5255
PROPOSED STANDARD
Internet Message Access Protocol Internationalization
Authors: C. Newman, A. Gulbrandsen, A. Melnikov
Date: June 2008
Area: app
Working Group: imapext
Stream: IETF
Abstract
Internet Message Access Protocol (IMAP) version 4rev1 has basic support for non-ASCII characters in mailbox names and search substrings. It also supports non-ASCII message headers and content encoded as specified by Multipurpose Internet Mail Extensions (MIME). This specification defines a collection of IMAP extensions that improve international support including language negotiation for international error text, translations for namespace prefixes, and comparator negotiation for search, sort, and thread. [STANDARDS-TRACK]
RFC 5255
PROPOSED STANDARD
Errata Exist
Network Working Group C. Newman
Request for Comments: 5255 Sun Microsystems
Category: Standards Track A. Gulbrandsen
Oryx Mail Systems GmhH
A. Melnikov
Isode Limited
June 2008
<span class="h1">Internet Message Access Protocol Internationalization</span>
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
Internet Message Access Protocol (IMAP) version 4rev1 has basic
support for non-ASCII characters in mailbox names and search
substrings. It also supports non-ASCII message headers and content
encoded as specified by Multipurpose Internet Mail Extensions (MIME).
This specification defines a collection of IMAP extensions that
improve international support including language negotiation for
international error text, translations for namespace prefixes, and
comparator negotiation for search, sort, and thread.
<span class="grey">Newman, et al. Standards Track [Page 1]</span><span id="page-2" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
Table of Contents
<a href="#section-1">1</a>. Introduction ....................................................<a href="#page-3">3</a>
<a href="#section-2">2</a>. Conventions Used in This Document ...............................<a href="#page-3">3</a>
<a href="#section-3">3</a>. LANGUAGE Extension ..............................................<a href="#page-3">3</a>
<a href="#section-3.1">3.1</a>. LANGUAGE Extension Requirements ............................<a href="#page-4">4</a>
<a href="#section-3.2">3.2</a>. LANGUAGE Command ...........................................<a href="#page-4">4</a>
<a href="#section-3.3">3.3</a>. LANGUAGE Response ..........................................<a href="#page-6">6</a>
<a href="#section-3.4">3.4</a>. TRANSLATION Extension to the NAMESPACE Response ............<a href="#page-7">7</a>
<a href="#section-3.5">3.5</a>. Formal Syntax ..............................................<a href="#page-8">8</a>
<a href="#section-4">4</a>. I18NLEVEL=1 and I18NLEVEL=2 Extensions ..........................<a href="#page-9">9</a>
<a href="#section-4.1">4.1</a>. Introduction and Overview ..................................<a href="#page-9">9</a>
<a href="#section-4.2">4.2</a>. Requirements Common to Both I18NLEVEL=1 and I18NLEVEL=2 ....<a href="#page-9">9</a>
<a href="#section-4.3">4.3</a>. I18NLEVEL=1 Extension Requirements ........................<a href="#page-10">10</a>
<a href="#section-4.4">4.4</a>. I18NLEVEL=2 Extension Requirements ........................<a href="#page-10">10</a>
<a href="#section-4.5">4.5</a>. Compatibility Notes .......................................<a href="#page-11">11</a>
<a href="#section-4.6">4.6</a>. Comparators and Character Encodings .......................<a href="#page-11">11</a>
<a href="#section-4.7">4.7</a>. COMPARATOR Command ........................................<a href="#page-13">13</a>
<a href="#section-4.8">4.8</a>. COMPARATOR Response .......................................<a href="#page-14">14</a>
<a href="#section-4.9">4.9</a>. BADCOMPARATOR Response Code ...............................<a href="#page-14">14</a>
<a href="#section-4.10">4.10</a>. Formal Syntax ............................................<a href="#page-14">14</a>
<a href="#section-5">5</a>. Other IMAP Internationalization Issues .........................<a href="#page-15">15</a>
<a href="#section-5.1">5.1</a>. Unicode Userids and Passwords .............................<a href="#page-15">15</a>
<a href="#section-5.2">5.2</a>. UTF-8 Mailbox Names .......................................<a href="#page-15">15</a>
<a href="#section-5.3">5.3</a>. UTF-8 Domains, Addresses, and Mail Headers ................<a href="#page-15">15</a>
<a href="#section-6">6</a>. IANA Considerations ............................................<a href="#page-16">16</a>
<a href="#section-7">7</a>. Security Considerations ........................................<a href="#page-16">16</a>
<a href="#section-8">8</a>. Acknowledgements ...............................................<a href="#page-16">16</a>
9. Relevant Sources of Documents for Internationalized IMAP
Implementations ................................................<a href="#page-17">17</a>
<a href="#section-10">10</a>. Normative References ..........................................<a href="#page-17">17</a>
<a href="#section-11">11</a>. Informative References ........................................<a href="#page-18">18</a>
<span class="grey">Newman, et al. Standards Track [Page 2]</span><span id="page-3" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
This specification defines two IMAP4rev1 [<a href="./rfc3501" title=""INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1"">RFC3501</a>] extensions to
enhance international support. These extensions can be advertised
and implemented separately.
The LANGUAGE extension allows the client to request a suitable
language for protocol error messages and in combination with the
NAMESPACE extension [<a href="./rfc2342" title=""IMAP4 Namespace"">RFC2342</a>] enables namespace translations.
