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RSS FAQs - Atom Syndiation Format RFC4287 Reference Document

By: M. Nottingham, Ed. & R. Sayre, Ed.

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   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.  Entities such as
   "&" and "<" represent their corresponding characters ("&" and
   "<" respectively), not markup.

   The atom:generator element MAY have a "uri" attribute whose value
   MUST be an IRI reference [RFC3987].  When dereferenced, the resulting
   URI (mapped from an IRI, if necessary) 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.

4.2.5.  The "atom:icon" Element

   The "atom:icon" element's content is an IRI reference [RFC3987] that
   identifies an image that provides iconic visual identification for a
   feed.

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

   The image SHOULD have an aspect ratio of one (horizontal) to one
   (vertical) and SHOULD be suitable for presentation at a small size.

4.2.6.  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.

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   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 they were mapped to URIs and 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 from 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.

4.2.6.1.  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 or URIs mapped from them.

   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, these are four distinct identifiers, despite the fact
   that they differ only in case:

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