3.3.4 XML

Extensible Markup Language (XML) is a markup language. XML defines a set of rules for encoding documents in human-readable and machine-readable formats.

The design goals of XML emphasize simplicity, generality, and usability over the Internet. Unicode support for the languages made it widely acceptable in world. Although the design of XML focuses on documents, it is widely used for the representation of arbitrary data structures, for example in web services.

Many application programming interfaces (APIs) have been developed for software developers to use to process XML data, and several schema systems exist to aid in the definition of XML-based languages.

XML is used to create web-development languages, including RSS, Atom, SOAP, and XHTML. XML-based formats have become the default for many office-productivity tools, including Microsoft Office (Office Open XML) and OpenOffice.org. XML has also been employed as the base language for communication protocols.

XML is used to transport data, while HTML is used to format and display data.