One document matched: draft-ietf-iri-3987bis-13.xml
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<!ENTITY DRAFT "draft-ietf-iri-3987bis-13">
<!ENTITY YEAR "2012">
]>
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<rfc ipr="pre5378Trust200902" docName="&DRAFT;" category="std" xml:lang="en" obsoletes="3987">
<front>
<title abbrev="IRIs">Internationalized Resource Identifiers (IRIs)</title>
<author initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst"
fullname="Martin J. Duerst (Note: Please write "Duerst" with u-umlaut wherever possible, for example as "Dürst" in XML and HTML.)">
<organization>Aoyama Gakuin University<ionly> (青山学院大学)</ionly> </organization>
<address>
<postal>
<street>5-10-1 Fuchinobe</street>
<street>Chuo-ku</street>
<city>Sagamihara</city>
<region>Kanagawa</region>
<code>252-5258</code>
<country>Japan</country>
</postal>
<phone>+81 42 759 6329</phone>
<facsimile>+81 42 759 6495</facsimile>
<email>duerst@it.aoyama.ac.jp</email>
<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>
</address>
</author>
<author initials="M.L." surname="Suignard" fullname="Michel Suignard">
<organization>Unicode Consortium</organization>
<address>
<postal>
<street></street>
<street>P.O. Box 391476</street>
<city>Mountain View</city>
<region>CA</region>
<code>94039-1476</code>
<country>U.S.A.</country>
</postal>
<phone>+1-650-693-3921</phone>
<email>michel@unicode.org</email>
<uri>http://www.suignard.com</uri>
</address>
</author>
<author initials="L." surname="Masinter" fullname="Larry Masinter">
<organization>Adobe</organization>
<address>
<postal>
<street>345 Park Ave</street>
<city>San Jose</city>
<region>CA</region>
<code>95110</code>
<country>U.S.A.</country>
</postal>
<phone>+1-408-536-3024</phone>
<email>masinter@adobe.com</email>
<uri>http://larry.masinter.net</uri>
</address>
</author>
<date year="&YEAR;" />
<area>Applications</area>
<workgroup>Internationalized Resource Identifiers (iri)</workgroup>
<keyword>IRI</keyword>
<keyword>Internationalized Resource Identifier</keyword>
<keyword>UTF-8</keyword>
<keyword>URI</keyword>
<keyword>IDN</keyword>
<keyword>LEIRI</keyword>
<abstract>
<t>This document defines the Internationalized Resource Identifier
(IRI) protocol element, as an extension of the Uniform Resource
Identifier (URI). An IRI is a sequence of characters from the
Universal Character Set (Unicode/ISO 10646). Grammar and processing
rules are given for IRIs and related syntactic forms.</t>
<t>Defining IRI as a new protocol element (rather than updating or
extending the definition of URI) allows independent orderly
transitions: protocols and languages that use URIs must
explicitly choose to allow IRIs.</t>
<t>Guidelines are provided for the use and deployment of IRIs and
related protocol elements when revising protocols, formats, and
software components that currently deal only with URIs.</t>
<t>This document is part of a set of documents intended to
replace RFC 3987.</t>
</abstract>
<note title='RFC Editor: Please remove the next paragraph before publication.'>
<t>This document, and several companion documents, are intended to obsolete RFC 3987.
For discussion and comments on these
drafts, please join the IETF IRI WG by subscribing to the mailing
list public-iri@w3.org, archives at http://lists.w3.org/archives/public/public-iri/.
For a list of open issues, please see
the issue tracker of the WG at http://trac.tools.ietf.org/wg/iri/trac/report/1.
For a list of individual edits, please see the change history at
http://trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis.</t>
<t>This document is available in (line-printer ready) plaintext ASCII and PDF.
It is also available in HTML from
<eref target="http://www.sw.it.aoyama.ac.jp/&YEAR;/pub/&DRAFT;.html"
>http://www.sw.it.aoyama.ac.jp/&YEAR;/pub/&DRAFT;.html</eref>,
and in UTF-8 plaintext from
<eref target="http://www.sw.it.aoyama.ac.jp/&YEAR;/pub/&DRAFT;.utf8.txt"
>http://www.sw.it.aoyama.ac.jp/&YEAR;/pub/&DRAFT;.utf8.txt</eref>.
While all these versions are identical in their technical content,
the HTML, PDF, and UTF-8 plaintext versions show non-Unicode characters directly.
This often makes it easier to understand examples, and readers are therefore advised
to consult these versions in preference or as a supplement to the ASCII version.</t>
</note>
</front>
<middle>
<section title="Introduction">
<section title="Overview and Motivation" anchor="overview">
<t>A Uniform Resource Identifier (URI) is defined in <xref
target="RFC3986"/> as a sequence of characters chosen from a limited
subset of the repertoire of US-ASCII <xref target="ASCII"/>
characters.</t>
<t>The characters in URIs are frequently used for representing words
of natural languages. This usage has many advantages: Such URIs are
easier to memorize, easier to interpret, easier to transcribe, easier
to create, and easier to guess. For most languages other than English,
however, the natural script uses characters other than A - Z. For many
people, handling Latin characters is as difficult as handling the
characters of other scripts is for those who use only the Latin
script. Many languages with non-Latin scripts are transcribed with
Latin letters. These transcriptions are now often used in URIs, but
they introduce additional difficulties.</t>
<t>The infrastructure for the appropriate handling of characters from
additional scripts is now widely deployed in operating system and
application software. Software that can handle a wide variety of
scripts and languages at the same time is increasingly common. Also,
an increasing number of protocols and formats can carry a wide range of
characters.</t>
<t>URIs are composed out of a very limited repertoire of characters;
this design choice was made to support global transcription (see <xref
target="RFC3986"/> section 1.2.1.). Reliable transition between a URI
(as an abstract protocol element composed of a sequence of characters)
and a presentation of that URI (written on a napkin, read out loud)
and back is relatively straightforward, because of the limited
repertoire of characters used. IRIs are designed to satisfy a
different set of use requirements; in particular, to allow IRIs to be
written in ways that are more meaningful to their users, even at the
expense of global transcribability. However, ensuring reliability of
the transition between an IRI and its presentation and back is more
difficult and complex when dealing with the larger set of Unicode
characters. For example, Unicode supports multiple ways of encoding
complex combinations of characters and accents, with multiple
character sequences that can result in the same presentation.</t>
<t>This document defines the protocol element called Internationalized
Resource Identifier (IRI), which allows applications of URIs to be
extended to use resource identifiers that have a much wider repertoire
of characters. It also provides corresponding "internationalized"
versions of other constructs from <xref target="RFC3986"/>, such as
URI references. The syntax of IRIs is defined in <xref
target="syntax"/>.
</t>
<t>Within this document,
<xref target="IRIuse"/> discusses the use
of IRIs in different situations. <xref target="guidelines"/> gives
additional informative guidelines. <xref target="security"/>
discusses IRI-specific security considerations.</t>
<t>This specification is part of a collection of specifications
intended to replace <xref target="RFC3987"/>.
<xref target="Bidi"/> discusses the special case of
bidirectional IRIs, IRIs using characters from scripts written
right-to-left.
<xref target="Equivalence"/> gives guidelines for applications wishing
to determine if two IRIs are equivalent, as well as defining
some equivalence methods.
<xref target="RFC4395bis"/> updates the URI scheme registration
guidelines and procedures to note that every URI scheme is also
automatically an IRI scheme and to allow scheme definitions
to be directly described in terms of Unicode characters.
</t>
</section> <!-- overview -->
<section title="Applicability" anchor="Applicability">
<t>IRIs are designed to allow protocols and software that deal with
URIs to be updated to handle IRIs. Processing of
IRIs is accomplished by extending the URI syntax while retaining (and
not expanding) the set of "reserved" characters, such that the syntax
for any URI scheme may be extended to allow non-ASCII
characters. In addition, following parsing of an IRI, it is possible
to construct a corresponding URI by first encoding characters outside
of the allowed URI range and then reassembling the components.
