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+Internet Engineering Task Force (IETF)                      F. Ellermann
+Request for Comments: 5538                                         xyzzy
+Category: Standards Track                                     April 2010
+ISSN: 2070-1721
+
+
+                   The 'news' and 'nntp' URI Schemes
+
+Abstract
+
+   This memo specifies the 'news' and 'nntp' Uniform Resource Identifier
+   (URI) schemes that were originally defined in RFC 1738.  The purpose
+   of this document is to allow RFC 1738 to be made obsolete while
+   keeping the information about these schemes on the Standards Track.
+
+Status of This Memo
+
+   This is an Internet Standards Track document.
+
+   This document is a product of the Internet Engineering Task Force
+   (IETF).  It represents the consensus of the IETF community.  It has
+   received public review and has been approved for publication by the
+   Internet Engineering Steering Group (IESG).  Further information on
+   Internet Standards is available in Section 2 of RFC 5741.
+
+   Information about the current status of this document, any errata,
+   and how to provide feedback on it may be obtained at
+   http://www.rfc-editor.org/info/5538.
+
+Copyright Notice
+
+   Copyright (c) 2010 IETF Trust and the persons identified as the
+   document authors.  All rights reserved.
+
+   This document is subject to BCP 78 and the IETF Trust's Legal
+   Provisions Relating to IETF Documents
+   (http://trustee.ietf.org/license-info) in effect on the date of
+   publication of this document.  Please review these documents
+   carefully, as they describe your rights and restrictions with respect
+   to this document.  Code Components extracted from this document must
+   include Simplified BSD License text as described in Section 4.e of
+   the Trust Legal Provisions and are provided without warranty as
+   described in the Simplified BSD License.
+
+   This document may contain material from IETF Documents or IETF
+   Contributions published or made publicly available before November
+   10, 2008.  The person(s) controlling the copyright in some of this
+   material may not have granted the IETF Trust the right to allow
+
+
+
+Ellermann                    Standards Track                    [Page 1]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+   modifications of such material outside the IETF Standards Process.
+   Without obtaining an adequate license from the person(s) controlling
+   the copyright in such materials, this document may not be modified
+   outside the IETF Standards Process, and derivative works of it may
+   not be created outside the IETF Standards Process, except to format
+   it for publication as an RFC or to translate it into languages other
+   than English.
+
+Table of Contents
+
+   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
+   2.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  3
+     2.1.  'nntp' URIs  . . . . . . . . . . . . . . . . . . . . . . .  3
+     2.2.  'news' URIs  . . . . . . . . . . . . . . . . . . . . . . .  4
+     2.3.  Query Parts, Fragments, and Normalization  . . . . . . . .  5
+   3.  Syntax of 'nntp' URIs  . . . . . . . . . . . . . . . . . . . .  5
+   4.  Syntax of 'news' URIs  . . . . . . . . . . . . . . . . . . . .  6
+   5.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  7
+   6.  Internationalization Considerations  . . . . . . . . . . . . .  8
+   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
+   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
+     8.1.  'snews' URIs . . . . . . . . . . . . . . . . . . . . . . .  9
+     8.2.  'news-message-ID' Access Type  . . . . . . . . . . . . . . 10
+   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
+     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
+     9.2.  Informative References . . . . . . . . . . . . . . . . . . 11
+   Appendix A.  Collected ABNF  . . . . . . . . . . . . . . . . . . . 13
+   Appendix B.  Detailed Example  . . . . . . . . . . . . . . . . . . 13
+
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+Ellermann                    Standards Track                    [Page 2]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+1.  Introduction
+
+   The first definition for many URI schemes appears in [RFC1738].  This
+   memo extracts the 'news' and 'nntp' URI schemes from it to allow that
+   material to remain on the Standards Track if [RFC1738] is moved to
+   "historic" status.  It belongs to a series of similar documents like
+   [RFC4156], [RFC4157], [RFC4248], and [RFC4266], which are discussed
+   on the <mailto:uri@w3.org> list.
