I've decided to get back into coding, while doing this going to try and code everything so it is valid according to the W3.org validation checker. The first site I've re-coded for a friend passes their tests, but there are 36 warnings for the CSS (you can pass with warnings by the looks of it). Would you leave it as is, or try and fix the warnings? Also once passed, would you include their valid code icons on your page? Cheers.
Just make sure the page is properly viewed across multiple browsing platforms. I dont bother putting the validation on the page. The validation is primarily so that it is properly viewed no matter what platform/browser you're using, unlike a security certificate.
Valid HTML is a must. Valid CSS is next to impossible, especially if you need to use browser hacks for different browsers or special custom browser specific stylesheet commands - for example -moz-something from https://developer.mozilla.org/en/CSS .
Google gives no SEO boost to valid markup. CSS warnings could be due to browser prefixes and or CSS3 features, make sure you select the CSS version on the validation page. If it loads correctly, loads as you wish in your browser tests, then validating really doesn't matter. Don't loose sleep over it.