The I18NLEVEL=2 extension allows the client to request a suitable
collation that will modify the behavior of the base specification's
SEARCH command as well as the SORT and THREAD extensions [<a href="#ref-SORT" title=""Internet Message Access Protocol - SORT and THREAD Extensions"">SORT</a>].
This leverages the collation registry [<a href="./rfc4790" title=""Internet Application Protocol Collation Registry"">RFC4790</a>]. The I18NLEVEL=1
extension updates SEARCH/SORT/THREAD to use i;unicode-casemap
comparator, as defined in [<a href="#ref-UCM" title=""i;unicode-casemap - Simple Unicode Collation Algorithm"">UCM</a>]. I18NLEVEL=1 is a simpler version of
I18NLEVEL=2 with no ability to select a different collation.
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Conventions Used in This Document</span>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [<a href="./rfc2119" title=""Key words for use in RFCs to Indicate Requirement Levels"">RFC2119</a>].
The formal syntax uses the Augmented Backus-Naur Form (ABNF)
[<a href="./rfc5234" title=""Augmented BNF for Syntax Specifications: ABNF"">RFC5234</a>] notation including the core rules defined in <a href="#appendix-A">Appendix A</a>.
The UTF-8-related productions are defined in [<a href="./rfc3629" title=""UTF-8, a transformation format of ISO 10646"">RFC3629</a>].
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively. If a single "C:" or "S:" label applies to
multiple lines, then the line breaks between those lines are for
editorial clarity only and are not part of the actual protocol
exchange.
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. LANGUAGE Extension</span>
IMAP allows server responses to include human-readable text that in
many cases needs to be presented to the user. But that text is
limited to US-ASCII by the IMAP specification [<a href="./rfc3501" title=""INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1"">RFC3501</a>] in order to
preserve backwards compatibility with deployed IMAP implementations.
This section specifies a way for an IMAP client to negotiate which
language the server should use when sending human-readable text.
<span class="grey">Newman, et al. Standards Track [Page 3]</span><span id="page-4" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
The LANGUAGE extension only provides a mechanism for altering fixed
server strings such as response text and NAMESPACE folder names.
Assigning localized language aliases to shared mailboxes would be
done with a separate mechanism such as the proposed METADATA
extension (see [<a href="#ref-METADATA" title=""IMAP METADATA Extension"">METADATA</a>]).
<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>. LANGUAGE Extension Requirements</span>
IMAP servers that support this extension MUST list the keyword
LANGUAGE in their CAPABILITY response as well as in the greeting
CAPABILITY data.
A server that advertises this extension MUST use the language
"i-default" as described in [<a href="./rfc2277" title=""IETF Policy on Character Sets and Languages"">RFC2277</a>] as its default language until
another supported language is negotiated by the client. A server
MUST include "i-default" as one of its supported languages. IMAP
servers SHOULD NOT advertise the LANGUAGE extension if they discover
that they only support "i-default".
Clients and servers that support this extension MUST also support the
NAMESPACE extension [<a href="./rfc2342" title=""IMAP4 Namespace"">RFC2342</a>].
The LANGUAGE command is valid in all states. Clients SHOULD issue
LANGUAGE before authentication, since some servers send valuable user
information as part of authentication (e.g., "password is correct,
but expired"). If a security layer (such as SASL or TLS) is
subsequently negotiated by the client, it MUST re-issue the LANGUAGE
command in order to make sure that no previous active attack (if any)
on LANGUAGE negotiation has effect on subsequent error messages.
(See <a href="#section-7">Section 7</a> for a more detailed explanation of the attack.)
<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>. LANGUAGE Command</span>
Arguments: Optional language range arguments.
Response: A possible LANGUAGE response (see <a href="#section-3.3">Section 3.3</a>).
A possible NAMESPACE response (see <a href="#section-3.4">Section 3.4</a>).
Result: OK - Command completed
NO - Could not complete command
BAD - Arguments invalid
The LANGUAGE command requests that human-readable text emitted by the
server be localized to a language matching one of the language range
argument as described by <a href="./rfc4647#section-2">Section 2 of [RFC4647]</a>.
<span class="grey">Newman, et al. Standards Track [Page 4]</span><span id="page-5" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
If the command succeeds, the server will return human-readable
responses in the first supported language specified. These responses
will be in UTF-8 [<a href="./rfc3629" title=""UTF-8, a transformation format of ISO 10646"">RFC3629</a>]. The server MUST send a LANGUAGE response
specifying the language used, and the change takes effect immediately
after the LANGUAGE response.
If the command fails, the server continues to return human-readable
responses in the language it was previously using.
The special "default" language range argument indicates a request to
use a language designated as preferred by the server administrator.
The preferred language MAY vary based on the currently active user.
If a language range does not match a known language tag exactly but
does match a language by the rules of [<a href="./rfc4647" title=""Matching of Language Tags"">RFC4647</a>], the server MUST send
an untagged LANGUAGE response indicating the language selected.
If there aren't any arguments, the server SHOULD send an untagged
LANGUAGE response listing the languages it supports. If the server
is unable to enumerate the list of languages it supports it MAY
return a tagged NO response to the enumeration request. If, after
receiving a LANGUAGE request, the server discovers that it doesn't
support any language other than i-default, it MUST return a tagged NO
response to the enumeration request.
