Also known as: Extensible Markup Language
Extensible Markup Language, or XML, is a language used to describe and structure data. Its predecessor, SGML, is much more diverse, but is too complex for general usage; as a result, a thinned down version was created, which became eXtensible Markup Language. It is used in creating other web-markup methods such as Wireless Markup Language (WML), Scalable Vector Graphics (SVG), or Synchronised Multimedia Integration Language (SMIL).
XML is particularly suitable for web applications because it:
is compatible with web and internet protocolscan represent most character setssupports data structures such as records, lists and treescopes with hierarchical document structures; andis independent of any particular equipment or technology. Unlike HTML (which is a fixed-format language), XML is "extensible" - which means that its markup symbols are unlimited. Although there are certain similarities between the HTML and XML - both contain markup symbols that describe the contents of a document - HTML is a much laxer language with more room for error and a lot of leniency; as a result, the HTML specification is not always adhered to very strongly, and has different interpretations in each piece of software.
A version of HTML exists that also abides by the stricter rules set by XML, called XHTML. Eventually, HTML should be superceded by this cleaner, standardised and more well defined language