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XML - Interview Questions
What is XML?
XML stands for eXtensible Markup Language. It is a simple and flexible markup language which is designed to carry or transport and store data. XML tags are not as predefined as HTML, but we can define our own user tags for simplicity.

It mainly concentrates on storing of data, not on displaying of data.  It was evolved from an older standard format known as SGML in order to make it more Web-friendly.