< The server defaults to using English i-default responses until
the user explicitly changes the language. >
C: A001 LOGIN KAREN PASSWORD
S: A001 OK LOGIN completed
< Client requested MUL language, which no server supports. >
C: A002 LANGUAGE MUL
S: A002 NO Unsupported language MUL
< A LANGUAGE command with no arguments is a request to enumerate
the list of languages the server supports. >
C: A003 LANGUAGE
S: * LANGUAGE (EN DE IT i-default)
S: A003 OK Supported languages have been enumerated
C: B001 LANGUAGE
S: B001 NO Server is unable to enumerate supported languages
<span class="grey">Newman, et al. Standards Track [Page 5]</span><span id="page-6" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
< Once the client changes the language, all responses will be in
that language starting after the LANGUAGE response. Note that
this includes the NAMESPACE response. Because RFCs are in US-
ASCII, this document uses an ASCII transcription rather than
UTF-8 text, e.g., "ue" in the word "ausgefuehrt" >
C: C001 LANGUAGE DE
S: * LANGUAGE (DE)
S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION"
("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
"TRANSLATION" ("Gemeinsame Postf&AM8-cher/")))
S: C001 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
< If a server does not support the requested primary language,
responses will continue to be returned in the current language
the server is using. >
C: D001 LANGUAGE FR
S: D001 NO Diese Sprache ist nicht unterstuetzt
C: D002 LANGUAGE DE-IT
S: * LANGUAGE (DE-IT)
S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION"
("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
"TRANSLATION" ("Gemeinsame Postf&AM8-cher/")))
S: D002 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
C: D003 LANGUAGE "default"
S: * LANGUAGE (DE)
S: D003 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
< Server does not speak French, but does speak English. User
speaks Canadian French and Canadian English. >
C: E001 LANGUAGE FR-CA EN-CA
S: * LANGUAGE (EN)
S: E001 OK Now speaking English
<span class="h3"><a class="selflink" id="section-3.3" href="#section-3.3">3.3</a>. LANGUAGE Response</span>
Contents: A list of one or more language tags.
The LANGUAGE response occurs as a result of a LANGUAGE command. A
LANGUAGE response with a list containing a single language tag
indicates that the server is now using that language. A LANGUAGE
response with a list containing multiple language tags indicates the
server is communicating a list of available languages to the client,
and no change in the active language has been made.
<span class="grey">Newman, et al. Standards Track [Page 6]</span><span id="page-7" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
<span class="h3"><a class="selflink" id="section-3.4" href="#section-3.4">3.4</a>. TRANSLATION Extension to the NAMESPACE Response</span>
If localized representations of the namespace prefixes are available
in the selected language, the server SHOULD include these in the
TRANSLATION extension to the NAMESPACE response.
The TRANSLATION extension to the NAMESPACE response returns a single
string, containing the modified UTF-7 [<a href="./rfc3501" title=""INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1"">RFC3501</a>] encoded translation
of the namespace prefix. It is the responsibility of the client to
convert between the namespace prefix and the translation of the
namespace prefix when presenting mailbox names to the user.
In this example, a server supports the IMAP4 NAMESPACE command. It
uses no prefix to the user's Personal Namespace, a prefix of "Other
Users" to its Other Users' Namespace, and a prefix of "Public
Folders" to its only Shared Namespace. Since a client will often
display these prefixes to the user, the server includes a translation
of them that can be presented to the user.
C: A001 LANGUAGE DE-IT
S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION"
("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
"TRANSLATION" ("Gemeinsame Postf&AM8-cher/")))
S: A001 OK LANGUAGE-Befehl ausgefuehrt
<span class="grey">Newman, et al. Standards Track [Page 7]</span><span id="page-8" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
<span class="h3"><a class="selflink" id="section-3.5" href="#section-3.5">3.5</a>. Formal Syntax</span>
The following syntax specification inherits ABNF [<a href="./rfc5234" title=""Augmented BNF for Syntax Specifications: ABNF"">RFC5234</a>] rules from
IMAP4rev1 [<a href="./rfc3501" title=""INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1"">RFC3501</a>], IMAP4 Namespace [<a href="./rfc2342" title=""IMAP4 Namespace"">RFC2342</a>], Tags for the
Identifying Languages [<a href="./rfc4646" title=""Tags for Identifying Languages"">RFC4646</a>], UTF-8 [<a href="./rfc3629" title=""UTF-8, a transformation format of ISO 10646"">RFC3629</a>], and Collected
Extensions to IMAP4 ABNF [<a href="./rfc4466" title=""Collected Extensions to IMAP4 ABNF"">RFC4466</a>].
command-any =/ language-cmd
; LANGUAGE command is valid in all states
language-cmd = "LANGUAGE" *(SP lang-range-quoted)
response-payload =/ language-data
language-data = "LANGUAGE" SP "(" lang-tag-quoted *(SP
lang-tag-quoted) ")"
namespace-trans = SP DQUOTE "TRANSLATION" DQUOTE SP "(" string ")"
; the string is encoded in Modified UTF-7.
; this is a subset of the syntax permitted by
; the Namespace-Response-Extension rule in [<a href="./rfc4466" title=""Collected Extensions to IMAP4 ABNF"">RFC4466</a>]
lang-range-quoted = astring
; Once any literal wrapper or quoting is removed, this
; follows the language-range rule in [<a href="./rfc4647" title=""Matching of Language Tags"">RFC4647</a>]
lang-tag-quoted = astring
; Once any literal wrapper or quoting is removed, this follows
; the Language-Tag rule in [<a href="./rfc4646" title=""Tags for Identifying Languages"">RFC4646</a>]
resp-text = ["[" resp-text-code "]" SP ] UTF8-TEXT-CHAR
*(UTF8-TEXT-CHAR / "[")
; After the server is changed to a language other than
; i-default, this resp-text rule replaces the resp-text
; rule from [<a href="./rfc3501" title=""INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1"">RFC3501</a>].
