XML (W3C standard 1996) stands for eXtensible Markup Language
XML was designed to describe, store and transmit data and be readable by people.
XML is a markup language both like and unlike HTML.
XML tags are not predefined in XML. You can define your own tags or use other peoples.
XML uses an optional DTD (Document Type Definition) or xml schema to describe the tags and data used.
XHTML is the replacement for Html 4 and is an application of XML.