i wanna add this small sentence that xml is developing so fastly and so many softwares are accepting xml as to transform data or else....

The tags used to mark up HTML documents and the structure of HTML documents are predefined. The author of HTML documents can only use tags that are defined in the HTML standard (like <p>, <h1>,...

And Also i wanna say this too that : Maybe it is a little hard to understand, but XML does not DO anything. XML was created to structure, store and to send information.
....

XML is not a replacement for HTML.
XML and HTML were designed with different goals:

XML was designed to describe data and to focus on what data is.
HTML was designed to display data and to focus...