Extensible Markup Language (XML)

The Extensible Markup Language (XML) defines a syntax for describing a structured document that consists of tags, attributes, and associated semantics that are defined by the author of the particular XML document.

For that reason, XML is a generic markup language, unlike many other markup languages before it. In fact, there are no pre-defined tags or attributes within XML: only the syntax for defining tags and attributes are defined.

XML is used in a variety of applications. For example, XML is now the default file format used popular word processing packages available on the market today. XML is also widely used in communication systems in order to convey messages. Perhaps most notable of these is XMPP, which is an IETF standard for instant messaging.

Below is an example XML document that shows an IP address and an associated ISO country code:

<?xml version="1.0" encoding="UTF-8"?>

Resources: W3C XML, XML 1.0 Specification, XML 1.1 Specification