"We built SuperPreview to simplify the process of testing and debugging layout issues across different web browsers and platforms. You can view your pages in multiple browsers simultaneously or view how a page renders in a browser and compare it to a comp or mock-up image of a page.
SuperPreview will be included as part of a future version of Expression Web. The final feature set and its availability have not been announced. The SuperPreview demo shown at the MIX09 conference was a technology preview and not a product announcement. However, because we'd like to get feedback on this technology and on its implementation, we have announced a beta version of SuperPreview for Internet Explorer. This free download will allow you to compare renderings of IE6 with whatever other version of IE you have installed on your machine. If you have installed IE8, you'll be able to compare IE6, IE8 and IE8 running in IE7 compatibility mode, side-by-side. The final 'shipping' version of SuperPreview for Internet Explorer will continue to be available for free. The Expression Web team hopes that it will be useful in helping to make the process of developing web pages for IE (and in general), faster and easier."