XML

XML (eXtensible Markup Language) is a text-based, Unicode-friendly format for representing structured data using nested elements (tags) and attributes, making documents both human- and machine-readable. It’s “extensible” because you define your own vocabulary (element and attribute names), organize data hierarchically, and use namespaces to avoid naming collisions. XML supports validation with DTDs or XML Schema (XSD), and a rich toolset—XPath for querying, XSLT for transformation, DOM/SAX for parsing—though it’s more verbose than alternatives like JSON. Common uses include configuration files, document publishing, and system-to-system data exchange.

XML grew out of SGML (ISO 8879:1986) in the mid-1990s as a simpler, web-friendly subset led at the W3C by Jon Bosak and others; the XML 1.0 spec became a W3C Recommendation in February 1998 (with a minor 1.1 revision in 2004). Around it, a family of standards emerged—Namespaces (1999), XPath and XSLT 1.0 (1999), DOM levels (late 1990s–2000s), XML Schema 1.0 (2001), and related formats like SVG (2001), SOAP (2000/2003), RSS/Atom (early 2000s), and office document formats (ODF, OOXML). XML powered early web services, configuration, publishing, and data interchange across enterprises; while JSON later became dominant for browser-centric APIs, XML remains entrenched in many protocols, document workflows, and enterprise systems.

License: W3C Document License

Tags: Data Formats

Properties: Namespaces, Infosets, Tree Models, Character Data Forms, Instructions, Links, Declarations

GitHub: https://www.w3.org/TR/xml/