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Network Working Group                                 M. Nottingham, Ed.
Internet-Draft
Expires: July 11, 27, 2005                                     R. Sayre, Ed.
                                               Boswijck Memex Consulting
                                                        January 10, 26, 2005


                      The Atom Syndication Format
                      draft-ietf-atompub-format-04
                      draft-ietf-atompub-format-05

Status of this Memo

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   and any of which I become aware will be disclosed, in accordance with
   RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on July 11, 27, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).  All Rights Reserved.

Abstract

   This document specifies Atom, an XML-based Web content and metadata
   syndication format.









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Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1  Editorial Notes  . . . . . . . . . . . . . . . . . . . . .   4
     1.2  Example  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.3  Conformance  . . . . . . . . . . . . . . . . . . . . . . .   5
     1.4  Notational Conventions . . . . . . . . . . . . . . . . . .   5
   2.   Atom Documents . . . . . . . . . . . . . . . . . . . . . . .   7
   3.   Common Atom Constructs . . . . . . . . . . . . . . . . . . .   8   9
     3.1  Text Constructs  . . . . . . . . . . . . . . . . . . . . .   8   9
       3.1.1  "type" Attribute . . . . . . . . . . . . . . . . . . .   8   9
     3.2  Person Constructs  . . . . . . . . . . . . . . . . . . . .   9  10
       3.2.1  The "atom:name" Element  . . . . . . . . . . . . . . . . .   9  10
       3.2.2  The "atom:uri" Element . . . . . . . . . . . . . . . . . .   9  10
       3.2.3  The "atom:email" Element . . . . . . . . . . . . . . . . .   9  11
     3.3  Date Constructs  . . . . . . . . . . . . . . . . . . . . .   9  11
     3.4  Service Constructs . . . . . . . . . . . . . . . . . . . .   9  11
       3.4.1  The "href" Attribute . . . . . . . . . . . . . . . . . . .  10  11
     3.5  Link  Identity Constructs  . . . . . . . . . . . . . . . . . . . . .  10  11
       3.5.1  "rel" Attribute  . . . . . . . . .  Dereferencing Identity Constructs  . . . . . . . . . .  10  12
       3.5.2  "type" Attribute . . . . . .  Comparing Identity Constructs  . . . . . . . . . . . .  12
   4.   Element Definitions  .  11
       3.5.3  "href" Attribute . . . . . . . . . . . . . . . . . . .  11
       3.5.4  "hreflang" Attribute  14
     4.1  The "atom:feed" Element  . . . . . . . . . . . . . . . . .  11
       3.5.5  "title"  14
       4.1.1  The "version" Attribute  . . . . . . . . . . . . . . . . . .  11
       3.5.6  "length" Attribute .  14
     4.2  The "atom:head" Element  . . . . . . . . . . . . . . . . .  11
     3.6  Identity Constructs  14
       4.2.1  Usage of "atom:head" within "atom:entry" . . . . . . .  16
     4.3  The "atom:entry" Element . . . . . . . . . . . .  12
       3.6.1  Dereferencing Identity Constructs . . . . .  16
     4.4  The "atom:title" Element . . . . .  12
       3.6.2  Comparing Identity Constructs . . . . . . . . . . . .  12
     3.7  18
     4.5  The Category Construct "atom:id" Element  . . . . . . . . . . . . . . . . . .  13
       3.7.1  18
     4.6  The "term" Attribute "atom:link" Element  . . . . . . . . . . . . . . . . .  13
       3.7.2  18
       4.6.1  The "scheme" "href" Attribute . . . . . . . . . . . . . . . .  13
       3.7.3 .  19
       4.6.2  The "label" attribute "rel" Attribute  . . . . . . . . . . . . . . . .  13
   4.   The "atom:feed" Element .  19
       4.6.3  The "type" Attribute . . . . . . . . . . . . . . . . .  14
     4.1  "version"  20
       4.6.4  The "hreflang" Attribute . . . . . . . . . . . . . . . . . . .  14
     4.2  20
       4.6.5  The "atom:head" Element  . . "title" Attribute  . . . . . . . . . . . . . . .  14
       4.2.1  "atom:title" Element .  20
       4.6.6  The "length" Attribute . . . . . . . . . . . . . . . .  14
       4.2.2  "atom:link"  20
     4.7  The "atom:updated" Element . . . . . . . . . . . . . . . . .  14
       4.2.3  "atom:category"  20
     4.8  The "atom:published" Element . . . . . . . . . . . . . . .  15
       4.2.4  "atom:introspection"  21
     4.9  The "atom:author" Element  . . . . . . . . . . . . .  15
       4.2.5  "atom:post" Element  . . . .  21
     4.10   The "atom:contributor" Element . . . . . . . . . . . . .  15
       4.2.6  "atom:author"  21
     4.11   The "atom:host" Element  . . . . . . . . . . . . . . . .  15
       4.2.7  "atom:contributor"  21
     4.12   The "atom:copyright" Element . . . . . . . . . . . . . .  15
       4.2.8  "atom:tagline"  21
     4.13   The "atom:category" Element  . . . . . . . . . . . . . . . .  15
       4.2.9  "atom:id" Element  22
       4.13.1   The "term" Attribute . . . . . . . . . . . . . . . .  22
       4.13.2   The "scheme" Attribute . .  16
       4.2.10   "atom:generator" Element . . . . . . . . . . . . .  22
       4.13.3   The "label" attribute  .  16
       4.2.11   "atom:copyright" Element . . . . . . . . . . . . . .  16
       4.2.12   "atom:info"  22
     4.14   The "atom:summary" Element . . . . . . . . . . . . . . . .  16
       4.2.13   "atom:updated"  22
     4.15   The "atom:content" Element . . . . . . . . . . . . . . .  16  23



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   5.


       4.15.1   The "atom:entry" Element . "type" attribute . . . . . . . . . . . . . . . .  23
       4.15.2   The "src" attribute  .  18
     5.1  "atom:title" Element . . . . . . . . . . . . . . . . . . .  18
     5.2  "atom:link" Element  . . . . . . . . . . . . . . . . . . .  18
     5.3  "atom:category" Element  . . . . . . . . . . . . . . . . .  18
     5.4  "atom:edit" Element  . . . . . . . . . . . . . . . . . . .  19
     5.5  "atom:author" Element  23
       4.15.3   Processing Model . . . . . . . . . . . . . . . . . .  19
     5.6  "atom:contributor"  24
     4.16   The "atom:introspection" Element . . . . . . . . . . . . . . . .  19
     5.7  "atom:host"  25
     4.17   The "atom:post" Element  . . . . . . . . . . . . . . . . . . .  19
     5.8  "atom:id"  25
     4.18   The "atom:edit" Element  . . . . . . . . . . . . . . . . . . . .  19
     5.9  "atom:updated"  25
     4.19   The "atom:tagline" Element . . . . . . . . . . . . . . . . . .  19
     5.10   "atom:published"  25
     4.20   The "atom:generator" Element . . . . . . . . . . . . . . . .  20
     5.11   "atom:summary"  25
     4.21   The "atom:info" Element  . . . . . . . . . . . . . . . . .  20
     5.12   "atom:content" Element . . . . . . . . . . .  26
   5.   Managing Feed State  . . . . . .  20
       5.12.1   "type" attribute . . . . . . . . . . . . . .  27
   6.   Securing Atom Documents  . . . .  20
       5.12.2   "src" attribute . . . . . . . . . . . . . .  28
     6.1  Digital Signatures . . . .  21
       5.12.3   Processing Model . . . . . . . . . . . . . . . .  28
     6.2  Encryption . .  21
     5.13   "atom:copyright" Element . . . . . . . . . . . . . . . .  22
     5.14   "atom:head" Element . . . . . .  28
   7.   Embedding Atom in Other Formats  . . . . . . . . . . . .  22
   6.   Managing Feed State . .  29
   8.   Extending Atom . . . . . . . . . . . . . . . . . .  23
   7.   Securing Atom Documents . . . . .  30
   9.   IANA Considerations  . . . . . . . . . . . . .  24
     7.1  Digital Signatures . . . . . . .  31
     9.1  Registry of Link Relations . . . . . . . . . . . . .  24
     7.2  Encryption . . .  31
   10.  Security Considerations  . . . . . . . . . . . . . . . . . .  33
   11.  References . . .  24
   8.   Embedding Atom in Other Formats . . . . . . . . . . . . . .  25
   9.   Extending Atom . . . . . . . .  34
   11.1   Normative References . . . . . . . . . . . . . . .  26
   10.  IANA Considerations . . . .  34
   11.2   Informative References . . . . . . . . . . . . . . . .  27
     10.1   Registry of Link Relations . .  35
        Authors' Addresses . . . . . . . . . . . . .  27
   11.  Security Considerations . . . . . . . .  36
   A.   Contributors . . . . . . . . . .  29
   12.  References . . . . . . . . . . . . . .  37
   B.   Collected RELAX NG Compact Schema  . . . . . . . . . . .  30
   12.1   Normative References . .  38
   C.   Revision History . . . . . . . . . . . . . . . . .  30
   12.2   Informative References . . . . .  45
        Intellectual Property and Copyright Statements . . . . . . . . . . . . .  31
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  32
   A.   Contributors . . . . . . . . . . . . . . . . . . . . . . . .  33
   B.   Revision History . . . . . . . . . . . . . . . . . . . . . .  34
        Intellectual Property and Copyright Statements . . . . . . .  36  47

























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1.  Introduction

   Atom is an XML-based document format intended to allow which describes lists of related information,
   information known as "feeds".  Feeds are composed of a number of
   items, known as "entries", each with an extensible set of attached
   metadata.  For example, each entry has a title.

