XML namespaces provide a simple method for qualifying element and attribute names used in Extensible Markup Language documents by associating them with namespaces identified by URI references. (W3C Recommendation 14 January 1999)
an HTML-based markup language designed to contain a human-readable description of an XML namespace as well as pointers to multiple resources related to that namespace. Examples of such related resources include schemas, stylesheets, human-readable doc...