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What are HTML and XHTML? HTML is HyperText Markup Language, developed by Propellerhead scientists in the early 1990s so that they could share scientific papers over the Internet. It was based on SGML, Standard Generalized Markup Language, because SGML was designed to deal with documents and that seemed like the thing to do with the time. As the use of HTML spread and people started using its hyperlinks feature a lot, the World Wide Web was born. Then things got ugly.
As the World Wide Web grew and grew, it became a more popular medium and a less scientific medium and HTML's limitations became a barrier to the web's development. People didn't want just words and pictures; they wanted presentation and they got it and HTML was extended to meet that need. As the saying goes, check all the parks in all your cities, you'll find no statues of any committees. As the web grew, the market demanded more presentation-oriented features in HTML and the scientists on the HTML committees, being scientists and not graphic artists, dragged their feet and the market said, okay, then we'll do it ourselves.
Features were born of the necessity and they were chaotic and they were useful and they were chaotic. Over time, the Standards Committees caught up with the market and we now have HTML 4 and it's mostly functional and it mostly does what it needs to do and it's still chaotic. HTML 4 works and it works well and it has serious flaws that most people will never notice. What makes them serious is it takes a lot of computing power to take the average HTML page and render it in a coherent and consistent manner. That's what XHTML is for.
XHTML stands for eXtensible HyperText Markup Language. Don't let the name fool you. It's not actually extensible. The X is there because it's based upon XML, eXtensible Markup Language. So it's technically an extension of XML, but XHTML was not itself extensible. Think of it as HTML but with stricter rules. The strictness of XHTML is good for computers. It makes it easier to build a program that reads the markup and renders the page or reads it to blind people or something else.
Of course, the other side of the coin is that no one can force the whole Internet to stop using messy old HTML. So it's really useless, right? Well, perhaps that's true, but it's really not that much harder to write strict XHTML than it is to write sloppy HTML. So, I'm going to do my part and I'm going to show you how all of this works. Why should you use XHTML instead of HTML? HTML is very forgiving of inconsistent and even erroneous documents. XHTML requires the documents follow a specific and well-defined structure.
Stricter rules means less variance among browsers and more consistent results. It means your web pages will behave more consistently on new devices and it makes it easier for developers to create wonderful new applications that will ultimately enhance all of our lives.
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