</t>
<t>Practical use of IRIs forms in place of URIs forms depends on the
following conditions being met:</t>
<t><list style="hanging">
<t hangText="a.">A protocol or format element MUST be explicitly designated to be
able to carry IRIs. The intent is to avoid introducing IRIs into
contexts that are not defined to accept them. For example, XML
schema <xref target="XMLSchema"/> has an explicit type "anyURI" that
includes IRIs and IRI references. Therefore, IRIs and IRI references
can be used in attributes and elements of type "anyURI". On the other
hand, in HTTP/1.1 (<xref target="RFC2616"/>) , the
Request URI is defined as a URI, which means that direct use of IRIs
is not allowed in HTTP requests.</t>
<t hangText="b.">The protocol or format carrying the IRIs MUST have a
mechanism to represent the wide range of characters used in IRIs,
either natively or by some protocol- or format-specific escaping
mechanism (for example, numeric character references in <xref
target="XML1"/>).</t>
<t hangText="c.">The URI scheme definition, if it explicitly allows a
percent sign ("%") in any syntactic component, SHOULD define the
interpretation of sequences of percent-encoded octets (using "%XX"
hex octets) as octets from sequences of UTF-8 encoded characters; this
is recommended in the guidelines for registering new schemes, <xref
target="RFC4395bis"/>. For example, this is the practice for IMAP URLs
<xref target="RFC2192"/>, POP URLs <xref target="RFC2384"/> and the
URN syntax <xref target="RFC2141"/>). Note that use of
percent-encoding may also be restricted in some situations, for
example, URI schemes that disallow percent-encoding might still be
used with a fragment identifier which is percent-encoded (e.g.,
<xref target="XPointer"/>). See <xref target="UTF8use"/> for further
discussion.</t>
</list></t>
</section> <!-- applicability -->
<section title="Definitions" anchor="sec-Definitions">
<t>Various terms used in this document are defined in <xref target="RFC6365"/>
and <xref target="RFC3986"/>. In addition, we define the following terms for use in
this document.</t>
<t><list style="hanging">
<t hangText="octet:">An ordered sequence of eight bits considered as a
unit.</t>
<t hangText="sequence of characters:">A sequence of characters (one
after another).</t>
<t hangText="sequence of octets:">A sequence of octets (one after
another).</t>
<t hangText="character encoding:">A method of representing a sequence
of characters as a sequence of octets (maybe with variants). Also,
a method of (unambiguously) converting a sequence of octets into a
sequence of characters.</t>
<t hangText="charset:">The name of a parameter or attribute used to
identify a character encoding.</t>
<t hangText="UCS:">Universal Character Set. The coded character set
defined by ISO/IEC 10646 <xref target="ISO10646"/> and the Unicode
Standard <xref target="UNIV6"/>.</t>
<t hangText="IRI reference:">Denotes the common usage of an
Internationalized Resource Identifier. An IRI reference may be
absolute or relative. However, the "IRI" that results from such a
reference only includes absolute IRIs; any relative IRI references
are resolved to their absolute form. Note that in <xref
target="RFC2396"/> URIs did not include fragment identifiers, but
in <xref target="RFC3986"/> fragment identifiers are part of
URIs.</t>
<t hangText="LEIRI (Legacy Extended IRI):"> This term is used in
various XML specifications to refer
to strings that, although not valid IRIs, are acceptable input to
the processing rules in <xref target="LEIRIspec" />.</t>
<t hangText="protocol element:">Any portion of a message that affects
processing of that message by the protocol in question.</t>
<t hangText="create (a URI or IRI):">With respect to URIs and IRIs,
the term is used for the initial creation. This may be the
initial creation of a resource with a certain identifier, or the
initial exposition of a resource under a particular
identifier.</t>
<t hangText="generate (a URI or IRI):">With respect to URIs and IRIs,
the term is used when the identifier is generated by derivation
from other information.</t>
<t hangText="parsed URI component:">When a URI processor parses a URI
(following the generic syntax or a scheme-specific syntax, the result
is a set of parsed URI components, each of which has a type
(corresponding to the syntactic definition) and a sequence of URI
characters. </t>
<t hangText="parsed IRI component:">When an IRI processor parses
an IRI directly, following the general syntax or a scheme-specific
syntax, the result is a set of parsed IRI components, each of
which has a type (corresponding to the syntactic definition)
and a sequence of IRI characters. (This definition is analogous
to "parsed URI component".)</t>
<t hangText="IRI scheme:">A URI scheme may also be known as
an "IRI scheme" if the scheme's syntax has been extended to
allow non-US-ASCII characters according to the rules in this
document.</t>
</list></t>
</section> <!-- definitions -->
<section title="Notation" anchor="sec-Notation">
<t>RFCs and Internet Drafts currently do not allow any characters
outside the US-ASCII repertoire. Therefore, this document uses various
special notations for such characters in examples.</t>
<t>In text, characters outside US-ASCII are sometimes referenced by
using a prefix of 'U+', followed by four to six hexadecimal
digits.</t>
<t>To represent characters outside US-ASCII in a document format
that is limited to US-ASCII, this document
uses 'XML Notation'.
XML Notation uses a leading '&#x', a trailing ';', and the
hexadecimal number of the character in the UCS in between. For
example, Я stands for CYRILLIC CAPITAL LETTER YA<ionly> (Я)</ionly>.
In this notation, an actual '&' is denoted by '&'.
This notation is only used in the ASCII version(s) of this document,
because in the other versions, non-ASCII characters are used directly.</t>
<t>To denote actual octets in examples (as opposed to percent-encoded
octets), the two hex digits denoting the octet are enclosed in "<"
and ">". For example, the octet often denoted as 0xc9 is denoted
here as <c9>.</t>
<t> In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in <xref
target="RFC2119"/>.</t>
</section> <!-- notation -->
</section> <!-- introduction -->
<section title="IRI Syntax" anchor="syntax">
<t>This section defines the syntax of Internationalized Resource
Identifiers (IRIs).</t>
<t>As with URIs, an IRI is defined as a sequence of characters, not as
a sequence of octets.
This definition accommodates the fact that IRIs
may be written on paper or read over the radio as well as stored or
transmitted digitally. The same IRI might be represented as different
sequences of octets in different protocols or documents if these
protocols or documents use different character encodings (and/or
transfer encodings). Using the same character encoding as the
containing protocol or document ensures that the characters in the IRI
can be handled (e.g., searched, converted, displayed) in the same way
as the rest of the protocol or document.</t>
<section title="Summary of IRI Syntax" anchor="summary">
<t>The IRI syntax extends the URI syntax in <xref
target="RFC3986"/> by extending the class of unreserved characters,
primarily by adding the characters of the UCS (Universal Character Set, <xref
target="ISO10646"/>) beyond U+007F, subject to the limitations given
in the syntax rules below and in <xref target="limitations"/>.</t>
<t>The syntax and use of components and reserved characters is the
same as that in <xref target="RFC3986"/>. Each URI scheme thus also
functions as an IRI scheme, in that scheme-specific parsing rules
for URIs of a scheme are extended to allow parsing of IRIs using
the same parsing rules.</t>
<t>All the operations defined in <xref target="RFC3986"/>, such as the
resolution of relative references, can be applied to IRIs by
IRI-processing software in exactly the same way as they are for URIs
by URI-processing software.</t>
<t>Characters outside the US-ASCII repertoire MUST NOT be reserved and
therefore MUST NOT be used for syntactical purposes, such as to
delimit components in newly defined schemes. For example, U+00A2, CENT
SIGN, is not allowed as a delimiter in IRIs, because it is in the
'iunreserved' category. This is similar to the fact that it is not
possible to use '-' as a delimiter in URIs, because it is in the
'unreserved' category.</t>
</section> <!-- summary -->
<section title="ABNF for IRI References and IRIs" anchor="abnf">
<t>An ABNF definition for IRI references (which are the most general
concept and the start of the grammar) and IRIs is given here. The
syntax of this ABNF is described in <xref target="STD68"/>. Character
numbers are taken from the UCS, without implying any actual binary
encoding. Terminals in the ABNF are characters, not octets.</t>
<t>The following grammar closely follows the URI grammar in <xref
target="RFC3986"/>, except that the range of unreserved characters is
expanded to include UCS characters, with the restriction that private
UCS characters can occur only in query parts. The grammar is split
into two parts: Rules that differ from <xref target="RFC3986"/>
because of the above-mentioned expansion, and rules that are the same
as those in <xref target="RFC3986"/>. For rules that are different
than those in <xref target="RFC3986"/>, the names of the non-terminals
have been changed as follows. If the non-terminal contains 'URI', this
has been changed to 'IRI'. Otherwise, an 'i' has been prefixed.
The rule <pct-form> has been introduced in order to be able to reference it from other parts of
the document.</t>
<!--
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<figure>
<preamble>The following rules are different from those in <xref target="RFC3986"/>:</preamble>
<artwork>
IRI = scheme ":" ihier-part [ "?" iquery ]
[ "#" ifragment ]
ihier-part = "//" iauthority ipath-abempty
/ ipath-absolute
/ ipath-rootless
/ ipath-empty
IRI-reference = IRI / irelative-ref
absolute-IRI = scheme ":" ihier-part [ "?" iquery ]
irelative-ref = irelative-part [ "?" iquery ] [ "#" ifragment ]
irelative-part = "//" iauthority ipath-abempty
/ ipath-absolute
/ ipath-noscheme
/ ipath-empty
iauthority = [ iuserinfo "@" ] ihost [ ":" port ]
iuserinfo = *( iunreserved / pct-form / sub-delims / ":" )
ihost = IP-literal / IPv4address / ireg-name
pct-form = pct-encoded
ireg-name = *( iunreserved / sub-delims )
ipath = ipath-abempty ; begins with "/" or is empty
/ ipath-absolute ; begins with "/" but not "//"
/ ipath-noscheme ; begins with a non-colon segment
/ ipath-rootless ; begins with a segment
/ ipath-empty ; zero characters
ipath-abempty = *( path-sep isegment )
ipath-absolute = path-sep [ isegment-nz *( path-sep isegment ) ]
ipath-noscheme = isegment-nz-nc *( path-sep isegment )
ipath-rootless = isegment-nz *( path-sep isegment )
ipath-empty = ""
path-sep = "/"
isegment = *ipchar
isegment-nz = 1*ipchar
isegment-nz-nc = 1*( iunreserved / pct-form / sub-delims
/ "@" )
; non-zero-length segment without any colon ":"
ipchar = iunreserved / pct-form / sub-delims / ":"
/ "@"
iquery = *( ipchar / iprivate / "/" / "?" )
ifragment = *( ipchar / "/" / "?" )
iunreserved = ALPHA / DIGIT / "-" / "." / "_" / "~" / ucschar
ucschar = %xA0-D7FF / %xF900-FDCF / %xFDF0-FFEF
/ %x10000-1FFFD / %x20000-2FFFD / %x30000-3FFFD
/ %x40000-4FFFD / %x50000-5FFFD / %x60000-6FFFD
/ %x70000-7FFFD / %x80000-8FFFD / %x90000-9FFFD
/ %xA0000-AFFFD / %xB0000-BFFFD / %xC0000-CFFFD
/ %xD0000-DFFFD / %xE1000-EFFFD
iprivate = %xE000-F8FF / %xE0000-E0FFF / %xF0000-FFFFD
/ %x100000-10FFFD
</artwork>
</figure>
<t>Some productions are ambiguous. The "first-match-wins" (a.k.a. "greedy")
algorithm applies. For details, see <xref target="RFC3986"/>.</t>
<figure>
<preamble>The following rules are the same as those in <xref target="RFC3986"/>:</preamble>
<artwork>
scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
port = *DIGIT
IP-literal = "[" ( IPv6address / IPvFuture ) "]"
IPvFuture = "v" 1*HEXDIG "." 1*( unreserved / sub-delims / ":" )
IPv6address = 6( h16 ":" ) ls32
/ "::" 5( h16 ":" ) ls32
/ [ h16 ] "::" 4( h16 ":" ) ls32
/ [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
/ [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
/ [ *3( h16 ":" ) h16 ] "::" h16 ":" ls32
/ [ *4( h16 ":" ) h16 ] "::" ls32
/ [ *5( h16 ":" ) h16 ] "::" h16
/ [ *6( h16 ":" ) h16 ] "::"
h16 = 1*4HEXDIG
ls32 = ( h16 ":" h16 ) / IPv4address
IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet
dec-octet = DIGIT ; 0-9
/ %x31-39 DIGIT ; 10-99
/ "1" 2DIGIT ; 100-199
/ "2" %x30-34 DIGIT ; 200-249
/ "25" %x30-35 ; 250-255
pct-encoded = "%" HEXDIG HEXDIG
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
reserved = gen-delims / sub-delims
gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@"
sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="
</artwork></figure>
<t>This syntax does not support IPv6 scoped addressing zone identifiers.</t>
</section> <!-- abnf -->
</section> <!-- syntax -->
<section title="Processing IRIs and related protocol elements" anchor="processing">
<t>IRIs are meant to replace URIs in identifying resources within new
versions of protocols, formats, and software components that use a
UCS-based character repertoire. Protocols and components may use and
process IRIs directly. However, there are still numerous systems and
protocols which only accept URIs or components of parsed URIs; that is,
they only accept sequences of characters within the subset of US-ASCII
characters allowed in URIs. </t>
<t>This section defines specific processing steps for IRI consumers
which establish the relationship between the string given and the
interpreted derivatives. These
processing steps apply to both IRIs and IRI references (i.e., absolute
or relative forms); for IRIs, some steps are scheme specific. </t>
<section title="Converting to UCS" anchor="ucsconv">
<t>Input that is already in a Unicode form (i.e., a sequence of Unicode
characters or an octet-stream representing a Unicode-based character
encoding such as UTF-8 or UTF-16) should be left as is and not
normalized or changed.</t>
<t>An IRI or IRI reference is a sequence of characters from the UCS.