UTF8-TEXT-CHAR = %x20-5A / %x5C-7E / UTF8-2 / UTF8-3 / UTF8-4
; UTF-8 excluding 7-bit control characters and "["
<span class="grey">Newman, et al. Standards Track [Page 8]</span><span id="page-9" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. I18NLEVEL=1 and I18NLEVEL=2 Extensions</span>
<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a>. Introduction and Overview</span>
IMAP4rev1 [<a href="./rfc3501" title=""INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1"">RFC3501</a>] includes the SEARCH command that can be used to
locate messages matching criteria including human-readable text. The
SORT extension [<a href="#ref-SORT" title=""Internet Message Access Protocol - SORT and THREAD Extensions"">SORT</a>] to IMAP allows the client to ask the server to
determine the order of messages based on criteria including human-
readable text. These mechanisms require the ability to support non-
English search and sort functions.
<a href="#section-4">Section 4</a> defines two IMAP extensions for internationalizing IMAP
SEARCH, SORT, and THREAD [<a href="#ref-SORT" title=""Internet Message Access Protocol - SORT and THREAD Extensions"">SORT</a>] using the comparator framework
[<a href="./rfc4790" title=""Internet Application Protocol Collation Registry"">RFC4790</a>].
The I18NLEVEL=1 extension updates SEARCH/SORT/THREAD to use
i;unicode-casemap comparator, as defined in [<a href="#ref-UCM" title=""i;unicode-casemap - Simple Unicode Collation Algorithm"">UCM</a>]. See Sections <a href="#section-4.2">4.2</a>
and 4.3 for more details.
The I18NLEVEL=2 extension is a superset of the I18NLEVEL=1 extension.
It adds to I18NLEVEL=1 extension the ability to determine the active
comparator (see definition below) and to negotiate use of comparators
using the COMPARATOR command. It also adds the COMPARATOR response
that indicates the active comparator and possibly other available
comparators. See Sections <a href="#section-4.2">4.2</a> and <a href="#section-4.4">4.4</a> for more details.
<span class="h3"><a class="selflink" id="section-4.2" href="#section-4.2">4.2</a>. Requirements Common to Both I18NLEVEL=1 and I18NLEVEL=2</span>
The term "default comparator" refers to the comparator that is used
by SEARCH and SORT absent any negotiation using the COMPARATOR
command (see <a href="#section-4.7">Section 4.7</a>). The term "active comparator" refers to
the comparator which will be used within a session, e.g., by SEARCH
and SORT. The COMPARATOR command is used to change the active
comparator.
The active comparator applies to the following SEARCH keys: "BCC",
"BODY", "CC", "FROM", "SUBJECT", "TEXT", "TO", and "HEADER". If the
server also advertises the "SORT" extension, then the active
comparator applies to the following SORT keys: "CC", "FROM",
"SUBJECT", and "TO". If the server advertises THREAD=ORDEREDSUBJECT,
then the active comparator applies to the ORDEREDSUBJECT threading
algorithm. If the server advertises THREAD=REFERENCES, then the
active comparator applies to the subject field comparisons done by
REFERENCES threading algorithm. Future extensions may choose to
apply the active comparator to their SEARCH keys.
<span class="grey">Newman, et al. Standards Track [Page 9]</span><span id="page-10" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
For SORT and THREAD, the pre-processing necessary to extract the base
subject text from a Subject header occurs prior to the application of
a comparator.
A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST
implement the i;unicode-casemap comparator, as defined in [<a href="#ref-UCM" title=""i;unicode-casemap - Simple Unicode Collation Algorithm"">UCM</a>].
A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST
support UTF-8 as a SEARCH charset.
<span class="h3"><a class="selflink" id="section-4.3" href="#section-4.3">4.3</a>. I18NLEVEL=1 Extension Requirements</span>
An IMAP server that satisfies all requirements specified in Sections
4.2 and 4.6 (and that doesn't support/advertise any other
I18NLEVEL=<n> extension, where n > 1) MUST list the keyword
I18NLEVEL=1 in its CAPABILITY data once IMAP enters the authenticated
state, and MAY list that keyword in other states.
<span class="h3"><a class="selflink" id="section-4.4" href="#section-4.4">4.4</a>. I18NLEVEL=2 Extension Requirements</span>
An IMAP server that satisfies all requirements specified in Sections
4.2, 4.4, and 4.6-4.10 (and that doesn't support/advertise any other
I18NLEVEL=<n> extension, where n > 2) MUST list the keyword
I18NLEVEL=2 in its CAPABILITY data once IMAP enters the authenticated
state, and MAY list that keyword in other states.
A server that advertises this extension MUST implement the
i;unicode-casemap comparator, as defined in [<a href="#ref-UCM" title=""i;unicode-casemap - Simple Unicode Collation Algorithm"">UCM</a>]. It MAY implement
other comparators from the IANA registry established by [<a href="./rfc4790" title=""Internet Application Protocol Collation Registry"">RFC4790</a>].
See also <a href="#section-4.5">Section 4.5</a> of this document.
A server that advertises this extension SHOULD use i;unicode-casemap
as the default comparator. (Note that i;unicode-casemap is the
default comparator for I18NLEVEL=1, but not necessarily the default
for I18NLEVEL=2.) The selection of the default comparator MAY be
adjustable by the server administrator, and MAY be sensitive to the
current user. Once the IMAP connection enters authenticated state,
the default comparator MUST remain static for the remainder of that
connection.