+
+   The definitions for the 'news' and 'nntp' URI schemes given here are
+   updates from [RFC1738] based on modern usage of these schemes.  This
+   memo intentionally limits its description of the 'news' URI scheme to
+   essential features supposed to work with "any browser" and Network
+   News Transfer Protocol (NNTP) server.
+
+   [RFC3986] specifies how to define schemes for URIs; it also explains
+   the term "Uniform Resource Locator" (URL).  The Network News Transfer
+   Protocol (NNTP) is specified in [RFC3977].  The Netnews Article
+   Format is defined in [RFC5536].
+
+   The key word "MUST" in this memo is to be interpreted as described in
+   [RFC2119].  UTF-8 is specified in [RFC3629].  The syntax uses the
+   ABNF defined in [RFC5234].
+
+2.  Background
+
+   The 'news' and 'nntp' URI schemes identify resources on an NNTP
+   server, individual articles, individual newsgroups, or sets of
+   newsgroups.
+
+   User agents like Web browsers supporting these schemes use the NNTP
+   protocol to access the corresponding resources.  The details of how
+   they do this, e.g., employing a separate or integrated newsreader,
+   depend on the implementation.  The default <port> associated with
+   NNTP in [RFC3977] is 119.
+
+2.1.  'nntp' URIs
+
+   The 'nntp' URI scheme identifies articles in a newsgroup on a
+   specific NNTP server.  In [RFC3986] terminology, this means that
+   'nntp' URIs have a non-empty <authority> component; there is no
+   default <host> as for the 'file' or 'news' URI schemes.
+
+   Netnews is typically distributed among several news servers, using
+   the same newsgroup names but local article numbers.  An article
+   available as number 10 in group "example" on server
+   "news.example.com" has most likely a different number on any other
+
+
+
+
+Ellermann                    Standards Track                    [Page 3]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+   server where the same article is still available.  Users allowed to
+   read and post articles on "their" server may not be allowed to access
+   articles on an "arbitrary" server specified in an 'nntp' URI.
+
+   For these reasons, the use of the 'nntp' URI scheme is limited, and
+   it is less widely supported by user agents than the similar 'news'
+   URI scheme.
+
+2.2.  'news' URIs
+
+   The 'news' URI scheme identifies articles by their worldwide unique
+   "Message-ID", independent of the server and the newsgroup.
+   Newsreaders support access to articles by their "Message-ID", without
+   the overhead of a URI scheme.  In simple cases, they do this directly
+   as an NNTP client of a default or currently used server as configured
+   by the user.  More general user agents use the 'news' URI scheme to
+   distinguish "Message-IDs" from similar constructs such as other URI
+   schemes in contexts such as a plain text message body.
+
+   The 'news' URI scheme also allows the identification of newsgroups or
+   sets of newsgroups independent of a specific server.  For Netnews, a
+   group "example" has the same name on any server carrying this group,
+   exotic cases involving gateways notwithstanding.  To distinguish
+   "Message-IDs" and newsgroup names, the 'news' URI scheme relies on
+   the "@" between local part (left-hand side) and domain part (right-
+   hand side) of "Message-IDs".
+
+   [RFC1738] offered only one wildcard for sets of newsgroups in 'news'
+   URIs, a "*" used to refer to "all available newsgroups".  In common
+   practice, this was extended to varying degrees by different user
+   agents.  An NNTP extension known as <wildmat>, specified in [RFC2980]
+   and now part of the base NNTP specification, allows pattern matching
+   in the style of the [POSIX] "find" command.  For the purpose of this
+   memo, this means that some additional special characters have to be
+   allowed in 'news' URIs, some of them percent-encoded as required by
+   the overall [RFC3986] URI syntax.  User agents and NNTP servers not
+   yet compliant with [RFC3977] do not implement all parts of this new
+   feature.
+
+   Another commonly supported addition to the [RFC1738] syntax is the
+   optional specification of a server at the beginning of 'news' URIs.
+   This optional <authority> component follows the overall [RFC3986]
+   syntax, preceded by a double slash "//" and terminated by the next
+   slash "/", question mark "?", number sign "#", or the end of the URI.
