This tool, geared by an XSLT stylesheet, tries to extract some information from a HTML semantic rich document. It only uses information available through a good usage of the semantics defined in HTML.
The aim is to show that providing a semantically rich HTML gives much more value to your code: using a semantically rich HTML code allows a better use of CSS, makes your HTML intelligible to a wider range of user agents (especially search engines bots).
As an aside, it can give clues to user agents developers on some hooks that could be interesting to add in their product.