WDIFF

draft-ietf-atompub-format-05.txt --> draft-ietf-atompub-format-06.txt

Network Working Group M. Nottingham, Ed.
Internet-Draft
Expires: July 27, September 13, 2005 R. Sayre, Ed.
Boswijck Memex Consulting
January 26,
March 12, 2005

The Atom Syndication Format
draft-ietf-atompub-format-05
draft-ietf-atompub-format-06

Status of this Memo

This document is an Internet-Draft and is subject to all provisions
of Section 3 of RFC 3667. By submitting this Internet-Draft, I certify each
author represents that any applicable patent or other IPR claims of
which I am he or she is aware have been or will be disclosed, and any of
which I he or she 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
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Internet-Drafts are draft documents valid for a maximum of six months
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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 27, September 13, 2005.

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 . . . . . . . . . . . . . . . . . . . 9
3.1 Text Constructs . . . . . . . . . . . . . . . . . . . . . 9
3.1.1 "type" Attribute . . . . . . . . . . . . . . . . . . . 9
3.2 Person Constructs . . . . . . . . . . . . . . . . . . . . 10 11
3.2.1 The "atom:name" Element . . . . . . . . . . . . . . . 10 11
3.2.2 The "atom:uri" Element . . . . . . . . . . . . . . . . 10 11
3.2.3 The "atom:email" Element . . . . . . . . . . . . . . . 11
3.3 Date Constructs . . . . . . . . . . . . . . . . . . . . . 11
3.4 Service Constructs .
4. Atom Element Definitions . . . . . . . . . . . . . . . . . . 13
4.1 Container Elements . 11
3.4.1 The "href" Attribute . . . . . . . . . . . . . . . . . 11
3.5 Identity Constructs . . 13
4.1.1 The "atom:feed" Element . . . . . . . . . . . . . . . 13
4.1.2 The "atom:entry" Element . . 11
3.5.1 Dereferencing Identity Constructs . . . . . . . . . . 12
3.5.2 Comparing Identity Constructs . . . 14
4.1.3 The "atom:content" Element . . . . . . . . . 12
4. Element Definitions . . . . . 16
4.2 Metadata Elements . . . . . . . . . . . . . . . 14
4.1 The "atom:feed" Element . . . . . 19
4.2.1 The "atom:author" Element . . . . . . . . . . . . 14
4.1.1 The "version" Attribute . . 19
4.2.2 The "atom:category" Element . . . . . . . . . . . . . 14
4.2 20
4.2.3 The "atom:head" "atom:contributor" Element . . . . . . . . . . . . 20
4.2.4 The "atom:copyright Element . . . . . 14
4.2.1 Usage of "atom:head" within "atom:entry" . . . . . . . 16
4.3 . 20
4.2.5 The "atom:entry" "atom:generator" Element . . . . . . . . . . . . . . . . . 16
4.4 21
4.2.6 The "atom:title" "atom:icon" Element . . . . . . . . . . . . . . . . . 18
4.5 21
4.2.7 The "atom:id" Element . . . . . . . . . . . . . . . . . . 18
4.6 21
4.2.8 The "atom:link" "atom:image" Element . . . . . . . . . . . . . . . . . 18
4.6.1 23
4.2.9 The "href" Attribute . . "atom:link" Element . . . . . . . . . . . . . . . 19
4.6.2 23
4.2.10 The "rel" Attribute . "atom:published" Element . . . . . . . . . . . . 26
4.2.11 The "atom:source-feed" Element . . . . 19
4.6.3 The "type" Attribute . . . . . . . 26
4.2.12 The "atom:subtitle" Element . . . . . . . . . . 20
4.6.4 The "hreflang" Attribute . . 26
4.2.13 The "atom:summary" Element . . . . . . . . . . . . . 20
4.6.5 27
4.2.14 The "title" Attribute . . "atom:title" Element . . . . . . . . . . . . . . 20
4.6.6 27
4.2.15 The "length" Attribute . "atom:updated" Element . . . . . . . . . . . . . 27
5. Securing Atom Documents . . 20
4.7 The "atom:updated" Element . . . . . . . . . . . . . . . . 20
4.8 The "atom:published" Element 28
5.1 Digital Signatures . . . . . . . . . . . . . . . 21
4.9 The "atom:author" Element . . . . . 28
5.2 Encryption . . . . . . . . . . . 21
4.10 The "atom:contributor" Element . . . . . . . . . . . . . 21
4.11 The "atom:host" Element 28
6. Extending Atom . . . . . . . . . . . . . . . . 21
4.12 The "atom:copyright" Element . . . . . . . 29
6.1 Extensions From Non-Atom Vocabularies . . . . . . . 21
4.13 The "atom:category" Element . . . 29
6.2 Extensions To the Atom Vocabulary . . . . . . . . . . . 22
4.13.1 The "term" Attribute . . 29
6.3 Software Processing of Foreign Markup . . . . . . . . . . 29
6.4 Extension Elements . . . . 22
4.13.2 The "scheme" Attribute . . . . . . . . . . . . . . . 22
4.13.3 The "label" attribute . 29
6.4.1 Simple Extension Elements . . . . . . . . . . . . . . 22
4.14 The "atom:summary" Element 30
6.4.2 Structured Extension Elements . . . . . . . . . . . . 30
7. IANA Considerations . . . 22
4.15 The "atom:content" Element . . . . . . . . . . . . . . . 23

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4.15.1 The "type" attribute . . 31
7.1 Registry of Link Relations . . . . . . . . . . . . . . 23
4.15.2 The "src" attribute . . 31

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8. Security Considerations . . . . . . . . . . . . . . 23
4.15.3 Processing Model . . . . 33
8.1 HTML and XHTML Content . . . . . . . . . . . . . . 24
4.16 The "atom:introspection" Element . . . . 33
8.2 URIs . . . . . . . . 25
4.17 The "atom:post" Element . . . . . . . . . . . . . . . . 25
4.18 The "atom:edit" Element . . . 33
8.3 IRIs . . . . . . . . . . . . . 25
4.19 The "atom:tagline" Element . . . . . . . . . . . . . . 33
8.4 Encryption and Signing . 25
4.20 The "atom:generator" Element . . . . . . . . . . . . . . 25
4.21 The "atom:info" Element . . . 33
9. References . . . . . . . . . . . . . 26
5. Managing Feed State . . . . . . . . . . . . 34
9.1 Normative References . . . . . . . . 27
6. Securing Atom Documents . . . . . . . . . . . 34
9.2 Informative References . . . . . . . 28
6.1 Digital Signatures . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . 28
6.2 Encryption . . . . . . . . . . . . 36
A. Contributors . . . . . . . . . . . . 28
7. Embedding Atom in Other Formats . . . . . . . . . . . . 37
B. Collected RELAX NG Compact Schema . . 29
8. Extending Atom . . . . . . . . . . . 38
C. Change Log . . . . . . . . . . . . 30
9. IANA Considerations . . . . . . . . . . . . . 45
Intellectual Property and Copyright Statements . . . . . . . 31
9.1 Registry of Link Relations . . . . . . . . . . . . . . . . 31
10. Security Considerations . . . . . . . . . . . . . . . . . . 33
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 34
11.1 Normative References . . . . . . . . . . . . . . . . . . . 34
11.2 Informative References . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 36
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 37
B. Collected RELAX NG Compact Schema . . . . . . . . . . . . . 38
C. Revision History . . . . . . . . . . . . . . . . . . . . . . 45
Intellectual Property and Copyright Statements . . . . . . . 47

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1. Introduction

Atom is an XML-based document format which describes lists 48

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1. Introduction

Atom is an XML-based document format that describes lists of related
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] <http://www.imc.org/atom-syntax/index.html>
The Atom Wiki Web site [2]
<http://www.intertwingly.net/wiki/pie/FrontPage>

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-05:do not deploy"
xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-05">
<head>
xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-06">

<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>
<id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
<updated>2003-12-13T18:30:02Z</updated>
</entry>
</feed>

[[anchor4: Ask yourself: is the example atom:entry valid?]]