For input from presentations (written on paper, read aloud)
or translation from other representations (a text stream using a legacy character
encoding), convert the input to Unicode.
Note that some character encodings or transcriptions can be converted
to or represented by more than one sequence of Unicode characters.
Ideally the resulting IRI would use a normalized form,
such as Unicode Normalization Form C <xref target="UTR15"/>,
since that ensures a stable, consistent representation
that is most likely to produce the intended results.
Previous versions of this specification required
normalization at this step. However, attempts to
require normalization in other protocols have met with
strong enough resistance that requiring normalization
here was considered impractical.
Implementers and users are cautioned that, while denormalized character sequences are valid,
they might be difficult for other users or processes to reproduce
and might lead to unexpected results.
<!-- raise on list:
It is recommended
that the processing of IRI components treat
strings with the same normalized forms as equivalent.
-->
</t>
</section> <!-- ucsconv -->
<section title="Parse the IRI into IRI components">
<t>Parse the IRI, either as a relative reference (no scheme)
or using scheme specific processing (according to the scheme
given); the result is a set of parsed IRI components.</t>
</section> <!-- parse -->
<section title="General percent-encoding of IRI components" anchor="compmapping">
<t>Except as noted in the following subsections, IRI components are mapped
to the equivalent URI components by percent-encoding those characters
not allowed in URIs. Previous processing steps will have removed
some characters, and the interpretation of reserved characters will
have already been done (with the syntactic reserved characters outside
of the IRI component). This mapping is defined for all sequences
of Unicode characters, whether or not they are valid for the component
in question. </t>
<t>For each character which is not allowed anywhere in a valid URI
apply the following steps. </t>
<t><list style="hanging">
<t hangText="Convert to UTF-8:">Convert the character to a sequence of
one or more octets using UTF-8 <xref target="STD63"/>.</t>
<t hangText="Percent encode:">Convert each octet of this sequence to %HH,
where HH is the hexadecimal notation of the octet value. The
hexadecimal notation SHOULD use uppercase letters. (This is the
general URI percent-encoding mechanism in Section 2.1 of <xref
target="RFC3986"/>.)</t>
</list></t>
<t>Note that the mapping is an identity transformation for parsed URI
components of valid URIs, and is idempotent: applying the mapping a
second time will not change anything.</t>
</section> <!-- general conversion -->
<section title="Mapping ireg-name" anchor="dnsmapping">
<t>The mapping from <ireg-name> to a <reg-name> requires a choice
between one of the two methods described below.</t>
<section title='Mapping using Percent-Encoding' anchor='dnspercent'>
<t>The ireg-name component SHOULD be converted
according to the general procedure for percent-encoding
of IRI components described in <xref target="compmapping"/>.</t>
<t>For example, the IRI
<vspace/><aonly>"http://résumé.example.org"</aonly><ionly>"http://résumé.example.org"</ionly><vspace/> will be
converted to <vspace/>"http://r%C3%A9sum%C3%A9.example.org".</t>
<t>This conversion for ireg-name is in line with Section 3.2.2
of <xref target="RFC3986"/>, which does not mandate
a particular registered name lookup technology. For further background,
see <xref target="RFC6055"/> and <xref target="Gettys"/>.</t>
</section> <!-- dnspercent -->
<section title="Mapping using Punycode" anchor='dnspunycode'>
<t>In situations where it is certain that <ireg-name> is intended
to be used as a domain name to be processed by Domain Name Lookup
(as per <xref target="RFC5891"/>), an alternative method MAY be
used, converting <ireg-name> as follows:</t>
<t>If there is any percent-encoding, and the
corresponding octets all represent valid UTF-8
octet sequences, then convert these back to Unicode
character sequences. (If any percent-encodings are not
valid UTF-8 octet sequences, then leave the entire field as is
without any change, since punycode encoding would not succeed.)</t>
<t>Replace the ireg-name part of the IRI by the part converted using
the Domain Name Lookup procedure (Subsections 5.3 to 5.5) of <xref target="RFC5891"/>.
on each dot-separated label, and by using U+002E
(FULL STOP) as a label separator.
This procedure may fail, but this would mean that the IRI cannot be resolved.
In such cases, if the domain name conversion fails, then the
entire IRI conversion fails. Processors that have no mechanism for
signalling a failure MAY instead substitute an otherwise
invalid host name, although such processing SHOULD be avoided.</t>
<t>For example, the IRI
<vspace/><aonly>"http://résumé.example.org"</aonly><ionly>"http://résumé.example.org"</ionly><vspace/> is
converted to <vspace/>"http://xn--rsum-bad.example.org".</t>
<t>This conversion for ireg-name will be better able to deal with legacy
infrastructure that cannot handle percent-encoding in domain names.</t>
</section> <!-- punicode -->
<section title="Additional Considerations">
<t>Domain Names can appear in parts of an IRI other
than the ireg-name part. It is the responsibility of scheme-specific
implementations (if the Internationalized Domain Name is part of the
scheme syntax) or of server-side implementations (if the
Internationalized Domain Name is part of 'iquery') to apply the
necessary conversions at the appropriate point. Example: Trying to
validate the Web page at<vspace/>
<aonly>http://résumé.example.org</aonly><ionly>http://résumé.example.org</ionly>
would lead to an IRI of
<vspace/>http://validator.w3.org/check?uri=http%3A%2F%2F<aonly>résumé</aonly><ionly>résumé</ionly><vspace/>.example.org,
which would convert to a URI
of<vspace/>http://validator.w3.org/check?uri=http%3A%2F%2Fr%C3%A9sum%C3%A9.<vspace/>example.org.
The server-side implementation is responsible for making the
necessary conversions to be able to retrieve the Web page.</t>
<t>In this process, characters allowed in URI
references and existing percent-encoded sequences are not encoded further.
(This mapping is similar to, but different from, the encoding applied
when arbitrary content is included in some part of a URI.)
For example, an IRI of
<vspace/><aonly>"http://www.example.org/red%09rosé#red"
(in XML notation)</aonly><ionly>"http://www.example.org/red%09rosé#red"</ionly>
is converted to
<vspace/>"http://www.example.org/red%09ros%C3%A9#red", not to
something like
<vspace/>"http%3A%2F%2Fwww.example.org%2Fred%2509ros%C3%A9%23red".</t>
</section> <!-- additional -->
</section> <!-- dnsmapping -->
<section title="Mapping query components" anchor="querymapping">
<t>For compatibility with existing deployed HTTP infrastructure, the following special case applies
for the schemes "http" and "https" when an IRI is found in a document whose charset is not
based on UCS (e.g., not UTF-8 or UTF-16). In such a case, the "query" component of an IRI
is mapped into a URI by using the document charset rather than UTF-8 as the binary
representation before percent-encoding. This mapping is not applied for any other schemes or
components.</t>
</section> <!-- querymapping -->
<section title="Mapping IRIs to URIs" anchor="mapping">
<t>The mapping from an IRI to URI is accomplished by applying the
mapping above (from IRI to URI components) and then reassembling a URI
from the parsed URI components using the original punctuation that
delimited the IRI components. </t>
</section> <!-- mapping -->
</section> <!-- processing -->
<section title="Converting URIs to IRIs" anchor="URItoIRI">
<t>In some situations, for presentation and further processing, it is desirable to convert a URI
into an equivalent IRI without unnecessary percent encoding. Of course, every URI is already
an IRI in its own right without any conversion. This section gives one possible procedure
for converting a URI to an IRI.</t>
<section title='Limitations'>
<t>The conversion described in this section, if given a valid URI, will result in an IRI that maps
back to the URI used as an input for the conversion (except for potential case differences
in percent-encoding and for potential percent-encoded unreserved characters). However, the
IRI resulting from this conversion may differ from the original IRI (if there ever was
one).</t>
<t>URI-to-IRI conversion removes percent-encodings, but not all
percent-encodings can be eliminated. There are several reasons for
this:</t>
<t><list style="hanging">
<t hangText="1.">Some percent-encodings are necessary to distinguish
percent-encoded and unencoded uses of reserved characters.</t>
<t hangText="2.">Some percent-encodings cannot be interpreted as sequences
of UTF-8 octets.<vspace blankLines="1"/>
(Note: The octet patterns of UTF-8 are highly regular.
