Namespaces in an XML Document 

XML namespaces associate element and attribute names in an XML document with custom and predefined URIs. The prefixes defined for namespace URIs are used to qualify element and attribute names in XML data to implement this association. Namespaces prevent element and attribute name collisions, and allows elements and attributes of the same name to be handled differently and validated differently.

See Also

Concepts

Namespace Declarations
Default Namespaces
Namespace Declaration Scope
Manage Namespaces Using the XmlNamespaceManager
Information Obtained from the XmlNamespaceManager