+
+
+
+
+
+
+
+Ellermann                    Standards Track                    [Page 4]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+2.3.  Query Parts, Fragments, and Normalization
+
+   Fragments introduced by a number sign "#" are specified in [RFC3986];
+   the semantics is independent of the URI scheme, and the resolution
+   depends on the media type.
+
+   This memo doesn't specify a query part introduced by a question mark
+   "?" for the 'news' and 'nntp' URI schemes, but some implementations
+   are known to use query parts instead of fragments internally to
+   address parts of a composite media type [RFC2046] in Multipurpose
+   Internet Mail Extensions (MIME).
+
+   There are no special "." or ".." path segments in 'news' and 'nntp'
+   URLs.  Please note that "." and ".." are not valid <newsgroup-name>s.
+
+   URI producers have to percent-encode some characters as specified
+   below (Section 4); otherwise, they MUST treat a "Message-ID" without
+   angle brackets for 'news' URLs as is, i.e., case-sensitive.
+
+3.  Syntax of 'nntp' URIs
+
+   An 'nntp' URI identifies an article by its number in a given
+   newsgroup on a specified server, or it identifies the newsgroup
+   without article number.
+
+       nntpURL         = "nntp:" server "/" group [ "/" article-number ]
+       server          = "//" authority               ; see RFC 3986
+       group           = 1*( group-char / pct-encoded )
+       article-number  = 1*16DIGIT                    ; see RFC 3977
+       group-char      = ALPHA / DIGIT / "-" / "+" / "_" / "."
+
+   In the form with an <article-number>, the URL corresponds roughly to
+   the content of an <xref> header field as specified in [RFC5536],
+   replacing its more general <article-locator> by the <article-number>
+   used with the NNTP.
+
+   A <newsgroup-name> as specified in [RFC5536] consists of dot-
+   separated components.  Each component contains one or more letters,
+   digits, "-" (hyphen-minus), "+", or "_" (underscore).  These
+   characters can be directly used in a segment of a path in an
+   [RFC3986] URI; no percent-encoding is necessary.  Example:
+
+       nntp://news.server.example/example.group.this/12345
+
+   A <wildmat-exact> newsgroup name as specified in [RFC3977] allows (in
+   theory) any <UTF8-non-ascii> (see Section 6) and most printable
+   US-ASCII characters, excluding "!", "*", ",", "?", "[", "\", and "]".
+   However, [RFC5536] does not (yet) permit characters outside of
+
+
+
+Ellermann                    Standards Track                    [Page 5]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+   <group-char> and so, to keep the syntax simple, the additional
+   characters are here covered by <pct-encoded> as defined in [RFC3986],
+   since most of them have to be percent-encoded anyway (with a few
+   exceptions, such as ":", ";", and "~").  Example:
+
+       nntp://wild.server.example/example.group.n%2Fa/12345
+
+   In the form without <article-number>, the URL identifies a single
+   group on the specified server.  This is also possible with an
+   equivalent 'news' URL, and the latter is better supported by user
+   agents.  Example:
+
+       nntp://news.server.example/example.group.this
+       news://news.server.example/example.group.this
+
+4.  Syntax of 'news' URIs
+
+   A 'news' URI identifies an article by its unique "Message-ID", or it
+   identifies a set of newsgroups.  Additionally, it can specify a
+   server; when the server is not specified, a configured default server
+   for Netnews access is used.
+
+       newsURL         = "news:" [ server "/" ] ( article / newsgroups )
+       article         = msg-id-core                  ; see RFC 5536
+
+   The form identifying an <article> is the <msg-id-core> from
+   [RFC5536]; it is a "Message-ID" without angle brackets.  According to
+   [RFC3986], characters that are in <gen-delims> (a subset of
+   <reserved>), together with the character "%", MUST be percent-encoded
+   (though it is not wrong to encode others).  Specifically, the
+   characters allowed in <msg-id-core> that must be encoded are
+
+       "/"  "?"  "#"  "[" "]" and "%"
+
+   Note that an agent which seeks to interpret a 'news' URI needs to
+   decode all percent-encoded characters before passing it on to an NNTP
+   server to be acted upon.
