The HTML markup language is nothing more than an elaborate extension of 
traditional desktop publishing, brought to the World Wide Web. While this 
technology will not be going away any time soon, its inflexibility and 
inability to adapt is a constant hinderance to the emerging features of recent 
years (such as client-side scripting, and integration with operating system 
aspects).

Enter XML. While this tool is practically useless by itself, the beauty of XML 
(or eXtensible Markup Language) is in the simplicity of the design. The core 
feature of XML is its capacity to organize information into a streamlined 
format that can be interpreted by parsers and used by software for a variety of 
purposes.

You will often notice XML used in such games as World of Warcraft. 
Cooperatively paired with the "LUA" scripting language, XML enables the game to 
include customized addons which enhance the player's experience. However, XML is not just used in games; practically at any time that you need to organize 
data into a simplified format, and then call that data from a database or 
script ... XML could be your solution.

An example of XML could be:

<!-- XML Fruits Example -->

<fruit>
   <apple>
      <color>red</color>
   </apple>
   <pear>
      <color>green</color>
   </pear>
   <plum>
      <color>purple</color>
   </plum>
</fruit>

<!-- End of XML -->

If you are interested in learning more about this fascinating technology,
your best bet would be to go browse for books in your local store that sells
such things. However, if you'd like to get your feet wet before delving into
the deep water, here are some helpful sites...

www.w3schools.com/xml/

www.webmonkey.com

Good luck, and thanks for reading.