New feature: HTML and CSS validation 25 October
Last week we rolled out a new feature on our web page testing service. From now on, when you test any page we'll run it through the W3C validators and report back within the Litmus interface.
Whilst I was working on a refresh of the Litmus site design recently, I had an unclosed HTML tag which was causing the page to all but disappear in Explorer 7. I ended up tracking down down the problem when I next tested the HTML was valid. Certainly if your HTML and CSS is valid, it's more likely your pages will render correctly across different browsers.
I hope this new feature will also help you track down your cross-browser problems more easily!