For example This is a sentence validates under html 4.01 transitional or html5 where the closing tag is not required, but not under xhtml 1.0 transitional where the closing tag is required.I’ve included some screenshots at the bottom of this post to show the full code I used to check under each doctype.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.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.
Let’s face it no one can really list every potential show stopping error where search engines are concerned.In this lesson, you will have an opportunity to use the W3C HTML Validator, and to correct invalid code based on validation tool feedback.An invalid web page might look fine in your browser, but someone accessing the page in another browser might have an entirely different experience with the same content.Right click on the website in the solution and click 'Property Pages'.Under references, find the reference which is failing (it will say 'unavailable' next to it), remove and then re-add it.