Network Working Group M. Nottingham, Ed.
Internet-Draft R. Sayre, Ed.
Expires: October 20, 2005 April 18, 2005
The Atom Syndication Format
draft-ietf-atompub-format-08
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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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Notational Conventions . . . . . . . . . . . . . . . . . . 5
2. Atom Documents . . . . . . . . . . . . . . . . . . . . . . . 6
3. Common Atom Constructs . . . . . . . . . . . . . . . . . . . 8
3.1 Text Constructs . . . . . . . . . . . . . . . . . . . . . 8
3.1.1 The "type" Attribute . . . . . . . . . . . . . . . . . 8
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 . . . . . . . . . . . . . . . . . . . . . 12
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 . . . . . . . . . . . . . . . 15
4.1.3 The "atom:content" Element . . . . . . . . . . . . . . 17
4.2 Metadata Elements . . . . . . . . . . . . . . . . . . . . 20
4.2.1 The "atom:author" Element . . . . . . . . . . . . . . 20
4.2.2 The "atom:category" Element . . . . . . . . . . . . . 20
4.2.3 The "atom:contributor" Element . . . . . . . . . . . . 20
4.2.4 The "atom:copyright" Element . . . . . . . . . . . . . 21
4.2.5 The "atom:generator" Element . . . . . . . . . . . . . 21
4.2.6 The "atom:icon" Element . . . . . . . . . . . . . . . 21
4.2.7 The "atom:id" Element . . . . . . . . . . . . . . . . 22
4.2.8 The "atom:image" Element . . . . . . . . . . . . . . . 23
4.2.9 The "atom:link" Element . . . . . . . . . . . . . . . 24
4.2.10 The "atom:published" Element . . . . . . . . . . . . 26
4.2.11 The "atom:source" Element . . . . . . . . . . . . . 26
4.2.12 The "atom:subtitle" Element . . . . . . . . . . . . 27
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 . . . . . . . . . . . . . . . . . . 29
6. Extending Atom . . . . . . . . . . . . . . . . . . . . . . . 30
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . 33
8. Security Considerations . . . . . . . . . . . . . . . . . . 35
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.1 Normative References . . . . . . . . . . . . . . . . . . . 36
9.2 Informative References . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 38
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 39
B. RELAX NG Compact Schema . . . . . . . . . . . . . . . . . . 40
C. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 48
Intellectual Property and Copyright Statements . . . . . . . 51
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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.
1.1 Examples
A minimal, single-entry Atom Feed Document:
Example Feed2003-12-13T18:30:02ZJohn DoeAtom-Powered Robots Run Amokurn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a2003-12-13T18:30:02ZSome text.
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A more extensive, single-entry Atom Feed Document:
dive into mark
A <em>lot</em> of effort
went into making this effortless
2005-04-02T12:29:29Ztag:example.org,2003:3Copyright (c) 2003, Mark Pilgrim
Example Toolkit
Atom draft-07 snapshottag:example.org,2003:3.23972005-04-02T12:29:29Z2003-12-13T08:29:29-04:00Mark Pilgrimhttp://example.org/f8dy@example.comSam Rubyhttp://intertwingly.net/blog/Joe Gregoriohttp://bitworking.org/
[Update: The Atom draft-07 snapshot is out.]
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1.2 Notational Conventions
This specification describes conformance in terms of two artifacts;
Atom Feed Documents and Atom Entry documents. Additionally, it
places some requirements on Atom Processors.
This specification uses XML Namespaces [W3C.REC-xml-names-19990114]
to uniquely identify XML element names. It uses the following
namespace prefix for the indicated namespace URI;
"atom": http://purl.org/atom/ns#draft-ietf-atompub-format-08
[[anchor4: This paragraph to be removed by the RFC Editor. The
namespace here is a temporary one and will be changed when the IESG
approves this document as a standard. At that time, the namespace
will be drawn from W3C URI space. The choice of that namespace will
be coordinated between the IETF and W3C through their respective
liaisons.]]
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
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
complete schema appears in Appendix B.
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.
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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-08"
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. This specification does not
define a DTD for Atom Documents, and hence does not require them to
be valid (in the sense used by XML).
Any element defined by this specification 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 defined by this specification 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], as well as URIs [RFC3986].
IRIs can easily be converted to URIs. Every URI is an IRI, so any
URI can be used where an IRI is needed. When comparing IRIs serving
as atom:id values, they MUST NOT be converted to URIs.
Atom is an extensible format. See Section 6 of this document for a
full description of how Atom Documents can be extended.
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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.
