Extensible Markup Language (XML)

Extensible Markup Language (XML) is a flexible markup language for structured electronic documents. Extensible Markup Language (XML) is a programming language commonly used by data-exchange services (like blog feeds) to send information between otherwise incompatible systems. It is readable by both humans and computers and is based on SGML (standard generalized markup language), an international standard for electronic documents. Many other languages, such as RSS and XHTML, are based on XML.

Unlike HTML, XML allows users to define their own markup. Using XML, one user could choose to denote a footnote with the tag <footnote>, while another user could opt for <fn>. Using HTML, only one pre-determined tag can be used to denote a specific type of information. XML documents are meant to be easy to read since they contain user-defined tags and since the documents only consist of markup and content. Markup is the text that appears between two pointed brackets (e.g., <footnote>), and content is everything else.