Note that since SEARCH uses the substring operation, IMAP servers can
only implement collations that offer the substring operation (see
<a href="./rfc4790#section-4.2.2">[RFC4790], Section 4.2.2</a>). Since SORT uses the ordering operation
(which in turn uses the equality operation), IMAP servers that
advertise the SORT extension can only implement collations that offer
all three operations (see [<a href="./rfc4790" title=""Internet Application Protocol Collation Registry"">RFC4790</a>], Sections <a href="#section-4.2.2">4.2.2</a>-<a href="#section-4.2.4">4.2.4</a>).
<span class="grey">Newman, et al. Standards Track [Page 10]</span><span id="page-11" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
If the active collation does not provide the operations needed by an
IMAP command, the server MUST respond with a tagged BAD.
<span class="h3"><a class="selflink" id="section-4.5" href="#section-4.5">4.5</a>. Compatibility Notes</span>
Several server implementations deployed prior to the publication of
this specification comply with I18NLEVEL=1 (see <a href="#section-4.3">Section 4.3</a>), but do
not advertise that. Other legacy servers use the i;ascii-casemap
comparator (see [<a href="./rfc4790" title=""Internet Application Protocol Collation Registry"">RFC4790</a>]).
There is no good way for a client to know which comparator a legacy
server uses. If the client has to assume the worst, it may end up
doing expensive local operations to obtain i;unicode-casemap
comparisons even though the server implements it.
Legacy server implementations which comply with I18NLEVEL=1 should be
updated to advertise I18NLEVEL=1. All server implementations should
eventually be updated to comply with the I18NLEVEL=2 extension.
<span class="h3"><a class="selflink" id="section-4.6" href="#section-4.6">4.6</a>. Comparators and Character Encodings</span>
<a href="./rfc3501#section-6.4.4">RFC 3501, Section 6.4.4</a>, says:
In all search keys that use strings, a message matches the key
if the string is a substring of the field. The matching is
case-insensitive.
When performing the SEARCH operation, the active comparator is
applied instead of the case-insensitive matching specified above.
An IMAP server which performs collation operations (e.g., as part of
commands such as SEARCH, SORT, and THREAD) does so according to the
following procedure:
(a) MIME encoding (for example, see [<a href="./rfc2047" title=""MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text"">RFC2047</a>] for headers and
[<a href="./rfc2045" title=""Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies"">RFC2045</a>] for body parts) MUST be removed in the texts being
collated.
If MIME encoding removal fails for a message (e.g., a body part
of the message has an unsupported Content-Transfer-Encoding, uses
characters not allowed by the Content-Transfer-Encoding, etc.),
the collation of this message is undefined by this specification,
and is handled in an implementation-dependent manner.
(b) The decoded text from (a) MUST be converted to the charset
expected by the active comparator.
<span class="grey">Newman, et al. Standards Track [Page 11]</span><span id="page-12" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
(c) For the substring operation:
If step (b) failed (e.g., the text is in an unknown charset,
contains a sequence that is not valid according in that charset,
etc.), the original decoded text from (a) (i.e., before the
charset conversion attempt) is collated using the i;octet
comparator (see [<a href="./rfc4790" title=""Internet Application Protocol Collation Registry"">RFC4790</a>]).
If step (b) was successful, the converted text from (b) is
collated according to the active comparator.
For the ordering operation:
All strings that were successfully converted by step (b) are
separated from all strings that failed step (b). Strings in each
group are collated independently. All strings successfully
converted by step (b) are then validated by the active
comparator. Strings that pass validation are collated using the
active comparator. All strings that either fail step (b) or fail
the active collation's validity operation are collated (after
applying step (a)) using the i;octet comparator (see [<a href="./rfc4790" title=""Internet Application Protocol Collation Registry"">RFC4790</a>]).
The resulting sorted list is produced by appending all collated
"failed" strings after all strings collated using the active
comparator.
Example: The following example demonstrates ordering of 4
different strings using the i;unicode-casemap [<a href="#ref-UCM" title=""i;unicode-casemap - Simple Unicode Collation Algorithm"">UCM</a>] comparator.
Strings are represented using hexadecimal notation used by ABNF
[<a href="./rfc5234" title=""Augmented BNF for Syntax Specifications: ABNF"">RFC5234</a>].
(1) %xD0 %xC0 %xD0 %xBD %xD0 %xB4 %xD1 %x80 %xD0 %xB5
%xD0 %xB9 (labeled with charset=UTF-8)
(2) %xD1 %x81 %xD0 %x95 %xD0 %xA0 %xD0 %x93 %xD0 %x95
%xD0 %x99 (labeled with charset=UTF-8)
(3) %xD0 %x92 %xD0 %xB0 %xD1 %x81 %xD0 %xB8 %xD0 %xBB
%xD0 %xB8 %xFF %xB9 (labeled with charset=UTF-8)
(4) %xE1 %xCC %xC5 %xCB %xD3 %xC5 %xCA (labeled with
charset=KOI8-R)
Step (b) will convert string (4) to the following sequence of
octets (in UTF-8):
%xD0 %x90 %xD0 %xBB %xD0 %xB5 %xD0 %xBA %xD1 %x81 %xD0
%xB5 %xD0 %xB9
and will reject strings (1) and (3), as they contain octets not
allowed in charset=UTF-8.
<span class="grey">Newman, et al. Standards Track [Page 12]</span><span id="page-13" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
After that, using the i;unicode-casemap collation, string (4)
will collate before string (2). Using the i;octet collation on
the original strings, string (3) will collate before string (1).
