
1217         
1218          <t>Surrogate code units (D800-DFFF):
1219          These do not represent Unicode codepoints.</t>
1220           <t>Non-characters (U+FFFE-FFFF): These are not allowed in XML nor LEIRIs.</t>
1221     
1222        </list>
1223      </t>
1224    </section>
1225  </section>
1226 
1227<section title='Processing of URIs/IRIs/URLs by Web Browsers'>
1228  <t>For legacy reasons, many web browsers exhibit some irregularities when processing URIs, IRIs,
1229        and URLs. This is being documented in <xref target="HTMLURL"/>, in the hope that it will
1230        lead to more uniform implementations of these irregularities across web browsers.</t>
1231  <t>As far as currently known, creators of content for web browsers (such as HTML) can use all URIs
1232        without problems. They can also use all IRIs without problems except that they should be
1233        aware of the fact that query parts for HTTP/HTTPS IRIs should be percent-escaped.</t>
1234</section>
1235 
1236<section title="URI/IRI Processing Guidelines (Informative)" anchor="guidelines">
1237
1238<t>This informative section provides guidelines for supporting IRIs in
1239the same software components and operations that currently process
1240URIs: Software interfaces that handle URIs, software that allows users
1241to enter URIs, software that creates or generates URIs, software that
1242displays URIs, formats and protocols that transport URIs, and software
1243that interprets URIs. These may all require modification before
1244functioning properly with IRIs. The considerations in this section
1245also apply to URI references and IRI references.</t>
1246
1247<section title="URI/IRI Software Interfaces">
1248<t>Software interfaces that handle URIs, such as URI-handling APIs and
1249protocols transferring URIs, need interfaces and protocol elements
1250that are designed to carry IRIs.</t>
1251
1252<t>In case the current handling in an API or protocol is based on
1253US-ASCII, UTF-8 is recommended as the character encoding for IRIs, as
1254it is compatible with US-ASCII, is in accordance with the
1255recommendations of <xref target="RFC2277"/>, and makes converting to
1256URIs easy. In any case, the API or protocol definition must clearly
1257define the character encoding to be used.</t>
1258
1259<t>The transfer from URI-only to IRI-capable components requires no
1260mapping, although the conversion described in <xref
1261target="URItoIRI"/> above may be performed. It is preferable not to
1262perform this inverse conversion unless it is certain this can be done
1263correctly.</t>
1264</section><!-- software interfaces -->
1265
1266<section title="URI/IRI Entry">
1267
1268<t>Some components allow users to enter URIs into the system
1269by typing or dictation, for example. This software must be updated to allow
1270for IRI entry.</t>
1271
1272<t>A person viewing a visual presentation of an IRI (as a sequence
1273of glyphs, in some order, in some visual display)
1274will use an entry method for characters in the user's language to
1275input the IRI. Depending on the script and the input method used, this
1276may be a more or less complicated process.</t>
1277
1278<t>The process of IRI entry must ensure, as much as possible, that the
1279restrictions defined in <xref target="abnf"/> are met. This may be
1280done by choosing appropriate input methods or variants/settings
1281thereof, by appropriately converting the characters being input, by
1282eliminating characters that cannot be converted, and/or by issuing a
1283warning or error message to the user.</t>
1284
1285<t>As an example of variant settings, input method editors for East
1286Asian Languages usually allow the input of Latin letters and related
1287characters in full-width or half-width versions. For IRI input, the
1288input method editor should be set so that it produces half-width Latin
1289letters and punctuation and full-width Katakana.</t>
1290
1291<t>An input field primarily or solely used for the input of URIs/IRIs
1292might allow the user to view an IRI as it is mapped to a URI.  Places
1293where the input of IRIs is frequent may provide the possibility for
1294viewing an IRI as mapped to a URI. This will help users when some of
1295the software they use does not yet accept IRIs.</t>
1296
1297<t>An IRI input component interfacing to components that handle URIs,
1298but not IRIs, must map the IRI to a URI before passing it to these
1299components.</t>
1300
1301<t>For the input of IRIs with right-to-left characters, please see
1302<xref target="Bidi"></xref>.</t>
1303</section><!-- entry -->
1304
1305<section title="URI/IRI Transfer between Applications">
1306
1307<t>Many applications (for example, mail user agents) try to detect
1308URIs appearing in plain text. For this, they use some heuristics based
1309on URI syntax. They then allow the user to click on such URIs and
1310retrieve the corresponding resource in an appropriate (usually
1311scheme-dependent) application.</t>
1312
1313<t>Such applications would need to be upgraded, in order to use the
1314IRI syntax as a base for heuristics. In particular, a non-ASCII
1315character should not be taken as the indication of the end of an IRI.
