Funny but a lot of things that seemed obvious when XML first sprang on the scene are still just percolating. Take microformats, please.
Microformats are promoted as a practical way to solve a common interoperability problem: “How to add structured data to existing documents (typically HTML) without changing the underlying schema or breaking existing implementations.” This per Doug Mahugh, Open XML Technical Evangelist with Microsoft, writing on his blog..
The basic concept is that a microformat is a set of “class” attributes that can be added to spans in an HTML page to tag content with semantic meaning. There have been microformats defined for reviews (hReview), calendar items (hCalendar), business cards (hCard), and other applications, and microformat-tagged content is starting to appear on many web pages.
Greasemonkey and Mozilla lab folks have worked with microformats. In his post, Mahugh looks at microformats and OpenXML