Network Working Group M. Nottingham, Ed.
Internet-Draft
Expires: September 13, 2005 R. Sayre, Ed.
Boswijck Memex Consulting
March 12, 2005
The Atom Syndication Format
draft-ietf-atompub-format-06
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
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Copyright Notice
Copyright (C) The Internet Society (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 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 . . . . . . . . . . . . . . . . . . . . 11
3.2.1 The "atom:name" Element . . . . . . . . . . . . . . . 11
3.2.2 The "atom:uri" Element . . . . . . . . . . . . . . . . 11
3.2.3 The "atom:email" Element . . . . . . . . . . . . . . . 11
3.3 Date Constructs . . . . . . . . . . . . . . . . . . . . . 11
4. Atom Element Definitions . . . . . . . . . . . . . . . . . . 13
4.1 Container Elements . . . . . . . . . . . . . . . . . . . . 13
4.1.1 The "atom:feed" Element . . . . . . . . . . . . . . . 13
4.1.2 The "atom:entry" Element . . . . . . . . . . . . . . . 14
4.1.3 The "atom:content" Element . . . . . . . . . . . . . . 16
4.2 Metadata Elements . . . . . . . . . . . . . . . . . . . . 19
4.2.1 The "atom:author" Element . . . . . . . . . . . . . . 19
4.2.2 The "atom:category" Element . . . . . . . . . . . . . 20
4.2.3 The "atom:contributor" Element . . . . . . . . . . . . 20
4.2.4 The "atom:copyright Element . . . . . . . . . . . . . 20
4.2.5 The "atom:generator" Element . . . . . . . . . . . . . 21
4.2.6 The "atom:icon" Element . . . . . . . . . . . . . . . 21
4.2.7 The "atom:id" Element . . . . . . . . . . . . . . . . 21
4.2.8 The "atom:image" Element . . . . . . . . . . . . . . . 23
4.2.9 The "atom:link" Element . . . . . . . . . . . . . . . 23
4.2.10 The "atom:published" Element . . . . . . . . . . . . 26
4.2.11 The "atom:source-feed" Element . . . . . . . . . . . 26
4.2.12 The "atom:subtitle" Element . . . . . . . . . . . . 26
4.2.13 The "atom:summary" Element . . . . . . . . . . . . . 27
4.2.14 The "atom:title" Element . . . . . . . . . . . . . . 27
4.2.15 The "atom:updated" Element . . . . . . . . . . . . . 27
5. Securing Atom Documents . . . . . . . . . . . . . . . . . . 28
5.1 Digital Signatures . . . . . . . . . . . . . . . . . . . . 28
5.2 Encryption . . . . . . . . . . . . . . . . . . . . . . . . 28
6. Extending Atom . . . . . . . . . . . . . . . . . . . . . . . 29
6.1 Extensions From Non-Atom Vocabularies . . . . . . . . . . 29
6.2 Extensions To the Atom Vocabulary . . . . . . . . . . . . 29
6.3 Software Processing of Foreign Markup . . . . . . . . . . 29
6.4 Extension Elements . . . . . . . . . . . . . . . . . . . . 29
6.4.1 Simple Extension Elements . . . . . . . . . . . . . . 30
6.4.2 Structured Extension Elements . . . . . . . . . . . . 30
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . 31
7.1 Registry of Link Relations . . . . . . . . . . . . . . . . 31
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8. Security Considerations . . . . . . . . . . . . . . . . . . 33
8.1 HTML and XHTML Content . . . . . . . . . . . . . . . . . . 33
8.2 URIs . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.3 IRIs . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.4 Encryption and Signing . . . . . . . . . . . . . . . . . . 33
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 34
9.1 Normative References . . . . . . . . . . . . . . . . . . . 34
9.2 Informative References . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 36
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 37
B. Collected RELAX NG Compact Schema . . . . . . . . . . . . . 38
C. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 45
Intellectual Property and Copyright Statements . . . . . . . 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.
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 <http://www.imc.org/atom-syntax/index.html>
The Atom Wiki Web site
<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.
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1.2 Example
A minimal, single-entry Atom Feed Document:
<?xml version="1.0" encoding="UTF-8"?>
<feed
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>
<entry>
<title>Atom-Powered Robots Run Amok</title>
<link href="http://example.org/2003/12/13/atom03"/>
<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 Notational Conventions
This specification describes conformance in terms of two kinds of
artefacts; Atom Feed Documents and Atom Entry documents.