1316Such applications also would need to make sure that they correctly
1317convert the detected IRI from the character encoding of the document
1318or application where the IRI appears, to the character encoding used
1319by the system-wide IRI invocation mechanism, or to a URI (according to
1320<xref target="mapping"/>) if the system-wide invocation mechanism only
1321accepts URIs.</t>
1322
1323<t>The clipboard is another frequently used way to transfer URIs and
1324IRIs from one application to another. On most platforms, the clipboard
1325is able to store and transfer text in many languages and scripts.
1326Correctly used, the clipboard transfers characters, not octets, which
1327will do the right thing with IRIs.</t>
1328</section><!-- transfer -->
1329
1330<section title="URI/IRI Generation">
1331
1332<t>Systems that offer resources through the Internet, where those
1333resources have logical names, sometimes automatically generate URIs
1334for the resources they offer. For example, some HTTP servers can
1335generate a directory listing for a file directory and then respond to
1336the generated URIs with the files.</t>
1337
1338<t>Many legacy character encodings are in use in various file systems.
1339Many currently deployed systems do not transform the local character
1340representation of the underlying system before generating URIs.</t>
1341
1342<t>For maximum interoperability, systems that generate resource
1343identifiers should make the appropriate transformations. For example,
1344if a file system contains a file named
1345  <aonly>"r&amp;#xE9;sum&amp;#xE9;.html"</aonly><ionly>"résumé.html"</ionly>,
1346  a server should expose this as
1347"r%C3%A9sum%C3%A9.html" in a URI, which allows use of
1348  <aonly>"r&amp;#xE9;sum&amp;#xE9;.html"</aonly><ionly>"résumé.html"</ionly>
1349  in an IRI, even if locally the file
1350name is kept in a character encoding other than UTF-8.
1351</t>
1352
1353<t>This recommendation particularly applies to HTTP servers. For FTP
1354servers, similar considerations apply; see <xref target="RFC2640"/>.</t>
1355</section><!-- generation -->
1356
1357<section title="URI/IRI Selection" anchor="selection">
1358<t>In some cases, resource owners and publishers have control over the
1359IRIs used to identify their resources. This control is mostly
1360executed by controlling the resource names, such as file names,
1361directly.</t>
1362
1363<t>In these cases, it is recommended to avoid choosing IRIs that are
1364easily confused. For example, for US-ASCII, the lower-case ell ("l") is
1365easily confused with the digit one ("1"), and the upper-case oh ("O") is
1366easily confused with the digit zero ("0"). Publishers should avoid
1367confusing users with "br0ken" or "1ame" identifiers.</t>
1368
1369<t>Outside the US-ASCII repertoire, there are many more opportunities for
1370confusion; a complete set of guidelines is too lengthy to include
1371here. As long as names are limited to characters from a single script,
1372native writers of a given script or language will know best when
1373ambiguities can appear, and how they can be avoided. What may look
1374ambiguous to a stranger may be completely obvious to the average
1375native user. On the other hand, in some cases, the UCS contains
1376variants for compatibility reasons; for example, for typographic purposes.
1377These should be avoided wherever possible. Although there may be exceptions,
1378newly created resource names should generally be in NFKC
1379<xref target="UTR15"></xref> (which means that they are also in NFC).</t>
1380
1381<t>As an example, the UCS contains the "fi" ligature at U+FB01
1382for compatibility reasons.
1383Wherever possible, IRIs should use the two letters "f" and "i" rather
1384than the "fi" ligature. An example where the latter may be used is
1385in the query part of an IRI for an explicit search for a word written
1386containing the "fi" ligature.</t>
1387
1388<t>In certain cases, there is a chance that characters from different
1389scripts look the same. The best known example is the similarity of the
1390Latin "A", the Greek "Alpha", and the Cyrillic "A". To avoid such
1391cases, IRIs should only be created where all the characters in a
1392single component are used together in a given language. This usually
1393means that all of these characters will be from the same script, but
1394there are languages that mix characters from different scripts (such
1395as Japanese).  This is similar to the heuristics used to distinguish
1396between letters and numbers in the examples above. Also, for Latin,
1397Greek, and Cyrillic, using lowercase letters results in fewer
1398ambiguities than using uppercase letters would.</t>
1399</section><!-- selection -->
1400
1401<section title="Display of URIs/IRIs" anchor="display">
1402<t>
1403In situations where the rendering software is not expected to display
1404non-ASCII parts of the IRI correctly using the available layout and font
1405resources, these parts should be percent-encoded before being displayed.</t>
1406
1407<t>For display of Bidi IRIs, please see <xref target="Bidi"/>.</t>
1408</section> <!-- display -->
1409
1410<section title="Interpretation of URIs and IRIs">
1411<t>Software that interprets IRIs as the names of local resources should
1412accept IRIs in multiple forms and convert and match them with the
1413appropriate local resource names.</t>
1414
1415<t>First, multiple representations include both IRIs in the native
1416character encoding of the protocol and also their URI counterparts.</t>
1417
1418<t>Second, it may include URIs constructed based on character
1419encodings other than UTF-8. These URIs may be produced by user agents that do
1420not conform to this specification and that use legacy character encodings to
1421convert non-ASCII characters to URIs. Whether this is necessary, and what
1422character encodings to cover, depends on a number of factors, such as
1423the legacy character encodings used locally and the distribution of
1424various versions of user agents. For example, software for Japanese
1425may accept URIs in Shift_JIS and/or EUC-JP in addition to UTF-8.</t>
1426
1427<t>Third, it may include additional mappings to be more user-friendly
1428and robust against transmission errors. These would be similar to how
1429some servers currently treat URIs as case insensitive or perform
1430additional matching to account for spelling errors. For characters
1431beyond the US-ASCII repertoire, this may, for example, include
1432ignoring the accents on received IRIs or resource names. Please note
1433that such mappings, including case mappings, are language
1434dependent.</t>
1435
1436<t>It can be difficult to identify a resource unambiguously if too
1437many mappings are taken into consideration. However, percent-encoded
1438and not percent-encoded parts of IRIs can always be clearly distinguished.
