Hi!

In addition to what mtajim said, the web is supposed to go the way of XML, which is, well, a different beast from HTML. However, we can't go directly from HTML to XML, as that would leave 99% of the web in the dark.

So W3C developed a compromise to bridge that gap, XHTML. So it looks something like this:

HTML ==> XHTML ==> XML

If you are just starting to code in HTML, it would be better to start in the right footing and go with XHTML. Actually, there's not much of a difference between the two, XHTML only being unforgiving. :D

You can find a list of tags accepted by XHTML HERE.

For a more definitive differentiation of HTML and XHTML, go HERE.

Hope that helps.

:D