Additionally, it places some requirements on 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], as
scoped to those conformance targets.
This specification uses XML Namespaces [W3C.REC-xml-names-19990114]
to uniquely identify XML elements names. It uses the following
namespace prefixes for the indicated namespace URIs;
"atom": 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-20040204]. However, this specification uses a
shorthand for two common terms; the phrase "Information Item" is
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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 root is the atom:feed element.
An Atom Entry Document represents exactly one Atom Entry, outside of
the context of an Atom Feed. Its root is the atom:entry element.
namespace
atom ="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 [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 for the 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], Section 2.12.
atomCommonAttributes =
attribute xml:base { atomUri }?,
attribute xml:lang { atomLanguageTag }?
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 is an
IRI, so any URI can be used where an IRI is needed.
[[anchor7: discussion of white space]]
Atom is an extensible format. See the section titled 'Extending
Atom' later in this document for a full description of how Atom
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 small
quantities. Except for the "type" attribute, the content of Text
constructs is language-sensitive.
atomPlainTextConstruct =
atomCommonAttributes,
attribute type { "text" | "html" }?,
text
atomXHTMLTextConstruct =
atomCommonAttributes,
attribute type { "xhtml" },
(text|anyElement)*
atomTextConstruct = atomPlainTextConstruct | atomXHTMLTextConstruct
3.1.1 "type" Attribute
Text constructs MAY have a "type" attribute. [[anchor11: Some feel
type attributes with different allowable values in different elements
is confusing.]]. When present, the value MUST be one of "text",
"html" or "xhtml". If the "type" attribute is not provided, Atom
Processors MUST behave as though it were present with a value of
"text".
Note that MIME media types [RFC2045] are not acceptable values for
the "type" attribute.
If the value is "text", the content of the Text construct MUST NOT
contain child elements. Such text is intended to be presented to
humans in a readable fashion. Thus, 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", the content of the Text construct
MUST NOT contain child elements, and SHOULD be suitable for handling
as HTML [W3C.REC-html401-19991224]. Any markup within MUST be
escaped; for example, "<br>" as "<br>". HTML markup within SHOULD
be such that it could validly appear directly within an HTML <DIV>
element, after unescaping. Atom Processors that display such content
MAY use markup to aid in its display.
[[anchor12: example atom entry w/ escaped markup]]
If the value of "type" is "xhtml", the content of the Text construct
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 within an XHTML div element. The XHTML div element itself
MUST NOT be considered part of the content. Atom Processors which
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 (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 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 an IRI reference [RFC3987].
xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to the
atom:uri element's content.
3.2.3 The "atom:email" Element
The "atom:email" element's content conveys an e-mail address
associated with the person. Person constructs MAY contain an
atom:email element, but MUST NOT contain more than one. Its content
MUST 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
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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 is the document (i.e., top-level) element of
an Atom Feed Document, acting as a container for metadata and data
associated with 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.
atomFeed =
element atom:feed {
atomCommonAttributes,
(atomAuthor?
& atomCategory*
& atomContributor*
& atomCopyright?
& atomGenerator?
& atomIcon?
& atomId?
& atomImage?
& atomLink+
& atomSubtitle?
& atomTitle
& atomUpdated
& anyElement* ),
atomEntry*
}
The following child elements are defined by this specification (note
that the presence of some of these elements is required):
o atom:feed elements MUST contain exactly one atom:author element,
UNLESS all of the atom:feed element's child atom:entry elements
contain an atom:author element. atom:feed elements MUST NOT
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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o atom:feed elements MAY contain any number of atom:contributor
elements.
o atom:feed elements MUST NOT contain more than one atom:copyright
element.
o atom:feed elements MUST NOT contain more than one atom:generator
element.
o atom:feed elements MUST NOT contain more than one atom:icon
element.
o atom:feed elements MUST NOT contain more than one atom:image
element.
o atom:feed elements MUST NOT contain more than one atom:id element.
o atom:feed elements MUST contain at least one atom:link element
with a relation of "alternate".
o atom:feed elements SHOULD contain one atom:link element with a rel
attribute value of "self" and SHOULD contain a href attribute with
an absolute URI as its value. This URI identifies the feed and a
representation equivalent to the feed.
o atom:feed 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: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:entry" Element
The "atom:entry" element represents an individual entry, acting as a
container for metadata and data associated with the entry. This
element can appear as a child of the atom:feed element, or it can
appear as the document (i.e., top-level) element of a standalone Atom
Entry Document.
