XML - Wikipedia
Extensible Markup Language (XML) is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable.
XML Tutorial
Why Study XML? XML plays an important role in many different IT systems. XML is often used for distributing data over the Internet. It is important (for all types of software developers!) to have a good...
Extensible Markup Language (XML) 1.0 (Fifth Edition)
The Extensible Markup Language (XML) is a subset of SGML that is completely described in this XML has been designed for ease of implementation and for interoperability with both SGML and HTML.