1.3 Conformance

[[ talk about atom documents and atom consumers, Notational Conventions

This specification describes conformance in terms of two kinds of
artefacts; Atom Feed Documents and how Atom Entry documents.
Additionally, it places some requirements
are placed on them ]]

1.4 Notational Conventions Atom Processors.

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]. [RFC2119], as
scoped to those conformance targets.

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-05 http://purl.org/atom/ns#draft-ietf-atompub-format-06

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].
[W3C.REC-xml-infoset-20040204]. However, this specification uses a
shorthand for two common terms; the phrase "Information Item" is
omitted when naming Element Information Items and Attribute

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omitted when naming Element Information Items and Attribute
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 root is atom:feed. the atom:feed element.

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

namespace
atom =
"http://purl.org/atom/ns#draft-ietf-atompub-format-05" ="http://purl.org/atom/ns#draft-ietf-atompub-format-06"

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.

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 [RFC3986] [RFC3987] 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 natural language of for the element's content. element and its
children. The language context is only significant for elements and
attributes declared to be "language-sensitive" by this specification.
Requirements regarding the content and interpretation of xml:lang are
specified in XML 1.0 [W3C.REC-xml-20040204] [W3C.REC-xml-20040204], Section 2.12.

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

[[ discussion

Atom allows the use of IRIs [RFC3987], rather than only URIs
[RFC3986]. For resolution, IRIs can easily be converted to URIs.
When comparing IRIs serving as Identity Constructs, they MUST NOT be

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converted to URIs. Please note that by definition, every URI escaping and i18n, is an
IRI, so any URI can be used where an IRI ]]

[[ is needed.

[[anchor7: discussion of white space ]] space]]

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

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Documents can be extended.

Atom Processors MAY keep state (e.g., metadata in atom:feed, entries)
sourced from Atom Feed Documents and combine them with other Atom
Feed Documents, in order to facilitate a contiguous view of the
contents of a feed. The manner in which Atom Feed Documents are
combined in order to reconstruct a feed (e.g., updating entries and
metadata, dealing with missing entries) is out of the scope of this
specification, but may be defined by an extension to Atom.

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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 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. Except for the "type" attribute, the content of Text
constructs is language-sensitive.

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

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

atomTextConstruct = atomPlainTextConstruct | atomXHTMLTextConstruct

3.1.1 "type" Attribute

Text constructs MAY have a "type" attribute. [[anchor11: Some feel
type attributes with different allowable values in different elements
is confusing.]]. When present, the value MUST be one of "TEXT", "HTML" "text",
"html" or "XHTML". "xhtml". If the "type" attribute is not provided, software Atom
Processors MUST behave as though it were present with a value of "TEXT".
"text".

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

If the value is "TEXT", "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 Atom Processors MAY display it
using normal text rendering techniques such as proportional fonts,
white-space collapsing, and justification.

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If the value of "type" is "HTML", "html", the content of the Text construct
MUST NOT contain child elements, and SHOULD be suitable for handling
by software that knows HTML. The
as HTML [W3C.REC-html401-19991224]. Any markup must within MUST be
escaped; for example, "<br>" as "&lt;br>". The HTML markup within SHOULD
be such that it

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Receiving software which displays the
element, after unescaping. Atom Processors that display such content
MAY use the markup to aid in displaying it.

[[example its display.

[[anchor12: example atom entry w/ escaped markup]]

If the value of "type" is "XHTML", "xhtml", the content of the Text construct
MAY contain child elements. The content SHOULD
MUST be a single XHTML div element [W3C.REC-xhtml-basic-20001219].
The XHTML div MUST contain XHTML text and markup that could validly
appear directly within an xhtml:div XHTML div element. Receiving software The XHTML div element itself
MUST NOT be considered part of the content. Atom Processors which displays
display 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.

Example:

...
<summary type="xhtml">
<div xmlns="http://www.w3.org/1999/xhtml">
This is <b>XHTML</b> content.
</div>
</summary>
...
<summary type="xhtml">
<xhtml:div xmlns:xhtml="http://www.w3.org/1999/xhtml">
This is <xhtml:b>XHTML</xhtml:b> content.
</xhtml:div>
</summary>
...

The following example assumes that the XHTML namespace has been bound
to the "xh" prefix earlier in the document:

...
<summary type="xhtml">
<xh:div>
This is <xh:b>XHTML</xh:b> content.
</xh:div>
</summary>
...

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3.2 Person Constructs

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

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

This specification assigns no significance to the order of appearance
of the child elements 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. The content of atom:name is language sensitive. 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 an IRI 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 an IRI reference [RFC3986]. [RFC3987].

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. Person constructs MAY contain an
atom:email element, but MUST NOT contain more than one. Its content
MUST be an e-mail address conform to the addr-spec BNF rule in [RFC2822].

3.3 Date Constructs

A Date construct is an element whose content MUST conform to the
date-time BNF rule in [RFC3339]. I.e., the content of this element
matches this regular expression:

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[0-9]{8}T[0-9]{2}:[0-9]{2}:[0-9]{2}(\.[0-9]+)
?(Z|[\+\-][0-9]{2}:[0-9]{2})

As a result, the date values conform to the following specifications:
[RFC3339], [W3C.REC-xmlschema-2-20041028],
[W3C.NOTE-datetime-19980827], and [ISO.8601.1988].

atomDateConstruct =
atomCommonAttributes,
xsd:dateTime

3.4 Service Constructs

A Service construct is an empty

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4. Atom Element Definitions

4.1 Container Elements

4.1.1 The "atom:feed" Element

[[anchor21: Substantially changed from format-05, review carefully.]]

The "atom:feed" element that conveys is the URI document (i.e., top-level) element of
an Atom Publishing Protocol [Atom-protocol] service Feed Document, acting as a container for metadata and data
associated with an
entry the feed. Its element children consist of one or
more metadata elements followed by zero or more atom:entry child
elements.

This specification assigns no significance to the order of atom:entry
elements within the feed.

atomServiceConstruct

atomFeed =
atomCommonAttributes,
attribute href
element atom:feed { atomUri }

3.4.1 The "href" Attribute
atomCommonAttributes,
(atomAuthor?
& atomCategory*
& atomContributor*
& atomCopyright?
& atomGenerator?
& atomIcon?
& atomId?
& atomImage?
& atomLink+
& atomSubtitle?
& atomTitle
& atomUpdated
& anyElement* ),
atomEntry*
}

The "href" attribute contains the a URI of the service. atom:service following child elements MUST have a "href" attribute, whose value MUST be a URI
reference [RFC3986].

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

3.5 Identity Constructs

An Identity construct is an element whose content conveys a
permanent, universally unique identifier for the construct's parent.
Its content MUST be a URI, as are defined by [RFC3986]. 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:feed elements MUST contain exactly one atom:author element,
UNLESS all of its Identity
construct the atom:feed element's child atom:entry elements
contain an atom:author element. atom:feed elements MUST NOT change. Put another way, an Identity construct
contain more than one atom:author element. [[anchor22:
inheritance]]
o atom:feed elements MAY contain any number of atom:category
elements.

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pertains to all instantiations of a particular Atom entry or feed;
revisions retain the same content in their Identity constructs.

atomIdentityConstruct =
atomCommonAttributes,
(atomUri)

3.5.1 Dereferencing Identity Constructs

The content of an Identity construct

o atom:feed elements MAY be dereferencable (e.g. an
HTTP URI). However, processors contain any number of atom:contributor
elements.
o atom:feed elements MUST NOT assume it to be
dereferencable.

The content of an Identity construct contain more than one atom:copyright
element.
o atom:feed elements MUST be created in a way that
assures uniqueness, and it is suggested that the Identity construct
be stored along with the associated resource.

