XHTML is a programming language that replaces HTML as the framework of a Web page. But, to begin learning XHTML, you need a good understanding of HTML. It is a very close copy of HTML, but has stricter rules, making it more adaptable to various platforms.
What Makes XHTML Unique?
XHTML code is cleaner than HTML code. It tells the browser only about the structure of the document, not the style, whereas HTML does both. Rather than telling the browser which fonts to use or what size, XHTML relies on cascading style sheets to take care of the document style and concerns itself only with structure such as headings, lists, body text, etc.
HTML also allows for a degree of sloppiness in code. For example, many browsers will correctly display an element with only the opening tag. But some won't. XHTML requires end tags so that all browsers display the information uniformly.
XHTML is easy to learn. It's best to learn along side HTML so you pick up the best code-writing habits from the beginning.