I'm going to break tradition and recommend something that few web designers currently bother doing: I'm going to suggest that you validate all of your web pages. Few web designers bother with validation because we're still in the early stages of the rebirth of the Web as a more structured web of consistent pages, as opposed to a cobbled-together jungle of hacked code. It's one thing to design and draw a beautiful set of house plans, but it's quite another for an architect to stamp it as a safe structure suitable for construction. Validating your web pages is a similar process, except in this case the architect is an application instead of a person.

Validation is the process of running your pages through a special application that searches for errors and makes sure that your pages follow the strict XHTML standard.

The good news about web page validation is that it's very easy to do. In fact, the standards body responsible for developing web standards, the World Wide Web Consortium, or W3C for short, offers an online validation tool you can use. Follow this URL to try validating a page: http://validator.w3.org/.