   The primary use case that Atom addresses is the syndication of Web
   content such as Weblogs and news headlines to Web sites as well as
   directly to user agents.  However, nothing precludes it from being
   used for other purposes and kinds of content.

   Details of communication protocols between software agents using Atom
   can be found in the Atom Protocol specification [Atom-protocol].

   [[ more motivation / design principles ]]

1.1  Editorial Notes

   The Atom format is a work-in-progress, and this draft is both
   incomplete and likely to change rapidly.  As a result, THE FORMAT
   DESCRIBED BY THIS DRAFT SHOULD NOT BE DEPLOYED, either in production
   systems or in any non-experimental fashion on the Internet.

   Discussion of this draft happens in two fora;

      The mailing list [1]
      The Atom Wiki Web site [2]

   Active development takes place on the mailing list, while the Wiki is
   used for issue tracking and new proposals.

   This document is an early draft and known to be incomplete.  Topics
   marked [[like this]] indicate where additional text is likely to be
   added.
















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1.2  Example

   A minimal, single-entry Atom Feed Document:

   <?xml version="1.0" encoding="UTF-8"?>
   <feed version="draft-ietf-atompub-format-04
   : do version="draft-ietf-atompub-format-05:do not deploy"
    xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-04
   ">
   xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-05">
     <head>
       <title>Example Feed</title>
       <link href="http://example.org/"/>
       <updated>2003-12-13T18:30:02Z</updated>
       <author>
         <name>John Doe</name>
       </author>
     </head>
     <entry>
       <title>Atom-Powered Robots Run Amok</title>
       <link href="http://example.org/2003/12/13/atom03"/>
       <id>vemmi://example.org/2003/32397</id>
       <updated>2003-12-13T18:30:02Z</updated>
     </entry>
   </feed>


1.3  Conformance

   [[ talk about atom documents and atom consumers, and how requirements
   are placed on them ]]

1.4  Notational Conventions

   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 BCP 14, [RFC2119].

   This specification uses XML Namespaces [W3C.REC-xml-names-19990114]
   to uniquely identify XML elements and attribute names.  It uses the
   following namespace prefixes for the indicated namespace URIs;

   "atom":  http://purl.org/atom/ns#draft-ietf-atompub-format-04  http://purl.org/atom/ns#draft-ietf-atompub-format-05

   Note that the choice of any namespace prefix is arbitrary and not
   semantically significant.

   Atom is specified using terms from the XML Infoset
   [W3C.REC-xml-infoset-20011024].  However, this specification uses a



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   shorthand for two common terms; the phrase "Information Item" is
   omitted when naming Element Information Items and Attribute



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   Information Items.

   Therefore, when this specification uses the term "element," it is
   referring to an Element Information Item in Infoset terms.  Likewise,
   when it uses the term "attribute," it is referring to an Attribute
   Information Item.

   Some sections of this specification are illustrated with fragments of
   a non-normative RELAX NG Compact schema [RELAX-NG].  However, the
   text of this specification provides the definition of conformance.  A
   collected schema appears in an informative appendix.








































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2.  Atom Documents

   This specification describes two kinds of Atom Documents; Atom Feed
   Documents and Atom Entry Documents.

   An Atom Feed Document is a representation of an Atom feed, including
   metadata about the feed, and some or all of the entries associated
   with it.  Its document element is atom:feed.

   An Atom Entry Document represents exactly one Atom Entry, outside of
   the context of an Atom Feed.  Its document element is atom:entry.

   namespace atom =
     "http://purl.org/atom/ns#draft-ietf-atompub-format-05"

   start = atomFeed | atomEntry

   Both kinds of Atom documents are specified in terms of the XML
   Information Set, serialised as XML 1.0 [W3C.REC-xml-20040204] and
   identified with the "application/atom+xml" media type.  Atom
   Documents MUST be well-formed XML.

   [[ Validity? ]]

   Atom constrains the appearance and content of elements and
   attributes; unless otherwise stated, Atom Documents MAY contain other
   Information Items as appropriate.  In particular, Comment Information
   Items and Processing Instruction Information Items SHOULD be ignored
   in the normal processing of an Atom Document.

   Any element in an Atom Document MAY have an xml:base attribute.  XML
   Base [W3C.REC-xmlbase-20010627] processing MUST be applied to any
   relative reference [RFC2396bis] [RFC3986] present in an Atom Document.  This
   includes such elements and attributes as specified by Atom itself, as
   well as those specified by extensions to Atom.

   Any element in an Atom Document MAY have an xml:lang attribute, whose
   content indicates the default natural language of the element's content.
   Requirements regarding the content and interpretation of xml:lang are
   specified in XML 1.0 [W3C.REC-xml-20040204] Section 2.12.

   atomCommonAttributes =
      attribute xml:base { atomUri }?,
      attribute xml:lang { atomLanguageTag }?

   [[ discussion of URI escaping and i18n, IRI ]]

   [[ discussion of white space ]]

   Atom is extensible.  See the section titled 'Extending Atom' later in



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   this document for a full description of how Atom Documents can be
   extended.

















































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3.  Common Atom Constructs

   Many of Atom's elements share a few common structures.  This section
   defines a few such structures and their requirements, requirements for convenient
   reference by the appropriate element definitions.

   When an element is identified as being a particular kind of
   construct, it inherits the corresponding requirements from that
   construct's definition in this section.

3.1  Text Constructs

   A Text construct contains human readable text, usually in fairly
   small quantities.


   atomPlainTextConstruct =
      atomCommonAttributes,
      attribute type { "TEXT" | "HTML" }?,
      text

   atomXHTMLTextConstruct =
      atomCommonAttributes,
      attribute type { "XHTML" },
      (text|anyElement)*

   atomTextConstruct = atomPlainTextConstruct | atomXHTMLTextConstruct

3.1.1  "type" Attribute

   Text constructs MAY have a "type" attribute.  When present, the value
   MUST be one of "TEXT", "HTML" or "XHTML".  If the "type" attribute is
   not provided, software MUST behave as though it were present with a
   value of "TEXT".

   Note that MIME media types [RFC2045] are not acceptable values for
   the "type" attribute.

   If the value is "TEXT", the content of the Text construct MUST NOT
   contain child elements.  Such text is intended to be presented to
   humans in a readable fashion.  Thus, software MAY display it using
   normal text rendering techniques such as proportional fonts,
   white-space collapsing, and justification.

   If the value of "type" is "HTML", the content of the Text construct
   MUST NOT contain child elements, and SHOULD be suitable for handling
   by software that knows HTML.  The HTML markup must be escaped; for
   example, "<br>" as "&lt;br>".  The HTML markup SHOULD be such that it



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   could validly appear directly within an HTML <DIV> element.
   Receiving software which displays the content MAY use the markup to
   aid in displaying it.

   [[example atom entry w/ escaped markup]]

   If the value of "type" is "XHTML", the content of the Text construct
   MAY contain child elements.  The content SHOULD be XHTML text and
   markup that could validly appear directly within an xhtml:div
   element.  Receiving software which displays the content MAY use the
   markup to aid in displaying it.  Escaped markup is interpreted as a
   text representation of markup, and MUST NOT be interpreted as markup
   itself.