1439Also, the regularity of UTF-8 (see <xref target="Duerst97"/>) makes the
1440potential for collisions lower than it may seem at first.</t>
1441</section> <!-- interpretation -->
1442
1443<section title="Upgrading Strategy">
1444<t>Where this recommendation places further constraints on software
1445for which many instances are already deployed, it is important to
1446introduce upgrades carefully and to be aware of the various
1447interdependencies.</t>
1448
1449<t>If IRIs cannot be interpreted correctly, they should not be created,
1450generated, or transported. This suggests that upgrading URI interpreting
1451software to accept IRIs should have highest priority.</t>
1452
1453<t>On the other hand, a single IRI is interpreted only by a single or
1454very few interpreters that are known in advance, although it may be
1455entered and transported very widely.</t>
1456
1457<t>Therefore, IRIs benefit most from a broad upgrade of software to be
1458able to enter and transport IRIs. However, before an
1459individual IRI is published, care should be taken to upgrade the corresponding
1460interpreting software in order to cover the forms expected to be
1461received by various versions of entry and transport software.</t>
1462
1463<t>The upgrade of generating software to generate IRIs instead of using a
1464local character encoding should happen only after the service is upgraded
1465to accept IRIs. Similarly, IRIs should only be generated when the service
1466accepts IRIs and the intervening infrastructure and protocol is known
1467to transport them safely.</t>
1468
1469<t>Software converting from URIs to IRIs for display should be upgraded
1470only after upgraded entry software has been widely deployed to the
1471population that will see the displayed result.</t>
1472
1473
1474<t>Where there is a free choice of character encodings, it is often
1475possible to reduce the effort and dependencies for upgrading to IRIs
1476by using UTF-8 rather than another encoding. For example, when a new
1477file-based Web server is set up, using UTF-8 as the character encoding
1478for file names will make the transition to IRIs easier. Likewise, when
1479a new Web form is set up using UTF-8 as the character encoding of the
1480form page, the returned query URIs will use UTF-8 as the character
1481encoding (unless the user, for whatever reason, changes the character
1482encoding) and will therefore be compatible with IRIs.</t>
1483
1484
1485<t>These recommendations, when taken together, will allow for the
1486extension from URIs to IRIs in order to handle characters other than
1487US-ASCII while minimizing interoperability problems. For
1488considerations regarding the upgrade of URI scheme definitions, see
1489<xref target="UTF8use"/>.</t>
1490
1491</section> <!-- upgrading -->
1492</section> <!-- guidelines -->
1493
1494<section title="IANA Considerations" anchor="iana">
1495
1496  <t>This specification does not affect IANA.
1497    For details on how to define a URI/IRI scheme and register it with IANA,
1498    see <xref target="RFC4395bis"/>.</t>
1499
1500</section> <!-- IANA -->
1501   
1502<section title="Security Considerations" anchor="security">
1503<t>The security considerations discussed in <xref target="RFC3986"/>
1504also apply to IRIs. In addition, the following issues require
1505particular care for IRIs.</t>
1506<t>Incorrect encoding or decoding can lead to security problems.
1507For example, some UTF-8 decoders do not check against overlong
1508byte sequences. See <xref target='UTR36'/> Section 3 for details.</t>
1509
1510  <t>There are serious difficulties with relying on a human to verify that a
1511    an IRI (whether presented visually or aurally)
1512    is the same as another IRI or is the one intended.
