What does xhtml look like?
In fact it looks very much like html. Providing you stick to lower-case and follow the rules it will be an easy transition.
Exercise - Carefully type, do not copy, the xhtml code below into Notepad, paying particular attention to upper and lowercase.
Save your file with an html extension and open it with your Web browser.
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
<title> Minimal xhtml Document</title>
</head>
<body>
<h1>My First Valid xhtml Web Page?</h1>
<p>If you enter this page carefully it will be xhtml valid.</p>
</body>
</html>