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3. Common Atom Constructs
Many of Atom's elements share a few common structures. This section
defines those 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. The content of Text constructs is language-sensitive.
atomPlainTextConstruct =
atomCommonAttributes,
attribute type { "text" | "html" }?,
text
atomXHTMLTextConstruct =
atomCommonAttributes,
attribute type { "xhtml" },
xhtmlDiv
atomTextConstruct = atomPlainTextConstruct | atomXHTMLTextConstruct
3.1.1 The "type" Attribute
Text constructs MAY have a "type" attribute. When present, the value
MUST be one of "text", "html" or "xhtml". If the "type" attribute is
not provided, Atom Processors MUST behave as though it were present
with a value of "text". MIME media types [MIMEREG] MUST NOT be used
as values for the "type" attribute.
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3.1.1.1 Text
Example atom:title with text content:
...
Less: <
...
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 collapse
white-space (including line-breaks), and display the text using
typographic techniques such as justification and proportional fonts.
3.1.1.2 HTML
Example atom:title with HTML content:
...
Less: <em> < </em>
...
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 [HTML]. Any markup within MUST be escaped; for example,
" " as "<br>". HTML markup within SHOULD be such that it could
validly appear directly within an HTML
element, after
unescaping. Atom Processors that display such content MAY use that
markup to aid in its display.
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3.1.1.3 XHTML
Example atom:title with XHTML content:
...
Less: <
...
If the value of "type" is "xhtml", the content of the Text construct
MUST be a single XHTML div element [XHTML]. 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
characters, such as "&" and ">", represent those characters, not
markup.
Examples of valid XHTML content:
...
This is XHTML content.
...
This is XHTML content.
...
The following example assumes that the XHTML namespace has been bound
to the "xh" prefix earlier in the document:
...
This is XHTML content.
...
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3.2 Person Constructs
A Person construct is an element that describes a person,
corporation, or similar entity (hereafter, 'person').
atomPersonConstruct =
atomCommonAttributes,
(element atom:name { text }
& element atom:uri { atomUri }?
& element atom:email { atomEmailAddress }?
& extensionElement*)
This specification assigns no significance to the order of appearance
of the child elements in a Person construct. Person constructs allow
extension Metadata Elements (see Section 6.4).
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].
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" production in [RFC2822].
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3.3 Date Constructs
A Date construct is an element whose content MUST conform to the
"date-time" production in [RFC3339]. In addition, an uppercase "T"
character MUST be used to separate date and time, and an uppercase
"Z" character MUST be present in the absence of a numeric time zone
offset.
atomDateConstruct =
atomCommonAttributes,
xsd:dateTime
Such date values happen to be compatible with the following
specifications: [ISO.8601.1988], [W3C.NOTE-datetime-19980827], and
[W3C.REC-xmlschema-2-20041028].
Date values SHOULD be as accurate as possible. For example, it would
be generally inappropriate for a publishing system to apply the same
timestamp to several entries which were published during the course
of a single day.
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4. Atom Element Definitions
4.1 Container Elements
4.1.1 The "atom:feed" Element
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 metadata
elements followed by zero or more atom:entry child elements.
atomFeed =
element atom:feed {
atomCommonAttributes,
(atomAuthor?
& atomCategory*
& atomContributor*
& atomCopyright?
& atomGenerator?
& atomIcon?
& atomId?
& atomImage?
& atomLink+
& atomSubtitle?
& atomTitle
& atomUpdated
& extensionElement*),
atomEntry*
}
This specification assigns no significance to the order of atom:entry
elements within the feed.
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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.
o atom:feed elements MUST NOT contain more than one atom:author
element.
o atom:feed elements MAY contain any number of atom:category
elements.
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". 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. 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.
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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.
atomEntry =
element atom:entry {
atomCommonAttributes,
(atomAuthor?
& atomCategory*
& atomContent?
& atomContributor*
& atomCopyright?
& atomId
& atomLink*
& atomPublished?
& atomSource?
& atomSummary?
& atomTitle
& atomUpdated
& extensionElement*)
}
This specification assigns no significance to the order of appearance
of the child elements of atom:entry.
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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 the atom:entry contains an atom:source element which
contains an atom:author element, or, in an Atom Feed Document, the
atom:feed element contains an atom:author element itself.
o atom:entry elements MUST NOT contain more than one atom:author
element.
o atom:entry elements MAY contain any number of atom:category
elements.
o atom:entry elements MUST NOT contain more than one atom:content
element.
