W3C’s New Validator
Earlier today W3C released their latest version of the Markup Validation Service. Their November 26th latest news listing tells what’s new under the hood in addition to improved accessibility features and wider support. Their new validator will validate your HTML as always, and it will also validate XHTML, SVG, MathML, and more.
W3C has also provided several handy Validator favelets to easily validate pages, along with information about which browsers and versions support them.