The days of “this site is best viewed in...” are over! We shall no longer be discriminated against for using the browser of our choice. Forget tedious template management, and be prepared to save some dollars on bandwidth! The World Wide Web Consortium have come to agreement on the new Web Standards that will allow us to code and maintain our pages with far less effort, all the while resting assured that everyone can see them as we intended.
A rule that applies to attributes as well as the element they describe, is that they must be in lowercase. That's fine for most of us, but some may have to change their coding style, or even the IDE they use. Also, attribute values must always be quoted, even if we're dealing with numeric values.
Oh and one more thing, no more minimization. This means that
<hr noshade>
must now be written as:
<hr noshade=”noshade” />
What's My Name?
XHTML 1.0 has deprecated the 'name' attribute, and further versions will drop it altogether. That means we will identify elements by their 'id'. We'll see the use of this as we get into the style sheets.
XML / DOCTYPE / NameSpace
We need to define that our page is complying with the rules, and here's how we do it, at the top of every page.
<?xml version="1.0"? > <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional //EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
It's best to use the transitional Document Type Definition while we're getting accustomed to the ins and outs of Web Standards. And really, we only need the XML declaration if the character encoding is anything other than UTF-8 or UTF-16.
And that's about it for a brief overview of XHTML, we can get into the meat now!
HTML 
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XHTML Explained
