What Is XML?
 - XML stands for eXtensible Markup Language.
- XML is a markup language much like HTML.
- XML was designed to describe data.
- XML tags are not predefined. You must define your own tags.
- XML uses a Document Type Definition (DTD) to describe the data.
- XML with a DTD is designed to be self-descriptive.
The Main Differences between XML and HTML:
 - 
XML was designed to carry data.
- 
XML is not a replacement for HTML.
- 
XML and HTML were designed with different goals:
  
   - XML was designed to describe data and to focus on what data is.
- HTML was designed to display data and to focus on how data looks.
 
- 
HTML is about displaying information, while XML is about describing information.
 
 
XML Does Not Do Anything.
XML was not designed to do anything.  Maybe it is a little hard to understand, but XML does not do anything. XML is created to structure, store, and to send information.  The following example is a note to Tove from Jani, stored as XML:
 <note>
   <to>Tove</to>
   <from>Jani</from>
   <heading>Reminder</heading>
   <body>Don't forget me this weekend!</body>
 </note>
The note has a header and a message body. It also has sender and receiver information.  But still, this XML document does not do anything.  It is just pure information wrapped in XML tags.  Someone must write a piece of software to send, receive, or display it.
 An Example of non-XML data