Because of the risk of confusion between URIs that would be
equivalent if dereferenced, the following normalization strategy is
strongly encouraged when generating Identity constructs:

o Provide the scheme in lowercase characters.
o Provide the host, if any, in lowercase characters. NOT contain more than one atom:generator
element.
o Only perform percent-encoding where it is essential. atom:feed elements MUST NOT contain more than one atom:icon
element.
o Use uppercase A-through-F characters when percent-encoding. atom:feed elements MUST NOT contain more than one atom:image
element.
o Prevent dot-segments appearing in paths. atom:feed elements MUST NOT contain more than one atom:id element.
o For schemes that define atom:feed elements MUST contain at least one atom:link element
with a default authority, use an empty
authority if the default is desired. relation of "alternate".
o For schemes that define an empty path to be equivalent to atom:feed elements SHOULD contain one atom:link element with a path rel
attribute value of "/", use "/".
o For schemes that define "self" and SHOULD contain a port, use href attribute with
an empty port if absolute URI as its value. This URI identifies the default
is desired.
o Preserve empty fragment identifiers feed and queries.
o Ensure that all portions of the URI are UTF-8 encoded NFC form
Unicode strings.

3.5.2 Comparing Identity Constructs

Instances of Identity constructs can be compared a
representation equivalent to determine whether
an entry or feed is the same as one seen before. Processors feed.
o atom:feed elements MUST
compare Identity constructs on a character-by-character basis in a
case-sensitive fashion.

As NOT contain more than one atom:link
element with a result, two URIs rel attribute value of "alternate" that resolve to has the
same resource but are not
character-for-character identical will be considered different for
the purposes of Identifier comparison.

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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 type attribute value. 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 purposes of comparison.

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4. Element Definitions

4.1 feed. atom:feed elements MAY contain
additional atom:link elements beyond those described above.
o atom:feed elements MUST NOT contain more than one atom:subtitle
element.
o atom:feed elements MUST contain exactly one atom:title element.
o atom:feed elements MUST contain exactly one atom:updated element.
o atom:feed elements MUST NOT contain atom:entry elements with
identical atom:id values.

4.1.2 The "atom:feed" "atom:entry" Element

The "atom:feed" element is the document (i.e., top-level) "atom:entry" element of represents an Atom Feed Document, individual entry, acting as a
container for metadata and data associated with the feed. Its first entry. This
element can appear as a child MUST be atom:head,
which MAY be followed zero of the atom:feed element, or more it can
appear as the document (i.e., top-level) element of a standalone Atom
Entry Document.

The 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.

atomFeed elements of atom:entry.

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atomEntry =
element atom:feed atom:entry {
atomCommonAttributes,
atomVersionAttribute,
(atomHead
(atomAuthor?
& atomEntry* atomCategory*
& anyElement*)
}

4.1.1 The "version" Attribute

atom:feed elements MUST have a "version" attribute whose content
indicates the version of the Atom specification that the feed
conforms to. The content of this attribute is unstructured text.

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

atomVersionAttribute =
attribute version {"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 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.

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atomHead =
element atom:head {
atomCommonAttributes,
(atomTitle
& atomUpdated
& atomLink+
& atomId?
& atomAuthor? atomContent?
& atomContributor*
& atomTagline? atomCopyright?
& atomGenerator? atomId
& atomInfo? atomLink*
& atomCopyright? atomPublished?
& atomCategory* atomSourceFeed?
& atomIntrospection? atomSummary?
& atomTitle
& atomPost? atomUpdated &
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 MUST contain exactly one atom:author element,
unless, in an Atom Feed Document, the atom:feed element contains
an atom:author element itself. atom:entry elements MUST NOT
contain more than one atom:author element. [[anchor24: What if
there's a source-feed element? This is required): busted. We should make
author required for atom:feed and optional for atom:entry. No
inheritance co-constraints required. --R. Sayre]]
o atom:head atom:entry elements MAY contain any number of atom:category
elements.
o atom:entry elements MAY contain any number of atom:contributor
elements.
o atom:entry elements MUST NOT contain more than one atom:copyright
element.
o atom:entry elements MUST contain exactly one atom:title atom:id element.
o atom:head 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".
o atom:head [[anchor25: "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. 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 value." This
requirement predates @hreflang. Keep it? --R. Sayre]] atom:entry
elements MAY contain additional atom:link elements beyond those
described above.
o atom:head atom:entry elements MUST NOT contain exactly more than one atom:author element,
UNLESS all of the 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 atom:head elements MUST NOT contain more than one an
atom:contributor element.
o atom:head elements MUST NOT contain more than one an
atom:copyright element.
o atom:head elements MUST NOT contain more than one an atom:id
element.
o atom:head elements MUST contain exactly one atom:updated atom:published
element.
o atom:head elements MAY contain any number of atom:category
elements.
o atom:head atom:entry elements MUST NOT contain more than one atom:post
atom:source-feed element.

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o atom:head atom:entry elements MUST NOT contain more than one
atom:introspection an atom:summary element in any of
the following cases: [[anchor26: Do these requirements reflect the
WG's decisions? --R. Sayre]]
* the atom:entry element contains no atom:content element.
[[anchor27: Net result: Atom entries MUST have an atom:summary
or an atom:content element.]]
* the atom:entry contains an atom:content that has a "src"
attribute (and is thus empty).
* the atom:entry contains content that is encoded in Base64; i.e.
the "type" attribute of atom:content is a MIME media type
[RFC2045] and does not begin with "text/" nor end with "+xml".
o atom:head atom:entry elements MUST NOT contain more than one atom:tagline atom:summary
element.
o atom:head atom:entry elements MUST NOT contain more than have exactly one atom:generator "atom:title" element.
o atom:head atom:entry elements MUST NOT contain more than exactly one atom:info atom:updated element.

4.2.1 Usage

4.1.3 The "atom:content" Element

The "atom:content" element either contains or links to the content of "atom:head" within "atom:entry"

In this case,
the atom:head element acts as a container entry. Except for metadata
about the feed within which the entry was created.

If an atom:entry is copied into one feed from another feed, then "type" and "src" attributes, the
atom:head element content
of the source feed SHOULD be inserted into the atom:content is language-sensitive. atom:entry unless the entry, as copied, already contains an atom:head
element. If the atom:entry already contains an atom:head, then that
atom:head SHOULD be copied without modification.

[[ ... example ... ]]

4.3 The "atom:entry" Element

The "atom:entry" elements MUST
contain zero or one atom:content elements.

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atomInlineTextContent =
element represents an individual entry. This atom:content {
atomCommonAttributes,
attribute type { "text" | "html" | atomMediaType }?,
(text)*
}

atomInlineXHTMLContent =
element can appear as 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

4.1.3.1 The "type" attribute

atom:content MAY have a child of "type" attribute. When present, the atom:feed element, value
MAY be one of "text", "html", or "xhtml". Failing that, it can
appear as the document (i.e., top-level) element of MUST be a standalone Atom
Entry Document.

When appearing in an
MIME media type [RFC2045] with a discrete top-level type (see Section
5 of [RFC2045]). If the type attribute is not provided, Atom Entry Document, atom:entry elements
Processors MUST
have behave as though it were present with a "version" value of
"text".

4.1.3.2 The "src" attribute

atom:content MAY have a "src" attribute, whose content indicates the version of the
Atom specification that value MUST be an IRI
reference [RFC3987]. If the entry conforms to.

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

The atom:entry element present, Atom
Processors MAY contain any namespace-qualified
[W3C.REC-xml-names-19990114] elements as children. This
specification assigns no significance use the IRI to retrieve the order of appearance of content. If the child elements of atom:entry. "src"

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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 MUST have exactly one "atom:title" element.
o atom:entry elements MUST contain exactly one atom:id element.
o atom:entry elements that contain no child

attribute is present, atom:content element MUST contain at least one atom:link element with a rel be empty. That is to say,
the content may be retrievable using "src=" IRI, or it may be
contained within atom:content, but not both.

