As part of an effort to promote the current work on HTML to web developers, Olivier Thereaux has been working lately on integrating the W3C Markup Validator with the HTML5 parser and checker developed over the past few years by Henri Sivonen.
A simple PHP HTML DOM parser written in PHP5+. I wrote it is because using PHP DOM XML library to parse HTML is really a pain. The origional idea is from Jose Solorzano's HTML Parser for PHP 4.