System.Xml.XPath.XPathNavigator.LookupPrefix C# (CSharp) Method

        public virtual string LookupPrefix(string namespaceURI)
        {
            if (namespaceURI == null)
                return null;

            XPathNavigator navClone = Clone();

            if (NodeType != XPathNodeType.Element)
            {
                // If current item is not an element, then try parent
                if (navClone.MoveToParent())
                    return navClone.LookupPrefix(namespaceURI);
            }
            else
            {
                if (navClone.MoveToFirstNamespace(XPathNamespaceScope.All))
                {
                    // Loop until a matching namespace is found
                    do
                    {
                        if (namespaceURI == navClone.Value)
                            return navClone.LocalName;
                    }
                    while (navClone.MoveToNextNamespace(XPathNamespaceScope.All));
                }
            }

            // Check for default, "xml", and "xmlns" namespaces
            if (namespaceURI == LookupNamespace(string.Empty))
                return string.Empty;
            else if (namespaceURI == XmlReservedNs.NsXml)
                return "xml";
            else if (namespaceURI == XmlReservedNs.NsXmlNs)
                return "xmlns";

            return null;
        }

 string IXmlNamespaceResolver.LookupPrefix(string namespaceName)
 {
     return(_nav.LookupPrefix(namespaceName));
 }