Where does HTML end and XHTML begin? HTML became so popular because of it was easy to use. But the very features which made it so popular are the same features that are now drawing it back. A lack of rules regarding tags, and case sensitivity have attributed to the demise of HTML. One can't see this format being used for much longer, it's sure to die out in the next few years. Step up XHTML. XHTML is a much stricter version of HTML with three diferent levels of grammatical strictness - strict, transitional and framset. XHTML is in my opinion, a much clear-cut version, and should replace HTML altogether as soon as possible.