What is XML and what is it used for?

XML (eXtensible Markup Language) is a W3C initiative that allows information and services to be encoded with meaningful structure and semantics that both computers and humans can understand. XML is great for information exchange, and can easily be extended to include user-specified and industry-specified tags.

Look at this simple example defining a FAQ:

<?xml version="1.0"?>
<!DOCTYPE question-list SYSTEM "faq.dtd">
<?xml-stylesheet type="text/xml" href="faq.xsl"?>

<FAQ-LIST>
 <QUESTION>
   <QUERY>Question goes here</QUERY>
   <RESPONSE>Answer goes here.</RESPONSE>
 </QUESTION>
 <QUESTION>
   <QUERY>Another question goes here.</QUERY>
   <RESPONSE>The answer goes here.</RESPONSE>
 </QUESTION>
</FAQ-LIST>