The latest HTML standard is Version 4.01, but most updates and changes to the language standard were made in Version 4.0. Therefore, throughout the book, we generally refer to the HTML standard as HTML 4, encompassing Versions 4.0 and later. We explicitly state the "dot" version number only when it is relevant.
The XHTML standard is currently in its first iteration, 1.0. A second version (XHTML 1.1) has been proposed but not yet established. For the most part, XHTML 1.0 is identical to HTML 4.01; we detail their differences in Chapter 16. Throughout the book, we specifically note cases where XHTML handles a feature or element differently than the original language, HTML.
The HTML and XHTML standards make very clear the distinction between "element types" of a document and the markup "tags" that delimit those elements. For example, the standard refers to the paragraph element type, which is not the same as the <p> tag. The paragraph element consists of the accepted element-type name within the starting tag (<p>), intervening content, and the ending paragraph tag (</p>). The <p> tag is the starting tag for the paragraph element, and its contents, known as attributes, ultimately affect the paragraph element type's contents.
Although these are important distinctions, we're pragmatists. It is the markup tag that authors apply in their documents and that affects any intervening content. Accordingly, throughout the book, we relax the distinction between element types and tags, often talking about tags and all related contents and not necessarily using the term "element-type" when it would be technically appropriate to make the distinction. Forgive us the transgression, but we do so for the sake of clarity.