So the final ordering is as follows: (4) (2) (3) (1).
If the substring operation (e.g., IMAP SEARCH) of the active
comparator returns the "undefined" result (see <a href="./rfc4790#section-4.2.3">Section 4.2.3 of
[RFC4790]</a>) for either the text specified in the SEARCH command or the
message text, then the operation is repeated on the result of step
(a) using the i;octet comparator.
The ordering operation (e.g., IMAP SORT and THREAD) SHOULD collate
the following together: strings encoded using unknown or invalid
character encodings, strings in unrecognized charsets, and invalid
input (as defined by the active collation).
<span class="h3"><a class="selflink" id="section-4.7" href="#section-4.7">4.7</a>. COMPARATOR Command</span>
Arguments: Optional comparator order arguments.
Response: A possible COMPARATOR response (see <a href="#section-4.8">Section 4.8</a>).
Result: OK - Command completed
NO - No matching comparator found
BAD - Arguments invalid
The COMPARATOR command is valid in authenticated and selected states.
The COMPARATOR command is used to determine or change the active
comparator. When issued with no arguments, it results in a
COMPARATOR response indicating the currently active comparator.
When issued with one or more comparator arguments, it changes the
active comparator as directed. (If more than one installed
comparator is matched by an argument, the first argument wins.) The
COMPARATOR response lists all matching comparators if more than one
matches the specified patterns.
The argument "default" refers to the server's default comparator.
Otherwise, each argument is a collation specification as defined in
the Internet Application Protocol Comparator Registry [<a href="./rfc4790" title=""Internet Application Protocol Collation Registry"">RFC4790</a>].
< The client requests activating a Czech comparator if possible,
or else a generic international comparator which it considers
suitable for Czech. The server picks the first supported
comparator. >
<span class="grey">Newman, et al. Standards Track [Page 13]</span><span id="page-14" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
C: A001 COMPARATOR "cz;*" i;basic
S: * COMPARATOR i;basic
S: A001 OK Will use i;basic for collation
<span class="h3"><a class="selflink" id="section-4.8" href="#section-4.8">4.8</a>. COMPARATOR Response</span>
Contents: The active comparator. An optional list of available
matching comparators
The COMPARATOR response occurs as a result of a COMPARATOR command.
The first argument in the comparator response is the name of the
active comparator. The second argument is a list of comparators
which matched any of the arguments to the COMPARATOR command and is
present only if more than one match is found.
<span class="h3"><a class="selflink" id="section-4.9" href="#section-4.9">4.9</a>. BADCOMPARATOR Response Code</span>
This response code SHOULD be returned as a result of server failing
an IMAP command (returning NO), when the server knows that none of
the specified comparators match the requested comparator(s).
<span class="h3"><a class="selflink" id="section-4.10" href="#section-4.10">4.10</a>. Formal Syntax</span>
The following syntax specification inherits ABNF [<a href="./rfc5234" title=""Augmented BNF for Syntax Specifications: ABNF"">RFC5234</a>] rules from
IMAP4rev1 [<a href="./rfc3501" title=""INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1"">RFC3501</a>] and the Internet Application Protocol Comparator
Registry [<a href="./rfc4790" title=""Internet Application Protocol Collation Registry"">RFC4790</a>].
command-auth =/ comparator-cmd
resp-text-code =/ "BADCOMPARATOR"
comparator-cmd = "COMPARATOR" *(SP comp-order-quoted)
response-payload =/ comparator-data
comparator-data = "COMPARATOR" SP comp-sel-quoted [SP "("
comp-id-quoted *(SP comp-id-quoted) ")"]
comp-id-quoted = astring
; Once any literal wrapper or quoting is removed, this
; follows the collation-id rule from [<a href="./rfc4790" title=""Internet Application Protocol Collation Registry"">RFC4790</a>]
comp-order-quoted = astring
; Once any literal wrapper or quoting is removed, this
; follows the collation-order rule from [<a href="./rfc4790" title=""Internet Application Protocol Collation Registry"">RFC4790</a>]
<span class="grey">Newman, et al. Standards Track [Page 14]</span><span id="page-15" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
comp-sel-quoted = astring
; Once any literal wrapper or quoting is removed, this
; follows the collation-selected rule from [<a href="./rfc4790" title=""Internet Application Protocol Collation Registry"">RFC4790</a>]
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. Other IMAP Internationalization Issues</span>
The following sections provide an overview of various other IMAP
internationalization issues. These issues are not resolved by this
specification, but could be resolved by other standards work, such as
that being done by the EAI working group (see [<a href="#ref-IMAP-EAI" title=""IMAP Support for UTF-8"">IMAP-EAI</a>]).
<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>. Unicode Userids and Passwords</span>
IMAP4rev1 currently restricts the userid and password fields of the
LOGIN command to US-ASCII. The "userid" and "password" fields of the
IMAP LOGIN command are restricted to US-ASCII only until a future
standards track RFC states otherwise. Servers are encouraged to
validate both fields to make sure they conform to the formal syntax
of UTF-8 and to reject the LOGIN command if that syntax is violated.
Servers MAY reject the LOGIN command if either the "userid" or
"password" field contains an octet with the highest bit set.
When AUTHENTICATE is used, some servers may support userids and
passwords in Unicode [<a href="./rfc3490" title=""Internationalizing Domain Names in Applications (IDNA)"">RFC3490</a>] since SASL (see [<a href="./rfc4422" title=""Simple Authentication and Security Layer (SASL)"">RFC4422</a>]) allows
that. However, such userids cannot be used as part of email
addresses.
