PHP5 Feed parser and normaliser

A feed parser to normalise typical feed data into Atom-like constructs. This parser supports / will support:

• RSS 2.0 plus it's descendant 0.9x versions
• RSS 1.0 (RDF Site Summary)
• Atom (not yet)

It also supports namespaces, through extensions. So far, it supports the following namespaces:

• iTunes
• Yahoo!'s Media RSS
• Feedburner
• Dublin Core metadata (partial)
• Syndication (from the OCS format)

The parser is just a layer on-top of the built-in SAX XML parser that keeps track of the element stack in a generic way. It offloads all of the real data work to PHP classes - one class per namespace. That means the parser itself can be extended to support any Feed based namespace.

The end result is a feed data structure where the three basic information elements in a feed -- title, link and summary -- are normalised to Atom-like equivalents, but all of the data from the XML feed is available within the data structure.

Also, when complete, the feed parser will allow feed and entry normalisation, so the actual contents of the feed structure can be tailored or simplified using Normalisation PHP classes.

In addition to this, domain-specific processing can be added so that sites that do things differently and oddly can be brought into line, and the end result is a feed data structure that's normalised to something more sane and easier for an application to consume.

List of issues

• atom:links structure needs to be normalised to remove duplicates (such as duplicates of enclosures thanks to multiple namespaces)
• where rss20:author is an email with a bracketed name, create a regex that will split the two up and populate both the atom:author name and email.
• how to deal with attributes that are namespaced (like flickr:profile on rss20:author
• how to deal with dublin core (or other external elements) when they are children of something other than feed and entry. And without dublin core having to know about other possible levels. Can we create a 'current parent' object that this info can be attached to? Something like $this->currentParent->{$elData->nsName} = $elData->text
• how to capture RSS2.0's isPermaLink attribute on the rss20:guid field.
• media:content - when video links don't supply a valid mime-type, but return an attribute with a value of 'video' or 'audio', how to map that adequately into a valid atom:link type.
• A flag/option that normalises times into a user-specified timezone. At the moment, any conversions are made to GMT, which is a decent start, I guess.
• How to handle invalid RFC-822 formats - do I write a custom method that gets called when we get 1 Jan 1970?
• dc:creator on the Flickr RDF feed returns a bracketed website URL and an unbracketed name. That can be translated into name and url of atom:author.
• When the rss20:author contains two people, whether to convert that into two atom:authors, and whether to remove the 'By' prefix on some rss20:author fields.
• Need to type-check the title/summary type fields and process the content if needed.
• deal with xml:base and xml:lang attributes in the Atom feed - at any point.
• How to deal with proper XHTML content in an Atom Feed?
• atom:source is being ignored for the moment.