+
+   Please note that "%3E" (">") is not allowed; <msg-id-core> is
+   otherwise identical to
+
+           id-left "@" id-right
+
+   as defined in [RFC5322].
+
+   The form identifying <newsgroups> corresponds to the [RFC3977]
+   <wildmat-pattern>, a newsgroup name with wildcards "*" and "?".  Any
+   "?" has to be percent-encoded as "%3F" in this part of a URI.
+
+
+
+Ellermann                    Standards Track                    [Page 6]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+   Examples (the first two are equivalent):
+
+       news://news.server.example/*
+       news://news.server.example/
+       news://wild.server.example/example.group.th%3Fse
+       news:example.group.*
+       news:example.group.this
+
+   Without wildcards, this form of the URL identifies a single group if
+   it is not empty.  User agents would typically try to present an
+   overview of the articles available in this group, likely somehow
+   limiting this overview to the newest unread articles up to a
+   configured maximum.
+
+   With wildcards, user agents could try to list matching group names on
+   the specified or default server.  Some user agents support only a
+   specific <group> without wildcards, or an optional single "*".
+
+   As noted above (Section 2.2), the presence of an "@" in a 'news' URI
+   disambiguates <article> and <newsgroups> for URI consumers.  The new
+   <message-id> construct specified in [RFC3977] does not require an
+   "@".  Since [RFC0822], the "Message-ID" syntax has been closely
+   related to the syntax of mail addresses with an "@" separating left-
+   hand side (local part of addresses, unique part of message
+   identifiers) and right-hand side (domain part), and this memo sticks
+   to the known [RFC1738] practice.
+
+5.  Acknowledgments
+
+   Henry Spencer was the driving force to adopt MIME in Netnews; he
+   registered the MIME 'message/external-body' access type
+   'news-message-ID', discussed below (Section 8.2), in 1993 as recalled
+   in "Son-of-1036" [RFC1849].
+
+   "The 'news' URL scheme" [GILMAN], by Alfred S. Gilman (March 1998),
+   introduced additions to the original [RFC1738] 'news' URI scheme.
+   Some of these ideas are now widely supported and reflected by the
+   revised 'news' URI scheme specified here.
+
+   Thanks to Alfred Hoenes, Charles Lindsey, Clive Feather, Chris
+   Newman, Ken Murchinson, Kjetil T. Homme, Lars Magne Ingebrigtsen,
+   Martin Duerst, Matt Seitz, Nicolas Krebs, Paul Hoffman, Pasi Eronen,
+   Roy T. Fielding, Russ Allbery, Stephane Bortzmeyer, and Tom Petch for
+   their feedback, contributions, or encouragement.
+
+   Bill Fenner's _xml2rfc validator_ and _ABNF checker_ were a great
+   help in the creation of (not only) this memo.  The same goes for
+   various great _IETF tools_ written by Henrik Levkowetz.
+
+
+
+Ellermann                    Standards Track                    [Page 7]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+6.  Internationalization Considerations
+
+   The URI schemes were updated to support percent-encoded UTF-8
+   characters in NNTP newsgroup names as specified in [RFC3977] and
+   [RFC3987].
+
+   The Netnews Article Format in [RFC5536] does not yet allow UTF-8 in
+   <newsgroup-name>s; therefore, well-known Unicode and UTF-8 security
+   considerations are not listed below.  For an overview, see [UTR36]
+   and [RFC3629].
+
+   The work on Email Address Internationalization (EAI), started in
+   [RFC4952], is not expected to change the syntax of a "Message-ID".
+
+7.  Security Considerations
+
+   There are many security considerations for URI schemes discussed in
+   [RFC3986].  The NNTP protocol may use passwords in the clear for
+   authentication or offer no privacy, both of which are considered
+   extremely unsafe in current practice.  Alternatives and further
+   security considerations with respect to the NNTP are discussed in
+   [RFC4642] and [RFC4643].
+
+   The syntax for the 'news' and 'nntp' URI schemes contains the general
+   <authority> construct with an optional <userinfo> defined in
+   [RFC3986].  As noted in [RFC3986], the "user:password" form of a
+   <userinfo> is deprecated.