If the "src" attribute
value of "alternate". atom:entry elements is present, the "type" attribute SHOULD be
provided and MUST NOT contain more
than one atom:link element with be a rel attribute MIME media type [RFC2045], rather than "text",
"html", or "xhtml". The value of
"alternate" is advisory; that has is to say, upon
dereferencing the same IRI 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 begins with "text/" or ends with "+xml", the
content SHOULD be local; that is to say, no "src" attribute value. atom:entry
elements MAY contain additional atom:link elements beyond those
described above.
o atom:entry elements MUST contain exactly one atom:updated element.
o atom:entry elements MUST NOT contain more than one atom:published
element.
o atom:entry elements MUST contain exactly one atom:author element,
unless, in an Atom Feed Document, should be
provided. [[anchor31: J. Reschke: I'm not sure I understand what
this is for. It seems to discourage putting XML data out-of-band.
Why? ... Explaining the atom:head element contains
an atom:author element itself. atom:entry elements MUST NOT
contain more than one atom:author element.
o atom:entry elements MUST NOT contain more than one
atom:contributor element.
o atom:entry elements MUST NOT contain more than one atom:host
element.
o atom:entry elements MUST NOT contain more than one atom:copyright
element.
o atom:entry elements MAY contain any number issue instead of atom:category
elements.

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may lead to better results...]]

4.1.3.3 Processing Model

Atom Format January 2005

o atom:entry elements Documents MUST contain an atom:summary element in any of conform to the following cases:
* the atom:entry element contains no rules. Atom Processors
MUST interpret atom:content element.
* according to the atom:entry contains an first applicable rule.

1. If the value of "type" is "text", the content of atom:content which has
MUST NOT contain child elements. Such text is intended to be
presented to humans in a "src"
attribute (and readable fashion. Thus, Atom Processors
MAY display it using normal text rendering techniques such as
proportional fonts, white-space collapsing, and justification.
2. If the value of "type" is thus empty).
* "html", the content of atom:content
MUST NOT contain child elements, and SHOULD be suitable for
handling as HTML [W3C.REC-html401-19991224]. 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. Atom Processors that display the atom:entry contains
content which is encoded SHOULD use the markup to aid in Base64;
i.e. displaying it.
3. If the value of "type" attribute is "xhtml", the content of atom:content is a MIME media type
[RFC2045] and does not begin with "text/" nor end with "+xml".
o atom:entry elements MUST NOT contain more than one atom:summary
element.
o atom:entry elements MUST NOT contain more than one atom:edit
element.
o atom:entry elements
MUST NOT contain more than one atom:head
element.

4.4 The "atom:title" Element

The "atom:title" element is a Text construct that conveys be a
human-readable title for an entry or feed.

atomTitle = single XHTML div element atom:title { atomTextConstruct }

4.5 The "atom:id" Element
[W3C.REC-xhtml-basic-20001219]. The "atom:id" element is an Identity construct XHTML div MUST contain XHTML
text and markup that conveys a
permanent, universally unique identifier for could validly appear within an entry or feed.

atomId = element atom:id { atomIdentityConstruct }

4.6 The "atom:link" Element XHTML div
element. The atom:link element is an empty XHTML div element that defines a reference
from an itself MUST NOT be considered
part of the content. Atom Document Processors that display the content
MAY use the markup to aid in displaying it. Escaped markup is
interpreted as a Web resource.

atomLink = element atom:link {
atomCommonAttributes,
attribute href { atomUri },
attribute rel { atomNCName | atomUri }?,
attribute type { atomMediaType }?,
attribute hreflang { atomLanguageTag }?,
attribute title { text }?, representation of markup, and MUST NOT be
interpreted as markup itself.
4. If the value of "type" ends with "+xml" or "/xml"
(case-insensitive), the content of atom:content may include child
elements, and SHOULD be suitable for handling as the indicated
media type. If the "src" attribute length { text }?,
empty is not provided, this would

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}

4.6.1 The "href" Attribute

The "href" attribute contains

normally mean that the link's URI. Link constructs MUST
have a href attribute, whose value MUST be "atom:content" element would contain a URI reference [RFC3986].

xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to
single child element which would serve as the
href attribute's content.

4.6.2 The "rel" Attribute

Link elements MAY have an "rel" attribute that indicates root element of the link
relation
XML document of the indicated type.
5. If the "rel" attribute is not present, value of "type" begins with "text/" (case-insensitive),
the link
element content of atom:content MUST be interpreted as if NOT contain child elements.
6. For all other values of "type", the link relation type is
"alternate".

rel_attribute = segment-nz-nc / URI

The value content of "rel" atom:content MUST
be either a name, valid Base64 encoding [RFC3548], which is non-empty and does
not contain any colon (":") characters, or a URI [RFC3986]. Note
that use of a relative reference is not allowed. If a name is given,
implementations MUST consider the link relation type to when decoded SHOULD
be equivalent
to suitable for handling as the same name registered within indicated media type. In this
case, the IANA Registry of Link
Relations Section 9, and thus characters in the URI that would Base64 encoding may be obtained by
appending preceded and
followed in the value of atom:content element by whitespace, and lines are
separated by a single newline (U+000A) character.

4.1.3.4 Examples

XHTML inline:

...
<content type="xhtml">
<div xmlns="http://www.w3.org/1999/xhtml">
This is <b>XHTML</b> content.
</div>
</content>
...
<content type="xhtml">
<xhtml:div xmlns:xhtml="http://www.w3.org/1999/xhtml">
This is <xhtml:b>XHTML</xhtml:b> content.
</xhtml:div>
</content>
...

The following example assumes that the rel attribute XHTML namespace has been bound
to the string
"http://www.iana.org/assignments/relation/". The value of "rel"
describes the meaning of "xh" prefix earlier in the link, but does not impose any behavioral
requirements on implementations. document:

...
<content type="xhtml">
<xh:div>
This document defines two initial values for the Registry of Link
Relations: is <xh:b>XHTML</xh:b> content.
</xh:div>
</content>
...

4.2 Metadata Elements

4.2.1 The value "alternate" signifies "atom:author" Element

The "atom:author" element is a Person construct that indicates the URI in the value
author of the href entry or feed.

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atomAuthor = element atom:author { atomPersonConstruct }

4.2.2 The "atom:category" Element

The "atom:category" element conveys information about a category
associated with an entry or feed.

atomCategory =
element atom:category {
atomCommonAttributes, attribute term { text },
attribute scheme { atomUri }?,
attribute label { text }?,
empty
}

4.2.2.1 The "term" Attribute

The "term" attribute is a string that identifies an alternate version of the resource described
by category to
which the containing element. entry or feed belongs. Category elements MUST have a
"term" attribute.

4.2.2.2 The value "related" signifies "scheme" Attribute

The "scheme" attribute is an IRI that the URI identifies a categorization
scheme. Category elements MAY have a "scheme" attribute.

4.2.2.3 The "label" attribute

The "label" attribute provides a human-readable label for display in the value
end-user applications. The content of the href "label" attribute identifies is
language-sensitive. Category elements MAY have a resource related "label" attribute.

4.2.3 The "atom:contributor" Element

The "atom:contributor" element is a Person construct that indicates a
person or other entity who contributed to the resource described by
the containing atom:feed entry or atom:entry element. For example, the
feed for feed.

atomContributor = element atom:contributor { atomPersonConstruct }

4.2.4 The "atom:copyright Element

The "atom:copyright" element is a site which discusses the performance of the search engine
at "http://search.example.com" might contain, as Text construct that conveys a child of
atom:head:

atomCopyright = element atom:copyright { atomTextContstruct }

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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.

4.6.3

The "type" Attribute

Link elements MAY have a type attribute, whose value MUST conform atom:copyright element SHOULD NOT be used to
the syntax of a MIME media type [RFC2045].

