An XML Namespace is a Prefix An XML namespace uses a URL as a prefix in front of the "local name." The combination of URL and local name makes the element or attribute name unique. The URL is used ...

What RSS 2.0 feeds can't do, lacking a top-level namespace declaration, is embed directly in other XML vocabularies. For that scenario to work, RSS 2.0's top-level namespace would have to be non-empty ...