+
+   Articles on NNTP servers typically expire after some time.  After
+   that time, corresponding 'news' and 'nntp' URLs may not work anymore
+   depending on the server.  While a "Message-ID" is supposed to be
+   worldwide unique forever, the NNTP protocol does not guarantee this.
+   Under various conditions depending on the servers, the same
+   "Message-ID" could be used for different articles, and attackers
+   could try to distribute malicious content for known 'news' or 'nntp'
+   URLs.
+
+   If a URI does not match the generic syntax in [RFC3986], it is
+   invalid, and broken URIs can cause havoc.  Compare [RFC5064] for
+   similar security considerations.
+
+8.  IANA Considerations
+
+   The IANA registry of URI schemes has been updated to point to this
+   memo instead of [RFC1738] for the 'news' and 'nntp' URI schemes.
+
+
+
+
+
+
+Ellermann                    Standards Track                    [Page 8]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+8.1.  'snews' URIs
+
+   This section contains the [RFC4395] template for the registration of
+   the historical 'snews' scheme specified in [GILMAN].
+
+   URI scheme name:   snews
+
+   Status:            historical
+
+   URI scheme syntax: Same as for 'news' (Section 4)
+
+   URI scheme semantics:
+                      Syntactically equivalent to 'news', but using NNTP
+                      over SSL/TLS (SSL/TLS with security layer is
+                      negotiated immediately after establishing the TCP
+                      connection) with a default port of 563, registered
+                      as "nntps"
+
+   Encoding considerations:
+                      Same as for 'news' (Section 6)
+
+   Applications/protocols that use this URI scheme name:
+                      For some user agents, 'snews' URLs trigger the use
+                      of "nntps" instead of NNTP for their access on
+                      Netnews
+
+   Interoperability considerations:
+                      This URI scheme was not widely deployed; its
+                      further use is deprecated in favor of ordinary
+                      'news' URLs in conjunction with NNTP servers
+                      supporting [RFC4642]
+
+   Security considerations:
+                      See [RFC4642]; the use of a dedicated port for
+                      secure variants of a protocol was discouraged in
+                      [RFC2595]
+
+   Contact:           <mailto:uri@w3.org> (URI mailing list)
+
+   Change controller: IETF
+
+   References:        RFC 5538, [RFC4642], [GILMAN]
+
+
+
+
+
+
+
+
+
+Ellermann                    Standards Track                    [Page 9]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+8.2.  'news-message-ID' Access Type
+
+   The MIME 'news-message-ID' access type was erroneously listed as a
+   subtype.  IANA has removed 'news-message-ID' from the application
+   subtype registry, and has added it to the access types registry
+   defined in [RFC4289].
+
+   [RFC4289] requires an RFC (preferably on the Standards Track) for the
+   access types registry.  To provide a definition meeting this
+   requirement, the following paragraph is reproduced verbatim from
+   [RFC1849]:
+
+      NOTE: In the specific case where it is desired to essentially make
+      another article PART of the current one, e.g., for annotation of
+      the other article, MIME's "message/external-body" convention can
+      be used to do so without actual inclusion.  "news-message-ID" was
+      registered as a standard external-body access method, with a
+      mandatory NAME parameter giving the message ID and an optional
+      SITE parameter suggesting an NNTP site that might have the article
+      available (if it is not available locally), by IANA 22 June 1993.
+
+   Please note that 'news' URLs offer a very similar and (today) more
+   common way to access articles by their Message-ID; compare [RFC2017].
+
+9.  References
+
+9.1.  Normative References
+
+   [RFC2119]      Bradner, S., "Key words for use in RFCs to Indicate
+                  Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+   [RFC3977]      Feather, C., "Network News Transfer Protocol (NNTP)",
+                  RFC 3977, October 2006.
+
+   [RFC3986]      Berners-Lee, T., Fielding, R., and L. Masinter,
+                  "Uniform Resource Identifier (URI): Generic Syntax",
+                  STD 66, RFC 3986, January 2005.
+
+   [RFC5234]      Crocker, D. and P. Overell, "Augmented BNF for Syntax
+                  Specifications: ABNF", STD 68, RFC 5234, January 2008.
