XML Basic-from w3schools.com

In our XML tutorial you will learn what XML is and the difference between XML and HTML. You will also learn how to start using XML in your applications.
Introduction to XML
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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.
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What you should already know
Before you continue, you should have some basic understanding of the following:
WWW, HTML and the basics of building Web pages
Web scripting languages like JavaScript or VBScript
If you want to study these subjects first, before you start reading about XML, you can find the tutorials you need at W3Schools' Home Page.
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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) or an XML Schema to describe the data
XML with a DTD or XML Schema is designed to be self-descriptive
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The main difference 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.