Chapter 16. Essential XHTML

Probably the biggest XML application today is XHTML, which is the World Wide Web Consortium (W3C's)implementation of HTML 4.0 in XML. XHTML is a true XML application, which means that XHTML documents are XML documents that can be checked for well-formedness and validity.

There are two big advantages to using XHTML. HTML predefines all its elements and attributes, and that's not something you can change—unless you use XHTML. Because XHTML is really XML, you can extend it with your own elements, and we'll see how to do that in the next chapter. Need <INVOICE>, <DELIVERY_DATE>, and <PRODUCT_ID> elements in your Web page? Now you can add them. (This aspect of XHTML isn't supported by the major browsers yet, but it's coming.) The other big advantage, as far as HTML authors are concerned, is that you can display XHTML documents in today's browsers without modification. That's the whole idea behind XHTML—it's supposed to provide a bridge between XML and HTML. XHTML is true XML, but you can use it today in browsers. And that has made it very popular.