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3.2  Person Constructs

   A Person construct is an element that describes a person,
   corporation, or similar entity.

   Person constructs MAY be extended by namespace-qualified element
   children.

   This specification assigns no significance to the order of appearance
   of the child elements of in a Person construct.


   atomPersonConstruct =
      atomCommonAttributes,
      (element atom:name { text }
       & element atom:uri { atomUri }?
       & element atom:email { atomEmailAddress }?)


3.2.1  The "atom:name" Element

   The "atom:name" element's content conveys a human-readable name for
   the person.  Person constructs MUST contain exactly one "atom:name"
   element.

3.2.2  The "atom:uri" Element

   The "atom:uri" element's content conveys a URI associated with the
   person.  Person constructs MAY contain an atom:uri element, but MUST
   NOT contain more than one.  The content of atom:uri in a Person
   construct MUST be a URI reference [RFC2396bis]. [RFC3986].

   xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to the
   atom:uri element's content.



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3.2.3  The "atom:email" Element

   The "atom:email" element's content conveys an e-mail address
   associated with the persons.  Person constructs MAY contain an
   atom:email element, but MUST NOT contain more than one.  Its content
   MUST be an e-mail address [RFC2822].

3.3  Date Constructs

   A Date construct is an element whose content MUST conform to the
   date-time BNF rule in [RFC3339].


   atomDateConstruct =
      atomCommonAttributes,
      xsd:dateTime


3.4  Service Constructs

   A Service construct is an empty element that conveys the URI of an
   Atom Publishing Protocol [Atom-protocol] service associated with an
   entry or feed.


   atomServiceConstruct =
      atomCommonAttributes,
      attribute href { atomUri }


3.4.1  The type "href" Attribute

   The "href" attribute contains the a URI of service is identified by the element
   name.

   A Service construct has the following attribute:




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3.4.1  "href" Attribute

   The "href" attribute contains the a URI pointing to the endpoint of
   the service named by the name attribute. service.  atom:service
   elements MUST have a "href" attribute, whose value MUST be a URI
   reference
   [RFC2396bis]. [RFC3986].

   xml:base processing MUST be applied to the "href" attribute.

3.5  Link  Identity Constructs

   A Link

   An Identity construct is an empty element that describes whose content conveys a connection from
   an Atom Document to another Web resource.

3.5.1  "rel" Attribute

   Link constructs MAY have an optional "rel" attribute that indicates
   permanent, universally unique identifier for the link relation type.  If construct's parent.
   Its content MUST be a URI, as defined by [RFC3986].  Note that the "rel" attribute
   definition of "URI" excludes relative references.

   When an Atom document is not present, relocated, migrated, syndicated,
   republished, exported or imported, the
   link content of its Identity
   construct MUST be interpreted as if NOT change.  Put another way, an Identity construct



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   pertains to all instantiations of a particular Atom entry or feed;
   revisions retain the link relation type is
   "alternate".

   rel_attribute same content in their Identity constructs.


   atomIdentityConstruct = segment-nz-nc / URI
      atomCommonAttributes,
      (atomUri)


3.5.1  Dereferencing Identity Constructs

   The value content of "rel" an Identity construct MAY be dereferencable (e.g.  an
   HTTP URI).  However, processors MUST NOT assume it to be either
   dereferencable.

   The content of an Identity construct MUST be created in a name, which is non-empty way that
   assures uniqueness, and does
   not contain any colon (":") characters, or a URI [RFC2396bis].  Note it is suggested that use the Identity construct
   be stored along with the associated resource.

   Because of a relative reference to the "rel" value URI is not
   allowed.  If a name is given, implementations MUST consider the link
   relation type to be equivalent to the same name registered within the
   IANA Registry risk of Link Relations Section 10, and thus the URI confusion between URIs that would be obtained by appending the value of the rel attribute to the
   string "http://www.iana.org/assignments/relation/".  The value of
   "rel" describes the meaning of the link, but does not impose any
   behavioral requirements on implementations.

   This document defines two initial values for
   equivalent if dereferenced, the Registry of Link
   Relations:

   The value "alternate" signifies that following normalization strategy is
   strongly encouraged when generating Identity constructs:

   o  Provide the URI scheme in lowercase characters.
   o  Provide the value of host, if any, in lowercase characters.
   o  Only perform percent-encoding where it is essential.
   o  Use uppercase A-through-F characters when percent-encoding.
   o  Prevent dot-segments appearing in paths.
   o  For schemes that define a default authority, use an empty
      authority if the href
   attribute identifies default is desired.
   o  For schemes that define an alternate version empty path to be equivalent to a path
      of "/", use "/".
   o  For schemes that define a port, use an empty port if the resource described
   by the containing element.

   The value "related" signifies default
      is desired.
   o  Preserve empty fragment identifiers and queries.
   o  Ensure that all portions of the URI in the value are UTF-8 encoded NFC form
      Unicode strings.

3.5.2  Comparing Identity Constructs

   Instances of the href
   attribute identifies a resource Identity constructs can be compared to which the resource described by
   the containing atom:feed determine whether
   an entry or atom:entry element is related.  For
   example, the feed for a site which discusses is the performance of the
   search engine at "http://search.example.com" might contain, same as one seen before.  Processors MUST
   compare Identity constructs on a
   child character-by-character basis in a
   case-sensitive fashion.

   As a result, two URIs that resolve to the same resource but are not
   character-for-character identical will be considered different for
   the purposes of atom:head:
   <link rel="related" href="http://search.example.com/"> Identifier comparison.



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   An identical link might appear as a child of any atom:entry whose
   content contains a discussion of that same search engine.

3.5.2  "type" Attribute

   Link constructs MAY have a type attribute, whose value MUST conform
   to


   For example, "http://www.example.org/thing",
   "http://www.example.org/Thing", "http://www.EXAMPLE.org/thing" and
   "HTTP://www.example.org/thing" will all be considered different
   identifiers, despite their differences in case.

   Likewise, "http://www.example.com/~bob",
   "http://www.example.com/%7ebob" and "http://www.example.com/%7Ebob"
   will all be considered different identifiers, because URI %-escaping
   is significant for the syntax purposes of a MIME media type [RFC2045]. comparison.










































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4.  Element Definitions

4.1  The type attribute's value "atom:feed" Element

   The "atom:feed" element is the document (i.e., top-level) element of
   an advisory media type; it MAY be used Atom Feed Document, acting as a hint to determine the type of container for metadata and data
   associated with the representation feed.  Its first element child MUST be atom:head,
   which is
   expected to MAY be returned when followed zero or more atom:entry child elements.


   atomFeed =
      element atom:feed {
         atomCommonAttributes,
         atomVersionAttribute,
         (atomHead
          & atomEntry*
          & anyElement*)
      }


4.1.1  The "version" Attribute

   atom:feed elements MUST have a "version" attribute whose content
   indicates the value version of the href attribute is
   dereferenced.  Note Atom specification that the type feed
   conforms to.  The content of this attribute does not override the
   actual media type returned with the representation.

3.5.3  "href" Attribute is unstructured text.

   The "href" version identifier for this specification is
   "draft-ietf-atompub-format-05: do not deploy".


   atomVersionAttribute =
    attribute contains the link's URI.  Link constructs MUST
   have a href attribute, whose value MUST be a URI reference
   [RFC2396bis].

   xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to the
   href attribute's content.

3.5.4  "hreflang" Attribute

   The "hreflang" attribute's content describes the language of the
   resource pointed to by the href attribute.  When used together with
   the rel="alternate", it implies a translated version of the entry.
   Link constructs MAY have an hreflang attribute, whose value MUST be a
   language tag [RFC3066].

3.5.5  "title" Attribute {"draft-ietf-atompub-format-05 : do not deploy"}


4.2  The "title" attribute conveys human-readable information "atom:head" Element

   The atom:head element acts as a container for metadata about the
   link.  Link constructs MAY have a title attribute.

3.5.6  "length" Attribute feed
   itself.

   The "length" attribute indicates an advisory length of the linked
   content in octets; it atom:head element MAY be used contain any namespace-qualified
   [W3C.REC-xml-names-19990114] elements as a hint children.  This
   specification assigns no significance to determine the content
   length order of the representation returned when the URI in the href
   attribute is dereferenced.  Note that the length attribute does not
   override the actual content length appearance of
   the representation as reported
   by the underlying protocol.

   Link constructs MAY have a length attribute. child elements of atom:head.








