Extensible markup language (XML)

Summary

XML (Extensible Markup Language) defines data objects called XML documents and partially describes their processing behavior. As a subset of SGML, XML documents are made up of entities containing parsed or unparsed data, with parsed data comprising characters and markup. XML processors read XML documents and provide access to their content for applications. Developed by the W3C XML Working Group in 1996, XML aims for Internet usability, broad application support, SGML compatibility, ease of processing, minimal optional features, human-legibility, formal design, and ease of creation. Key terms include error, fatal error, validity constraint, and well-formedness constraint, with specific rules and conditions for XML processors and document validity. This specification ensures a formal understanding of XML and guides the construction of compliant processing programs.