Therefore, there is a very high probability, but no guarantee,
that percent-encodings that can be interpreted as sequences of UTF-8
octets actually originated from UTF-8. For a detailed discussion,
see <xref target="Duerst97"/>.)</t>
<t hangText="3.">The conversion may result in a character that is not
appropriate in an IRI. See <xref target="abnf"/>,
and <xref target="limitations"/> for further details.</t>
<t hangText="4.">As described in <xref target="querymapping"/>, IRI to URI conversion may work
somewhat differently for query components.</t>
</list></t>
</section>
<section title="Conversion">
<t>Conversion from a URI to an IRI MAY be done by using the following
steps:
<list style="hanging">
<t hangText="1.">Represent the URI as a sequence of octets in
US-ASCII.</t>
<t hangText="2.">Convert all percent-encodings ("%" followed by two
hexadecimal digits) to the corresponding octets, except those
corresponding to "%", characters in "reserved", and characters
in US-ASCII not allowed in URIs.</t>
<t hangText="3.">Re-percent-encode any octet produced in step 2 that
is not part of a strictly legal UTF-8 octet sequence.</t>
<t hangText="4.">Re-percent-encode all octets produced in step 3 that
in UTF-8 represent characters that are not appropriate according
to <xref target="abnf"/> and <xref
target="limitations"/>.</t>
<t hangText="5.">Optionally, re-percent-encode octets in the query component if the scheme
is one of those mentioned in <xref target="querymapping"/>.</t>
<t hangText="6.">Interpret the resulting octet sequence as a sequence of characters encoded in
UTF-8.</t>
<t hangText="7.">URIs known to contain domain names in the reg-name component SHOULD convert
punycode-encoded domain name labels to the corresponding characters using the ToUnicode
procedure. </t>
</list></t>
<t>This procedure will convert as many percent-encoded characters as possible to characters in an
IRI. Because there are some choices in steps 4 (see also <xref target="limitations"/>) and
5, results may vary.</t>
<t>Conversions from URIs to IRIs MUST NOT use any character
encoding other than UTF-8 in steps 3 and 4, even if it might be
possible to guess from the context that another character encoding
than UTF-8 was used in the URI. For example, the URI
"http://www.example.org/r%E9sum%E9.html" might with some guessing be
interpreted to contain two e-acute characters encoded as
iso-8859-1. It must not be converted to an IRI containing these
e-acute characters. Otherwise, in the future the IRI will be mapped to
"http://www.example.org/r%C3%A9sum%C3%A9.html", which is a different
URI from "http://www.example.org/r%E9sum%E9.html".</t>
</section>
<section title="Examples">
<t>This section shows various examples of converting URIs to IRIs.
Each example shows the result after each of the steps 1 through 6 is
applied. XML Notation is used for the final result. Octets are
denoted by "<" followed by two hexadecimal digits followed by
">".</t>
<t>The following example contains the sequence "%C3%BC", which is a
strictly legal UTF-8 sequence, and which is converted into the actual
character U+00FC, LATIN SMALL LETTER U WITH DIAERESIS (also known as
u-umlaut).
<list style="hanging">
<t hangText="1.">http://www.example.org/D%C3%BCrst</t>
<t hangText="2.">http://www.example.org/D<c3><bc>rst</t>
<t hangText="3.">http://www.example.org/D<c3><bc>rst</t>
<t hangText="4.">http://www.example.org/D<c3><bc>rst</t>
<t hangText="5."><aonly>http://www.example.org/Dürst</aonly><ionly>http://www.example.org/Dürst</ionly></t>
<t hangText="6."><aonly>http://www.example.org/Dürst</aonly><ionly>http://www.example.org/Dürst</ionly></t>
</list>
</t>
<t>The following example contains the sequence "%FC", which might
represent U+00FC, LATIN SMALL LETTER U WITH DIAERESIS, in
the<vspace/>iso-8859-1 character encoding. (It might represent other
characters in other character encodings. For example, the octet
<fc> in iso-8859-5 represents U+045C, CYRILLIC SMALL LETTER
KJE.) Because <fc> is not part of a strictly legal UTF-8
sequence, it is re-percent-encoded in step 3.
<list style="hanging">
<t hangText="1.">http://www.example.org/D%FCrst</t>
<t hangText="2.">http://www.example.org/D<fc>rst</t>
<t hangText="3.">http://www.example.org/D%FCrst</t>
<t hangText="4.">http://www.example.org/D%FCrst</t>
<t hangText="5.">http://www.example.org/D%FCrst</t>
<t hangText="6.">http://www.example.org/D%FCrst</t>
</list>
</t>
<t>The following example contains "%e2%80%ae", which is the percent-encoded<vspace/>UTF-8
character encoding of U+202E, RIGHT-TO-LEFT OVERRIDE.
The direct use of this character is forbidden in an IRI. Therefore, the
corresponding octets are re-percent-encoded in step 4. This example shows
that the case (upper- or lowercase) of letters used in percent-encodings may not be preserved.
The example also contains a punycode-encoded domain name label (xn--99zt52a),
which is not converted.
<list style="hanging">
<t hangText="1.">http://xn--99zt52a.example.org/%e2%80%ae</t>
<t hangText="2.">http://xn--99zt52a.example.org/<e2><80><ae></t>
<t hangText="3.">http://xn--99zt52a.example.org/<e2><80><ae></t>
<t hangText="4.">http://xn--99zt52a.example.org/%E2%80%AE</t>
<t hangText="5.">http://xn--99zt52a.example.org/%E2%80%AE</t>
<t hangText="6."><aonly>http://納豆.example.org/%E2%80%AE</aonly><ionly>http://納豆.example.org/%E2%80%AE</ionly></t>
</list></t>
<t>Note that the label "xn--99zt52a" is converted to U+7D0D U+8C46
(Japanese Natto<ionly>, 納豆</ionly>). ((EDITOR NOTE: There is some inconsistency in this note.))</t>
</section> <!-- examples -->
</section> <!-- URItoIRI -->
<section title="Use of IRIs" anchor="IRIuse">
<section title="Limitations on UCS Characters Allowed in IRIs" anchor="limitations">
<t>This section discusses limitations on characters and character
sequences usable for IRIs beyond those given in <xref target="abnf"/>.
The considerations in this section are
relevant when IRIs are created and when URIs are converted to
IRIs.</t>
<t>
<list style="hanging"><t hangText="a.">The repertoire of characters allowed
in each IRI component is limited by the definition of that component.
For example, the definition of the scheme component does not allow
characters beyond US-ASCII.
<vspace blankLines="1"/>
(Note: In accordance with URI practice, generic IRI
software cannot and should not check for such limitations.)</t>
<t hangText="b.">The UCS contains many areas of characters for which
there are strong visual look-alikes. Because of the likelihood of
transcription errors, these also should be avoided. This includes
the full-width equivalents of Latin characters, half-width
Katakana characters for Japanese, and many others. It also
includes many look-alikes of "space", "delims", and "unwise",
characters excluded in <xref target="RFC3491"/>.</t>
<t hangText="c.">At the start of a component, the use of combining marks is strongly discouraged. As
an example, a COMBINING TILDE OVERLAY (U+0334) would be very confusing at the start of
a <isegment>. Combined with the preceeding '/', it might look like a solidus
with combining tilde overlay, but IRI processing software will parse and process the
'/' separately.</t>
<t hangText='d.'>The ZERO WIDTH NON-JOINER (U+200C) and ZERO WIDTH
JOINER (U+200D) are invisible in most contexts, but are crucial in
some very limited contexts. Appendix A of <xref target="RFC5892"/>
contains contextual restrictions for these and some other characters.
The use of these characters are strongly discouraged except
in the relevant contexts.</t>
</list>
</t>
<t>Additional information is available from <xref target="UNIXML"/>.
<xref target="UNIXML"/> is written in the context of general purpose text
rather than in that of identifiers. Nevertheless, it discusses
many of the categories of characters not appropriate for IRIs.</t>
</section> <!-- limitations -->
<section title="Software Interfaces and Protocols">
<t>Although an IRI is defined as a sequence of characters, software
interfaces for URIs typically function on sequences of octets or other
kinds of code units. Thus, software interfaces and protocols MUST
define which character encoding is used.</t>
<t>Intermediate software interfaces between IRI-capable components and
URI-only components MUST map the IRIs per <xref target="mapping"/>,
when transferring from IRI-capable to URI-only components.
This mapping SHOULD be applied as late as possible. It SHOULD NOT be
applied between components that are known to be able to handle IRIs.</t>
</section> <!-- software -->
<section title="Format of URIs and IRIs in Documents and Protocols">
<t>Document formats that transport URIs may have to be upgraded to allow
the transport of IRIs. In cases where the document as a whole
has a native character encoding, IRIs MUST also be encoded in this
character encoding and converted accordingly by a parser or interpreter.