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".
o atom:entry elements MUST NOT contain more than one atom:link
element with a rel attribute value of "alternate" that has the
same combination of type and hreflang attribute values.
o 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
element.
o atom:entry elements MUST contain an atom:summary element in any of
the following cases:
* the atom:entry element contains no 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
[MIMEREG] 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.
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4.1.3 The "atom:content" Element
The "atom:content" element either contains or links to the content of
the entry. The content of atom:content is language-sensitive.
atomInlineTextContent =
element atom:content {
atomCommonAttributes,
attribute type { "text" | "html" }?,
(text)*
}
atomInlineXHTMLContent =
element atom:content {
atomCommonAttributes,
attribute type { "xhtml" },
xhtmlDiv
}
atomInlineOtherContent =
element atom:content {
atomCommonAttributes,
attribute type { atomMediaType }?,
(text|anyForeignElement)*
}
atomOutOfLineContent =
element atom:content {
atomCommonAttributes,
attribute type { atomMediaType }?,
attribute src { atomUri },
empty
}
atomContent = atomInlineTextContent
| atomInlineXHTMLContent
| atomInlineOtherContent
| atomOutOfLineContent
4.1.3.1 The "type" attribute
On the atom:content element, the value of the "type" attribute MAY be
one of "text", "html", or "xhtml". Failing that, it MUST be a MIME
media type, but MUST NOT be a composite type (see Section 4.2.6 of
[MIMEREG]). If the type attribute is not provided, Atom Processors
MUST behave as though it were present with a value of "text".
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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"
attribute is present, atom:content MUST be empty.
If the "src" attribute is present, the "type" attribute SHOULD be
provided and MUST be a MIME media type [MIMEREG], 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.
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 collapse white-space (including line-breaks), and display the
text using typographic techniques such as justification and
proportional fonts.
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 [HTML]. The HTML markup must be escaped; for
example, " " as "<br>". The HTML markup SHOULD be such
that it could validly appear directly within an HTML
element. Atom Processors that display the content MAY 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 [XHTML], and SHOULD be
suitable for handling as XHTML. 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 characters, such as "&" and ">", represent those
characters, not markup.
4. If the value of "type" ends with "+xml" or "/xml"
(case-insensitive), the content of atom:content MAY include child
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elements, and SHOULD be suitable for handling as the indicated
media type. If the "src" attribute is not provided, this would
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 white-space, and lines
are separated by a single newline (U+000A) character.
4.1.3.4 Examples
XHTML inline:
...
This is XHTML content.
...
This is XHTML content.
...
The following example assumes that the XHTML namespace has been bound
to the "xh" prefix earlier in the document:
...
This is XHTML content.
...
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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.
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 }
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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 { atomTextConstruct }
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 reference [RFC3987] which
identifies an image which provides iconic visual identification for a
feed.
atomIcon = element atom:icon {
atomCommonAttributes,
(atomUri)
}
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The image SHOULD have an aspect ratio of one (horizontal) to one
(vertical), and should be suitable for presentation at a small size.
4.2.7 The "atom:id" Element
The "atom:id" element conveys a permanent, universally unique
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. It is suggested that the
atom:id element be stored along with the associated resource.
The content of an atom:id element MUST be created in a way that
assures uniqueness.
Because of the risk of confusion between IRIs that would be
equivalent if dereferenced, the following normalization strategy
SHOULD be applied 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.
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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.
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 reference [RFC3987]
which identifies an image which provides visual identification for a
feed.
atomImage = element atom:image {
atomCommonAttributes,
(atomUri)
}
The image SHOULD have an aspect ratio of 2 (horizontal) to 1
(vertical).
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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
}
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].
4.2.9.2 The "rel" Attribute
atom:link elements MAY have a "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".
The value of "rel" MUST be string that is non-empty, and matches the
"isegment-nz-nc" or "IRI" production in [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:
1. 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.
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2. 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:
An identical link might appear as a child of any atom:entry whose
content contains a discussion of that same search engine.
3. The value "self" signifies that the IRI in the value of the href
attribute identifies a resource equivalent to the containing
element.
4. 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 might require special handling by consuming
software. For Link elements with rel="enclosure", the length
attribute SHOULD be provided.
5. 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
On the link element, 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. Link elements
MAY have a type attribute, whose value MUST conform to the syntax of
a MIME media type [MIMEREG].
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
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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. 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.
atomPublished = element atom:published { atomDateConstruct }
Typically, atom:published will be associated with the initial
creation or first availability of the resource.
4.2.11 The "atom:source" 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 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 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.
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atomSource =
element atom:source {
atomCommonAttributes,
(atomAuthor?
& atomCategory*
& atomContributor*
& atomCopyright?