The type attribute's value is convey
machine-readable licensing information.

If an advisory media type; it is a hint
about atom:entry element does not contain an atom:copyright element,
then the type atom:copyright element of the representation which containing atom:feed element's
atom:head element, if present, is expected considered to apply to be returned
when the value of the href attribute is dereferenced. Note that the
type attribute does not override the actual media type returned with the representation.

4.6.4 entry.

4.2.5 The "hreflang" Attribute "atom:generator" Element

The "hreflang" attribute's "atom:generator" element's content describes the language of the
resource pointed to by identifies the href attribute. When agent used together with
the rel="alternate", it implies to
generate a translated feed, for debugging and other purposes.

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

The content of the entry.
Link elements MAY have an hreflang attribute, whose value this element, when present, MUST be a
language tag [RFC3066].

4.6.5 The "title" Attribute

The "title" attribute conveys string that is a
human-readable information about the
link. Link elements name for the generating agent.

The atom:generator element MAY have a title attribute.

4.6.6 The "length" Attribute

The "length" "uri" attribute indicates whose value
MUST be an advisory length of the linked
content in octets; it is IRI reference [RFC3987]. When dereferenced, that IRI
SHOULD produce a hint about the content length of the representation returned when the URI in the href attribute that is
dereferenced. Note relevant to that the length agent.

The atom:generator element MAY have a "version" attribute does not override that
indicates the
actual content length version of the representation as reported by the
underlying protocol.

Link elements MAY have a length attribute.

4.7 generating agent. When present, its
value is unstructured text.

4.2.6 The "atom:updated" "atom:icon" Element

The "atom:updated" element "atom:icon" element's content is a Date construct indicating the most
recent instant in time when an entry or feed was modified in IRI [RFC3987] which
identifies an image which provides iconic visual identification for a way
the producer considers significant. Therefore, not all modifications
necessarily result in
feed. The image SHOULD have an aspect ratio of one (horizontal) to
one (vertical), and should be suitable for presentation at a small
size.

atomIcon = element atom:icon { atomCommonAttributes, (atomUri) }

4.2.7 The "atom:id" Element

[[anchor45: Substantially changed atom:updated value.

Publishers MAY change the value of this from format-05, review carefully]]

The "atom:id" element over time.
Processors MAY present entries sorted using this value. Processors
MAY choose not to present entries until the instant in time specified conveys a permanent, universally unique

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in Format March 2005

identifier for an entry or feed.

atomId = element atom:id { atomCommonAttributes, (atomUri) }

Its content MUST be an IRI, as defined by [RFC3987]. Note that the
definition of "IRI" excludes relative references. Though the IRI
might use a dereferencable scheme, Atom Processors MUST NOT assume it
can be dereferenced.

When an Atom document is relocated, migrated, syndicated,
republished, exported or imported, the atom:updated element has passed.

atomUpdated = content of its atom:id element atom:updated { atomDateConstruct }

4.8 The "atom:published" Element

The "atom:published"
MUST NOT change. Put another way, an atom:id element is pertains to all
instantiations of a Date construct indicating an
instant particular Atom entry or feed; revisions retain
the same content in time associated with their atom:id elements.

The content of an event early atom:id element MUST be created in a way that
assures uniqueness; it is suggested that the life cycle of
the entry. Typically, atom:published will atom:id element be associated
stored along with the
initial creation or first availability associated resource.

Because of the resource.

Processors MAY present entries sorted using this value. Processors
MAY choose not to present entries until risk of confusion between IRIs that would be
equivalent if dereferenced, the instant following normalization strategy is
strongly encouraged when generating atom:id elements:

o Provide the scheme in time specified lowercase characters.
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 atom:published element has passed.

4.9 The "atom:author" Element

The "atom:author" element default is desired.
o For schemes that define an empty path to be equivalent to a Person construct path
of "/", use "/".
o For schemes that indicates define a port, use an empty port if the default author
is desired.
o Preserve empty fragment identifiers and queries.
o Ensure that all components of the IRI are appropriately
character-normalized, e.g. by using NFC or NFKC.

4.2.7.1 Comparing atom:id

Instances of atom:id elements can be compared to determine whether an
entry or feed

atomAuthor = element atom:author { atomPersonConstruct }

4.10 The "atom:contributor" Element

The "atom:contributor" element is a Person construct that indicates a
person or other entity who contributes to the entry.

atomContributor = element atom:contributor { atomPersonConstruct }

4.11 The "atom:host" Element

The "atom:host" element's content conveys a domain name or network
address associated with an entry's origin. Its content same as one seen before. Processors MUST be a
domain name [RFC1035], a dotted-decimal IPv4 address [RFC0791], or a
colon-delimited IPv6 address [RFC2460].

4.12 The "atom:copyright" Element

The "atom:copyright" element is
compare atom:id elements on a Text construct that conveys character-by-character basis (in a
human-readable copyright statement for an entry or feed.

The atom:copyright element SHOULD NOT
case-sensitive fashion). Comparison operations MUST be used to convey based solely
on the IRI character strings, and MUST NOT rely on dereferencing the
IRIs.

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machine-readable licensing information.

If an atom:entry element does not contain an atom:copyright element,
then the atom:copyright element of the containing atom:feed element's
atom:head element, if present, should be considered to apply to the
entry.

4.13 The "atom:category" Element

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

atomCategory = element atom:category {
atomCommonAttributes,
attribute term { text },
attribute scheme { atomUri }?,
attribute label { text }?,
empty
}

4.13.1 The "term" Attribute

The "term" attribute is a string which identifies the category to
which the entry or feed belongs. Category elements MUST have a
"term" attribute.

4.13.2 The "scheme" Attribute

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

4.13.3 The "label" attribute

The "label" attribute provides

As a human-readable label result, two IRIs that may resolve to the same resource but are not
character-for-character identical will be
displayed considered different for
the purposes of identifier comparison.

For example:

http://www.example.org/thing
http://www.example.org/Thing
http://www.EXAMPLE.org/thing
HTTP://www.example.org/thing

are four distinct identifiers, despite their differences in end-user applications. Category elements MAY have a
"label" attribute.

4.14 case.

Likewise,

http://www.example.com/~bob
http://www.example.com/%7ebob
http://www.example.com/%7Ebob

are three distinct identifiers, because IRI %-escaping is significant
for the purposes of comparison.

4.2.8 The "atom:summary" "atom:image" Element

The "atom:summary" element "atom:image" element's content is an IRI [RFC3987] which
identifies an image which provides visual identification for a Text construct that conveys a short
summary, abstract or excerpt of feed.
The image SHOULD have an entry.

atomSummary aspect ratio of 2 (horizontal) to 1
(vertical).

atomImage = element atom:summary atom:image { atomTextConstruct atomCommonAttributes, (atomUri) }

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4.15

4.2.9 The "atom:content" "atom:link" Element

The "atom:content" "atom:link" element either contains is an empty element that defines a reference
from an entry or links feed to the content of
the entry. atom:entry elements MUST contain zero or one atom:content
elements.

atomInlineTextContent a Web resource.

atomLink =
element atom:content atom:link {
atomCommonAttributes,
attribute type href { "TEXT" | "HTML" atomUri },
attribute rel { atomNCName | atomMediaType atomUri }?,
(text)*
}

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

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

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}

atomContent = atomInlineTextContent
| atomInlineXHTMLContent
| atomOutOfLineContent

4.15.1

4.2.9.1 The "type" "href" Attribute

The "href" attribute contains the link's IRI. atom:link elements
MUST have a href attribute, whose value MUST be a IRI reference
[RFC3987].

