“Internet Explorer 8 has been designed to include three rendering modes: one that reflects Microsoft’s implementation of current Web standards, a second reflecting Microsoft’s implementation of Web standards at the time of the release of Internet Explorer 7 in 2006, and a third based on rendering methods dating back to the early Web. The newest rendering mode is forward-looking and preferred by Web designers, while the others are present to enable compatibility with the myriad sites across the Web that are currently optimized for previous versions of Internet Explorer.”

Full article here.