.XML is generally a configuration file, formally formatted xml document, with xml declaration statements, with one and only one root element, tags are case sensitive, attribute values are double quoted, tags come in pairs, empty tags are closed, and elements are properly nested.
Expanded:
xml is a powerful technology for working with structured document information. xml helps to shuttle structured data between servers, which gives developers more control over the storage and transfer of data.
Xml is a markup language used to mark up electronic documents to make them structured, and can be used to mark up data, define data types, and is a source language that allows users to define their own markup language. xml is a subset of the Standard Generalized Markup Language (SGML), which is well-suited for Web delivery. xml provides a uniform way to describe and exchange structured data independent of the application or vendor. XML provides a unified way to describe and exchange structured data independent of an application or vendor.