It is you who has missed the point. I mention in my comment specifically that W3 validation errors are not comparable to compiler errors or run time errors in p

It is you who has missed the point. I mention in my comment specifically that W3 validation errors are not comparable to compiler errors or run time errors in programming. As far as things working in one browser and not another, if you're working with standard features they tend to work across all modern browsers. If you are using features which are still only candidates, then yes they may not work but you've chosen to implement non-standard features so you've done this to yourself.