IRI characters not expressible in the native character encoding SHOULD
be escaped by using the escaping conventions of the document format if
such conventions are available. Alternatively, they MAY be
percent-encoded according to <xref target="mapping"/>. For example, in
HTML or XML, numeric character references SHOULD be used. If a
document as a whole has a native character encoding and that character
encoding is not UTF-8, then IRIs MUST NOT be placed into the document
in the UTF-8 character encoding.</t>
<t>((UPDATE THIS NOTE)) Note: Some formats already accommodate IRIs,
although they use different terminology. HTML 4.0 <xref
target="HTML4"/> defines the conversion from IRIs to URIs as
error-avoiding behavior. XML 1.0 <xref target="XML1"/>, XLink <xref
target="XLink"/>, XML Schema <xref target="XMLSchema"/>, and
specifications based upon them allow IRIs. Also, it is expected that
all relevant new W3C formats and protocols will be required to handle
IRIs <xref target="CharMod"/>.</t>
</section> <!-- format -->
<section title="Use of UTF-8 for Encoding Original Characters" anchor="UTF8use">
<t>This section discusses details and gives examples for point c) in
<xref target="Applicability"/>. To be able to use IRIs, the URI
corresponding to the IRI in question has to encode original characters
into octets by using UTF-8. This can be specified for all URIs of a
URI scheme or can apply to individual URIs for schemes that do not
specify how to encode original characters. It can apply to the whole
URI, or only to some part. For background information on encoding
characters into URIs, see also Section 2.5 of <xref
target="RFC3986"/>.</t>
<t>For new URI/IRI schemes, using UTF-8 is recommended in <xref
target="RFC4395bis"/>. Examples where UTF-8 is already used are the URN
syntax <xref target="RFC2141"/>, IMAP URLs <xref target="RFC2192"/>,
POP URLs <xref target="RFC2384"/>, XMPP URLs <xref target='RFC5122'/>,
and the 'mailto:' scheme <xref target='RFC6068'/>. On the other hand, because the
HTTP URI scheme does not specify how to encode original characters,
only some HTTP URLs can have corresponding but different IRIs.</t>
<t>For example, for a document with a URI
of<vspace/>"http://www.example.org/r%C3%A9sum%C3%A9.html", it is
possible to construct a corresponding IRI
<aonly>(in XML notation, see <xref target="sec-Notation"/>):
"http://www.example.org/résumé.html"
("é" stands for the e-acute character, and "%C3%A9" is the UTF-8 encoded
and percent-encoded representation of that character).</aonly>
<ionly>: "http://www.example.org/résumé.html"
("é" is the e-acute character, and "%C3%A9" is the UTF-8 encoded
and percent-encoded representation of that character).</ionly>
On the other hand, for a document with a URI of
"http://www.example.org/r%E9sum%E9.html", the percent-encoded octets
cannot be converted to actual characters in an IRI, as the
percent-encoding is not based on UTF-8.</t>
<t>For most URI schemes, there is no need to upgrade their scheme
definition in order for them to work with IRIs. The main case where
upgrading makes sense is when a scheme definition, or a particular
component of a scheme, is strictly limited to the use of US-ASCII
characters with no provision to include non-ASCII characters/octets
via percent-encoding, or if a scheme definition currently uses highly
scheme-specific provisions for the encoding of non-ASCII characters.</t>
<t>Scheme definitions can impose restrictions on the syntax of
scheme-specific URIs; i.e., URIs that are admissible under the generic
URI syntax <xref target="RFC3986"/> may not be admissible due to
narrower syntactic constraints imposed by a URI scheme
specification. URI scheme definitions cannot broaden the syntactic
restrictions of the generic URI syntax; otherwise, it would be
possible to generate URIs that satisfied the scheme-specific syntactic
constraints without satisfying the syntactic constraints of the
generic URI syntax. However, additional syntactic constraints imposed
by URI scheme specifications are applicable to IRI, as the
corresponding URI resulting from the mapping defined in <xref
target="mapping"/> MUST be a valid URI under the syntactic
restrictions of generic URI syntax and any narrower restrictions
imposed by the corresponding URI scheme specification.</t>
<t>The requirement for the use of UTF-8 generally applies to all parts
of a URI. However, it is possible that the capability of IRIs to
represent a wide range of characters directly is used just in some
parts of the IRI (or IRI reference). The other parts of the IRI may
only contain US-ASCII characters, or they may not be based on
UTF-8. They may be based on another character encoding, or they may
directly encode raw binary data (see also <xref
target="RFC2397"/>). </t>
<t>For example, it is possible to have a URI reference
of<vspace/>"http://www.example.org/r%E9sum%E9.xml#r%C3%A9sum%C3%A9",
where the document name is encoded in iso-8859-1 based on server
settings, but where the fragment identifier is encoded in UTF-8 according
to <xref target="XPointer"/>. The IRI corresponding to the above URI would be
<aonly>(in XML notation)<vspace/>"http://www.example.org/r%E9sum%E9.xml#résumé".</aonly>
<ionly><vspace/>"http://www.example.org/r%E9sum%E9.xml#résumé".</ionly>
</t>
<t>Similar considerations apply to query parts. The functionality
of IRIs (namely, to be able to include non-ASCII characters) can
only be used if the query part is encoded in UTF-8.</t>
</section> <!-- utf8 -->
<section title="Relative IRI References">
<t>Processing of relative IRI references against a base is handled
straightforwardly; the algorithms of <xref target="RFC3986"/> can
be applied directly, treating the characters additionally allowed
in IRI references in the same way that unreserved characters are treated in URI
references.</t>
</section> <!-- relative -->
</section> <!-- IRIuse -->
<section title="Legacy Extended IRIs (LEIRIs)">
<t>In some cases, there have been formats which have used a protocol element
which is a variant of the IRI definition; these variants have usually been
somewhat less restricted in syntax. This section provides
a definition and a name (Legacy Extended IRI or LEIRI) for one of these
variants used widely in XML-based protocols. This variant has to be used with care;
it requires further processing before being fully interchangeable as IRIs.
New protocols and formats SHOULD NOT use Legacy Extended IRIs.
Even where Legacy Extended IRIs are allowed, only IRIs fully conforming
to the syntax definition in <xref target="abnf"></xref> SHOULD be created,
generated, and used. The provisions in this section also apply to
Legacy Extended IRI references.</t>
<section title="Legacy Extended IRI Syntax">
<figure>
<preamble>This section defines Legacy Extended IRIs (LEIRIs). The syntax of
Legacy Extended IRIs is the same as that for <IRI-reference>, except
that the ucschar production is replaced by the leiri-ucschar
production:
</preamble>
<artwork>
leiri-ucschar = " " / "<" / ">" / '"' / "{" / "}" / "|"
/ "\" / "^" / "`" / %x0-1F / %x7F-D7FF
/ %xE000-FFFD / %x10000-10FFFF
</artwork>
<postamble>The restriction on bidirectional formatting characters in <xref target="Bidi"></xref> is lifted.
The iprivate production becomes redundant.</postamble>
</figure>
<t>Likewise, the syntax for Legacy Extended IRI references
(LEIRI references) is the same as that for IRI references with
the above replacement of ucschar with leiri-ucschar.</t>
</section>
<section title="Conversion of Legacy Extended IRIs to IRIs" anchor="LEIRIspec">
<t>To convert a Legacy Extended IRI (reference) to
an IRI (reference), each character allowed in a Legacy Extended IRI (reference)
but not allowed in an IRI (reference) (see <xref target="notAllowed"></xref>) MUST be percent-encoded
by applying the steps in <xref target="compmapping"></xref>.</t>
</section>
<section title="Characters Allowed in Legacy Extended IRIs but not in IRIs" anchor="notAllowed">
<t>This section provides a list of the groups of characters and code points
that are allowed in Legacy Extedend IRIs, but are not allowed in IRIs
or are allowed in IRIs only in the query part. For each group of characters,
advice on the usage of these characters is also given, concentrating on the
reasons for why not to use them.</t>
<t>
<list>
<t>Space (U+0020): Some formats and applications use space as a delimiter,
e.g., for items in a list. Appendix C of <xref target="RFC3986"></xref>
also mentions that white space may have to be added when displaying
or printing long URIs; the same applies to long IRIs.
Spaces might disappear, or a single Legacy Extended IRI
might incorrectly be interpreted as two or more separate ones.</t>
<t>Delimiters "<" (U+003C), ">" (U+003E), and '"' (U+0022):
Appendix C of <xref target="RFC3986"></xref> suggests the use of
double-quotes ("http://example.com/") and angle brackets
(<http://example.com/>) as delimiters for URIs in plain text.
These conventions are often used, and also apply to IRIs.
Legacy Extended IRIs using these characters might be cut off at the wrong place.</t>
<t>Unwise characters "\" (U+005C),
"^" (U+005E), "`" (U+0060), "{" (U+007B), "|" (U+007C), and "}" (U+007D):
These characters originally were excluded from URIs because
the respective codepoints are assigned to different graphic characters
in some 7-bit or 8-bit encoding. Despite the move to Unicode,
some of these characters are still occasionally displayed differently
on some systems, e.g., U+005C as a Japanese Yen symbol.
Also, the fact that these characters are not used in URIs or IRIs
has encouraged their use outside URIs or IRIs in contexts that may
include URIs or IRIs. In case a Legacy Extended IRI with such a character
is used in such a context, the Legacy Extended IRI will be interpreted piecemeal.</t>
<t>The controls (C0 controls, DEL, and C1 controls, #x0 - #x1F #x7F - #x9F):
There is no way to transmit these characters reliably except potentially
in electronic form. Even when in electronic form, some software components
might silently filter out some of these characters,
or may stop processing alltogether when encountering some of them.
These characters may affect text display in subtle, unnoticable ways
or in drastic, global, and irreversible ways depending
on the hardware and software involved.
The use of some of these characters may allow malicious users
to manipulate the display of a Legacy Extended IRI and its context.</t>
<t>Bidi formatting characters (U+200E, U+200F, U+202A-202E):
These characters affect the display ordering of characters.
Displayed Legacy Extended IRIs containing these characters
cannot be converted back to electronic form (logical order) unambiguously.
These characters may allow malicious users to manipulate
the display of a Legacy Extended IRI and its context.</t>
<t>Specials (U+FFF0-FFFD): These code points provide functionality
beyond that useful in a Legacy Extended IRI, for example byte order identification,
annotation, and replacements for unknown characters and objects.
Their use and interpretation in a Legacy Extended IRI
serves no purpose and may lead to confusing display variations.</t>
<t>Private use code points (U+E000-F8FF, U+F0000-FFFFD, U+100000-10FFFD):
Display and interpretation of these code points is by definition
undefined without private agreement. Therefore, these code points
are not suited for use on the Internet. They are not interoperable and may have
unpredictable effects.</t>
<t>Tags (U+E0000-E0FFF): These characters provide a way to language tag in Unicode plain text.