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3.6  Identity Constructs

   An Identity construct is an


   atomHead =
         element whose content conveys a
   permanent, universally unique identifier for the construct's parent.
   Its content MUST be a URI, as atom:head {
         atomCommonAttributes,
         (atomTitle
          & atomUpdated
          & atomLink+
          & atomId?
          & atomAuthor?
          & atomContributor*
          & atomTagline?
          & atomGenerator?
          & atomInfo?
          & atomCopyright?
          & atomCategory*
          & atomIntrospection?
          & atomPost?
          & anyElement*)
      }

   The following child elements are defined by [RFC2396bis].  Note this specification (note
   that the
   definition presence of "URI" excludes relative references.

   When an Atom document some of these elements is relocated, migrated, syndicated,
   republished, exported or imported, the content required):

   o  atom:head elements MUST contain exactly one atom:title element.
   o  atom:head elements MUST contain at least one atom:link element
      with a rel attribute value of its Identity
   construct "alternate".
   o  atom:head elements MUST NOT change.  Put another way, an Identity construct
   pertains to all instantiations of contain more than one atom:link
      element with a particular Atom entry or feed;
   revisions retain rel attribute value of "alternate" that has the
      same content in their Identity constructs.

3.6.1  Dereferencing Identity Constructs

   The content of an Identity construct MAY be dereferencable (e.g.  an
   HTTP URI).  However, processors MUST NOT assume it type attribute value.  If a feed's atom:link element with
      type="alternate" resolves to be
   dereferencable.

   The content of an Identity construct MUST be created in a way HTML document, then that
   assures uniqueness, and it is suggested document
      SHOULD have a autodiscovery link element [Atom-autodiscovery] that
      reflects back to the Identity construct
   be stored along with the associated resource.

   Because of the risk feed.  atom:head elements MAY contain
      additional atom:link elements beyond those described above.
   o  atom:head elements MUST contain exactly one atom:author element,
      UNLESS all of confusion between URIs that would be
   equivalent if dereferenced, the following normalization strategy is
   strongly encouraged when generating Identity constructs: atom:feed element's child atom:entry elements
      contain an atom:author element.  atom:head elements MUST NOT
      contain more than one atom:author element.  [[inheritance]]
   o  Provide the scheme in lowercase characters.  atom:head elements MUST NOT contain more than one an
      atom:contributor element.
   o  Provide the host, if any, in lowercase characters.
   o  Only perform percent-encoding where it is essential.
   o  Use uppercase A-through-F characters when percent-encoding.
   o  Prevent dot-segments appearing in paths.
   o  For schemes that define a default authority, use an empty
      authority if the default is desired.
   o  For schemes that define  atom:head elements MUST NOT contain more than one an empty path to be equivalent to a path
      of "/", use "/".
      atom:copyright element.
   o  For schemes that define a port, use  atom:head elements MUST NOT contain more than one an empty port if the default
      is desired. atom:id
      element.
   o  Preserve empty fragment identifiers and queries.  atom:head elements MUST contain exactly one atom:updated element.
   o  Ensure that all portions of the URI are UTF-8 encoded NFC form
      Unicode strings.

3.6.2  Comparing Identity Constructs

   Instances  atom:head elements MAY contain any number of Identity constructs can be compared to determine whether
   an entry or feed is the same as one seen before.  Processors atom:category
      elements.
   o  atom:head elements MUST
   compare Identity constructs on a character-by-character basis in a
   case-sensitive fashion. NOT contain more than one atom:post
      element.




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   As a result, two URIs that resolve to


   o  atom:head elements MUST NOT contain more than one
      atom:introspection element.
   o  atom:head elements MUST NOT contain more than one atom:tagline
      element.
   o  atom:head elements MUST NOT contain more than one atom:generator
      element.
   o  atom:head elements MUST NOT contain more than one atom:info
      element.

4.2.1  Usage of "atom:head" within "atom:entry"

   In this case, the same resource but are not
   character-for-character identical will be considered different atom:head element acts as a container for metadata
   about the purposes of Identifier comparison.

   For example, "http://www.example.org/thing",
   "http://www.example.org/Thing", "http://www.EXAMPLE.org/thing" and
   "HTTP://www.example.org/thing" will all be considered different
   identifiers, despite their differences in case.

   Likewise, "http://www.example.com/~bob",
   "http://www.example.com/%7ebob" and "http://www.example.com/%7Ebob"
   will all be considered different identifiers, because URI %-escaping feed within which the entry was created.

   If an atom:entry is significant for copied into one feed from another feed, then the purposes
   atom:head element of comparison.

3.7  The Category Construct

   Category constructs contain information about a category to which an
   Atom the source feed or entry is associated.

3.7.1  The "term" Attribute

   The "term" attribute will SHOULD be a string which identifies inserted into the category
   within
   atom:entry unless the categorization scheme to which entry, as copied, already contains an atom:head
   element.  If the entry or feed belongs.
   Category constructs MUST have a "term" attribute.

3.7.2  The "scheme" Attribute

   The is a URI that identifies a categorization scheme.  Category
   constructs MAY have a "scheme" attribute.

3.7.3  The "label" attribute

   The "label" attribute provides a human-readable label atom:entry already contains an atom:head, then that may
   atom:head SHOULD be
   displayed in end-user applications.  Category constructs MAY have a
   "label" attribute.
















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4. copied without modification.

   [[ ...  example ...  ]]

4.3  The "atom:feed" "atom:entry" Element

   The "atom:feed" "atom:entry" element is represents an individual entry.  This
   element can appear as a child of the atom:feed element, or it can
   appear as the document (i.e., top-level) element of a standalone Atom
   Entry Document.

   When appearing in an Atom Feed Entry Document, acting as atom:entry elements MUST
   have a container for metadata and data
   associated with the feed.  Its first element child MUST be atom:head,
   which MAY be followed zero or more atom:entry child elements.

4.1  "version" Attribute

   atom:feed elements MUST have a "version" attribute whose content
   indicates "version" attribute whose content indicates the version of the
   Atom specification that the feed entry conforms to.

   The content of this attribute is unstructured text.

   The version identifier for this specification is
   "draft-ietf-atompub-format-04 :
   "draft-ietf-atompub-format-05: do not deploy".

4.2  The "atom:head" Element

   The atom:head element acts as a container for metadata about the feed
   itself.

   The atom:head atom:entry element MAY contain any namespace-qualified
   [W3C.REC-xml-names-19990114] elements as children.  This
   specification assigns no significance to the order of appearance of
   the child elements of atom:head. atom:entry.











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   atomEntry =
         element atom:entry {
         atomCommonAttributes,
         atomVersionAttribute?,
         (atomTitle
          & atomId
          & atomLink*
          & atomUpdated
          & atomPublished?
          & atomAuthor?
          & atomContributor*
          & atomHost?
          & atomCopyright?
          & atomCategory*
          & atomEdit?
          & atomSummary?
          & atomContent?
          & atomHead?
          & anyElement*)
      }

   The following child elements are defined by this specification (note
   that it requires the presence of some of these elements):

   o  atom:entry elements is required):

4.2.1  "atom:title" Element

   The MUST have exactly one "atom:title" element is a Text construct that conveys a
   human-readable title for the feed.  atom:head element.
   o  atom:entry elements MUST contain exactly one atom:title atom:id element.

4.2.2  "atom:link" Element

   The "atom:link" element is a Link construct that conveys a URI
   associated with the feed.  The nature of the relationship is
   determined by the construct's rel attribute.

   atom:head
   o  atom:entry elements that contain no child atom:content element
      MUST contain at least one atom:link element with a rel attribute
      value of "alternate".

   atom:head  atom:entry elements MUST NOT contain more
      than one atom:link element with a rel attribute value of
      "alternate" that has the same type attribute value.




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   If a feed's atom:link element with type="alternate" resolves to an
   HTML document, then that document SHOULD have a autodiscovery link
   element [Atom-autodiscovery] that reflects back to the feed.

   atom:head  atom:entry
      elements MAY contain additional atom:link elements beyond those
      described above.

4.2.3  "atom:category" Element

   A Category Construct identifying a category with which the feed is
   associated.  atom:head
   o  atom:entry elements MAY MUST contain any number of
   atom:category elements.

4.2.4  "atom:introspection" Element

   The "atom:introspection" element is a Service construct that conveys
   the URI of an introspection file associated with the feed.  atom:head exactly one atom:updated element.
   o  atom:entry elements MUST NOT contain more than one atom:introspection atom:published
      element.