1513    These problems exist with ASCII-only URIs (bl00mberg.com vs. bloomberg.com)
1514    but are strongly exacerbated when using the much larger character repertoire of Unicode.
1515    For details, see Section 2 of <xref target='UTR36'/>.
1516    Using administrative and technical means to reduce the availability
1517    of such exploits is possible, but they are difficult to eliminate altogether.
1518    User agents SHOULD NOT rely on visual or perceptual comparison or verification of IRIs
1519    as a means of validating or assuring safety, correctness or appropriateness of an IRI.
1520    Other means of presenting users with the validity, safety, or appropriateness
1521    of visited sites are being developed in the browser community
1522    as an alternative means of avoiding these difficulties.</t>
1523
1524<t>Besides the large character repertoire of Unicode, reasons for
1525  confusion include different forms of normalization and different normalization
1526  expectations, use of percent-encoding with various legacy encodings,
1527  and bidirectionality issues. See also <xref target="Bidi"/>.</t>
1528
1529<t>Confusion can occur in various IRI components, such as the
1530domain name part or the path part, or between IRI components. For considerations specific
1531to the domain name part, see <xref target="RFC5890"/>. For considerations specific to
1532particular protocols or schemes, see the security sections of the relevant specifications
1533and registration templates.
1534Administrators of sites that allow independent
1535users to create resources in the same sub area have to be careful.
1536Details are discussed in <xref target="selection"/>.</t>
1537
1538  <t>The characters additionally allowed in Legacy Extended IRIs
1539    introduce additional security issues. For details, see <xref target='notAllowed'/>.</t>
1540</section><!-- security -->
1541
1542<section title="Acknowledgements">
1543<t>This document was derived from <xref target="RFC3987"/>; the acknowledgments from
1544that specification still apply.</t>
1545<t>In addition, this document was influenced by contributions from (in no particular order)
1546  Norman Walsh, Richard Tobin,
1547  Henry S. Thomson, John Cowan, Paul Grosso, the XML Core Working Group of the W3C,
1548  Chris Lilley, <aonly>Bjoern Hoehrmann</aonly><ionly>Björn Höhrmann</ionly>,
1549Felix Sasaki, Jeremy Carroll, Frank Ellermann, Michael Everson, Cary Karp, Matitiahu Allouche,
1550Richard Ishida, Addison Phillips, Jonathan Rosenne, Najib Tounsi, Debbie Garside, Mark Davis,
1551Sarmad Hussain, Ted Hardie, Konrad Lanz, Thomas Roessler, Lisa Dusseault, Julian Reschke,
1552Giovanni Campagna, Anne van Kesteren, Mark Nottingham, Erik van der Poel, Marcin Hanclik, Marcos Caceres,
1553Roy Fielding, Greg Wilkins, Pieter Hintjens, Daniel R. Tobias, Marko Martin, Maciej Stanchowiak,
1554Wil Tan, Yui Naruse<ionly> (成瀬ゆい)</ionly>, Michael A. Puls II, Dave Thaler, Tom Petch, John Klensin, Shawn Steele,
1555Peter Saint-Andre, Geoffrey Sneddon, Chris Weber, Alex Melnikov, Slim Amamou, S. Moonesamy, Tim Berners-Lee,
1556Yaron Goland, Sam Ruby, Adam Barth, Abdulrahman I. ALGhadir, Aharon Lanin, Thomas Milo, Murray Sargent,
1557Marc Blanchet, and Mykyta Yevstifeyev.</t>
1558  <t>Anne van Kesteren is also gratefully acknowledged for his ongoing work documenting browser
1559        behavior with respect to URIs/URIs/URLs (see <xref target="HTMLURL"/>).</t>
1560</section> <!-- Acknowledgements -->
1561
1562<section title="Main Changes Since RFC 3987">
1563  <t>This section describes the main changes since <xref target="RFC3987"></xref>.</t>
1564  <section title="Split out Bidi, processing guidelines, comparison sections">
1565    <t>Move some components (comparison, bidi, processing) into separate documents.</t>
1566  </section>
1567  <section title="Major restructuring of IRI processing model" anchor="forkChanges">
1568    <t>Major restructuring of IRI processing model to make scheme-specific translation
1569      necessary to handle IDNA requirements and for consistency with web implementations. </t>
1570    <t>Starting with IRI, you want one of:
1571      <list style="hanging">
1572        <t hangText="a"> IRI components (IRI parsed into UTF8 pieces)</t>
1573        <t hangText="b"> URI components (URI parsed into ASCII pieces, encoded correctly) </t>
1574        <t hangText="c"> whole URI  (for passing on to some other system that wants whole URIs) </t>
1575      </list></t>
1576   
1577    <section title="OLD WAY">
1578      <t><list style="numbers">
1579       
1580        <t>Pct-encoding on the whole thing to a URI.