+
+   [RFC5536]      Murchison, K., Lindsey, C., and D. Kohn, "Netnews
+                  Article Format", RFC 5536, November 2009.
+
+
+
+
+
+
+
+
+Ellermann                    Standards Track                   [Page 10]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+9.2.  Informative References
+
+   [GILMAN]       Gilman, A., "The 'news' URL scheme", Work in Progress,
+                  March 1998.
+
+   [POSIX]        Institute of Electrical and Electronics Engineers,
+                  "The Open Group Base Specifications Issue 6",
+                  IEEE Standard 1003.1, 2004 edition.
+
+   [RFC0822]      Crocker, D., "Standard for the format of ARPA Internet
+                  text messages", STD 11, RFC 822, August 1982.
+
+   [RFC1738]      Berners-Lee, T., Masinter, L., and M. McCahill,
+                  "Uniform Resource Locators (URL)", RFC 1738,
+                  December 1994.
+
+   [RFC1849]      Spencer, H., ""Son of 1036": News Article Format and
+                  Transmission", RFC 1849, March 2010.
+
+   [RFC2017]      Freed, N. and K. Moore, "Definition of the URL MIME
+                  External-Body Access-Type", RFC 2017, October 1996.
+
+   [RFC2046]      Freed, N. and N. Borenstein, "Multipurpose Internet
+                  Mail Extensions (MIME) Part Two: Media Types",
+                  RFC 2046, November 1996.
+
+   [RFC2595]      Newman, C., "Using TLS with IMAP, POP3 and ACAP",
+                  RFC 2595, June 1999.
+
+   [RFC2980]      Barber, S., "Common NNTP Extensions", RFC 2980,
+                  October 2000.
+
+   [RFC3629]      Yergeau, F., "UTF-8, a transformation format of ISO
+                  10646", STD 63, RFC 3629, November 2003.
+
+   [RFC3987]      Duerst, M. and M. Suignard, "Internationalized
+                  Resource Identifiers (IRIs)", RFC 3987, January 2005.
+
+   [RFC4156]      Hoffman, P., "The wais URI Scheme", RFC 4156,
+                  August 2005.
+
+   [RFC4157]      Hoffman, P., "The prospero URI Scheme", RFC 4157,
+                  August 2005.
+
+   [RFC4248]      Hoffman, P., "The telnet URI Scheme", RFC 4248,
+                  October 2005.
+
+
+
+
+
+Ellermann                    Standards Track                   [Page 11]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+   [RFC4266]      Hoffman, P., "The gopher URI Scheme", RFC 4266,
+                  November 2005.
+
+   [RFC4289]      Freed, N. and J. Klensin, "Multipurpose Internet Mail
+                  Extensions (MIME) Part Four: Registration Procedures",
+                  BCP 13, RFC 4289, December 2005.
+
+   [RFC4395]      Hansen, T., Hardie, T., and L. Masinter, "Guidelines
+                  and Registration Procedures for New URI Schemes",
+                  BCP 35, RFC 4395, February 2006.
+
+   [RFC4642]      Murchison, K., Vinocur, J., and C. Newman, "Using
+                  Transport Layer Security (TLS) with Network News
+                  Transfer Protocol (NNTP)", RFC 4642, October 2006.
+
+   [RFC4643]      Vinocur, J. and K. Murchison, "Network News Transfer
+                  Protocol (NNTP) Extension for Authentication",
+                  RFC 4643, October 2006.
+
+   [RFC4952]      Klensin, J. and Y. Ko, "Overview and Framework for
+                  Internationalized Email", RFC 4952, July 2007.
+
+   [RFC5064]      Duerst, M., "The Archived-At Message Header Field",
+                  RFC 5064, December 2007.
+
+   [RFC5322]      Resnick, P., Ed., "Internet Message Format", RFC 5322,
+                  October 2008.
+
+   [UTR36]        Davis, M. and M. Suignard, "Unicode Security
+                  Considerations", Unicode Technical Reports #36,
+                  August 2006.