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 of atom:entry.
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atomEntry =
element atom:entry {
atomCommonAttributes,
(atomAuthor?
& atomCategory*
& atomContent?
& atomContributor*
& atomCopyright?
& atomId
& atomLink*
& atomPublished?
& atomSourceFeed?
& atomSummary?
& atomTitle
& 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 busted. We should make
author required for atom:feed and optional for atom:entry. No
inheritance co-constraints required. --R. Sayre]]
o 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:id element.
o atom:entry elements that contain no child atom:content element
MUST contain at least one atom:link element with a rel attribute
value of "alternate". [[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." This
requirement predates @hreflang. Keep it? --R. Sayre]] atom:entry
elements MAY contain additional atom:link elements beyond those
described above.
o atom:entry elements MUST NOT contain more than one atom:published
element.
o atom:entry elements MUST NOT contain more than one
atom:source-feed element.
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o atom:entry elements MUST contain 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:entry elements MUST NOT contain more than one atom:summary
element.
o atom:entry elements MUST have exactly one "atom:title" element.
o atom:entry elements MUST contain exactly one atom:updated element.
4.1.3 The "atom:content" Element
The "atom:content" element either contains or links to the content of
the entry. Except for the "type" and "src" attributes, the content
of atom:content is language-sensitive. atom:entry elements MUST
contain zero or one atom:content elements.
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atomInlineTextContent =
element atom:content {
atomCommonAttributes,
attribute type { "text" | "html" | atomMediaType }?,
(text)*
}
atomInlineXHTMLContent =
element atom:content {
atomCommonAttributes,
attribute type {
"xhtml" |
atomMediaType
}?,
(text|anyElement)*
}
atomOutOfLineContent =
element atom:content {
atomCommonAttributes,
attribute type {
"text" |
"html" |
"xhtml" |
atomMediaType }?,
attribute src { atomUri },
empty
}
atomContent =
atomInlineTextContent |
atomInlineXHTMLContent |
atomOutOfLineContent
4.1.3.1 The "type" attribute
atom:content MAY have a "type" attribute. When present, the value
MAY be one of "text", "html", or "xhtml". Failing that, it MUST be a
MIME media type [RFC2045] with a discrete top-level type (see Section
5 of [RFC2045]). If the type attribute is not provided, Atom
Processors MUST behave as though it were present with a value of
"text".
4.1.3.2 The "src" attribute
atom:content MAY have a "src" attribute, whose value MUST be an IRI
reference [RFC3987]. If the "src" attribute is present, Atom
Processors MAY use the IRI to retrieve the content. If the "src"
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attribute is present, atom:content MUST 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 is present, the "type" attribute SHOULD be
provided and MUST be a MIME media type [RFC2045], rather than "text",
"html", or "xhtml". The value is advisory; that is to say, upon
dereferencing the 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 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 issue instead of just trying to enforce it
may lead to better results...]]
4.1.3.3 Processing Model
Atom Documents MUST conform to the following rules. Atom Processors
MUST interpret atom:content according to the first applicable rule.
1. If the value of "type" is "text", the content of atom:content
MUST NOT contain child elements. Such text is intended to be
presented to humans in a 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 "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 "<br>". The HTML
markup SHOULD be such that it could validly appear directly
within an HTML <DIV> element. Atom Processors that display the
content SHOULD use the markup to aid in displaying it.
3. If the value of "type" is "xhtml", the content of atom:content
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 within an XHTML div
element. The XHTML div element itself MUST NOT be considered
part of the content. Atom Processors that 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.
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 is not provided, this would
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normally mean that the "atom:content" element would contain a
single child element which would serve as the root element of the
XML document of the indicated type.
5. If the value of "type" begins with "text/" (case-insensitive),
the content of atom:content MUST NOT contain child elements.
6. For all other values of "type", the content of atom:content MUST
be a valid Base64 encoding [RFC3548], which when decoded SHOULD
be suitable for handling as the indicated media type. In this
case, the characters in the Base64 encoding may be preceded and
followed in the atom:content element by whitespace, and lines are
separated by a single newline (U+000A) character.
4.1.3.4 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 XHTML namespace has been bound
to the "xh" prefix earlier in the document:
...
<content type="xhtml">
<xh:div>
This is <xh:b>XHTML</xh:b> content.
</xh:div>
</content>
...
4.2 Metadata Elements
4.2.1 The "atom:author" Element
The "atom:author" element is a Person construct that indicates the
author of the 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 the category to
which the entry or feed belongs. Category elements MUST have a
"term" attribute.
