At the core of DHTML is the Document Object Model, or DOM, which represents the HTML or XML of a Web page that is displayed in a browser. The Document Object Model that represents HTML content is referred to as the HTML DOM, and the Document Object Model that represents XML content is referred to as the XML DOM. Throughout this book, you have created Web pages that conform to XHTML. Because XHTML documents are just another type of XML document, you can manipulate them with both the HTML DOM and the XML DOM. But which is preferable?