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

4.2.9.2 The "rel" Attribute

atom:link elements MAY have an "rel" attribute that indicates the
link relation type. If the "rel" attribute

atom:content MAY have a "type" attribute, When is not present, the value MAY link
element MUST be one interpreted as if the link relation type is
"alternate".

rel_attribute = segment-nz-nc / IRI

The value of "TEXT", "HTML", or "XHTML". Failing that, it "rel" MUST be either a
MIME media name that is non-empty and does
not contain any colon (":") characters, or a IRI [RFC3987]. Note
that use of a relative reference is not allowed. If a name is given,
implementations MUST consider the link relation type [RFC2045] in which, to use be equivalent
to the same name registered within the terminology IANA Registry of Link
Relations Section
5 of [RFC2045], 7, and thus the top level is a discrete type. If IRI that would be obtained by
appending the type value of the rel attribute is not provided, software MUST behave as though it were
present with a to the string
"http://www.iana.org/assignments/relation/". The value of "TEXT".

4.15.2 "rel"
describes the meaning of the link, but does not impose any behavioral
requirements on implementations.

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

The "src" attribute

atom:content MAY have a "src" attribute, whose value MUST be a URI
reference [RFC3986]. If "alternate" signifies that the "src" IRI in the value of the href
attribute is present, software MAY
use identifies an alternate version of the URI to retrieve resource described
by the content. If containing element.

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

An identical link might appear as a child of any atom:entry whose

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present, atom:content MUST be empty. That is to say, the

content may
be retrievable using "src=" URI, or it may be contained within
atom:content, but not both.

If the "src" attribute is present, the "type" attribute SHOULD be
provided and MUST be contains a MIME media type [RFC2045], rather than "TEXT",
"HTML", or "XHTML". discussion of that same search engine.

The value is advisory; that is to say, upon
dereferencing the URI to retrieve the content, if the server
providing "self" signifies that content also provides a media type, the
server-provided media type is authoritative.

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

4.15.3 Processing Model

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

1. If the containing element.

The value is "TEXT", "enclosure" signifies that the content of atom:content MUST NOT
contain child elements. Such text is intended to be presented to
humans IRI 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" is "HTML", the content of atom:content
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 href
attribute identifies a related resource which displays is potentially large in
size and may require special handling by consuming software. For
Link constructs with rel="enclosure", the
content length attribute SHOULD use be
provided.

The value "via" signifies that the markup to aid IRI in displaying it.
3. If the value of "type" the href
attribute identifies a resource that is "XHTML", the content source 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 the content SHOULD
use information
provided in the markup containing element.

4.2.9.3 The "type" Attribute

Link elements MAY have a type attribute, whose value MUST conform to aid in displaying it. Escaped markup
the syntax of a MIME media type [RFC2045].

The type attribute's value is an advisory media type; it is
interpreted as a text representation hint
about the type of markup, and MUST NOT the representation that is expected to be
interpreted as markup itself.
4. If returned
when the value of "type" ends the href attribute is dereferenced. Note that the
type attribute does not override the actual media type returned with "+xml" or "/xml",
the representation.

4.2.9.4 The "hreflang" Attribute

The "hreflang" attribute's content describes the language of
atom:content may include child elements, and SHOULD be suitable
for handling the
resource pointed to by software that knows the indicated media type. If href attribute. When used together with
the "src" rel="alternate", it implies a translated version of the entry.
Link elements MAY have an hreflang attribute, whose value MUST be a
language tag [RFC3066].

4.2.9.5 The "title" Attribute

The "title" attribute conveys human-readable information about the
link. The content of the "title" attribute is not provided, this would normally mean
that language sensitive.
Link elements MAY have a title attribute.

4.2.9.6 The "length" Attribute

The "length" attribute indicates an advisory length of the "atom:content" element would contain linked
content in octets; it is a single child
element which would serve as hint about the root element content length of the XML document
of
representation returned when the indicated type.
5. If IRI in the value of "type" begins with "text/" href attribute is
dereferenced. Note that the length attribute does not override the
actual content length of
atom:content MUST NOT contain child elements. the representation as reported by the
underlying protocol.

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6. For all other values of "type",

Link elements MAY have a length attribute.

4.2.10 The "atom:published" Element

The "atom:published" element is a Date construct indicating an
instant in time associated with an event early in the content life cycle of atom:content MUST
the entry. Typically, atom:published will be a valid Base64 encoding [RFC3548], which when decoded SHOULD associated with the
initial creation or first availability of the resource.

atomPublished = element atom:published { atomDateConstruct }

4.2.11 The "atom:source-feed" Element

If an atom:entry is copied from one feed into another feed, then the
source atom:feed's metadata (all child elements of atom:feed other
than the atom:entry elements) MAY be suitable for handling preserved within the copied
entry by software that knows adding an atom:source-feed child element, if it is not
already present in the indicated
media type. In this case, entry, and including some or all of the characters in source
feed's metadata elements as the Base64 encoding
may atom:source-feed element's children.
Such metadata SHOULD be preceded preserved if the source atom:feed contains
any of the child elements atom:author, atom:contributor,
atom:copyright, or atom:category and followed those child elements are not
present in the atom:content source atom:entry.

atomSourceFeed =
element atom:source-feed {
atomCommonAttributes,
(atomAuthor?
& atomCategory*
& atomContributor*
& atomCopyright?
& atomGenerator?
& atomIcon?
& atomId?
& atomImage?
& atomLink+
& atomSubtitle?
& atomTitle
& atomUpdated
& anyElement* )
}

4.2.12 The "atom:subtitle" Element

The "atom:subtitle" element by
whitespace, and lines are separated by is a single newline (U+000A)
character.

4.16 Text construct that conveys a
human-readable description or subtitle for a feed.

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atomSubtitle = element atom:subtitle { atomTextConstruct }

4.2.13 The "atom:introspection" "atom:summary" Element

The "atom:introspection" "atom:summary" element is a Service Text construct that conveys
the URI a short
summary, abstract or excerpt of an introspection file associated with a feed.

atomIntrospection entry.

atomSummary = element atom:introspection atom:summary { atomServiceConstruct atomTextConstruct }

4.17

4.2.14 The "atom:post" "atom:title" Element

The "atom:post" "atom:title" element is a Service Text construct that conveys the URI
used to add entries to a
human-readable title for an entry or feed.

atomPost

atomTitle = element atom:post atom:title { atomServiceConstruct atomTextConstruct }

4.18

4.2.15 The "atom:edit" "atom:updated" Element

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

atomUpdated = element atom:updated { atomDateConstruct }

Publishers MAY change the value of this element over time.

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5. Securing Atom Documents

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

5.1 Digital Signatures

The root 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].

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 source representation signature.

In other words, the presence of an entry.

atomEdit = element atom:edit { atomServiceConstruct }

4.19 The "atom:tagline" Element

The "atom:tagline" element is with the namespace IRI
"http://www.w3.org/2000/09/xmldsig#" and a Text construct that conveys local name of "Signature"
as a
human-readable description or tagline for child of the feed.

atomTagline = document element atom:tagline { atomTextConstruct }

4.20 The "atom:generator" Element must not cause an Atom 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.

5.2 Encryption

The "atom:generator" element's content identifies root 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 software agent mechanisms described by XML Encryption Syntax and
Processing [W3C.REC-xmlenc-core-20021210].

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6. Extending Atom

6.1 Extensions From Non-Atom Vocabularies

This specification describes Atom's XML markup vocabulary. Markup
from other vocabularies ("foreign markup") can be used in an Atom
document. Note that the atom:content element is designed to generate a feed, for debugging support
the inclusion of arbitrary foreign markup.

6.2 Extensions To the Atom Vocabulary

Future versions of this specification may add new elements and other purposes.

atomGenerator = element atom:generator {
atomCommonAttributes,
attribute url { atomUri }?,
attribute
attributes to the Atom markup vocabulary. Software written to
conform to this version { text }?,
text
}

The content of the specification will not be able to
process such markup correctly and, in fact, will not be able to
distinguish it from markup error. For the purposes of this
discussion, unrecognized markup from the Atom vocabulary will be
considered "foreign "markup".

