[wizofaus]

"The ‘be lenient in what you accept’ philosophy is a disaster" - I've seen that stated before, and I don't think I quite agree. It depends on how much market power you have - if you're Chrome or Safari, I agree, you should display non-compliant pages in a way that makes it obvious that they're broken. But if you're just developing a backend component that happens to consume data in a particular format and it's not part of a system that millions depend on daily, ensuring it can handle non-strictly-conforming input well usually pays off (but by all means, do what you can to warn relevant users).