4.2.2.2 The "scheme" Attribute
The "scheme" attribute is an IRI that 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
end-user applications. The content of the "label" attribute is
language-sensitive. Category elements MAY have a "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 entry or feed.
atomContributor = element atom:contributor { atomPersonConstruct }
4.2.4 The "atom:copyright Element
The "atom:copyright" element is a Text construct that conveys a
human-readable copyright statement for an entry or feed.
atomCopyright = element atom:copyright { atomTextContstruct }
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The atom:copyright element SHOULD NOT be used to convey
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, is considered to apply to the entry.
4.2.5 The "atom:generator" Element
The "atom:generator" element's content identifies the agent used to
generate a feed, for debugging and other purposes.
atomGenerator =
element atom:generator {
atomCommonAttributes,
attribute uri { atomUri }?,
attribute version { text }?,
text
}
The content of this element, when present, MUST be a string that is a
human-readable name for the generating agent.
The atom:generator element MAY have a "uri" attribute whose value
MUST be an IRI reference [RFC3987]. When dereferenced, that IRI
SHOULD produce a representation that is relevant to that agent.
The atom:generator element MAY have a "version" attribute that
indicates the version of the generating agent. When present, its
value is unstructured text.
4.2.6 The "atom:icon" Element
The "atom:icon" element's content is an IRI [RFC3987] which
identifies an image which provides iconic visual identification for a
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 from format-05, review carefully]]
The "atom:id" element conveys a permanent, universally unique
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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 content of its atom:id element
MUST NOT change. Put another way, an atom:id element pertains to all
instantiations of a particular Atom entry or feed; revisions retain
the same content in their atom:id elements.
The content of an atom:id element MUST be created in a way that
assures uniqueness; it is suggested that the atom:id element be
stored along with the associated resource.
Because of the risk of confusion between IRIs that would be
equivalent if dereferenced, the following normalization strategy is
strongly encouraged when generating atom:id elements:
o Provide the scheme in 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 default is desired.
o For schemes that define an empty path to be equivalent to a path
of "/", use "/".
o For schemes that define a port, use an empty port if the default
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 is the same as one seen before. Processors MUST
compare atom:id elements on a character-by-character basis (in a
case-sensitive fashion). Comparison operations MUST be based solely
on the IRI character strings, and MUST NOT rely on dereferencing the
IRIs.
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As a result, two IRIs that resolve to the same resource but are not
character-for-character identical will be 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 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:image" Element
The "atom:image" element's content is an IRI [RFC3987] which
identifies an image which provides visual identification for a feed.
The image SHOULD have an aspect ratio of 2 (horizontal) to 1
(vertical).
atomImage = element atom:image { atomCommonAttributes, (atomUri) }
4.2.9 The "atom:link" Element
The "atom:link" element is an empty element that defines a reference
from an entry or feed to a Web resource.
atomLink =
element atom:link {
atomCommonAttributes,
attribute href { atomUri },
attribute rel { atomNCName | atomUri }?,
attribute type { atomMediaType }?,
attribute hreflang { atomLanguageTag }?,
attribute title { text }?,
attribute length { text }?,
empty
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}
4.2.9.1 The "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 is not present, the link
element MUST be interpreted as if the link relation type is
"alternate".
rel_attribute = segment-nz-nc / IRI
The value of "rel" MUST be either a 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 to be equivalent
to the same name registered within the IANA Registry of Link
Relations Section 7, and thus the IRI that would be obtained by
appending the value of the rel attribute to the string
"http://www.iana.org/assignments/relation/". The value of "rel"
describes the meaning of the link, but does not impose any behavioral
requirements on implementations.
This document defines five initial values for the Registry of Link
Relations:
The value "alternate" signifies that the IRI in the value of the href
attribute identifies an alternate version of the resource described
by the containing element.
The value "related" signifies that the IRI in the value of the href
attribute 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:
<link rel="related" href="http://search.example.com/">
An identical link might appear as a child of any atom:entry whose
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content contains a discussion of that same search engine.
The value "self" signifies that the IRI in the value of the href
attribute identifies a resource equivalent to the containing element.
The value "enclosure" signifies that the IRI in the value of the href
attribute identifies a related resource which is potentially large in
size and may require special handling by consuming software. For
Link constructs with rel="enclosure", the length attribute SHOULD be
provided.
