If you’re relatively new to web design, you’re probably still learning how to get your pages to look the same in all browsers. Even more important, though, is learning how to get your pages to function correctly in all browsers.
The most arduous way of doing this is to open your site in every browser—at least the major ones—and check the functionality of every link, every Flash element, and so on. Of course, even if you’re willing to take the time to do this, you have no guarantee that the invisible elements of your site—your meta tags and doctype tags, for instance—are working correctly.
The only way to ensure that your site has been properly coded is to validate it in order to confirm that it adheres to accepted web standards. So, how do you do this? Well, let me introduce you to your new best friend, the W3C Markup Validation Service.