The base URI of the current node.
A networked XML document is comprised of chunks of data aggregated using various W3C standard inclusion mechanisms and therefore contains nodes that come from different places. DTD entities are an example of this, but this is not limited to DTDs. The base URI tells you where these nodes came from. If there is no base URI for the nodes being returned (for example, they were parsed from an in-memory string), String.Empty is returned.