The value "via" signifies that the IRI in the value of the href
attribute identifies a resource that is the source of the information
provided in the containing element.
4.2.9.3 The "type" Attribute
Link elements MAY have a type attribute, whose value MUST conform to
the syntax of a MIME media type [RFC2045].
The type attribute's value is an advisory media type; it is a hint
about the type of the representation that is expected 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.
4.2.9.4 The "hreflang" Attribute
The "hreflang" attribute's content describes the language of the
resource pointed to by the href attribute. When used together with
the rel="alternate", it implies a translated version of the entry.
Link 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 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 linked
content in octets; it is a hint about the content length of the
representation returned when the IRI in the href attribute is
dereferenced. Note that the length attribute does not override the
actual content length of the representation as reported by the
underlying protocol.
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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 life cycle of
the entry. Typically, atom:published will be 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 preserved within the copied
entry by adding an atom:source-feed child element, if it is not
already present in the entry, and including some or all of the source
feed's metadata elements as the atom:source-feed element's children.
Such metadata SHOULD be preserved if the source atom:feed contains
any of the child elements atom:author, atom:contributor,
atom:copyright, or atom:category and those child elements are not
present in the 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 is a 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:summary" Element
The "atom:summary" element is a Text construct that conveys a short
summary, abstract or excerpt of an entry.
atomSummary = element atom:summary { atomTextConstruct }
4.2.14 The "atom:title" Element
The "atom:title" element is a Text construct that conveys a
human-readable title for an entry or feed.
atomTitle = element atom:title { atomTextConstruct }
4.2.15 The "atom:updated" Element
The "atom:updated" element is a Date construct indicating the 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 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 signature.
In other words, the presence of an element with the namespace IRI
"http://www.w3.org/2000/09/xmldsig#" and a local name of "Signature"
as a child of the document 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 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 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 support
the inclusion of arbitrary foreign markup.
6.2 Extensions To the Atom Vocabulary
Future versions of this specification may add new elements and
attributes to the Atom markup vocabulary. Software written to
conform to this version 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 specification MUST NOT
stop processing or signal an error. It may be the case that the
software is able to process the foreign markup correctly and does so.
Otherwise, such markup is termed "unknown foreign markup".
When unknown foreign markup is encountered as a child of atom:entry,
atom:feed, or a Person Construct, software MAY [[anchor67: Changed to
MAY from SHOULD. Republishers might want to copy it. --R. Sayre]]
bypass the markup and any textual content and MUST NOT change its
behavior as a result of the markup's presence.
When unknown foreign markup is encountered in a Text Contruct or
atom:content element, software SHOULD ignore the markup and process
any text content of foreign elements as though the 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 to apply to the construct. The role of
other foreign markup is undefined by this specification.
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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
empty.
The element can be interpreted as a simple property (or name/value
pair) of the parent element that encloses it. The pair consisting of
the namespace-URI of the element and the local name of the element
can be interpreted as the name of the property. The character data
content of the element can be interpreted as the value of the
property. If the element is empty, then the property value can be
interpreted as an empty string.
6.4.2 Structured Extension Elements
The root element of 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 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 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
[RFC3023].
Encoding considerations: Identical to those of "application/xml" as
described in [RFC3023], section 3.2.
Security considerations: As defined in this specification.
[[anchor71: update upon publication]]
In addition, as this media type uses the "+xml" convention, it
shares the same security considerations as described in [RFC3023],
section 10.
Interoperability considerations: There are no known interoperability
issues.
Published specification: This specification. [[anchor72: update upon
publication]]
Applications that use this media type: No known applications
currently use this media type.
Additional information:
Magic number(s): As specified for "application/xml" in [RFC3023],
section 3.2.
File extension: .atom
Fragment identifiers: As specified for "application/xml" in
[RFC3023], section 5.
Base URI: As specified in [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).
[[anchor73: update upon publication]]
7.1 Registry of Link Relations
This registry is maintained by IANA and initially contains five
values: "alternate", "related", "self", "enclosure", and "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
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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 4.2.9.2
o Common name for link type.
o Description of link type semantics.
o Expected display characteristics.
o Security considerations.
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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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9. References
9.1 Normative References
[Atom-autodiscovery]
Pilgrim, M., "Atom Feed Autodiscovery", work-in-progress,
August 2004.
[ISO.8601.1988]
International Organization for Standardization, "Data
elements and interchange formats - Information interchange
- Representation of dates and 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.
