Hypertext Markup Language (HTML) is an application of a more general markup language known as Standard Generalized Markup Language (SGML). Every HTML document starts with an SGML declaration that gives its definition. This might not make a lot of sense to you right now - don't worry, you don't need to know anything about SGML to write HTML documents.
It wasn't always that way, and probably most of the Web user agents, like Netscape Navigator and Internet Explorer, do not use SGML to decode the HTML markup; however, it is the intent of the World Wide Web Consortium [W3C] (www.w3.org) which is responsible for the development of Internet Web Technologies to encourage this view of document markup.
