A string that represents the base URI.
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 aggregated data, but it is not limited to DTDs. The XPathNavigator.BaseURI property tells you where these nodes originate from.
For example, if the XML data is loaded from http://server/mydata.xml, the XPathNavigator.BaseURI property returns http://server/mydata.xml.
Nodes created using the System.Xml.XPath.XPathNavigator class have the same XPathNavigator.BaseURI as the XML document the System.Xml.XPath.XPathNavigator was created from.