They are not appropriate for Legacy Extended IRIs because language information
in identifiers cannot reliably be input, transmitted
(e.g., on a visual medium such as paper), or recognized.</t>
<t>Non-characters (U+FDD0-FDEF, U+1FFFE-1FFFF, U+2FFFE-2FFFF, U+3FFFE-3FFFF,
U+4FFFE-4FFFF, U+5FFFE-5FFFF, U+6FFFE-6FFFF, U+7FFFE-7FFFF, U+8FFFE-8FFFF,
U+9FFFE-9FFFF, U+AFFFE-AFFFF, U+BFFFE-BFFFF, U+CFFFE-CFFFF, U+DFFFE-DFFFF,
U+EFFFE-EFFFF, U+FFFFE-FFFFF, U+10FFFE-10FFFF):
These code points are defined as non-characters. Applications may use
some of them internally, but are not prepared to interchange them.</t>
</list>
</t>
<t>For reference, we here also list the code points and code units
not even allowed in Legacy Extended IRIs:
<list>
<t>Surrogate code units (D800-DFFF):
These do not represent Unicode codepoints.</t>
<t>Non-characters (U+FFFE-FFFF): These are not allowed in XML nor LEIRIs.</t>
</list>
</t>
</section>
</section>
<section title='Processing of URIs/IRIs/URLs by Web Browsers'>
<t>For legacy reasons, many web browsers exhibit some irregularities when processing URIs, IRIs,
and URLs. This is being documented in <xref target="HTMLURL"/>, in the hope that it will
lead to more uniform implementations of these irregularities across web browsers.</t>
<t>As far as currently known, creators of content for web browsers (such as HTML) can use all URIs
without problems. They can also use all IRIs without problems except that they should be
aware of the fact that query parts for HTTP/HTTPS IRIs should be percent-escaped.</t>
</section>
<section title="URI/IRI Processing Guidelines (Informative)" anchor="guidelines">
<t>This informative section provides guidelines for supporting IRIs in
the same software components and operations that currently process
URIs: Software interfaces that handle URIs, software that allows users
to enter URIs, software that creates or generates URIs, software that
displays URIs, formats and protocols that transport URIs, and software
that interprets URIs. These may all require modification before
functioning properly with IRIs. The considerations in this section
also apply to URI references and IRI references.</t>
<section title="URI/IRI Software Interfaces">
<t>Software interfaces that handle URIs, such as URI-handling APIs and
protocols transferring URIs, need interfaces and protocol elements
that are designed to carry IRIs.</t>
<t>In case the current handling in an API or protocol is based on
US-ASCII, UTF-8 is recommended as the character encoding for IRIs, as
it is compatible with US-ASCII, is in accordance with the
recommendations of <xref target="RFC2277"/>, and makes converting to
URIs easy. In any case, the API or protocol definition must clearly
define the character encoding to be used.</t>
<t>The transfer from URI-only to IRI-capable components requires no
mapping, although the conversion described in <xref
target="URItoIRI"/> above may be performed. It is preferable not to
perform this inverse conversion unless it is certain this can be done
correctly.</t>
</section><!-- software interfaces -->
<section title="URI/IRI Entry">
<t>Some components allow users to enter URIs into the system
by typing or dictation, for example. This software must be updated to allow
for IRI entry.</t>
<t>A person viewing a visual presentation of an IRI (as a sequence
of glyphs, in some order, in some visual display)
will use an entry method for characters in the user's language to
input the IRI. Depending on the script and the input method used, this
may be a more or less complicated process.</t>
<t>The process of IRI entry must ensure, as much as possible, that the
restrictions defined in <xref target="abnf"/> are met. This may be
done by choosing appropriate input methods or variants/settings
thereof, by appropriately converting the characters being input, by
eliminating characters that cannot be converted, and/or by issuing a
warning or error message to the user.</t>
<t>As an example of variant settings, input method editors for East
Asian Languages usually allow the input of Latin letters and related
characters in full-width or half-width versions. For IRI input, the
input method editor should be set so that it produces half-width Latin
letters and punctuation and full-width Katakana.</t>
<t>An input field primarily or solely used for the input of URIs/IRIs
might allow the user to view an IRI as it is mapped to a URI. Places
where the input of IRIs is frequent may provide the possibility for
viewing an IRI as mapped to a URI. This will help users when some of
the software they use does not yet accept IRIs.</t>
<t>An IRI input component interfacing to components that handle URIs,
but not IRIs, must map the IRI to a URI before passing it to these
components.</t>
<t>For the input of IRIs with right-to-left characters, please see
<xref target="Bidi"></xref>.</t>
</section><!-- entry -->
<section title="URI/IRI Transfer between Applications">
<t>Many applications (for example, mail user agents) try to detect
URIs appearing in plain text. For this, they use some heuristics based
on URI syntax. They then allow the user to click on such URIs and
retrieve the corresponding resource in an appropriate (usually
scheme-dependent) application.</t>
<t>Such applications would need to be upgraded, in order to use the
IRI syntax as a base for heuristics. In particular, a non-ASCII
character should not be taken as the indication of the end of an IRI.
Such applications also would need to make sure that they correctly
convert the detected IRI from the character encoding of the document
or application where the IRI appears, to the character encoding used
by the system-wide IRI invocation mechanism, or to a URI (according to
<xref target="mapping"/>) if the system-wide invocation mechanism only
accepts URIs.</t>
<t>The clipboard is another frequently used way to transfer URIs and
IRIs from one application to another. On most platforms, the clipboard
is able to store and transfer text in many languages and scripts.
Correctly used, the clipboard transfers characters, not octets, which
will do the right thing with IRIs.</t>
</section><!-- transfer -->
<section title="URI/IRI Generation">
<t>Systems that offer resources through the Internet, where those
resources have logical names, sometimes automatically generate URIs
for the resources they offer. For example, some HTTP servers can
generate a directory listing for a file directory and then respond to
the generated URIs with the files.</t>
<t>Many legacy character encodings are in use in various file systems.
Many currently deployed systems do not transform the local character
representation of the underlying system before generating URIs.</t>
<t>For maximum interoperability, systems that generate resource
identifiers should make the appropriate transformations. For example,
if a file system contains a file named
<aonly>"résumé.html"</aonly><ionly>"résumé.html"</ionly>,
a server should expose this as
"r%C3%A9sum%C3%A9.html" in a URI, which allows use of
<aonly>"résumé.html"</aonly><ionly>"résumé.html"</ionly>
in an IRI, even if locally the file
name is kept in a character encoding other than UTF-8.
</t>
<t>This recommendation particularly applies to HTTP servers. For FTP
servers, similar considerations apply; see <xref target="RFC2640"/>.</t>
</section><!-- generation -->
<section title="URI/IRI Selection" anchor="selection">
<t>In some cases, resource owners and publishers have control over the
IRIs used to identify their resources. This control is mostly
executed by controlling the resource names, such as file names,
directly.</t>
<t>In these cases, it is recommended to avoid choosing IRIs that are
easily confused. For example, for US-ASCII, the lower-case ell ("l") is
easily confused with the digit one ("1"), and the upper-case oh ("O") is
easily confused with the digit zero ("0"). Publishers should avoid
confusing users with "br0ken" or "1ame" identifiers.</t>
<t>Outside the US-ASCII repertoire, there are many more opportunities for
confusion; a complete set of guidelines is too lengthy to include
here. As long as names are limited to characters from a single script,
native writers of a given script or language will know best when
ambiguities can appear, and how they can be avoided. What may look
ambiguous to a stranger may be completely obvious to the average
native user. On the other hand, in some cases, the UCS contains
variants for compatibility reasons; for example, for typographic purposes.
These should be avoided wherever possible. Although there may be exceptions,
newly created resource names should generally be in NFKC
<xref target="UTR15"></xref> (which means that they are also in NFC).</t>
<t>As an example, the UCS contains the "fi" ligature at U+FB01
for compatibility reasons.
Wherever possible, IRIs should use the two letters "f" and "i" rather
than the "fi" ligature. An example where the latter may be used is
in the query part of an IRI for an explicit search for a word written
containing the "fi" ligature.</t>
<t>In certain cases, there is a chance that characters from different
scripts look the same. The best known example is the similarity of the
Latin "A", the Greek "Alpha", and the Cyrillic "A". To avoid such
cases, IRIs should only be created where all the characters in a
single component are used together in a given language. This usually
means that all of these characters will be from the same script, but
there are languages that mix characters from different scripts (such
as Japanese). This is similar to the heuristics used to distinguish
between letters and numbers in the examples above. Also, for Latin,
Greek, and Cyrillic, using lowercase letters results in fewer
ambiguities than using uppercase letters would.</t>
</section><!-- selection -->
<section title="Display of URIs/IRIs" anchor="display">
<t>
In situations where the rendering software is not expected to display
non-ASCII parts of the IRI correctly using the available layout and font
resources, these parts should be percent-encoded before being displayed.</t>
<t>For display of Bidi IRIs, please see <xref target="Bidi"/>.</t>
</section> <!-- display -->
<section title="Interpretation of URIs and IRIs">
<t>Software that interprets IRIs as the names of local resources should
accept IRIs in multiple forms and convert and match them with the
appropriate local resource names.</t>
<t>First, multiple representations include both IRIs in the native
character encoding of the protocol and also their URI counterparts.</t>
<t>Second, it may include URIs constructed based on character
encodings other than UTF-8. These URIs may be produced by user agents that do
not conform to this specification and that use legacy character encodings to
convert non-ASCII characters to URIs. Whether this is necessary, and what
character encodings to cover, depends on a number of factors, such as
the legacy character encodings used locally and the distribution of
various versions of user agents. For example, software for Japanese
may accept URIs in Shift_JIS and/or EUC-JP in addition to UTF-8.</t>
<t>Third, it may include additional mappings to be more user-friendly
and robust against transmission errors. These would be similar to how
some servers currently treat URIs as case insensitive or perform
additional matching to account for spelling errors. For characters
beyond the US-ASCII repertoire, this may, for example, include
ignoring the accents on received IRIs or resource names. Please note
that such mappings, including case mappings, are language
dependent.</t>
<t>It can be difficult to identify a resource unambiguously if too
many mappings are taken into consideration. However, percent-encoded
and not percent-encoded parts of IRIs can always be clearly distinguished.
Also, the regularity of UTF-8 (see <xref target="Duerst97"/>) makes the
potential for collisions lower than it may seem at first.</t>
</section> <!-- interpretation -->
<section title="Upgrading Strategy">
<t>Where this recommendation places further constraints on software
for which many instances are already deployed, it is important to
introduce upgrades carefully and to be aware of the various
interdependencies.</t>
<t>If IRIs cannot be interpreted correctly, they should not be created,
generated, or transported. This suggests that upgrading URI interpreting
software to accept IRIs should have highest priority.</t>
<t>On the other hand, a single IRI is interpreted only by a single or
very few interpreters that are known in advance, although it may be
entered and transported very widely.</t>
<t>Therefore, IRIs benefit most from a broad upgrade of software to be
able to enter and transport IRIs. However, before an
individual IRI is published, care should be taken to upgrade the corresponding
interpreting software in order to cover the forms expected to be
received by various versions of entry and transport software.</t>
<t>The upgrade of generating software to generate IRIs instead of using a
local character encoding should happen only after the service is upgraded
to accept IRIs. Similarly, IRIs should only be generated when the service
accepts IRIs and the intervening infrastructure and protocol is known
to transport them safely.</t>
<t>Software converting from URIs to IRIs for display should be upgraded
only after upgraded entry software has been widely deployed to the
population that will see the displayed result.</t>
<t>Where there is a free choice of character encodings, it is often
possible to reduce the effort and dependencies for upgrading to IRIs
by using UTF-8 rather than another encoding. For example, when a new
file-based Web server is set up, using UTF-8 as the character encoding
for file names will make the transition to IRIs easier. Likewise, when
a new Web form is set up using UTF-8 as the character encoding of the
form page, the returned query URIs will use UTF-8 as the character
encoding (unless the user, for whatever reason, changes the character
encoding) and will therefore be compatible with IRIs.</t>
<t>These recommendations, when taken together, will allow for the
extension from URIs to IRIs in order to handle characters other than
US-ASCII while minimizing interoperability problems. For
considerations regarding the upgrade of URI scheme definitions, see
<xref target="UTF8use"/>.</t>
</section> <!-- upgrading -->
</section> <!-- guidelines -->
<section title="IANA Considerations" anchor="iana">
<t>This specification does not affect IANA.
For details on how to define a URI/IRI scheme and register it with IANA,
see <xref target="RFC4395bis"/>.</t>
</section> <!-- IANA -->
<section title="Security Considerations" anchor="security">
<t>The security considerations discussed in <xref target="RFC3986"/>
also apply to IRIs. In addition, the following issues require
particular care for IRIs.</t>
<t>Incorrect encoding or decoding can lead to security problems.