[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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Raggett, D., Hors, A. and 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
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-20040204]
Cowan, J. and R. Tobin, "XML Information Set (Second
Edition)", W3C 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.
[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.
Authors' Addresses
Mark Nottingham (editor)
Email: mnot@pobox.com
URI: http://www.mnot.net/
Robert Sayre (editor)
Boswijck Memex Consulting
Email: rfsayre@boswijck.com
URI: http://boswijck.com
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Appendix A. Contributors
The following people contributed to preliminary drafts of this
document: Tim Bray, Mark Pilgrim, and Sam Ruby. Norman Walsh
provided the Relax NG schema. The content and concepts within are a
product of the Atom community and the Atom Publishing Format and
Protocol Working Group.
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Appendix B. Collected RELAX NG Compact Schema
This appendix is informative.
# -*- Relax NG -*-
namespace local = ""
namespace
atom = "http://purl.org/atom/ns#draft-ietf-atompub-format-06"
namespace s = "http://www.ascc.net/xml/schematron"
start = atomFeed | atomEntry
## Attribute definitions
atomCommonAttributes =
attribute xml:base { atomUri }?,
attribute xml:lang { atomLanguageTag }?
## 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
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## 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 =
[
s:rule [
context = "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: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:feed {
atomCommonAttributes,
(atomAuthor?
& atomCategory*
& atomContributor*
& atomCopyright?
& atomGenerator?
& atomIcon?
& atomId?
& atomImage?
& atomLink+
& atomSubtitle?
& atomTitle
& atomUpdated
& 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 = "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."
]
]
]
element atom:entry {
atomCommonAttributes,
(atomAuthor?
& atomCategory*
& atomContent?
& atomContributor*
& atomCopyright?
& atomId
& atomLink*
& atomPublished?
& atomSourceFeed?
& atomSummary?
& atomTitle
& atomUpdated &
anyElement*)
}
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# atom:content
atomInlineTextContent =
element atom:content {
atomCommonAttributes,
attribute type { "text | "html" | atomMediaType }?,
(text)*
}
atomInlineXHTMLContent =
element atom:content {
atomCommonAttributes,
attribute type { "xhtml" | atomMediaType }?,
(text|anyElement)*
}
atomOutOfLineContent =
element atom:content {
atomCommonAttributes,
attribute type { "text" | "html" | "xhtml" | atomMediaType }?,
attribute src { atomUri },
empty
}
atomContent = atomInlineTextContent
| atomInlineXHTMLContent
| atomOutOfLineContent
## Metadata Elements
# atom:author
atomAuthor = element atom:author { atomPersonConstruct }
# atom:category
atomCategory = element atom:category {
atomCommonAttributes,
attribute term { text },
attribute scheme { atomUri }?,
attribute label { text }?,
empty
}
# atom:contributor
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atomContributor = element atom:contributor { atomPersonConstruct }
# atom:copyright
atomCopyright = element atom:copyright { atomTextConstruct }
# atom:generator
atomGenerator = element atom:generator {
atomCommonAttributes,
attribute uri { atomUri }?,
attribute version { text }?,
text
}
# atom:icon
atomIcon = element atom:icon { atomCommonAttributes, (atomUri) }
# atom:id
atomId = element atom:id { }
# atom:image
atomImage = element atom:image { atomCommonAttributes, (atomUri) }
# atom:link
atomLink = element atom:link {
atomCommonAttributes,
attribute href { atomUri },
attribute rel { atomNCName | atomUri }?,
attribute type { atomMediaType }?,
attribute hreflang { atomLanguageTag }?,
attribute title { text }?,
attribute length { text }?,
empty
}
# atom:published
atomPublished = element atom:published { atomDateConstruct }
# atom:source-feed
atomSourceFeed =
element atom:source-feed {
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atomCommonAttributes,
( atomTitle
& atomUpdated
& atomLink+
& atomIcon
& atomId?
& atomImage?
& atomSubtitle?
& atomAuthor?
& atomContributor*
& atomCopyright?
& atomCategory*
& atomGenerator?
& anyElement* )
}
# atom:subtitle
atomSubtitle = element atom:subtitle { atomTextConstruct }
# atom:summary
atomSummary = element atom:summary { atomTextConstruct }
# atom:title
atomTitle = element atom:title { atomTextConstruct }
# atom:updated
# TODO: Test for a timezone that SHOULD be UTC
atomUpdated = element atom:updated { atomDateConstruct }
# 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. Change Log
[[anchor85: This section should be removed before final
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.
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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