1581          (c1) If you want a (maybe broken) whole URI, you might
1582          stop here.</t>
1583       
1584        <t>Parsing the URI into URI components.
1585          (b1) If you want (maybe broken) URI components, stop here.</t>
1586       
1587        <t> Decode the components (undoing the pct-encoding).
1588          (a) if you want IRI components, stop here.</t>
1589       
1590        <t> reencode:  Either using a different encoding some components
1591          (for domain names, and query components in web pages, which
1592          depends on the component, scheme and context), and otherwise
1593          using pct-encoding.
1594          (b2) if you want (good) URI components, stop here.</t>
1595       
1596        <t> reassemble the reencoded components.
1597          (c2) if you want a (*good*) whole URI stop here.</t>
1598      </list>
1599       
1600      </t>
1601     
1602    </section>
1603   
1604    <section title="NEW WAY">
1605      <t>
1606        <list style="numbers">
1607         
1608          <t> Parse the IRI into IRI components using the generic syntax.
1609            (a) if you want IRI components, stop here.</t>
1610         
1611          <t> Encode each components, using pct-encoding, IDN encoding, or
1612            special query part encoding depending on the component
1613            scheme or context. (b) If you want URI components, stop here.</t>
1614          <t> reassemble the a whole URI from URI components.
1615            (c) if you want a whole URI stop here.</t>
1616        </list></t>
1617    </section>
1618    <section title="Extension of Syntax">
1619      <t>Added the tag range (U+E0000-E0FFF) to the iprivate production.
1620        Some IRIs generated with the new syntax may fail to pass very strict checks
1621        relying on the old syntax. But characters in this range should be extremely infrequent
1622        anyway.</t>
1623    </section>
1624    <section title="More to be added"><t>TODO: There are more main changes that need to be
1625      documented in this section.</t></section>
1626</section>
1627
1628<section title="Change Log">
1629
1630<t>Note to RFC Editor: Please completely remove this section before publication.</t>
1631
1632<section title='Changes after draft-ietf-iri-3987bis-01'>
1633    <t>Changes from draft-ietf-iri-3987bis-01 onwards are available as changesets
1634      in the IETF tools subversion repository at
1635      http://trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis/draft-ietf-iri-3987bis.xml.</t>
1636</section>
1637 
1638<section title='Changes from draft-duerst-iri-bis-07 to draft-ietf-iri-3987bis-00'>
1639     <t>Changed draft name, date, last paragraph of abstract, and titles in change log, and added this section
1640     in moving from draft-duerst-iri-bis-07 (personal submission) to draft-ietf-iri-3987bis-00 (WG document).</t>
1641</section>
1642
1643<section title="Changes from -06 to -07 of draft-duerst-iri-bis">
1644  <t>Major restructuring of the processing model, see <xref target="forkChanges"></xref>.</t>
1645</section>
1646</section>
1647
1648<section title='Changes from -00 to -01'><t><list style="symbols">
1649  <t>Removed 'mailto:' before mail addresses of authors.</t>
1650  <t>Added "&lt;to be done&gt;" as right side of 'href-strip' rule. Fixed '|' to '/' for
1651    alternatives.</t>
1652</list></t>
1653</section>
1654
1655<section title="Changes from -05 to -06 of draft-duerst-iri-bis-00"><t><list style="symbols">
1656<t>Add HyperText Reference, change abstract, acks and references for it</t>
1657<t>Add Masinter back as another editor.</t>
1658<t>Masinter integrates HRef material from HTML5 spec.</t>
1659<t>Rewrite introduction sections to modernize.</t>
1660</list></t>
1661</section>
1662
1663<section title="Changes from -04 to -05 of draft-duerst-iri-bis">
1664  <t><list style="symbols">
1665    <t>Updated references.</t>
1666    <t>Changed IPR text to pre5378Trust200902.</t></list></t>
1667</section>
1668
1669<section title="Changes from -03 to -04 of draft-duerst-iri-bis">
1670  <t><list style="symbols">
1671    <t>Added explicit abbreviation for LEIRIs.</t>
1672    <t>Mentioned LEIRI references.</t>
1673    <t>Completed text in LEIRI section about tag characters and about specials.</t></list></t>
1674</section>
1675
1676<section title="Changes from -02 to -03 of draft-duerst-iri-bis">
1677  <t><list style="symbols">
1678    <t>Updated some references.</t>
1679    <t>Updated Michel Suginard's coordinates.</t></list></t>
1680</section>
1681
1682<section title="Changes from -01 to -02 of draft-duerst-iri-bis">
1683  <t><list style="symbols">
1684    <t>Added tag range to iprivate (issue private-include-tags-115).</t>
1685    <t>Added Specials (U+FFF0-FFFD) to Legacy Extended IRIs.</t></list></t>
1686</section>
1687<section title="Changes from -00 to -01 of draft-duerst-iri-bis">
1688  <t><list style="symbols">
1689    <t>Changed from "IRIs with Spaces/Controls" to "Legacy Extended IRI"
1690      based on input from the W3C XML Core WG.
