It's practically verbatim off the W3C site.

Please understand that I am not saying the initialism "XHTML" does not expand into the words "Extensible Hypertext Markup Language." Rather, I am pointing out that Extensible HTML "is" HTML no more than a horseless carriage "is" a carriage. The first replaces the second, and even through Horseless Carriage 1 seems a lot like Carriage 4, drivers ought to know whether they are driving an automobile or a horse and act accordingly.

The reason I keep responding to your posts is because I want people reading this thread to recognize that document types mean something: they define a document's content model and markup rules, and they ought to be understood and respected. That's why I have a problem with your "build good habits" advice:

Yes, but HTML4 allows closing non-empty tags such as li and p (li, specifically, being what we were talking about closing upthread); doing so does conform to the doctype; and doing so builds good habits -- because you will presumably not be writing only HTML4 forever. (Other good habbits you should develop, even when writing HTML4, include putting quotes around all attribute values, putting no spaces between the attribute name, the equal sign, and the value, and using the entity and attribute names in lowercase. These changes, perfectly acceptable in HTML4, form habits that will help you when you write XHTML.)

Your advice suggests that authors can turn off their brains and just write XHTML markup because it is always the "good" thing to do, which isn't true. While "write XHTML always" might work for today's stage of the HTML-to-XHTML transition, it won't work in general.

Rather, I would encourage readers to cultivate the following habit, which truly is good: Always know what type of content you are creating and always use the content model and markup rules associated with that specific type.

Cheers,
Tom