Xmlinputfactory is validating credit card required dating
Vender specific prefixes such as -webkit and -moz will never validate by definition.
That doesn’t mean you shouldn’t use those vendor specific prefixes.
Ideally all your pages would be 100% valid, though it’s not practical or even desirable at times to achieve 100% validation.
Some code that’s commonly used just won’t validate.
The home pages of Google (35), Yahoo (167), and Bing (14) all have validation errors.
However all things being equal I would think valid code better for search engines than invalid code.
Browsers won’t care much either as they’ll typically render much invalid code perfectly fine. Still there are good reasons to validate your code.
Some of those warnings aren’t going to be things you’ll want to fix.
Many tracking parameters you add to the end of a url will give a warning for example.
The only people likely to care or even know how to check are fellow web developers. The W3C offers 5 reasons for why you should validate your code. Valid code is more accessible as it’s compliant with standards.
It should work across more browsers and devices making it more usable and accessible.
There are plenty of browser extensions that will test the page you’re viewing in the W3C validators.