4.2.5  "atom:post" Element

   The "atom:post" element is a Service construct that conveys the URI
   used to add entries to the feed.  atom:head elements MUST NOT contain
   more than one atom:post element.

4.2.6  "atom:author" Element

   The "atom:author" element is a Person construct that indicates the
   default author of the feed.  atom:head
   o  atom:entry elements MUST contain exactly one atom:author element, UNLESS all of
      unless, in an Atom Feed Document, the atom:feed element's child
   atom:entry elements contain atom:head element contains
      an atom:author element.  atom:head element itself.  atom:entry elements MUST NOT
      contain more than one atom:author element.

   [[explain inheritance]]

4.2.7  "atom:contributor" Element

   The "atom:contributor" element is a Person construct that indicates a
   person or other entity who contributes to the feed.  atom:head
   o  atom:entry elements MAY MUST NOT contain one or more than one
      atom:contributor elements.

4.2.8  "atom:tagline" Element

   The "atom:tagline" element is a Text construct that conveys a
   human-readable description or tagline for the feed.  atom:head element.
   o  atom:entry elements MAY MUST NOT contain an atom:tagline element, but more than one atom:host
      element.
   o  atom:entry elements MUST NOT contain more than one. one atom:copyright
      element.
   o  atom:entry elements MAY contain any number of atom:category
      elements.



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4.2.9  "atom:id" Element

   The "atom:id"


   o  atom:entry elements MUST contain an atom:summary element is in any of
      the following cases:
      *  the atom:entry element contains no atom:content element.
      *  the atom:entry contains an Identity construct that conveys atom:content which has a
   permanent, universally unique identifier for "src"
         attribute (and is thus empty).
      *  the atom:entry contains content which is encoded in Base64;
         i.e.  the "type" attribute of atom:content is a feed.  atom:head MIME media type
         [RFC2045] and does not begin with "text/" nor end with "+xml".
   o  atom:entry elements MAY MUST NOT contain an atom:id element, but more than one atom:summary
      element.
   o  atom:entry elements MUST NOT contain more than one.

4.2.10  "atom:generator" Element

   The "atom:generator" element's content identifies the software agent
   used to generate the feed, for debugging and other purposes.
   atom:head one atom:edit
      element.
   o  atom:entry elements MAY contain an atom:generator element, but MUST NOT contain more than one.

   The content of this element, when present, MUST be a string that is a
   human-readable name for the generating agent.

   The atom:generator element MAY have a "uri" attribute whose value
   MUST be a URI reference [RFC2396bis].  When dereferenced, that URI
   SHOULD produce a representation that is relevant to that agent. one atom:head
      element.

4.4  The atom:generator element MAY have a "version" attribute that
   indicates the version of the generating agent.  When present, its
   value is unstructured text.

4.2.11  "atom:copyright" "atom:title" Element

   The "atom:copyright" "atom:title" element is a Text construct that conveys a
   human-readable copyright statement title for the feed.  atom:head elements
   MAY contain an atom:copyright element, but MUST NOT contain more than
   one.

   The atom:copyright entry or feed.


   atomTitle = element SHOULD NOT be used to convey
   machine-readable licensing information.

4.2.12  "atom:info" atom:title { atomTextConstruct }


4.5  The "atom:id" Element

   The "atom:info" "atom:id" element is a Text an Identity construct that conveys a
   human-readable explanation of the feed format itself.  atom:head
   elements MAY contain
   permanent, universally unique identifier for an atom:info element, but MUST NOT contain more
   than one.

   The atom:info entry or feed.


   atomId = element SHOULD NOT considered meaningful by processors;
   it is a convenience to publishers in certain situations.

4.2.13  "atom:updated" atom:id { atomIdentityConstruct }


4.6  The "atom:link" Element

   The "atom:updated" atom:link element is an empty element that defines a Date construct indicating the most reference
   from an Atom Document to a Web resource.


   atomLink = element atom:link {
      atomCommonAttributes,
      attribute href { atomUri },
      attribute rel { atomNCName | atomUri }?,
      attribute type { atomMediaType }?,
      attribute hreflang { atomLanguageTag }?,
      attribute title { text }?,
      attribute length { text }?,
      empty



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   recent instant in time when


   }


4.6.1  The "href" Attribute

   The "href" attribute contains the feed was modified in link's URI.  Link constructs MUST
   have a way the
   producer considers significant.  Therefore, not all modifications
   necessarily result in a changed atom:updated value.

   atom:head elements href attribute, whose value MUST contain exactly one atom:updated element.














































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5.  The "atom:entry" Element

   The "atom:entry" element represents an individual entry.  This
   element can appear as be a child of the atom:feed element, or it can
   appear as URI reference [RFC3986].

   xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to the document (i.e., top-level) element of a standalone Atom
   Entry Document.

   When appearing in an Atom Entry Document, atom:entry
   href attribute's content.

4.6.2  The "rel" Attribute

   Link elements MUST MAY have a "version" an "rel" attribute whose content that indicates the version of the
   Atom specification that link
   relation type.  If the entry conforms to.

   The version identifier for this specification "rel" attribute is
   "draft-ietf-atompub-format-04 : do not deploy".

   The atom:entry present, the link
   element MAY contain any namespace-qualified
   [W3C.REC-xml-names-19990114] elements MUST be interpreted as children.  This
   specification assigns no significance to the order of appearance of if the child elements of atom:entry. link relation type is
   "alternate".


   rel_attribute = segment-nz-nc / URI

   The following child elements are defined by this specification (note
   that it requires the presence of some value of these elements):

5.1  "atom:title" Element

   The "atom:title" element "rel" MUST be either a name, which is non-empty and does
   not contain any colon (":") characters, or a Text construct URI [RFC3986].  Note
   that conveys use of a
   human-readable title for the entry.  atom:entry elements MUST have
   exactly one "atom:title" element.

5.2  "atom:link" Element

   The "atom:link" element relative reference is not allowed.  If a Link construct that conveys a URI
   associated with the entry.  The nature of the relationship as well as name is given,
   implementations MUST consider the link itself is determined by relation type to be equivalent
   to the element's content.

   atom:entry elements same name registered within the IANA Registry of Link
   Relations Section 9, and thus the URI that contain no child atom:content element MUST
   contain at least one atom:link element with a rel attribute would be obtained by
   appending the value of
   "alternate".

   atom:entry elements MUST NOT contain more than one atom:link element
   with a the rel attribute to the string
   "http://www.iana.org/assignments/relation/".  The value of "rel"
   describes the meaning of the link, but does not impose any behavioral
   requirements on implementations.

   This document defines two initial values for the Registry of Link
   Relations:

   The value "alternate" signifies that has the same type URI in the value of the href
   attribute value.

   atom:entry elements MAY contain additional atom:link elements beyond
   those identifies an alternate version of the resource described above.

5.3  "atom:category" Element

   A Category Construct identifying
   by the containing element.

   The value "related" signifies that the URI in the value of the href
   attribute identifies a category with resource related to the resource described by
   the containing atom:feed or atom:entry element.  For example, the
   feed for a site which discusses the entry is performance of the search engine
   at "http://search.example.com" might contain, as a child of
   atom:head:

   <link rel="related" href="http://search.example.com/">




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   associated.  atom:entry elements MAY contain


   An identical link might appear as a child of any number atom:entry whose
   content contains a discussion of
   atom:category elements.

5.4  "atom:edit" Element that same search engine.

4.6.3  The "atom:edit" element is "type" Attribute

   Link elements MAY have a Service construct that conveys type attribute, whose value MUST conform to
   the URI
   used to retrieve and edit the source representation syntax of the entry.
   atom:entry elements MUST NOT contain more than one atom:edit element.

5.5  "atom:author" Element a MIME media type [RFC2045].

   The "atom:author" element type attribute's value is an advisory media type; it is a Person construct that indicates hint
   about the
   default author type of the entry.  atom:entry elements MUST contain
   exactly one atom:author element, unless, in an Atom Feed Document, representation which is expected to be returned
   when the atom:head element contains an atom:author element itself.
   atom:entry elements MUST NOT contain more than one atom:author
   element.

5.6  "atom:contributor" Element

   The "atom:contributor" element value of the href attribute is a Person construct dereferenced.  Note that indicates a
   person or other entity who contributes to the entry.  atom:entry
   elements MAY contain one or more atom:contributor elements.

5.7  "atom:host" Element
   type attribute does not override the actual media type returned with
   the representation.