For example, some UTF-8 decoders do not check against overlong
byte sequences. See <xref target='UTR36'/> Section 3 for details.</t>
<t>There are serious difficulties with relying on a human to verify that a
an IRI (whether presented visually or aurally)
is the same as another IRI or is the one intended.
These problems exist with ASCII-only URIs (bl00mberg.com vs. bloomberg.com)
but are strongly exacerbated when using the much larger character repertoire of Unicode.
For details, see Section 2 of <xref target='UTR36'/>.
Using administrative and technical means to reduce the availability
of such exploits is possible, but they are difficult to eliminate altogether.
User agents SHOULD NOT rely on visual or perceptual comparison or verification of IRIs
as a means of validating or assuring safety, correctness or appropriateness of an IRI.
Other means of presenting users with the validity, safety, or appropriateness
of visited sites are being developed in the browser community
as an alternative means of avoiding these difficulties.</t>
<t>Besides the large character repertoire of Unicode, reasons for
confusion include different forms of normalization and different normalization
expectations, use of percent-encoding with various legacy encodings,
and bidirectionality issues. See also <xref target="Bidi"/>.</t>
<t>Confusion can occur in various IRI components, such as the
domain name part or the path part, or between IRI components. For considerations specific
to the domain name part, see <xref target="RFC5890"/>. For considerations specific to
particular protocols or schemes, see the security sections of the relevant specifications
and registration templates.
Administrators of sites that allow independent
users to create resources in the same sub area have to be careful.
Details are discussed in <xref target="selection"/>.</t>
<t>The characters additionally allowed in Legacy Extended IRIs
introduce additional security issues. For details, see <xref target='notAllowed'/>.</t>
</section><!-- security -->
<section title="Acknowledgements">
<t>This document was derived from <xref target="RFC3987"/>; the acknowledgments from
that specification still apply.</t>
<t>In addition, this document was influenced by contributions from (in no particular order)
Norman Walsh, Richard Tobin,
Henry S. Thomson, John Cowan, Paul Grosso, the XML Core Working Group of the W3C,
Chris Lilley, <aonly>Bjoern Hoehrmann</aonly><ionly>Björn Höhrmann</ionly>,
Felix Sasaki, Jeremy Carroll, Frank Ellermann, Michael Everson, Cary Karp, Matitiahu Allouche,
Richard Ishida, Addison Phillips, Jonathan Rosenne, Najib Tounsi, Debbie Garside, Mark Davis,
Sarmad Hussain, Ted Hardie, Konrad Lanz, Thomas Roessler, Lisa Dusseault, Julian Reschke,
Giovanni Campagna, Anne van Kesteren, Mark Nottingham, Erik van der Poel, Marcin Hanclik, Marcos Caceres,
Roy Fielding, Greg Wilkins, Pieter Hintjens, Daniel R. Tobias, Marko Martin, Maciej Stanchowiak,
Wil Tan, Yui Naruse<ionly> (成瀬ゆい)</ionly>, Michael A. Puls II, Dave Thaler, Tom Petch, John Klensin, Shawn Steele,
Peter Saint-Andre, Geoffrey Sneddon, Chris Weber, Alex Melnikov, Slim Amamou, S. Moonesamy, Tim Berners-Lee,
Yaron Goland, Sam Ruby, Adam Barth, Abdulrahman I. ALGhadir, Aharon Lanin, Thomas Milo, Murray Sargent,
Marc Blanchet, and Mykyta Yevstifeyev.</t>
<t>Anne van Kesteren is also gratefully acknowledged for his ongoing work documenting browser
behavior with respect to URIs/URIs/URLs (see <xref target="HTMLURL"/>).</t>
</section> <!-- Acknowledgements -->
<section title="Main Changes Since RFC 3987">
<t>This section describes the main changes since <xref target="RFC3987"></xref>.</t>
<section title="Split out Bidi, processing guidelines, comparison sections">
<t>Move some components (comparison, bidi, processing) into separate documents.</t>
</section>
<section title="Major restructuring of IRI processing model" anchor="forkChanges">
<t>Major restructuring of IRI processing model to make scheme-specific translation
necessary to handle IDNA requirements and for consistency with web implementations. </t>
<t>Starting with IRI, you want one of:
<list style="hanging">
<t hangText="a"> IRI components (IRI parsed into UTF8 pieces)</t>
<t hangText="b"> URI components (URI parsed into ASCII pieces, encoded correctly) </t>
<t hangText="c"> whole URI (for passing on to some other system that wants whole URIs) </t>
</list></t>
<section title="OLD WAY">
<t><list style="numbers">
<t>Percent-encoding on the whole thing to a URI.
(c1) If you want a (maybe broken) whole URI, you might
stop here.</t>
<t>Parsing the URI into URI components.
(b1) If you want (maybe broken) URI components, stop here.</t>
<t>Decode the components (undoing the percent-encoding).
(a) if you want IRI components, stop here.</t>
<t>reencode: Either using a different encoding some components
(for domain names, and query components in web pages, which
depends on the component, scheme and context), and otherwise
using percent-encoding.
(b2) if you want (good) URI components, stop here.</t>
<t>reassemble the reencoded components.
(c2) if you want a (*good*) whole URI stop here.</t>
</list>
</t>
</section>
<section title="NEW WAY">
<t>
<list style="numbers">
<t>Parse the IRI into IRI components using the generic syntax.
(a) if you want IRI components, stop here.</t>
<t>Encode each components, using percent-encoding, IDN encoding, or
special query part encoding depending on the component
scheme or context. (b) If you want URI components, stop here.</t>
<t> reassemble the a whole URI from URI components.
(c) if you want a whole URI stop here.</t>
</list></t>
</section>
<section title="Extension of Syntax">
<t>Added the tag range (U+E0000-E0FFF) to the iprivate production.
Some IRIs generated with the new syntax may fail to pass very strict checks
relying on the old syntax. But characters in this range should be extremely infrequent
anyway.</t>
</section>
<section title="More to be added"><t>TODO: There are more main changes that need to be
documented in this section.</t></section>
</section>
<section title="Change Log">
<t>Note to RFC Editor: Please completely remove this section before publication.</t>
<section title='Changes after draft-ietf-iri-3987bis-01'>
<t>Changes from draft-ietf-iri-3987bis-01 onwards are available as changesets
in the IETF tools subversion repository at
http://trac.tools.ietf.org/wg/iri/trac/log/draft-ietf-iri-3987bis/draft-ietf-iri-3987bis.xml.</t>
</section>
<section title='Changes from draft-duerst-iri-bis-07 to draft-ietf-iri-3987bis-00'>
<t>Changed draft name, date, last paragraph of abstract, and titles in change log, and added this section
in moving from draft-duerst-iri-bis-07 (personal submission) to draft-ietf-iri-3987bis-00 (WG document).</t>
</section>
<section title="Changes from -06 to -07 of draft-duerst-iri-bis">
<t>Major restructuring of the processing model, see <xref target="forkChanges"></xref>.</t>
</section>
</section>
<section title='Changes from -00 to -01'><t><list style="symbols">
<t>Removed 'mailto:' before mail addresses of authors.</t>
<t>Added "<to be done>" as right side of 'href-strip' rule. Fixed '|' to '/' for
alternatives.</t>
</list></t>
</section>
<section title="Changes from -05 to -06 of draft-duerst-iri-bis-00"><t><list style="symbols">
<t>Add HyperText Reference, change abstract, acks and references for it</t>
<t>Add Masinter back as another editor.</t>
<t>Masinter integrates HRef material from HTML5 spec.</t>
<t>Rewrite introduction sections to modernize.</t>
</list></t>
</section>
<section title="Changes from -04 to -05 of draft-duerst-iri-bis">
<t><list style="symbols">
<t>Updated references.</t>
<t>Changed IPR text to pre5378Trust200902.</t></list></t>
</section>
<section title="Changes from -03 to -04 of draft-duerst-iri-bis">
<t><list style="symbols">
<t>Added explicit abbreviation for LEIRIs.</t>
<t>Mentioned LEIRI references.</t>
<t>Completed text in LEIRI section about tag characters and about specials.</t></list></t>
</section>
<section title="Changes from -02 to -03 of draft-duerst-iri-bis">
<t><list style="symbols">
<t>Updated some references.</t>
<t>Updated Michel Suginard's coordinates.</t></list></t>
</section>
<section title="Changes from -01 to -02 of draft-duerst-iri-bis">
<t><list style="symbols">
<t>Added tag range to iprivate (issue private-include-tags-115).</t>
<t>Added Specials (U+FFF0-FFFD) to Legacy Extended IRIs.</t></list></t>
</section>
<section title="Changes from -00 to -01 of draft-duerst-iri-bis">
<t><list style="symbols">
<t>Changed from "IRIs with Spaces/Controls" to "Legacy Extended IRI"
based on input from the W3C XML Core WG.