1691      Moved the relevant subsections to the back and promoted them to a section.</t>
1692    <t>Added some text re. Legacy Extended IRIs to the security section.</t>
1693    <t>Added a IANA Consideration Section.</t>
1694    <t>Added this Change Log Section.</t>
1695    <t>Added a section about "IRIs with Spaces/Controls" (converting from a Note in RFC 3987).</t></list></t>
1696</section> <!-- -00 to -01 -->
1697<section title="Changes from RFC 3987 to -00 of draft-duerst-iri-bis">
1698  <t><list>
1699    <t>Fixed errata (see http://www.rfc-editor.org/cgi-bin/errataSearch.pl?rfc=3987).</t></list></t>
1700</section> <!-- from 3987 -->
1701</section>
1702</middle>
1703
1704<back>
1705<references title="Normative References">
1706
1707<reference anchor="ASCII">
1708<front>
1709<title>Coded Character Set -- 7-bit American Standard Code for Information
1710Interchange</title>
1711<author>
1712<organization>American National Standards Institute</organization>
1713</author>
1714<date year="1986"/>
1715</front>
1716<seriesInfo name="ANSI" value="X3.4"/>
1717</reference>
1718
1719  <reference anchor="ISO10646" target='http://standards.iso.org/ittf/PubliclyAvailableStandards/c051273_ISO_IEC_10646_2011(E).zip'>
1720<front>
1721<title>ISO/IEC 10646:2011: Information Technology -
1722Universal Multiple-Octet Coded Character Set (UCS)</title>
1723<author>
1724<organization>International Organization for Standardization</organization>
1725</author>
1726<date month="March" year="20011"/>
1727</front>
1728<seriesInfo name="ISO" value="Standard 10646"/>
1729</reference>
1730
1731&rfc2119;
1732&rfc3491;
1733
1734  <reference anchor="STD63">
1735    <front>
1736      <title abbrev="UTF-8">UTF-8, a transformation format of ISO 10646</title>
1737      <author initials="F." surname="Yergeau" ifullname="François Yergeau" fullname="Francois Yergeau"></author>
1738      <date month="November" year="2003"/>
1739    </front>
1740    <seriesInfo name="STD" value="63"/>
1741    <seriesInfo name="RFC" value="3629"/>
1742   
1743  </reference>
1744 
1745&rfc3986;
1746
1747<reference anchor="STD68">
1748<front>
1749<title abbrev="ABNF">Augmented BNF for Syntax Specifications: ABNF</title>
1750<author initials="D." surname="Crocker" fullname="Dave Crocker"><organization/></author>
1751<author initials="P." surname="Overell" fullname="Paul Overell"><organization/></author>
1752<date month="January" year="2008"/></front>
1753<seriesInfo name="STD" value="68"/><seriesInfo name="RFC" value="5234"/>
1754</reference>
1755 
1756&rfc5890;
1757&rfc5891;
1758
1759  <reference anchor="RFC5892">
1760    <front>
1761      <title>The Unicode Code Points and Internationalized Domain Names for Applications (IDNA)</title>
1762      <author initials="P." surname="Faltstrom" isurname="Fältström" fullname="P. Faltstrom" ifullname="P. Fältström">
1763        <organization/>
1764      </author>
1765      <date year="2010" month="August"/>
1766    </front>
1767    <seriesInfo name="RFC" value="5892"/>
1768    <format type="TXT" octets="187370" target="http://www.rfc-editor.org/rfc/rfc5892.txt"/>
1769  </reference>
1770
1771  <reference anchor="UNIV6">
1772    <front>
1773      <title>The Unicode Standard, Version 6.2.0 (Mountain View, CA, The
1774        Unicode Consortium, 2012, ISBN 978-1-936213-07-8)</title>
1775      <author>
1776        <organization>The Unicode Consortium</organization>
1777      </author>
1778      <date year="2012" month="October"/>
1779    </front>
1780  </reference>
1781 
1782<reference anchor="UTR15" target="http://www.unicode.org/unicode/reports/tr15/tr15-23.html">
1783<front>
1784<title>Unicode Normalization Forms</title>
1785<author initials="M." surname="Davis" fullname="Mark Davis"><organization/></author>
1786  <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"><organization/></author>
1787<date year="2008" month="March"/>
1788</front>
1789<seriesInfo name="Unicode Standard Annex" value="#15"/>
1790</reference>
1791
1792</references>
1793
1794<references title="Informative References">
1795
1796  <reference anchor='CharMod' target='http://www.w3.org/TR/2004/CR-charmod-resid/'>
1797    <front>
1798      <title>Character Model for the World Wide Web 1.0: Resource Identifiers</title>