4.6.4  The "atom:host" element's "hreflang" Attribute

   The "hreflang" attribute's content conveys a domain name or network
   address associated describes the language of the
   resource pointed to by the href attribute.  When used together with
   the entry's origin.  atom:entry rel="alternate", it implies a translated version of the entry.
   Link elements MAY
   contain a single atom:host element.  Its content have an hreflang attribute, whose value MUST be a domain
   name [RFC1035], a dotted-decimal IPv4 address [RFC0791], or a
   colon-delimited IPv6 address [RFC2460].

5.8  "atom:id" Element
   language tag [RFC3066].

4.6.5  The "atom:id" element is an Identity construct that "title" Attribute

   The "title" attribute conveys a
   permanent, universally unique identifier for an entry.  atom:entry human-readable information about the
   link.  Link elements MUST contain exactly one atom:id element.

5.9  "atom:updated" Element

   The "atom:updated" element is MAY have a Date construct title attribute.

4.6.6  The "length" Attribute

   The "length" attribute indicates an advisory length of the linked
   content in octets; it is a hint about the content length of the
   representation returned when the URI in the href attribute is
   dereferenced.  Note that the length attribute does not override the
   actual content length of the representation as reported by the
   underlying protocol.

   Link elements MAY have a length attribute.

4.7  The "atom:updated" Element

   The "atom:updated" element is a Date construct indicating the most
   recent instant in time when the an entry or feed was modified in a way
   the producer considers significant.  Therefore, not all modifications
   necessarily result in a changed atom:updated value.

   atom:entry elements MUST contain exactly one atom:updated element.

   Publishers MAY change the value of this element over time.



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   Processors MAY present entries sorted using this value.  Processors
   MAY choose not to present entries until the instant in time specified



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   in the atom:updated element has passed.

5.10


   atomUpdated = element atom:updated { atomDateConstruct }


4.8  The "atom:published" Element

   The "atom:published" element is a Date construct indicating an
   instant in time associated with an event early in the life cycle of
   the entry.  Typically, atom:published will be associated with the
   initial creation or first availability of the resource.

   atom:entry elements MAY contain an atom:published element, but MUST
   NOT contain more than one.

   Processors MAY present entries sorted using this value.  Processors
   MAY choose not to present entries until the instant in time specified
   in the atom:published element has passed.

5.11  "atom:summary"

4.9  The "atom:author" Element

   The "atom:summary" "atom:author" element is a Text Person construct that conveys a short
   summary, abstract or excerpt indicates the
   default author of the entry.  atom:entry elements MAY
   contain an atom:summary element, but MUST NOT contain more than one.

   atom:entry elements MUST contain an atom:summary entry or feed


   atomAuthor = element in any of
   the following cases:

   o  the atom:entry atom:author { atomPersonConstruct }


4.10  The "atom:contributor" Element

   The "atom:contributor" element contains no atom:content element.
   o  the atom:entry contains an atom:content which has a "src"
      attribute (and is thus empty).
   o a Person construct that indicates a
   person or other entity who contributes to the atom:entry contains entry.


   atomContributor = element atom:contributor { atomPersonConstruct }


4.11  The "atom:host" Element

   The "atom:host" element's content which is encoded in Base64; i.e.
      the "type" attribute of atom:content is conveys a MIME media type
      [RFC2045] and does not begin with "text/" nor end with "+xml".

5.12  "atom:content" Element

   The "atom:content" element either contains domain name or links to the network
   address associated with an entry's origin.  Its content of
   the entry.  atom:entry elements MUST contain zero or one atom:content
   elements.

5.12.1  "type" attribute

   atom:content MAY have a "type" attribute, When present, the value MAY be one of "TEXT", "HTML", a
   domain name [RFC1035], a dotted-decimal IPv4 address [RFC0791], or "XHTML".  Failing that, it MUST be a
   MIME media type [RFC2045] in which, to use the terminology of Section
   5 of [RFC2045], the top level
   colon-delimited IPv6 address [RFC2460].

4.12  The "atom:copyright" Element

   The "atom:copyright" element is a discrete type.  If the type
   attribute is not provided, software MUST behave as though it were
   present with Text construct that conveys a value of "TEXT".
   human-readable copyright statement for an entry or feed.

   The atom:copyright element SHOULD NOT be used to convey



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5.12.2  "src" attribute

   atom:content MAY have a "src" attribute, whose value MUST be a URI
   reference [RFC2396bis].


   machine-readable licensing information.

   If an atom:entry element does not contain an atom:copyright element,
   then the "src" attribute is present, software
   MAY use the URI to retrieve the content.  If atom:copyright element of the "src" attribute is containing atom:feed element's
   atom:head element, if present, atom:content MUST should be empty.  That is considered to apply to say, the content may
   be retrievable using "src=" URI,
   entry.

4.13  The "atom:category" Element

   Category elements contain information about a category to which an
   Atom feed or it may be contained within
   atom:content, but not both.

   If the "src" attribute entry is present, the "type" associated.


   atomCategory = element atom:category {
      atomCommonAttributes,
      attribute SHOULD be
   provided and MUST be a MIME media type [RFC2045], rather than "TEXT",
   "HTML", or "XHTML". term { text },
      attribute scheme { atomUri }?,
      attribute label { text }?,
      empty
   }


4.13.1  The value is advisory; that "term" Attribute

   The "term" attribute is to say, upon
   dereferencing a string which identifies the URI category to retrieve the content, if
   which the server
   providing that content also provides entry or feed belongs.  Category elements MUST have a media type, the
   server-provided media type
   "term" attribute.

4.13.2  The "scheme" Attribute

   The "scheme"  attribute is authoritative.

   If the value of type begins with "text/" or ends with "+xml", the
   content SHOULD be local; a URI  that is to say, no "src" identifies a categorization
   scheme.  Category elements MAY have a "scheme" attribute.

4.13.3  The "label" attribute should

   The "label" attribute provides a human-readable label that may be
   provided.

5.12.3  Processing Model

   Software MUST apply the following rules in succession
   displayed in the order
   below end-user applications.  Category elements MAY have a
   "label" attribute.

4.14  The "atom:summary" Element

   The "atom:summary" element is a Text construct that conveys a short
   summary, abstract or excerpt of an entry.


   atomSummary = element atom:summary { atomTextConstruct }





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4.15  The "atom:content" Element

   The "atom:content" element either contains or links to ascertain the rules governing the content of "atom:content".

   1.  If the value is "TEXT",
   the content of atom:content entry.  atom:entry elements MUST NOT contain child zero or one atom:content
   elements.  Such text is intended to be presented to
       humans in


   atomInlineTextContent =
      element atom:content {
         atomCommonAttributes,
         attribute type { "TEXT" | "HTML" | atomMediaType }?,
         (text)*
      }

   atomInlineXHTMLContent =
      element atom:content {
         atomCommonAttributes,
         attribute type { "XHTML" | atomMediaType }?,
         (text|anyElement)*
      }

   atomOutOfLineContent =
      element atom:content {
         atomCommonAttributes,
         attribute type { "TEXT" | "HTML" | "XHTML" | atomMediaType }?,
         attribute src { atomUri },
         empty
      }

   atomContent = atomInlineTextContent
    | atomInlineXHTMLContent
    | atomOutOfLineContent


4.15.1  The "type" attribute

   atom:content MAY have a readable fashion.  Thus, software "type" attribute, When present, the value MAY display it
       using normal text rendering techniques such as proportional
       fonts, white-space collapsing, and justification.
   2.  If the value
   be one of "type" is "TEXT", "HTML", the content of atom:content or "XHTML".  Failing that, it MUST NOT contain child elements, and SHOULD be suitable for
       handling by software that knows HTML.  The HTML markup must be
       escaped; for example, "<br>" as "&lt;br>".  The HTML markup
       SHOULD be such that it could validly appear directly within an
       HTML <DIV> element.  Receiving software which displays the
       content SHOULD use the markup to aid a
   MIME media type [RFC2045] in displaying it.
   3.  If which, to use the value terminology of "type" is "XHTML", the content Section
   5 of atom:content
       MAY contain child elements.  The content SHOULD be XHTML text and
       markup that could validly appear directly within an xhtml:div
       element.  Receiving software which displays [RFC2045], the content SHOULD
       use top level is a discrete type.  If the markup to aid in displaying it.  Escaped markup type
   attribute is
       interpreted not provided, software MUST behave as though it were
   present with a text representation value of markup, and "TEXT".