+
+
+
+
+
+
+
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+
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+
+Ellermann                    Standards Track                   [Page 12]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+Appendix A.  Collected ABNF
+
+   In addition to the syntax given above, this appendix also lists the
+   sources of terms used in comments and the prose:
+
+       nntpURL         = "nntp:" server "/" group [ "/" article-number ]
+       server          = "//" authority               ; see RFC 3986
+       group           = 1*( group-char / pct-encoded )
+       article-number  = 1*16DIGIT                    ; see RFC 3977
+       group-char      = ALPHA / DIGIT / "-" / "+" / "_" / "."
+
+       newsURL         = "news:" [ server "/" ] ( article / newsgroups )
+       article         = msg-id-core                  ; see RFC 5536
+       newsgroups      = *( group-char / pct-encoded / "*" )
+
+       authority       = <see RFC 3986 Section 3.2>
+       host            = <see RFC 3986 Section 3.2.2>
+       pct-encoded     = <see RFC 3986 Section 2.1>
+       port            = <see RFC 3986 Section 3.2.3>
+       gen-delims      = <see RFC 3986 Section 2.2>
+       msg-id-core     = <see RFC 5536 Section 3.1.3>
+       reserved        = <see RFC 5536 Section 2.2>
+       userinfo        = <see RFC 3986 Section 3.2.1>
+
+       message-id      = <see RFC 3977 Section 9.8>
+       UTF8-non-ascii  = <see RFC 3977 Section 9.8>
+       wildmat         = <see RFC 3977 Section 4.1>
+       wildmat-exact   = <see RFC 3977 Section 4.1>
+       wildmat-pattern = <see RFC 3977 Section 4.1>
+
+       ALPHA           = <see RFC 5234 Appendix B.1>
+       DIGIT           = <see RFC 5234 Appendix B.1>
+
+       article-locator = <see RFC 5536 Section 3.2.14>
+       newsgroup-name  = <see RFC 5536 Section 3.1.4>
+       xref            = <see RFC 5536 Section 3.2.14>
+
+Appendix B.  Detailed Example
+
+   Here is an example of a mail to the <mailto:tools.discuss@ietf.org>
+   list with "Message-ID" <p0624081dc30b8699bf9b@[10.20.30.108]>.
+
+   <http://dir.gmane.org/gmane.ietf.tools> is one of the various list
+   archives; it converts mail into Netnews articles.  The header of this
+   article contains the following fields (among others):
+
+
+
+
+
+
+Ellermann                    Standards Track                   [Page 13]
+
+RFC 5538                 'news' and 'nntp' URIs               April 2010
+
+
+          Message-ID: <p0624081dc30b8699bf9b@[10.20.30.108]>
+          Xref: news.gmane.org gmane.ietf.tools:742
+          Archived-At: <http://permalink.gmane.org/gmane.ietf.tools/742>
+
+   The "Xref" roughly indicates the 742nd article in newsgroup
+   <news://news.gmane.org/gmane.ietf.tools> on this server.  An 'nntp'
+   URL might be <nntp://news.gmane.org/gmane.ietf.tools/742>.  For
+   details about the "Archived-At" URL, see [RFC5064].
+
+   The list software and list subscribers reading the list elsewhere
+   can't predict a server-specific article number 742 in this archive.
+   If they know this server, they can however guess the corresponding
+   <news://news.gmane.org/p0624081dc30b8699bf9b@%5B10.20.30.108%5D> URL.
+
+   In theory, the list software could use the guessed 'news' URL in an
+   "Archived-At" header field, but if a list tries this, it would likely
+   use <http://mid.gmane.org/p0624081dc30b8699bf9b@%5B10.20.30.108%5D>.
+
+   Using domain literals in a "Message-ID" could cause collisions.  A
+   collision might force the mail2news gateway in this example to invent
+   a new "Message-ID", and an attempt to guess the future URL on this
+   server would then fail.
+
+Author's Address
+
+   Frank Ellermann
+   xyzzy
+   Hamburg, Germany
+
+   EMail: hmdmhdfmhdjmzdtjmzdtzktdkztdjz@gmail.com
+   URI:   http://purl.net/xyzzy/
+
+
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+Ellermann                    Standards Track                   [Page 14]
+