The HTML document has two parts, headings and body. text. Headings are the section titles and they are listed in h1, h2, etc. The body text is listed in paragraphs and lists with a heading at the top of each list.
XHTML is a markup language that is used to describe web documents. It was created in order to make it possible for web pages to validate against XML standards and to be served with the correct MIME type.