& atomGenerator?
& atomIcon?
& atomId?
& atomImage?
& atomLink+
& atomSubtitle?
& atomTitle
& atomUpdated
& extensionElement*)
}
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.
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 }
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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 URI
"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 could 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".
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 might 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 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.
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6.4 Extension Elements
Atom allows foreign markup anywhere in an Atom document. Child
elements of atom:entry, atom:feed, and Person constructs 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.
6.4.1 Simple Extension Elements
A Simple Extension element MUST NOT have any attributes or child
elements. The element MAY contain character data, or be empty.
Simple Extension elements are not language-sensitive.
simpleExtensionElement =
element * - atom:* {
text
}
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. Structured Extension elements are language-sensitive.
structuredExtensionElement =
element * - atom:* {
(attribute * { text }+,
(text|anyElement)*)
| (attribute * { text }*,
(text?, anyElement+, (text|anyElement)*))
}
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,
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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.
[[anchor59: 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. [[anchor60: 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
Intended usage: COMMON
Author/Change controller: IESG
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 use the
following template:
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o Attribute Value: ( A value for the "rel" attribute that conforms
to the syntax rule given in Section 4.2.9.2 )
o Description:
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. 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 [RFC2854] and [HTML] 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 might 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 documents can be encrypted and signed using
[W3C.REC-xmlenc-core-20021210] and [W3C.REC-xmldsig-core-20020212],
respectively, and are subject to the security considerations implied
by their use.
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9. References
9.1 Normative References
[HTML] Raggett, D., Hors, A. and I. Jacobs, "HTML 4.01
Specification", W3C REC REC-html401-19991224, December
1999, .
[MIMEREG] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", work-in-progress
(draft-freed-media-type-reg-04), April 2005.
[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.
[RFC2854] Connolly, D. and L. Masinter, "The 'text/html' Media
Type", RFC 2854, June 2000.
[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.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
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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,
.
[XHTML] Altheim, M., Boumphrey, F., McCarron, S., Dooley, S.,
Schnitzenbaumer, S. and T. Wugofski, "Modularization of
XHTML[TM]", W3C REC REC-xhtml-modularization-20010410,
April 2001,
.
9.2 Informative References
[ISO.8601.1988]
International Organization for Standardization, "Data
elements and interchange formats - Information interchange
- Representation of dates and times", ISO Standard 8601,
June 1988.
[RELAX-NG]
Clark, J., "RELAX NG Compact Syntax", December 2001,
.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
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[W3C.NOTE-datetime-19980827]
Wolf, M. and C. Wicksteed, "Date and Time Formats", W3C
NOTE NOTE-datetime-19980827, August 1998,
.
[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,
.
Authors' Addresses
Mark Nottingham (editor)
Email: mnot@pobox.com
URI: http://www.mnot.net/
Robert Sayre (editor)
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. RELAX NG Compact Schema
This appendix is informative.
# -*- rnc -*-
# RELAX NG Compact Syntax Grammar for the
# Atom Format Specification Version 08
namespace atom =
"http://purl.org/atom/ns#draft-ietf-atompub-format-08"
namespace xhtml = "http://www.w3.org/1999/xhtml"
namespace s = "http://www.ascc.net/xml/schematron"
start = atomFeed | atomEntry
# Common attributes
atomCommonAttributes =
attribute xml:base { atomUri }?,
attribute xml:lang { atomLanguageTag }?
# Text Constructs
atomPlainTextConstruct =
atomCommonAttributes,
attribute type { "text" | "html" }?,
text
atomXHTMLTextConstruct =
atomCommonAttributes,
attribute type { "xhtml" },
xhtmlDiv
atomTextConstruct = atomPlainTextConstruct | atomXHTMLTextConstruct
# Person Construct
atomPersonConstruct =
atomCommonAttributes,
(element atom:name { text }
& element atom:uri { atomUri }?
& element atom:email { atomEmailAddress }?
& extensionElement*)
# Date Construct
atomDateConstruct =
atomCommonAttributes,
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xsd:dateTime
# atom:feed
atomFeed =
[
s:rule [
context = "atom:feed"
s:assert [
test = "atom:link[@rel='alternate'] "
~ "or atom:link[not(@rel)]"
"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[not(atom:author)])"
"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
& extensionElement*),
atomEntry*
}
# atom:entry
atomEntry =
[
s:rule [
context = "atom:entry"
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s:assert [
test = "atom:link[@rel='alternate'] "
~ "or atom:link[not(@rel)] "
~ "or atom:content"
"An atom:entry must have at least one link element "
~ "with a rel attribute of 'alternate' or content."