<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>. UTF-8 Mailbox Names</span>
The modified UTF-7 mailbox naming convention described in <a href="./rfc3501#section-5.1.3">Section</a>
<a href="./rfc3501#section-5.1.3">5.1.3 of RFC 3501</a> is best viewed as an transition from the status quo
in 1996 when modified UTF-7 was first specified. At that time, there
was widespread unofficial use of local character sets such as ISO-
8859-1 and Shift-JIS for non-ASCII mailbox names, with resultant
non-interoperability.
The requirements in <a href="./rfc3501#section-5.1">Section 5.1 of RFC 3501</a> are very important if
we're ever going to be able to deploy UTF-8 mailbox names. Servers
are encouraged to enforce them.
<span class="h3"><a class="selflink" id="section-5.3" href="#section-5.3">5.3</a>. UTF-8 Domains, Addresses, and Mail Headers</span>
There is now an IETF standard for "Internationalizing Domain Names in
Applications (IDNA)" [<a href="./rfc3490" title=""Internationalizing Domain Names in Applications (IDNA)"">RFC3490</a>]. While IMAP clients are free to
support this standard, an argument can be made that it would be
helpful to simple clients if the IMAP server could perform this
conversion (the same argument would apply to MIME header encoding
<span class="grey">Newman, et al. Standards Track [Page 15]</span><span id="page-16" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
[<a href="./rfc2047" title=""MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text"">RFC2047</a>]). However, it would be unwise to move forward with such
work until the work in progress to define the format of international
email addresses is complete.
<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. IANA Considerations</span>
IANA added LANGUAGE, I18NLEVEL=1, and I18NLEVEL=2 to the IMAP4
Capabilities Registry.
<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>. Security Considerations</span>
The LANGUAGE extension makes a new command available in "Not
Authenticated" state in IMAP. Some IMAP implementations run with
root privilege when the server is in "Not Authenticated" state and do
not revoke that privilege until after authentication is complete.
Such implementations are particularly vulnerable to buffer overflow
security errors at this stage and need to implement parsing of this
command with extra care.
A LANGUAGE command issued prior to activation of a security layer is
subject to an active attack that suppresses or modifies the
negotiation, and thus makes STARTTLS or authentication error messages
more difficult to interpret. This is not a new attack as the error
messages themselves are subject to active attack. Clients MUST re-
issue the LANGUAGE command once a security layer is active, in order
to prevent this attack from impacting subsequent protocol operations.
LANGUAGE, I18NLEVEL=1, and I18NLEVEL=2 extensions use the UTF-8
charset; thus, the security considerations for UTF-8 [<a href="./rfc3629" title=""UTF-8, a transformation format of ISO 10646"">RFC3629</a>] are
relevant. However, neither uses UTF-8 for identifiers, so the most
serious concerns do not apply.
<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>. Acknowledgements</span>
The LANGUAGE extension is based on a previous document by Mike
Gahrns, a substantial portion of the text in that section was written
by him. Many people have participated in discussions about an IMAP
Language extension in the various fora of the IETF and Internet
working groups, so any list of contributors is bound to be
incomplete. However, the authors would like to thank Andrew McCown
for early work on the original proposal, John Myers for suggestions
regarding the namespace issue, along with Jutta Degener, Mark
Crispin, Mark Pustilnik, Larry Osterman, Cyrus Daboo, Martin Duerst,
Timo Sirainen, Ben Campbell, and Magnus Nystrom for their many
suggestions that have been incorporated into this document.
Initial discussion of the I18NLEVEL=2 extension involved input from
Mark Crispin and other participants of the IMAP Extensions WG.
<span class="grey">Newman, et al. Standards Track [Page 16]</span><span id="page-17" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>. Relevant Sources of Documents for Internationalized IMAP</span>
<span class="h2"> Implementations</span>
This is a non-normative list of sources to consider when implementing
i18n-aware IMAP software.
o The LANGUAGE and I18NLEVEL=2 extensions to IMAP (this
specification).
o The 8-bit rules for mailbox naming in <a href="./rfc3501#section-5.1">Section 5.1 of RFC 3501</a>.
o The Mailbox International Naming Convention in <a href="./rfc3501#section-5.1.3">Section 5.1.3 of
RFC 3501</a>.
o MIME [<a href="./rfc2045" title=""Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies"">RFC2045</a>] for message bodies.
o MIME header encoding [<a href="./rfc2047" title=""MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text"">RFC2047</a>] for message headers.
o The IETF EAI working group.
o MIME Parameter Value and Encoded Word Extensions [<a href="./rfc2231" title=""MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations"">RFC2231</a>] for
filenames. Quality IMAP server implementations will
automatically combine multipart parameters when generating the
BODYSTRUCTURE. There is also some deployed non-standard use of
MIME header encoding inside double quotes for filenames.
o IDNA [<a href="./rfc3490" title=""Internationalizing Domain Names in Applications (IDNA)"">RFC3490</a>] and punycode [<a href="./rfc3492" title=""Punycode: A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA)"">RFC3492</a>] for domain names
(currently only relevant to IMAP clients).
o The UTF-8 charset [<a href="./rfc3629" title=""UTF-8, a transformation format of ISO 10646"">RFC3629</a>].
o The IETF policy on Character Sets and Languages [<a href="./rfc2277" title=""IETF Policy on Character Sets and Languages"">RFC2277</a>].
