Editorial note: If you’ve been following my tweets in the past 12 hours you’d have seen me hinting at something very cool for web developers coming out of Microsoft’s MIX09 event today. Well, it’s still at least 3 hours until MIX but it appears Microsoft’s own Expression Web team blog has let the dogs out early (their server is set to to New York time, not Las Vegas time), so consider the NDA broken 🙂

“Expression Web SuperPreview”, the name is typical of Microsoft products, it’s technically self-explanatory but mind-numbingly bland and ridiculously long.

To make matters worse, the beta being released today – a subset of the full release coming with Expression Web 3 – is called “Expression Web SuperPreview for Windows Internet Explorer”. Granted the name is not that important for a developer tool, a kickass one at that.

Every web developer today faces the challenge of checking website compatibility across a large pool of browsers and browser versions in the marketplace. Up and until now, either you could install every browser, verify the website via a visual inspection and debug with tools specialized to that browser, or you could send a URL to a third-party screenshotting service like BrowserShots for an all-in-one visual inspection. The former is messy and tedious but gives you more control and an opportunity to diagnose problems, whilst the latter is simple but slow and useless to fix the problem. Needless to say, SuperPreview is the best of both worlds.

Note: The following screenshots come from a newer unreleased internal build of the application and does not reflect accurately what you can do in Expression Web SuperPreview today. Please don’t hurt me. I like kittens.

SuperPreview as a tool allows you to compare different rendering engines in a single unified interface. Simple clicks gives you comparisons between Internet Explorer 6, the native version of Internet Explorer installed, other browsers you may have installed locally – Firefox 3.5, Safari 3, Safari 4 – and even an bitmap images of website prototypes.

Pushing the envelopes a little, Microsoft is also building in support for remote rendering, such as those on different operating systems even. Details about this feature is not entirely clear at the moment, but I would expect this to be more advanced than just an image rendering.

On top of just a visual inspection, you have a standard set of modern HTML debugging tools like a DOM inspector, CSS inspector, element highlighting, pixel rulers and guides.

And perhaps what I think is the coolest feature, an overlay mode to compare exactly what’s different for pixel-perfect alignment. Or if you cross your eyes, the web in 3D.

Finally, how you can get your dirty web developer paws on this awesome tool, and it’s a little complicated to say the least. The beta of this software available right now is downloadable from Microsoft.com (250MB). The catch being it only supports renderings between IE6 and versions of IE installed on your computer already, but it should ease the pain of testing for IE6/7/8 compatibility for a lot of devs.

The full and final version of this product will be bundled together with Expression Web 3, sometime later this year and will run as a separate standalone application. Unfortunately for the many Mac web developers out there, because Expression Web is not an application part of the Expression Mac suite, SuperPreview will not be available.

You can watch this announcement and more from MIX09 from the livestream website starting at 9AM PST (Las Vegas time), and not EDT (New York time).