]
]
s:rule [
context = "atom:entry"
s:assert [
test = "atom:author or "
~ "../atom:author or atom:source/atom:author"
"An atom:entry must have an atom:author "
~ "if its feed does not."
]
]
# N.B. This rule doesn't test
# for content with a non-binary type.
s:rule [
context = "atom:entry"
s:assert [
test = "atom:summary or atom:content[not(@src)]"
"An atom:entry must have an atom:summary "
~ "if the atom:content element is empty."
]
]
]
element atom:entry {
atomCommonAttributes,
(atomAuthor?
& atomCategory*
& atomContent?
& atomContributor*
& atomCopyright?
& atomId
& atomLink*
& atomPublished?
& atomSource?
& atomSummary?
& atomTitle
& atomUpdated
& extensionElement*)
}
# atom:content
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atomInlineTextContent =
element atom:content {
atomCommonAttributes,
attribute type { "text" | "html" }?,
(text)*
}
atomInlineXHTMLContent =
element atom:content {
atomCommonAttributes,
attribute type { "xhtml" },
xhtmlDiv
}
atomInlineOtherContent =
element atom:content {
atomCommonAttributes,
attribute type { atomMediaType }?,
(text|anyForeignElement)*
}
atomOutOfLineContent =
element atom:content {
atomCommonAttributes,
attribute type { atomMediaType }?,
attribute src { atomUri },
empty
}
atomContent = atomInlineTextContent
| atomInlineXHTMLContent
| atomInlineOtherContent
| atomOutOfLineContent
# atom:author
atomAuthor = element atom:author { atomPersonConstruct }
# atom:category
atomCategory =
element atom:category {
atomCommonAttributes,
attribute term { text },
attribute scheme { atomUri }?,
attribute label { text }?,
empty
}
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# atom:contributor
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 {
atomCommonAttributes,
(atomUri)
}
# 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 }?,
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attribute length { text }?,
empty
}
# atom:published
atomPublished = element atom:published { atomDateConstruct }
# atom:source
atomSource =
element atom:source {
atomCommonAttributes,
(atomAuthor?
& atomCategory*
& atomContributor*
& atomCopyright?
& atomGenerator?
& atomIcon?
& atomId?
& atomImage?
& atomLink+
& atomSubtitle?
& atomTitle
& atomUpdated
& extensionElement*)
}
# atom:subtitle
atomSubtitle = element atom:subtitle { atomTextConstruct }
# atom:summary
atomSummary = element atom:summary { atomTextConstruct }
# atom:title
atomTitle = element atom:title { atomTextConstruct }
# atom:updated
atomUpdated = element atom:updated { atomDateConstruct }
# Low-level simple types
atomNCName = xsd:string { minLength = "1" pattern = "[^:]*" }
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# Whatever a media type is, it contains at least one slash
atomMediaType = xsd:string { pattern = ".+/.+" }
# As defined in RFC 3066
atomLanguageTag = xsd:string {
pattern = "[A-Za-z]{1,8}(-[A-Za-z0-9]{1,8})*"
}
# Unconstrained; it's not entirely clear how IRI fit into
# xsd:anyURI so let's not try to constrain it here
atomUri = text
# Whatever an email address is, it contains at least one @
atomEmailAddress = xsd:string { pattern = ".+@.+" }
# Simple Extension
simpleExtensionElement =
element * - atom:* {
text
}
# Structured Extension
structuredExtensionElement =
element * - atom:* {
(attribute * { text }+,
(text|anyElement)*)
| (attribute * { text }*,
(text?, anyElement+, (text|anyElement)*))
}
# Other Extensibility
extensionElement =
simpleExtensionElement | structuredExtensionElement
anyElement =
element * {
(attribute * { text }
| text
| anyElement)*
}
anyForeignElement =
element * - atom:* {
(attribute * { text }
| text
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| anyElement)*
}
# XHTML
anyXHTML = element xhtml:* {
(attribute * { text }
| text
| anyXHTML)*
}
xhtmlDiv = element xhtml:div {
(attribute * { text }
| text
| anyXHTML)*
}
# EOF
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Appendix C. Change Log
[[anchor71: This section should be removed before final
publication.]]
-08: Remove BNF
complete rather than collected schema
Remove a couple introductory sentences
update MIME references
Many editorial adjustments
-07: Change atom:source-feed to atom:source.
Add ABNF reference
Many editorial tweaks
Rework extensibility
Adjust page breaks in txt version
-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.
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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
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).
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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.
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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