Return an XPath that will locate the given node within it's document and populate an XmlNamespaceManager with the namespace prefixes used in that XPath query. You can then use this XmlNamespaceManager in the call the SelectNodes or SelectSingleNode methods.
A namespace manager, it may be empty or it may be pre-populated with the prefixes you want to use. Either way if a namespace prefix is needed that is not defined or if it conflicts with another definition then a new prefix will be generated automatically.
Returns
The XPath expression needed to locate the given node or null if the node is not locatable by XPath because of it's NodeType.
