# XML Introduction * * * XML was designed to transport and store data. HTML was designed to display data. XML stands for eXtensible Markup Language. Extensible Markup Language (English: Extensible Markup Language, abbreviated: XML) is a markup language simplified and modified from Standard Generalized Markup Language (SGML). Its main applications include Extensible Markup Language, Extensible Stylesheet Language (XSL), XBRL, and XPath. !( * * * ## Prerequisites Before you continue, you should have a basic understanding of the following: * HTML * JavaScript If you wish to learn these topics first, visit these tutorials on our ( * * * ## What is XML? * XML stands for EXtensible Markup Language. * XML is a markup language very similar to HTML. * XML was designed to carry data, not to display data. * XML tags are not predefined. You must define your own tags. * XML was designed to be self-descriptive. * XML is a W3C Recommendation. * * * ## Differences Between XML and HTML XML is not a replacement for HTML. XML and HTML were designed with different goals: * XML was designed to carry and store data, with focus on what data is. * HTML was designed to display data, with focus on how data looks. HTML is designed to display information, while XML is designed to carry information. * * * ## XML Does Not Do Anything This might sound strange, but XML does not do anything. XML was designed to describe data, and to focus on what data is. The following example is a note from Jani to Tove, stored as XML: ToveJaniReminderDon't forget me this weekend! The note above is self-descriptive. It contains sender and receiver information, plus a heading and message body. However, this XML document does not do anything. It is merely pure information wrapped in XML tags. We need software or programs to transmit, receive, and display this document. * * * ## With XML You Can Invent Your Own Tags The tags in the example above (like and ) are not defined in any XML standard. These tags were invented by the author of the XML document. This is because XML does not have predefined tags. Tags used in HTML are predefined. HTML documents can only use tags defined in the HTML standard (like

,

, etc.). XML allows the author to define their own tags and their own document structure. * * * ## XML Is Not a Replacement for HTML **XML is a complement to HTML.** XML does not replace HTML, and it is important to understand this. In most web applications, XML is used to transport data, while HTML is used to format and display the data. The best description of XML is: **XML