papamike writes:  

I know, you've done all of this work to make your theme compliant, right? But are there errors that W3C doesn't show you? Well the answer is probably yes. Your theme may have errors that affect the performance of your site. I know(first hand) because I had a bunch of errors and warnings. But, with effort and my usual late nights, I have gotten it down to 3 warnings and 3 errors. Not bad but I want to get it down to zero. So I'll keep at it until I'm done. If you think that your website is compliant? Run it through Online Web Check and see what happens.