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What are XML namespaces for?
xmlns attribute of the xml element!
Just like the .NET namespaces, it is designed to allow you to clearly identify objects and avoid name conflicts.
E.g. you can have a Person in the http://mycompany.com/schemas/Internal XML namespace, and also another type Person in http://mycompany.com/schemas/ERP - and those two will not conflict on their name.
See this great article here The XML Files - Understanding XML Namespaces which explains it in much greater detail and much better than I do.