XML is a standard for creating markup languages which describe the structure of data. It is not a fixed set of elements like HTML, but rather, it is like SGML (Standard Generalized Markup Language) in that it is a metalanguage, or a language for describing languages. XML enables developers to define their own tags - for instance, an XML document can generate an HTML, PDF, and Word copy of the same file, enabling developers to have just one master document to update. XML is a formal specification of the World Wide Web Consortium.

We use XML in applications such as CarweB to define the structure of the data feeds to the end customers and in particular to b2b clients.