1799      <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
1800      <author initials="F." surname="Yergeau" ifullname="François Yergeau" fullname="Francois Yergeau"></author>
1801      <author fullname='Richard Ishida' surname='Ishida' initials='R. '/>
1802      <author fullname='Misha Wolf' surname='Wolf' initials='M. '/>
1803      <author fullname='Tex Texin' surname='Texin' initials='T. '/>
1804      <date year='2004' month='November' day='22'/>
1805    </front>
1806    <seriesInfo name='W3C Candidate Recommendation' value='CR-charmod-resid-20041122'/>
1807  </reference>
1808
1809  <reference anchor="Duerst97" target="http://www.sw.it.aoyama.ac.jp/2012/pub/IUC11-UTF-8.pdf">
1810<front>
1811<title>The Properties and Promises of UTF-8</title>
1812  <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"></author>
1813<date year="1997" month="September"/>
1814</front>
1815<seriesInfo name="Proc. 11th International Unicode Conference, San Jose" value=""/>
1816</reference>
1817
1818<reference anchor="Gettys" target="http://www.w3.org/DesignIssues/ModelConsequences">
1819<front>
1820<title>URI Model Consequences</title>
1821<author initials="J." surname="Gettys" fullname="Jim Gettys"><organization/></author>
1822<date month="" year=""/>
1823</front>
1824</reference>
1825
1826<reference anchor='HTML4' target='http://www.w3.org/TR/1999/REC-html401'>
1827<front>
1828<title>HTML 4.01 Specification</title>
1829<author fullname='David Raggett' surname='Raggett' initials='D. '/>
1830<author fullname='Arnaud Le Hors' surname='Le Hors' initials='A. '/>
1831<author fullname='Ian Jacobs' surname='Jacobs' initials='I. '/>
1832<date year='1999' month='December' day='24'/>
1833</front>
1834<seriesInfo name='W3C Recommendation' value='REC-html401-19991224'/>
1835</reference>
1836&rfc2130;
1837&rfc2141;
1838&rfc2192;
1839&rfc2277;
1840&rfc2384;
1841&rfc2396;
1842&rfc2397;
1843&rfc2616;
1844&rfc2640;
1845
1846  <reference anchor="RFC3987">
1847    <front>
1848      <title>Internationalized Resource Identifiers (IRIs)</title>
1849      <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
1850      <author initials="M." surname="Suignard" fullname="M. Suignard">
1851        <organization/>
1852      </author>
1853      <date year="2005" month="January"/>
1854    </front>
1855    <seriesInfo name="RFC" value="3987"/>
1856    <format type="TXT" octets="111190" target="http://www.rfc-editor.org/rfc/rfc3987.txt"/>
1857  </reference>
1858
1859&rfc5122;
1860&rfc6055;
1861
1862  <reference anchor="RFC6068">
1863    <front>
1864      <title>
1865        The 'mailto' URI Scheme
1866      </title>
1867      <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
1868      <author initials="L." surname="Masinter" fullname="L. Masinter">
1869        <organization/>
1870      </author>
1871      <author initials="J." surname="Zawinski" fullname="J. Zawinski">
1872        <organization/>
1873      </author>
1874      <date year="2010" month="October"/>
1875    </front>
1876    <seriesInfo name="RFC" value="6068"/>
1877    <format type="TXT" octets="36683" target="http://www.rfc-editor.org/rfc/rfc6068.txt"/>
1878  </reference>
1879
1880<reference anchor='Bidi'>
1881  <front>
1882    <title>Guidelines for Internationalized Resource Identifiers with Bi-directional Characters (Bidi IRIs)</title>
1883    <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
1884    <author initials='L.' surname='Masinter' />
1885    <author initials="A." isurname="Allawi (عادل علاوي)" surname="Allawi"
1886      ifullname="عادل علاوي" fullname="Adil Allawi"/>    <date year="2012" month="March" day="9" />
1887  </front>
1888  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-bidi-guidelines-02"/>
1889</reference>
1890
1891<reference anchor='Equivalence'>
1892  <front>
1893    <title>Equivalence and Canonicalization of Internationalized Resource Identifiers (IRIs)</title>
1894    <author initials='L.' surname='Masinter' />
1895    <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
1896    <date year="2012" month="March" day="2" />
1897  </front>
1898  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-comparison-01"/>
1899</reference>
1900
1901<reference anchor='RFC4395bis'>
1902  <front>
1903    <title>Guidelines and Registration Procedures for New URI/IRI Schemes</title>