Unlike markup from other vocabularies, foreign markup from the Atom
vocabulary MAY appear at any location in an Atom document.

6.3 Software Processing of Foreign Markup

Software processing an Atom Document which encounters foreign markup
in a location that is legal according to this element, when present, specification MUST NOT
stop processing or signal an error. It may be a string the case that the
software is a
human-readable name for able to process the generating agent.

The atom:generator element MAY have a "uri" attribute whose value
MUST be a URI reference [RFC3986]. foreign markup correctly and does so.
Otherwise, such markup is termed "unknown foreign markup".

When dereferenced, that URI
SHOULD produce a representation that unknown foreign markup is relevant encountered as a child of atom:entry,
atom:feed, or a Person Construct, software MAY [[anchor67: Changed to that agent.

The atom:generator element
MAY have a "version" attribute that
indicates from SHOULD. Republishers might want to copy it. --R. Sayre]]
bypass the version markup and any textual content and MUST NOT change its
behavior as a result of the generating agent. markup's presence.

When present, its
value is unstructured text.

4.21 The "atom:info" Element

The "atom:info" element unknown foreign markup is encountered in a Text construct that conveys a
human-readable explanation Contruct or
atom:content element, software SHOULD ignore the markup and process
any text content of foreign elements as though the feed format itself. The atom:info
element SHOULD NOT be surrounding markup
were not present.

6.4 Extension Elements

Atom allows foreign markup anywhere in an Atom document. Child
elements of atom:entry and atom:feed are considered "metadata"
elements, and are described below. Child elements of Person
Constructs are 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 apply to keep a view the construct. The role of a feed ]]
other foreign markup is undefined by this specification.

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6. Securing Atom Documents

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

6.4.1 Simple Extension Elements

A Simple Extension element MUST NOT have any attributes or child
elements. The element MAY contain either character data, or be used to secure its content.

6.1 Digital Signatures
empty.

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, can be interpreted as described by XML-Signature and Syntax
Processing [W3C.REC-xmldsig-core-20020212].

Processors MUST NOT reject an Atom document containing such a
signature because they are not capable simple property (or name/value
pair) of verifying it; they MUST
continue processing and MAY inform the user parent element that encloses it. The pair consisting of their failure to
validate the signature.

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

Other elements in an Atom document MUST NOT the
property. If the element is empty, then the property value can be signed unless their
definitions explicitly specify such a capability.

6.2 Encryption
interpreted as an empty string.

6.4.2 Structured Extension Elements

The document root element of an Atom document (i.e., atom:feed in an Atom
Feed Document, atom:entry in an Atom Entry Document) a Structured Extension element MUST have at least
one attribute or child element. It MAY have attributes, it MAY
contain well-formed XML content (including character data), or it MAY
be
encrypted, using empty.

The structure of a Structured Extension element, including the order
of its child elements, could be significant.

This specification does not provide an interpretation of a Structured
Extension element. The syntax of the XML contained in the element,
and an interpretation of how the element relates to its containing
element is defined by the specification of the mechanisms described by XML Encryption Syntax
and Processing [W3C.REC-xmlenc-core-20021210].

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7. Embedding Atom in Other Formats

[[ ... ]]

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8. Extending Atom

[[ ... ]] extension.

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7. 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
[[anchor71: 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 [[anchor72: update upon
publication]]
Applications which that 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
[[anchor73: update upon publication]]

9.1

7.1 Registry of Link Relations

This registry is maintained by IANA and initially contains the two five
values: "alternate" "alternate", "related", "self", "enclosure", and "related". "via". 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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discussion of at least the following five topics:

o A value for the "rel" attribute that conforms to the syntax rule
given in Section 4.6.2 4.2.9.2
o Common name for link type.
o Description of link type semantics.
o Expected display characteristics.
o Security considerations.

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10.

8. Security Considerations

8.1 HTML and XHTML Content

Text Constructs and atom:content allow the delivery of HTML and XHTML
to receiving software, which may process it. Many elements in these
languages are considered 'unsafe' in that they open clients to one or
more types of attack. Implementers of software which processes Atom
should carefully consider their handling of every type of element
when processing incoming (X)HTML in Atom documents. See the security
sections of RFC 2854 and HTML 4.01 for guidance.

Atom Processors should pay particular attention to the security of
the IMG, SCRIPT, EMBED, OBJECT, FRAME, FRAMESET, IFRAME, META, and
LINK elements, but other elements may also have negative security
properties.

(X)HTML can either directly contain or indirectly reference
executable content.

8.2 URIs

Atom Processors handle URIs. See Section 7 of [RFC3986].

8.3 IRIs

Atom Processors handle IRIs. See Section 8 of [RFC3987].

8.4 Encryption and Signing

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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11.

9. References

11.1

9.1 Normative References

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

[Atom-protocol]
Gregorio, J.

[ISO.8601.1988]
International Organization for Standardization, "Data
elements 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 interchange formats - implementation Information interchange
- Representation of dates and
specification", STD 13, RFC 1035, November 1987. times", ISO Standard 8601,
June 1988.

[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.

[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.

[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.

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

[W3C.REC-html401-19991224]

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Wolf, M. and C. Wicksteed, "Date

Raggett, D., Hors, A. and Time Formats", I. Jacobs, "HTML 4.01
Specification", W3C REC REC-html401-19991224, December
1999.

[W3C.REC-xhtml-basic-20001219]
Baker, M., Ishikawa, M., Matsui, S., Stark, P., Wugofski,
T. and T. Yamakami, "XHTML Basic", W3C
NOTE NOTE-datetime-19980827, August 1998.
REC REC-xhtml-basic-20001219, December 2000.

[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.

[W3C.REC-xml-infoset-20040204]
Cowan, J. and R. Tobin, "XML Information Set", Set (Second
Edition)", W3C
FirstEdition REC-xml-infoset-20011024, October 2001. REC REC-xml-infoset-20040204, February
2004.

[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.

11.2

[W3C.REC-xmlschema-2-20041028]
Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes
Second Edition", W3C REC REC-xmlschema-2-20041028, October
2004.

9.2 Informative References

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

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[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:

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

Robert Sayre (editor)
Boswijck Memex Consulting

EMail:

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" "http://purl.org/atom/ns#draft-ietf-atompub-format-06"

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)

## Container elements

# 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" "atom:feed"
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" "atom:feed"
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 atom:feed {

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

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}

# 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'."
]
]
s:rule [
context = "atom:entry"
s:assert [
test = "atom:author or ../atom:author"
"An atom:entry must have an atom:author
if the parent atom:feed does not."
]
]

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]

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

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# atom:title

atomTitle atom:content

atomInlineTextContent =
element atom:title 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 { atomTextConstruct "text" | "html" | "xhtml" | atomMediaType }?,
attribute src { atomUri },
empty
}

atomContent = atomInlineTextContent
| atomInlineXHTMLContent
| atomOutOfLineContent

## Metadata Elements

# atom:id

atomId atom:author

atomAuthor = element atom:id atom:author { atomIdentityConstruct atomPersonConstruct }

atomLink

# atom:category

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

# atom:updated
# TODO: Test for a timezone that SHOULD be UTC

atomUpdated = element atom:updated { atomDateConstruct }

# atom:published atom:contributor

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atomPublished

atomContributor = element atom:published atom:contributor { atomDateConstruct atomPersonConstruct }

# atom:author

atomAuthor atom:copyright

atomCopyright = element atom:author atom:copyright { atomPersonConstruct atomTextConstruct }

# atom:contributor

atomContributor atom:generator

atomGenerator = element atom:contributor atom:generator { atomPersonConstruct
atomCommonAttributes,
attribute uri { atomUri }?,
attribute version { text }?,
text
}

