Extensible markup language (XML) is a set of rules for programming files in such a way that they can be read by XML-compatible applications and humans alike.

XML is designed to enhance simplicity and usability over the internet, and it’s the most common tool to help disparate applications communicate with each other. Although the XML model is focused primarily on documents, it is generally used for the representation of random data structure, such as in web services.

Hundreds of XML-based languages have been produced, including XHTML, RSS and Atom. Many high-profile tools for office productivity are rooted in XML, such as Microsoft Office, OpenOffice.org and Apple’s iWork.

XML is sometimes confused with HTML; however, the two programming languages were designed for different purposes. XML was created to carry and store data, whereas HTML was made to display information. Therefore, XML is a complement to, not a replacement for, HTML.