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.One of the discussions that arises from time to time in web development circles is that of validating your code. It’s no different than comparing a sentence you write to the rules of grammar for the language you wrote it in.Some will insist your pages need to validate 100% and others will tell you it’s not even worth checking as long as your pages work. In fact the grammar analogy is a good one to keep in mind when you think of validating your code.One advantage of HTML Tidy is using an extension you can check your pages directly in the browser without having to visit one of the validators.Ultimately validation is simply a tool to help you code better.
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.
There are plenty of browser extensions that will test the page you’re viewing in the W3C validators.
HTML Tidy is another option for validating pages, though it may not offer the exact same results as the W3C validator.
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.
Vender specific prefixes such as -webkit and -moz will never validate by definition.