4.15.2  The "src" attribute

   atom:content MAY have a "src" attribute, whose value MUST NOT be
       interpreted as markup itself.
   4. a URI
   reference [RFC3986].  If the value of "type" ends with "+xml" or "/xml", the content of
       atom:content may include child elements, and SHOULD be suitable
       for handling by "src" attribute is present, software that knows MAY
   use the indicated media type. URI to retrieve the content.  If the "src" attribute is not provided, this would normally mean



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       that


   present, atom:content MUST be empty.  That is to say, the "atom:content" element would contain a single child
       element which would serve as content may
   be retrievable using "src=" URI, or it may be contained within
   atom:content, but not both.

   If the root element of "src" attribute is present, the XML document
       of "type" attribute SHOULD be
   provided and MUST be a MIME media type [RFC2045], rather than "TEXT",
   "HTML", or "XHTML".  The value is advisory; that is to say, upon
   dereferencing the indicated type.
   5. URI to retrieve the content, if the server
   providing that content also provides a media type, the
   server-provided media type is authoritative.

   If the value of "type" type begins with "text/" or ends with "+xml", the
   content SHOULD be local; that is to say, no "src" attribute should be
   provided.

4.15.3  Processing Model

   Software MUST apply the following rules in the order below to
   ascertain the rules governing the content of "atom:content".

   1.  If the value is "TEXT", the content of atom:content MUST NOT
       contain child elements.
   6.  For all other values  Such text is intended to be presented to
       humans in a readable fashion.  Thus, software MAY display it
       using normal text rendering techniques such as proportional
       fonts, white-space collapsing, and justification.
   2.  If the value of "type", "type" is "HTML", the content of atom:content
       MUST
       be a valid Base64 encoding [RFC3548], which when decoded NOT contain child elements, and SHOULD be suitable for
       handling by software that knows HTML.  The HTML markup must be
       escaped; for example, "<br>" as "&lt;br>".  The HTML markup
       SHOULD be such that it could validly appear directly within an
       HTML <DIV> element.  Receiving software which displays the indicated
       media type.  In this case,
       content SHOULD use the characters markup to aid in displaying it.
   3.  If the Base64 encoding
       may be preceded and followed in value of "type" is "XHTML", the atom:content element by
       whitespace, and lines are separated by a single newline (U+000A)
       character, as required by XML.

5.13  "atom:copyright" Element

   The "atom:copyright" element is a Text construct that conveys a
   human-readable copyright statement for the entry.  atom:entry
   elements content of atom:content
       MAY contain an atom:copyright element, but MUST NOT contain
   more than one. child elements.  The atom:copyright element content SHOULD NOT be used to convey
   machine-readable licensing information.

   If an atom:entry element does not contain XHTML text and
       markup that could validly appear directly within an atom:copyright element,
   then xhtml:div
       element.  Receiving software which displays the atom:copyright element of content SHOULD
       use the containing atom:feed element's
   atom:head element, if present, should be considered to apply markup to the
   entry.

5.14  "atom:head" Element

   The atom:head element acts aid in displaying it.  Escaped markup is
       interpreted as a container for metadata about text representation of markup, and MUST NOT be
       interpreted as markup itself.
   4.  If the feed
   within which value of "type" ends with "+xml" or "/xml", the entry was created.

   atom:entry elements MAY contain at most one atom:head element. content of
       atom:content may include child elements, and SHOULD be suitable
       for handling by software that knows the indicated media type.  If
       the atom:head element "src" attribute is present, it SHOULD be not provided, this would normally mean
       that the first "atom:content" element would contain a single child
       element of atom:entry.

   If an atom:entry is copied into one feed from another feed, then which would serve as the
   atom:head root element of the source feed SHOULD be inserted into the
   atom:entry unless XML document
       of the entry, as copied, already contains an atom:head
   element. indicated type.
   5.  If the atom:entry already contains an atom:head, then that
   atom:head SHOULD be copied without modification.

   [[ ...  example ...  ]] value of "type" begins with "text/" the content of
       atom:content MUST NOT contain child elements.



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   6.  Managing Feed State

   [[ talk about what it means  For all other values of "type", the content of atom:content MUST
       be a valid Base64 encoding [RFC3548], which when decoded SHOULD
       be suitable for handling by software that knows the indicated
       media type.  In this case, the characters in the Base64 encoding
       may be preceded and followed in the atom:content element by
       whitespace, and lines are separated by a single newline (U+000A)
       character.

4.16  The "atom:introspection" Element

   The "atom:introspection" element is a Service construct that conveys
   the URI of an introspection file associated with a feed.


   atomIntrospection =
             element atom:introspection { atomServiceConstruct }


4.17  The "atom:post" Element

   The "atom:post" element is a Service construct that conveys the URI
   used to add entries to keep a view feed.


   atomPost = element atom:post { atomServiceConstruct }


4.18  The "atom:edit" Element

   The "atom:edit" element is a Service construct that conveys the URI
   used to retrieve and edit the source representation of an entry.


   atomEdit = element atom:edit { atomServiceConstruct }


4.19  The "atom:tagline" Element

   The "atom:tagline" element is a feed ]] Text construct that conveys a
   human-readable description or tagline for the feed.


   atomTagline = element atom:tagline { atomTextConstruct }


4.20  The "atom:generator" Element

   The "atom:generator" element's content identifies the software agent



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7.  Securing Atom Documents

   Because Atom is an XML-based format, existing XML security mechanisms
   can be


   used to secure its content.

   Note that while these mechanisms are available to secure Atom
   documents, they should not be used indiscriminately.

7.1  Digital Signatures

   The document element of an Atom document (i.e., atom:feed generate a feed, for debugging and other purposes.


   atomGenerator = element atom:generator {
      atomCommonAttributes,
      attribute url { atomUri }?,
      attribute version { text }?,
      text
   }

   The content of this element, when present, MUST be a string that is a
   human-readable name for the generating agent.

   The atom:generator element MAY have a "uri" attribute whose value
   MUST be a URI reference [RFC3986].  When dereferenced, that URI
   SHOULD produce a representation that is relevant to that agent.

   The atom:generator element MAY have a "version" attribute that
   indicates the version of the generating agent.  When present, its
   value is unstructured text.

4.21  The "atom:info" Element

   The "atom:info" element is a Text construct that conveys a
   human-readable explanation of the feed format itself.  The atom:info
   element SHOULD NOT be considered meaningful by processors; it is a
   convenience to publishers.


   atomInfo = element atom:info { atomTextConstruct }





















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5.  Managing Feed State

   [[ talk about what it means to keep a view of a feed ]]
















































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6.  Securing Atom Documents

   Because Atom is an XML-based format, existing XML security mechanisms
   can be used to secure its content.

6.1  Digital Signatures

   The document element of an Atom document (i.e., atom:feed in an Atom
   Feed Document, atom:entry in an Atom Entry Document) MAY have an
   Enveloped Signature, as described by XML-Signature and Syntax
   Processing [W3C.REC-xmldsig-core-20020212].  Other XML signature
   mechanisms MUST NOT be used on the document element of an Atom
   document.

   Processors MUST NOT reject an Atom document containing such a
   signature because they are not capable of verifying it; they MUST
   continue processing and MAY inform the user of their failure to
   validate the signature.

   In other words, the presence of an element with the namespace URI
   "http://www.w3.org/2000/09/xmldsig#" and a local name of "Signature"
   as a child of the document element must not cause a processor to fail
   merely because of its presence.

   Other elements in an Atom document MUST NOT be signed unless their
   definitions explicitly specify such a capability.

7.2

6.2  Encryption

   The document element of an Atom document (i.e., atom:feed in an Atom
   Feed Document, atom:entry in an Atom Entry Document) MAY be
   encrypted, using the mechanisms described by XML Encryption Syntax
   and Processing [W3C.REC-xmlenc-core-20021210].  Other XML encryption
   mechanisms MUST NOT be used on the document element of an Atom
   document.




















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8.


7.  Embedding Atom in Other Formats

   [[ ...  ]]
















































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9.


8.  Extending Atom

   [[ ...  ]]
















































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10.


