The language format used to develop and write document pages on the World Wide Web. Webpages are built with HTML codes or tags (qv) embedded into the text. HTML defines the webpage layout, attributes, and graphic elements as well as the hypertext links to other documents on the Web. Each link contains the address or URL of a webpage residing on any Internet server. HTML 2.0 was defined by the Internet Engineering Task Force (IETF) with a basic set of features including interactive forms capability. From HTML 1 (1991) to HTML 4.0 (1999), subsequent versions added more features such as blinking text, custom backgrounds and tables of contents. Each new version requires agreement by the World Wide Web Consortium (W3C) on the codes or tags used, and browsers must be modified to implement those tags. HTML is not a programming language (ie: if this, do that), rather it could be considered a "presentation language". HTML was derived by Tim Berners-Lee from the Standard Generalized Markup Language (SGML), which is widely used to publish documents. HTML is an SGML document with a fixed set of tags that, although changing with each new revision, are not flexible. A subset of SGML, known as XML, allows the developer of the webpage to define the tags, and HTML 4.0 and XML 1.0 have been combined into a single format called "XHTML", which is expected to become the standard format for Webpages. XHTML also enables Web pages to be developed with different sets of data, depending on the type of browser used to access the Web. See DTD, CSS, image map, markup, webpage.