1904    <author initials='T.' surname='Hansen' fullname="Tony Hansen"><organization/></author>
1905    <author initials='T.' surname='Hardie' fullname="Ted Hardie"><organization/></author>
1906    <author initials='L.' surname='Masinter' fullname="Larry Masinter"><organization/></author>
1907    <date year='2011' month='December'/>
1908    <workgroup>IRI</workgroup>
1909  </front>
1910  <seriesInfo name="Internet-Draft" value="draft-ietf-iri-4395bis-irireg-04"/>
1911</reference>
1912 
1913 
1914<reference anchor="UNIXML" target="http://www.w3.org/TR/unicode-xml/">
1915<front>
1916<title>Unicode in XML and other Markup Languages</title>
1917  <author  initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"><organization/></author>
1918<author initials="A." surname="Freytag" fullname="Asmus Freytag"><organization/></author>
1919<date year="2003" month="June" day="18"/>
1920</front>
1921<seriesInfo name="Unicode Technical Report" value="#20"/>
1922<seriesInfo name="World Wide Web Consortium" value="Note"/>
1923</reference>
1924 
1925  <reference anchor='HTMLURL' target="http://url.spec.whatwg.org/">
1926    <front>
1927      <title>URL</title>
1928      <author  fullname="Anne van Kesteren" initials="A." isurname="" surname="van Kesteren"></author>
1929      <date  day="12" month="October" year="2012"/>
1930    </front>
1931  </reference>
1932 
1933<reference anchor="UTR36" target="http://unicode.org/reports/tr36/">
1934<front>
1935<title>Unicode Security Considerations</title>
1936<author initials="M." surname="Davis" fullname="Mark Davis"><organization/></author>
1937<author initials="M." surname="Suignard" fullname="Michel Suignard"><organization/></author>
1938<date year="2010" month="August" day="4"/>
1939</front>
1940<seriesInfo name="Unicode Technical Report" value="#36"/>
1941</reference>
1942
1943<reference anchor='XLink' target='http://www.w3.org/TR/xlink11/#link-locators'>
1944<front>
1945<title>XML Linking Language (XLink) Version 1.1</title>
1946<author fullname='Steve DeRose' surname='DeRose' initials='S. '/>
1947<author fullname='Eve Maler' surname='Maler' initials='E. '/>
1948<author fullname='David Orchard' surname='Orchard' initials='D. '/>
1949<author fullname='Norman Walsh' surname='Walsh' initials='N. '/>
1950<date year='2010' month='May' day='06'/>
1951</front>
1952<seriesInfo name='W3C Recommendation' value='REC-xlink11-20100506'/>
1953</reference>
1954 
1955<reference anchor='XML1' target='http://www.w3.org/TR/2008/REC-xml/'>
1956<front>
1957<title>Extensible Markup Language (XML) 1.0 (Fifth Edition)</title>
1958<author fullname='Tim Bray' surname='Bray' initials='T. '/>
1959<author fullname='Jean Paoli' surname='Paoli' initials='J. '/>
1960<author fullname='C. M. Sperberg-McQueen' surname='Sperberg-McQueen' initials='C. M. '/>
1961<author fullname='Eve Maler' surname='Maler' initials='E. '/>
1962<author initials="F." surname="Yergeau" ifullname="François Yergeau" fullname="Francois Yergeau"/>
1963<date year='2008' month='November' day='26'/>
1964</front>
1965<seriesInfo name='W3C Recommendation' value='REC-xml-20081126'/>
1966</reference>
1967 
1968<reference anchor="XMLSchema" target="http://www.w3.org/TR/xmlschema-2/#anyURI">
1969<front>
1970<title>XML Schema Part 2: Datatypes Second Edition</title>
1971<author fullname='Paul V. Biron' surname='Biron' initials='P. V. '/>
1972<author fullname='Ashok Malhotra' surname='Malhotra' initials='A. '/>
1973<date year='2004' month='October' day='28'/>
1974</front>
1975<seriesInfo name='W3C Recommendation' value='REC-xmlschema-2-20041028'/>
1976</reference>
1977 
1978<reference anchor="XPointer" target="http://www.w3.org/TR/xptr-framework/#escaping">
1979<front>
1980<title>XPointer Framework</title>
1981<author fullname='Paul Grosso' surname='Grosso' initials='P. '/>
1982<author fullname='Eve Maler' surname='Maler' initials='E. '/>
1983<author fullname='Jonathan Marsh' surname='Marsh' initials='J. '/>
1984<author fullname='Norman Walsh' surname='Walsh' initials='N. '/>
1985<date year='2003' month='March' day='25'/>
1986</front>
1987<seriesInfo name='W3C Recommendation' value='REC-xptr-framework-20030325'/>
1988</reference>
1989
1990</references>
1991
1992</back>
1993</rfc>
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