OPML 1.0 Specification (Outline Processor Markup Language)
http://www.opml.org/spec

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RSS 2.0 Specification (Really Simple Syndication)
http://blogs.law.harvard.edu/tech/rss

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Spec: RSS 1.0 (RSS-DEV)
http://purl.org/rss/1.0/

Version 1.0 of the RSS format, created by the members of RSS-DEV. It extends
RSS with RDF-style metadata, and modules.
dmoz.org: RDF > Applications > RSS > Specifications

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RSS 0.93
http://backend.userland.com/rss093

A work-in-progress of the Userland specification of RSS 0.93 - by Dave Winer,
April 20 2001


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RSS 0.92 
http://backend.userland.com/rss092

The Userland specification of RSS 0.92 - by Dave Winer, December 25 2000


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Spec: RSS 0.91 (Netscape)
http://my.netscape.com/publish/formats/rss-spec-0.91.html

Revision 3 of the 0.91 draft. By Dan Libby, Netscape.


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Spec: RSS 0.91 (UserLand) 
http://backend.userland.com/rss091

Description of RSS current practice. By Dave Winer, UserLand.


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Obsolete Spec: RSS 0.90 
http://www.purplepages.ie/RSS/netscape/rss0.90.html

A copy of the original Netscape version of the RSS0.90 specification. This
is no longer in use, and is here for historical reasons only.

===========================================================================

RSS Validator available online and for download
Written in Python (2.2) and using RSS 2.0

http://feeds.archive.org/validator/check?url=<url-to-your-rss>


===========================================================================
Interesting Articles:

"Parsing RSS at All Costs" Mark Pilgrim argues that the data is more
important than the letter of the XML law, and provides code for a
tolerant RSS parser.

http://www.xml.com/pub/a/2003/01/22/dive-into-xml.html