But if you've been building pages with an editor or by hand, you probably have pages that are not valid XHTML, and use old HTML styles like the font tag instead of Cascading Style Sheets. There are valid reasons for leaving your site in an older state than XHTML+CSS
XHTML+CSS is the latest iteration of Web design. It allows you to place your content into your documents separate from how that content should look. XHTML 1.0 is a backwards compatible version of HTML 4.0 converted into XML. This means that it is more flexible and ready to work with databases, dynamic content, and future developments in the field. XHTML is easy to learn, especially for designers who already know HTML. And Cascading Style Sheets (CSS) give you even more flexibility in designing the look of pages. CSS is also easy to learn. XHTML and CSS combined make up XHTML+CSS.
The primary issue is the amount of work it will take for most developers and designers to convert their existing sites from HTML to XHTML+CSS. But it doesn't have to be that hard. And the results can be very beneficial for the pro-active, forward-thinking developer. Documents written in XHTML+CSS are much easier to maintain than their older counterparts. Why? Because there are fewer tags messing with the display of the code. This also means that when you pass along your design to the next designer, he or she has much less to wade through to figure out how your page works. Pages that are built using XHTML+CSS are much less bloated in file size. So they download faster, and that will make your readers happier. If you've ever had to edit someone else's design-table, you know what a huge pain it is. With XHTML+CSS, most of those design decisions are moved to the CSS style sheet, and so are much easier to read and understand. Let's face it, XHTML+CSS is still fairly new, and designers that use it are closer to the cutting edge than those who don't. If you have a site with more than a few pages, it can take a long time to convert all the pages manually. Most modern Web page editors handle XHTML+CSS, so if yours won't, you should probably consider upgrading. If you have to go out and buy a modern Web page editor, it doesn't have to be expensive. There are even some good free editors. If you're not interested in upgrading your Web editor and the freeware editors just don't meet your needs, you can still convert to XHTML+CSS without a lot of hassle. One of the best tools for cleaning up your HTML is HTML Tidy. This tool will actually go through your pages and output valid XHTML. Then all you need to do is design the CSS style sheet and attach it. With a good search and replace, you can add a link to a stylesheet to even a huge site in just a matter of minutes.