9.  IANA Considerations

   An Atom Document, when serialized as XML 1.0, can be identified with
   the following media type:

   MIME media type name: application
   MIME subtype name: atom+xml
   Mandatory parameters: None.
   Optional parameters:
      "charset": This parameter has identical semantics to the charset
         parameter of the "application/xml" media type as specified in
         RFC 3023 [RFC3023].  [RFC3023].
   Encoding considerations: Identical to those of "application/xml" as
      described in RFC 3023 [RFC3023], section 3.2.
   Security considerations: As defined in this specification.  [[update
      upon publication]]
      In addition, as this media type uses the "+xml" convention, it
      shares the same security considerations as described in RFC 3023
      [RFC3023], section 10.
   Interoperability considerations: There are no known interoperability
      issues.
   Published specification: This specification.  [[update upon
      publication]]
   Applications which use this media type: No known applications
      currently use this media type.

   Additional information:

   Magic number(s): As specified for "application/xml" in RFC 3023
      [RFC3023], section 3.2.
   File extension: .atom
   Fragment identifiers: As specified for "application/xml" in RFC 3023
      [RFC3023], section 5.
   Base URI: As specified in RFC 3023 [RFC3023], section 6.
   Macintosh File Type code: TEXT
   Person and email address to contact for further information: Mark
      Nottingham <mnot@pobox.com>
   Intended usage: COMMON
   Author/Change controller: This specification's author(s).  [[update
      upon publication]]

10.1

9.1  Registry of Link Relations

   This registry is maintained by IANA and initially contains the two
   values: "alternate" and "related".  New assignments are subject to
   IESG Approval, as outlined in [RFC2434].  Requests should be made by
   email to IANA, which will then forward the request to the IESG
   requesting approval.  The request should contain discussion of at



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   least the following five topics:

   o  A value for the "rel" attribute that conforms to the syntax rule
      given in Section 3.5.1 4.6.2
   o  Common name for link type.
   o  Description of link type semantics.
   o  Expected display characteristics.
   o  Security considerations.











































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11.


10.  Security Considerations

   Atom document can be encrypted and signed using
   [W3C.REC-xmlenc-core-20021210] and [W3C.REC-xmldsig-core-20020212],
   respectively, and is subject to the security considerations implied
   by their use.













































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12.


11.  References

12.1

11.1  Normative References

   [Atom-autodiscovery]
              Pilgrim, M., "Atom Feed Autodiscovery",  work-in-progress,
              August 2004.

   [Atom-protocol]
              Gregorio, J. and R. Sayre, "The Atom Publishing Protocol",
              work-in-progress, July 2004.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791, September
              1981.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2396bis]
              Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax",  awaiting RFC
              number, December 2004.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2822]  Resnick, P., "Internet Message Format", RFC 2822, April
              2001.

   [RFC3023]  Murata, M., St. Laurent, S. and D. Kohn, "XML Media
              Types", RFC 3023, January 2001.

   [RFC3066]  Alvestrand, H., "Tags for the Identification of
              Languages", BCP 47, RFC 3066, January 2001.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, July 2002.

   [RFC3548]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 3548, July 2003.

   [RFC3986]  Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [W3C.NOTE-datetime-19980827]



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   [W3C.NOTE-datetime-19980827]


              Wolf, M. and C. Wicksteed, "Date and Time Formats", W3C
              NOTE NOTE-datetime-19980827, August 1998.

   [W3C.REC-xml-20040204]
              Yergeau, F., Paoli, J., Sperberg-McQueen, C., Bray, T. and
              E. Maler, "Extensible Markup Language (XML) 1.0 (Third
              Edition)", W3C REC REC-xml-20040204, February 2004.

   [W3C.REC-xml-infoset-20011024]
              Tobin, R. and J. Cowan, "XML Information Set", W3C
              FirstEdition REC-xml-infoset-20011024, October 2001.

   [W3C.REC-xml-names-19990114]
              Hollander, D., Bray, T. and A. Layman, "Namespaces in
              XML", W3C REC REC-xml-names-19990114, January 1999.

   [W3C.REC-xmlbase-20010627]
              Marsh, J., "XML Base", W3C REC REC-xmlbase-20010627, June
              2001.

   [W3C.REC-xmldsig-core-20020212]
              Solo, D., Reagle, J. and D. Eastlake, "XML-Signature
              Syntax and Processing", W3C REC REC-xmldsig-core-20020212,
              February 2002.

   [W3C.REC-xmlenc-core-20021210]
              Reagle, J. and D. Eastlake, "XML Encryption Syntax and
              Processing", W3C REC REC-xmlenc-core-20021210, December
              2002.

12.2

11.2  Informative References

   [RELAX-NG]
              OASIS Technical Committee: RELAX NG, "RELAX NG
              Specification", December 2001.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.












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URIs

   [1]  <http://www.imc.org/atom-syntax/index.html>

   [2]  <http://www.intertwingly.net/wiki/pie/FrontPage>


Authors' Addresses

   Mark Nottingham (editor)

   EMail: mnot@pobox.com
   URI:   http://www.mnot.net/


   Robert Sayre (editor)
   Boswijck Memex Consulting

   EMail: rfsayre@boswijck.com
   URI:   http://boswijck.com































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Appendix A.  Contributors

   The following people contributed to preliminary drafts of this
   document: Tim Bray, Mark Pilgrim, and Sam Ruby.  Norman Walsh
   provided the Relax NG schema.  The content and concepts within are a
   product of the Atom community and the Atom Publishing Format and
   Protocol Working Group.












































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Appendix B.  Collected RELAX NG Compact Schema

   This appendix is informative.

   # -*- Relax NG -*-

   namespace local = ""
   namespace atom =
      "http://purl.org/atom/ns#draft-ietf-atompub-format-04"
   namespace s = "http://www.ascc.net/xml/schematron"

   start = atomFeed | atomEntry

   # Attribute definitions

   atomCommonAttributes =
      attribute xml:base { atomUri }?,
      attribute xml:lang { atomLanguageTag }?

   atomVersionAttribute =
    attribute version {"draft-ietf-atompub-format-05 : do not deploy"}

   # Common Atom Constructs

   atomPlainTextConstruct =
      atomCommonAttributes,
      attribute type { "TEXT" | "HTML" }?,
      text

   atomXHTMLTextConstruct =
      atomCommonAttributes,
      attribute type { "XHTML" },
      (text|anyElement)*

   atomTextConstruct = atomPlainTextConstruct | atomXHTMLTextConstruct

   atomPersonConstruct =
      atomCommonAttributes,
      (element atom:name { text }
       & element atom:uri { atomUri }?
       & element atom:email { atomEmailAddress }?)

   atomDateConstruct =
      atomCommonAttributes,
      xsd:dateTime

   atomServiceConstruct =
      atomCommonAttributes,



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      attribute href { atomUri }

   atomIdentityConstruct =
      atomCommonAttributes,
      (atomUri)


   # atom:feed
   # TODO: Test for multiple atom:link/@rel='alternate' with
   # the same @type The following tests are simple to do,
   # but my validator is giving me trouble.
   # TODO: Debug and add them back
   #       Test for at least one atom:link/@rel='alternate'
   #       Test for atom:author or all atom:entry have atom:author

   # atom:feed

   atomFeed =
      element atom:feed {
         atomCommonAttributes,
         atomVersionAttribute,
         (atomHead
          & atomEntry*
          & anyElement*)
      }

   # atom:head

   atomHead =
      [
         s:rule [
            context = "atom:head"
            s:assert [
               test = "atom:link[@rel='alternate']"
               "An atom:feed must have at least one link element
                with a rel attribute of 'alternate'."
            ]
         ]
         s:rule [
            context = "atom:head"
            s:assert [
     test = "atom:author or not(../atom:entry[count(atom:author) = 0])"
     "An atom:feed must have an atom:author unless all of
      its atom:entry children have an atom:author."
            ]
         ]
      ]
      element atom:head {



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         atomCommonAttributes,
         (atomTitle
          & atomUpdated
          & atomLink+
          & atomId?
          & atomAuthor?
          & atomContributor*
          & atomTagline?
          & atomGenerator?
          & atomInfo?
          & atomCopyright?
          & atomCategory*
          & atomIntrospection?
          & atomPost?
          & anyElement*)
      }

   # atom:entry
   # TODO: Test for multiple atom:link @rel='alternate'
   # with the same @type
   # TODO: Test for required atom:summary

   atomEntry =
      [
         s:rule [
            context = "/atom:entry"
            s:assert [
               test = "@version"
               "The version attribute is required on standalone
                atom:entry elements."
            ]
         ]
         s:rule [
            context = "atom:entry"
            s:assert [
               test = "atom:link[@rel='alternate']"
               "An atom:entry must have at least one link element
                with a rel attribute of 'alternate'