It adds support for 19 CSS3 pseudo-classes, 2 pseudo-elements and every attribute selector to older versions of IE. It can also fix a few of the browsers native selector implementations. You have to have to be using a JS library for this to work. here is a look at the library support:
To grab this beauty head to the selectivizr website. Leave me a comment if you have used selectivizr and if it worked out for you.