# atom:host atom:icon

atomIcon = element atom:icon { atomCommonAttributes, (atomUri) }

# TODO: tighten this up
atomHost atom:id

atomId = element atom:host atom:id { text }

# atom:copyright

atomCopyright atom:image

atomImage = element atom:copyright atom:image { atomTextConstruct atomCommonAttributes, (atomUri) }

# atom:category

atomCategory atom:link

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

# atom:summary

atomSummary atom:published

atomPublished = element atom:summary atom:published { atomTextConstruct atomDateConstruct }

# atom:content

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

atomInlineXHTMLContent atom:source-feed

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

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atomOutOfLineContent =
element atom:content {

atomCommonAttributes,
attribute type { "TEXT" | "HTML" | "XHTML" | atomMediaType }?,
attribute src { atomUri },
empty
}

atomContent = atomInlineTextContent
| atomInlineXHTMLContent
| atomOutOfLineContent

# atom:introspection

atomIntrospection =
element atom:introspection { atomServiceConstruct
( atomTitle
& atomUpdated
& atomLink+
& atomIcon
& atomId?
& atomImage?
& atomSubtitle?
& atomAuthor?
& atomContributor*
& atomCopyright?
& atomCategory*
& atomGenerator?
& anyElement* )
}

# atom:post

atomPost atom:subtitle

atomSubtitle = element atom:post atom:subtitle { atomServiceConstruct atomTextConstruct }

# atom:edit

atomEdit atom:summary

atomSummary = element atom:edit atom:summary { atomServiceConstruct atomTextConstruct }

# atom:tagline

atomTagline atom:title

atomTitle = element atom:tagline atom:title { atomTextConstruct }

# atom:generator

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

atomInfo TODO: Test for a timezone that SHOULD be UTC

atomUpdated = element atom:info atom:updated { atomTextConstruct atomDateConstruct }

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# Low-level simple types

# TODO: can anything more specific be said about these types?

atomNCName = xsd:string { minLength = "1" pattern = "[^:]*" }
atomMediaType = text
atomLanguageTag = text
atomUri = text
atomEmailAddress = text

# Extensibility

anyForeignElement =
element * - (atom:* | local:*)

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{
(attribute * { text }
| text
| anyForeignElement)*
}

anyForeignAttribute =
attribute * - (atom:* | local:* | xml:*) { text }

anyElement =
element * - atom:*
{
(attribute * { text }
| text
| anyElement)*
}

# EOF

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Appendix C. Revision History

[[ this Change Log

[[anchor85: This section should be removed before final publication. ]]
publication.]]

-06: Move Identity Construct into atom:id (only place it's used)
atom:id values must be unique within a feed.
restore atom:copyright definition mistakenly dropped during
alphabetizing.
Remove atom:head, add atom:source-feed, and "Extension Construct"
text in an effort to accurately reflect WG consensus on data model
and extensibility, acknowledging two opinions in favor of
atom:head.
Note @hreflang issue.
Add comment on atom:entry/atom:summary requirements.
Rework atom:id text. The dereferencing section didn't talk about
dereferencing.
Remove protocol reference.
Alphabetize where appropriate (PaceOrderSpecAlphabetically).
Add mI language (PaceExtendingAtom).
Add atom:icon and atom:image (PaceImageAndIcon).
Change atom:tagline to atom:subtitle
Add inline XHTML language (PaceXHTMLNamespaceDiv).
Change "TEXT" etc, to lowercase
Change example id IRI to urn:uuid:...
Add rel="self" (PaceFeedLink).
Add Feed State text (PaceNoFeedState).
Move to IRIs (PaceIRI).
Add rel="via" (PaceLinkRelVia).
Add rel="enclosure" (PaceEnclosuresAndPix).
Remove info and host (PaceRemoveInfoAndHost)
Clarify order of entries (PaceEntryOrder).
Remove version attribute (PaceRemoveVersionAttr).
Date format roundup (PaceDatesXSD).
Remove Service construct and elements.
fix atom:contributor cardinality typo
Removed motivation/design principles note; if we haven't come up
with them by now...
Put conformance text into notational conventions.
Removed instances of 'software'; too specific.
Added refs to HTML and XHTML.
Updated ref to Infoset.
Various editorial tweaks.
Fix RFC 3023 refs in IANA section
Adjust head/link requirement

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fix @version typos
-05: Add RNC from N. Walsh.
Re-organize element definitions.
Lift the prohibition on other types of DSig and encryption.
Remove text on "indiscriminate use" of DSig and XMLEnc.
-04: Update URI terms for 2396bis.
Add Category construct (PaceCategoryRevised).
Insert paranoid XHTML interpretation guidelines.
Adjust atom:copyright, per chairs' instruction.
Add atom:host as child element of atom:entry, per chairs'
direction (PacePersonConstruct).
Add link/content co-constraint (PaceContentOrLink).
Remove atom:origin as a side effect of adding atom:head to
atom:entry (PaceHeadInEntry).
Add optional length attribute to atom:link (PaceLinkRelated).
Add Link registry to Link Construct, IANA Considerations
placeholder (PaceFieldingLinks).
Change definition of atom:updated (PaceUpdatedDefinition).
-03: Move definition of Link @rel to format spec, restrict
acceptable values (PaceMoveLinkElement, PaceLinkAttrDefaults).
Add Service Construct, head/post, head/introspection, entry/edit
(PaceServiceElement).
Add Text Construct, entry/content (PaceReformedContent3).
Add entry/published (PaceDatePublished).
Adjust definition of Identity Construct per chairs' direction to
"fix it."
Add Sayre to editors.
-02: Removed entry/modified, entry/issued, entry/created; added
entry/updated (PaceDateUpdated).
Changed date construct from W3C date-time to RFC3339
(PaceDateUpdated).
Feed links to HTML pages should be reflected back
(PaceLinkReflection).
Added Identity construct (PaceIdConstruct).
Changed feed/id and entry/id to be Identity constructs
(PaceIdConstruct).
Changed entry/origin's content so that it's the same as the feed's
id, rather than its link/@rel="alternate" (PaceIdConstruct).
Added "Securing Atom Documents" (PaceDigitalSignatures).
-01: Constrained omission of "Information Item" to just elements and
attributes.
Clarified xml:lang inheritence.

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Removed entry- and feed-specific langauge about xml:lang (covered
by general discussion of xml:lang)
Changed xml:lang to reference XML for normative requirements.

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Changed "... MUST be a string" to "... is unstructued text."
Remomved langauge about DOCTYPEs, PIs, Comments, Entities.
Changed atom:url to atom:uri, @url to @uri
Introduced atom:head
Introduced "Atom Feed Document" and "Atom Entry Document".
Removed requirement for all elements and attributes to be
namespace-qualified; now children of selective elements
Added extensibility to Person constructs.
Removed requirement for media types to be registered
(non-registered media types are legal)
Added atom:origin (PaceEntryOrigin)
Added requirement for entry/id to be present and a URI
(PaceEntryIdRequired).
Clarified approach to Comments, PIs and well-formedness, as per
RFC3470.
Referenced escaping algorithm in XML.
Assorted editorial nits and cleanup, refactoring
-00: Initial IETF Internet-Draft submission.
Added optional version attribute to entry
(PaceEntryElementNeedsVersionAttribute).
Added hreflang attribute (PaceHrefLang).
Clarified inheritence of copyright element (PaceItemCopyright).
Added xml:lang to entries (PaceItemLang).
Tweaked Infoset-related language (PaceNoInfoSet).
Clarified lack of structure in version attribute
(PaceVersionAsText).
Changed approach to XML Base (PaceXmlBaseEverywhere).
Added XML Base processing to atom:id (PaceXmlBaseId).
Various editorial cleanup and adjustments for IETF publication.

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Intellectual Property Statement

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pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
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on the procedures with respect to rights in RFC documents can be
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specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.

Disclaimer of Validity

This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
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ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.

Acknowledgment

Funding for the RFC Editor function is currently provided by the
Internet Society.

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