XML is a markup language. A markup language used tags to indicate how a file should look when displayed on a web page. Some examples of markup language are standard generalized markup language (SGML)and Hypertext markup language (HTML)
SGML was related in1980. SGML allows documents to describe their own grammar by specifying the tag set used in the documents and the structural relationship that these represent. this makes it possible to define your own formats for documents, handle large and complex and difficult for developers to master.