<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a>. Normative References</span>
[<a id="ref-RFC2119">RFC2119</a>] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.
[<a id="ref-RFC2277">RFC2277</a>] Alvestrand, H., "IETF Policy on Character Sets and
Languages", <a href="https://www.rfc-editor.org/bcp/bcp18">BCP 18</a>, <a href="./rfc2277">RFC 2277</a>, January 1998.
[<a id="ref-RFC2342">RFC2342</a>] Gahrns, M. and C. Newman, "IMAP4 Namespace", <a href="./rfc2342">RFC 2342</a>, May
1998.
[<a id="ref-RFC3501">RFC3501</a>] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", <a href="./rfc3501">RFC 3501</a>, March 2003.
<span class="grey">Newman, et al. Standards Track [Page 17]</span><span id="page-18" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
[<a id="ref-RFC3629">RFC3629</a>] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, <a href="./rfc3629">RFC 3629</a>, November 2003.
[<a id="ref-RFC5234">RFC5234</a>] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, <a href="./rfc5234">RFC 5234</a>, January
2008.
[<a id="ref-RFC4422">RFC4422</a>] Melnikov, A., Ed., and K. Zeilenga, Ed., "Simple
Authentication and Security Layer (SASL)", <a href="./rfc4422">RFC 4422</a>, June
2006.
[<a id="ref-RFC4466">RFC4466</a>] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4
ABNF", <a href="./rfc4466">RFC 4466</a>, April 2006.
[<a id="ref-RFC4646">RFC4646</a>] Phillips, A. and M. Davis, "Tags for Identifying
Languages", <a href="https://www.rfc-editor.org/bcp/bcp47">BCP 47</a>, <a href="./rfc4646">RFC 4646</a>, September 2006.
[<a id="ref-RFC4647">RFC4647</a>] Phillips, A. and M. Davis, "Matching of Language Tags",
<a href="https://www.rfc-editor.org/bcp/bcp47">BCP 47</a>, <a href="./rfc4647">RFC 4647</a>, September 2006.
[<a id="ref-RFC4790">RFC4790</a>] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet
Application Protocol Collation Registry", <a href="./rfc4790">RFC 4790</a>, March
2007.
[<a id="ref-SORT">SORT</a>] Crispin, M. and K. Murchison, "Internet Message Access
Protocol - SORT and THREAD Extensions", <a href="./rfc5256">RFC 5256</a>, June
2008.
[<a id="ref-UCM">UCM</a>] Crispin, M., "i;unicode-casemap - Simple Unicode Collation
Algorithm", <a href="./rfc5051">RFC 5051</a>, October 2007.
[<a id="ref-RFC2045">RFC2045</a>] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", <a href="./rfc2045">RFC 2045</a>, November 1996.
[<a id="ref-RFC2047">RFC2047</a>] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions for Non-ASCII Text",
<a href="./rfc2047">RFC 2047</a>, November 1996.
<span class="h2"><a class="selflink" id="section-11" href="#section-11">11</a>. Informative References</span>
[<a id="ref-RFC2231">RFC2231</a>] Freed, N. and K. Moore, "MIME Parameter Value and Encoded
Word Extensions: Character Sets, Languages, and
Continuations", <a href="./rfc2231">RFC 2231</a>, November 1997.
[<a id="ref-RFC3490">RFC3490</a>] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
<a href="./rfc3490">RFC 3490</a>, March 2003.
<span class="grey">Newman, et al. Standards Track [Page 18]</span><span id="page-19" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
[<a id="ref-RFC3492">RFC3492</a>] Costello, A., "Punycode: A Bootstring encoding of Unicode
for Internationalized Domain Names in Applications
(IDNA)", <a href="./rfc3492">RFC 3492</a>, March 2003.
[<a id="ref-METADATA">METADATA</a>] Daboo, C., <a style="text-decoration: none" href='https://www.google.com/search?sitesearch=datatracker.ietf.org%2Fdoc%2Fhtml%2F&q=inurl:draft-+%22IMAP+METADATA+Extension%22'>"IMAP METADATA Extension"</a>, Work in Progress,
April 2008.
[<a id="ref-IMAP-EAI">IMAP-EAI</a>] Resnick, P., and C. Newman, <a style="text-decoration: none" href='https://www.google.com/search?sitesearch=datatracker.ietf.org%2Fdoc%2Fhtml%2F&q=inurl:draft-+%22IMAP+Support+for+UTF-8%22'>"IMAP Support for UTF-8"</a>, Work
in Progress, November 2007.
Authors' Addresses
Chris Newman
Sun Microsystems
3401 Centrelake Dr., Suite 410
Ontario, CA 91761
US
EMail: [email protected]
Arnt Gulbrandsen
Oryx Mail Systems GmbH
Schweppermannstr. 8
D-81671 Muenchen
Germany
EMail: [email protected]
Fax: +49 89 4502 9758
Alexey Melnikov
Isode Limited
5 Castle Business Village, 36 Station Road,
Hampton, Middlesex, TW12 2BX, UK
EMail: [email protected]
<span class="grey">Newman, et al. Standards Track [Page 19]</span><span id="page-20" ></span>
<span class="grey"><a href="./rfc5255">RFC 5255</a> IMAP Internationalization June 2008</span>
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a>, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and <a href="https://www.rfc-editor.org/bcp/bcp79">BCP 79</a>.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
<a href="http://www.ietf.org/ipr">http://www.ietf.org/ipr</a>.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
[email protected].
Newman, et al. Standards Track [Page 20]
Annotations
Select text to annotate