pageoneresults - 2:41 pm on Feb 19, 2011 (gmt 0)
Here, let's run a simple test. Mind you, this tool is somewhat strict and I've found that if it cannot extract a semantic outline from your document, there may be some challenges at hand...
Semantic Data Extractor
When I attempt to extract a semantic outline from your "valid" document, I get a Tidy message which I've not seen before. I do believe they've corrected the display of an old school message that used to appear which few understood. Basically, if you cannot extract a semantic outline using this tool, you have to consider that the "meaning" of your document may be incorrectly conveyed to the bots, referred to as Machine Readable Grammar in the protocol for UAs.
Even though this document validates, there are problems with its semantic structure. This is where much of the confusion takes place when discussing validation. Even though a document validates, that does not mean that it has proper structure. There are plenty of online tools that allow you to perform tests to determine whether or not you may have challenges in this area. The Semantic Data Extractor from the W3 is an excellent tool to use regularly.