Moved the relevant subsections to the back and promoted them to a section.</t>
<t>Added some text re. Legacy Extended IRIs to the security section.</t>
<t>Added a IANA Consideration Section.</t>
<t>Added this Change Log Section.</t>
<t>Added a section about "IRIs with Spaces/Controls" (converting from a Note in RFC 3987).</t></list></t>
</section> <!-- -00 to -01 -->
<section title="Changes from RFC 3987 to -00 of draft-duerst-iri-bis">
<t><list>
<t>Fixed errata (see http://www.rfc-editor.org/cgi-bin/errataSearch.pl?rfc=3987).</t></list></t>
</section> <!-- from 3987 -->
</section>
</middle>
<back>
<references title="Normative References">
<reference anchor="ASCII">
<front>
<title>Coded Character Set -- 7-bit American Standard Code for Information
Interchange</title>
<author>
<organization>American National Standards Institute</organization>
</author>
<date year="1986"/>
</front>
<seriesInfo name="ANSI" value="X3.4"/>
</reference>
<reference anchor="ISO10646" target='http://standards.iso.org/ittf/PubliclyAvailableStandards/c051273_ISO_IEC_10646_2011(E).zip'>
<front>
<title>ISO/IEC 10646:2011: Information Technology -
Universal Multiple-Octet Coded Character Set (UCS)</title>
<author>
<organization>International Organization for Standardization</organization>
</author>
<date month="March" year="20011"/>
</front>
<seriesInfo name="ISO" value="Standard 10646"/>
</reference>
&rfc2119;
&rfc3491;
<reference anchor="STD63">
<front>
<title abbrev="UTF-8">UTF-8, a transformation format of ISO 10646</title>
<author initials="F." surname="Yergeau" ifullname="François Yergeau" fullname="Francois Yergeau"></author>
<date month="November" year="2003"/>
</front>
<seriesInfo name="STD" value="63"/>
<seriesInfo name="RFC" value="3629"/>
</reference>
&rfc3986;
<reference anchor="STD68">
<front>
<title abbrev="ABNF">Augmented BNF for Syntax Specifications: ABNF</title>
<author initials="D." surname="Crocker" fullname="Dave Crocker"><organization/></author>
<author initials="P." surname="Overell" fullname="Paul Overell"><organization/></author>
<date month="January" year="2008"/></front>
<seriesInfo name="STD" value="68"/><seriesInfo name="RFC" value="5234"/>
</reference>
&rfc5890;
&rfc5891;
<reference anchor="RFC5892">
<front>
<title>The Unicode Code Points and Internationalized Domain Names for Applications (IDNA)</title>
<author initials="P." surname="Faltstrom" isurname="Fältström" fullname="P. Faltstrom" ifullname="P. Fältström">
<organization/>
</author>
<date year="2010" month="August"/>
</front>
<seriesInfo name="RFC" value="5892"/>
<format type="TXT" octets="187370" target="http://www.rfc-editor.org/rfc/rfc5892.txt"/>
</reference>
<reference anchor="UNIV6">
<front>
<title>The Unicode Standard, Version 6.2.0 (Mountain View, CA, The
Unicode Consortium, 2012, ISBN 978-1-936213-07-8)</title>
<author>
<organization>The Unicode Consortium</organization>
</author>
<date year="2012" month="October"/>
</front>
</reference>
<reference anchor="UTR15" target="http://www.unicode.org/unicode/reports/tr15/tr15-23.html">
<front>
<title>Unicode Normalization Forms</title>
<author initials="M." surname="Davis" fullname="Mark Davis"><organization/></author>
<author initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"><organization/></author>
<date year="2008" month="March"/>
</front>
<seriesInfo name="Unicode Standard Annex" value="#15"/>
</reference>
</references>
<references title="Informative References">
<reference anchor='CharMod' target='http://www.w3.org/TR/2004/CR-charmod-resid/'>
<front>
<title>Character Model for the World Wide Web 1.0: Resource Identifiers</title>
<author initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
<author initials="F." surname="Yergeau" ifullname="François Yergeau" fullname="Francois Yergeau"></author>
<author fullname='Richard Ishida' surname='Ishida' initials='R. '/>
<author fullname='Misha Wolf' surname='Wolf' initials='M. '/>
<author fullname='Tex Texin' surname='Texin' initials='T. '/>
<date year='2004' month='November' day='22'/>
</front>
<seriesInfo name='W3C Candidate Recommendation' value='CR-charmod-resid-20041122'/>
</reference>
<reference anchor="Duerst97" target="http://www.sw.it.aoyama.ac.jp/2012/pub/IUC11-UTF-8.pdf">
<front>
<title>The Properties and Promises of UTF-8</title>
<author initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"></author>
<date year="1997" month="September"/>
</front>
<seriesInfo name="Proc. 11th International Unicode Conference, San Jose" value=""/>
</reference>
<reference anchor="Gettys" target="http://www.w3.org/DesignIssues/ModelConsequences">
<front>
<title>URI Model Consequences</title>
<author initials="J." surname="Gettys" fullname="Jim Gettys"><organization/></author>
<date month="" year=""/>
</front>
</reference>
<reference anchor='HTML4' target='http://www.w3.org/TR/1999/REC-html401'>
<front>
<title>HTML 4.01 Specification</title>
<author fullname='David Raggett' surname='Raggett' initials='D. '/>
<author fullname='Arnaud Le Hors' surname='Le Hors' initials='A. '/>
<author fullname='Ian Jacobs' surname='Jacobs' initials='I. '/>
<date year='1999' month='December' day='24'/>
</front>
<seriesInfo name='W3C Recommendation' value='REC-html401-19991224'/>
</reference>
&rfc2141;
&rfc2192;
&rfc2277;
&rfc2384;
&rfc2396;
&rfc2397;
&rfc2616;
&rfc2640;
<reference anchor="RFC3987">
<front>
<title>Internationalized Resource Identifiers (IRIs)</title>
<author initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
<author initials="M." surname="Suignard" fullname="M. Suignard">
<organization/>
</author>
<date year="2005" month="January"/>
</front>
<seriesInfo name="RFC" value="3987"/>
<format type="TXT" octets="111190" target="http://www.rfc-editor.org/rfc/rfc3987.txt"/>
</reference>
&rfc5122;
&rfc6055;
<reference anchor="RFC6068">
<front>
<title>
The 'mailto' URI Scheme
</title>
<author initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
<author initials="L." surname="Masinter" fullname="L. Masinter">
<organization/>
</author>
<author initials="J." surname="Zawinski" fullname="J. Zawinski">
<organization/>
</author>
<date year="2010" month="October"/>
</front>
<seriesInfo name="RFC" value="6068"/>
<format type="TXT" octets="36683" target="http://www.rfc-editor.org/rfc/rfc6068.txt"/>
</reference>
&rfc6365;
<reference anchor='Bidi'>
<front>
<title>Guidelines for Internationalized Resource Identifiers with Bi-directional Characters (Bidi IRIs)</title>
<author initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
<author initials='L.' surname='Masinter' />
<author initials="A." isurname="Allawi (عادل علاوي)" surname="Allawi"
ifullname="عادل علاوي" fullname="Adil Allawi"/> <date year="2012" month="March" day="9" />
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-iri-bidi-guidelines-02"/>
</reference>
<reference anchor='Equivalence'>
<front>
<title>Equivalence and Canonicalization of Internationalized Resource Identifiers (IRIs)</title>
<author initials='L.' surname='Masinter' />
<author initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"/>
<date year="2012" month="March" day="2" />
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-iri-comparison-01"/>
</reference>
<reference anchor='RFC4395bis'>
<front>
<title>Guidelines and Registration Procedures for New URI/IRI Schemes</title>
<author initials='T.' surname='Hansen' fullname="Tony Hansen"><organization/></author>
<author initials='T.' surname='Hardie' fullname="Ted Hardie"><organization/></author>
<author initials='L.' surname='Masinter' fullname="Larry Masinter"><organization/></author>
<date year='2011' month='December'/>
<workgroup>IRI</workgroup>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-iri-4395bis-irireg-04"/>
</reference>
<reference anchor="UNIXML" target="http://www.w3.org/TR/unicode-xml/">
<front>
<title>Unicode in XML and other Markup Languages</title>
<author initials="M.J." isurname="Dürst" surname="Duerst" ifullname="Martin J. Dürst" fullname="Martin J. Duerst"><organization/></author>
<author initials="A." surname="Freytag" fullname="Asmus Freytag"><organization/></author>
<date year="2003" month="June" day="18"/>
</front>
<seriesInfo name="Unicode Technical Report" value="#20"/>
<seriesInfo name="World Wide Web Consortium" value="Note"/>
</reference>
<reference anchor='HTMLURL' target="http://url.spec.whatwg.org/">
<front>
<title>URL</title>
<author fullname="Anne van Kesteren" initials="A." isurname="" surname="van Kesteren"></author>
<date day="12" month="October" year="2012"/>
</front>
</reference>
<reference anchor="UTR36" target="http://unicode.org/reports/tr36/">
<front>
<title>Unicode Security Considerations</title>
<author initials="M." surname="Davis" fullname="Mark Davis"><organization/></author>
<author initials="M." surname="Suignard" fullname="Michel Suignard"><organization/></author>
<date year="2010" month="August" day="4"/>
</front>
<seriesInfo name="Unicode Technical Report" value="#36"/>
</reference>
<reference anchor='XLink' target='http://www.w3.org/TR/xlink11/#link-locators'>
<front>
<title>XML Linking Language (XLink) Version 1.1</title>
<author fullname='Steve DeRose' surname='DeRose' initials='S. '/>
<author fullname='Eve Maler' surname='Maler' initials='E. '/>
<author fullname='David Orchard' surname='Orchard' initials='D. '/>
<author fullname='Norman Walsh' surname='Walsh' initials='N. '/>
<date year='2010' month='May' day='06'/>
</front>
<seriesInfo name='W3C Recommendation' value='REC-xlink11-20100506'/>
</reference>
<reference anchor='XML1' target='http://www.w3.org/TR/2008/REC-xml/'>
<front>
<title>Extensible Markup Language (XML) 1.0 (Fifth Edition)</title>
<author fullname='Tim Bray' surname='Bray' initials='T. '/>
<author fullname='Jean Paoli' surname='Paoli' initials='J. '/>
<author fullname='C. M. Sperberg-McQueen' surname='Sperberg-McQueen' initials='C. M. '/>
<author fullname='Eve Maler' surname='Maler' initials='E. '/>
<author initials="F." surname="Yergeau" ifullname="François Yergeau" fullname="Francois Yergeau"/>
<date year='2008' month='November' day='26'/>
</front>
<seriesInfo name='W3C Recommendation' value='REC-xml-20081126'/>
</reference>
<reference anchor="XMLSchema" target="http://www.w3.org/TR/xmlschema-2/#anyURI">
<front>
<title>XML Schema Part 2: Datatypes Second Edition</title>
<author fullname='Paul V. Biron' surname='Biron' initials='P. V. '/>
<author fullname='Ashok Malhotra' surname='Malhotra' initials='A. '/>
<date year='2004' month='October' day='28'/>
</front>
<seriesInfo name='W3C Recommendation' value='REC-xmlschema-2-20041028'/>
</reference>
<reference anchor="XPointer" target="http://www.w3.org/TR/xptr-framework/#escaping">
<front>
<title>XPointer Framework</title>
<author fullname='Paul Grosso' surname='Grosso' initials='P. '/>
<author fullname='Eve Maler' surname='Maler' initials='E. '/>
<author fullname='Jonathan Marsh' surname='Marsh' initials='J. '/>
<author fullname='Norman Walsh' surname='Walsh' initials='N. '/>
<date year='2003' month='March' day='25'/>
</front>
<seriesInfo name='W3C Recommendation' value='REC-xptr-framework-20030325'/>
</reference>
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-24 01:51:45 |