    /*
     * call-seq:
     *   namespace_uri
     *
     * Get the URI defining the namespace associated with the node
     */
    static VALUE namespace_uri(VALUE self)
    {
      xmlTextReaderPtr reader;
      const char *uri;

      Data_Get_Struct(self, xmlTextReader, reader);
      uri = (const char *)xmlTextReaderConstNamespaceUri(reader);
      if(uri == NULL) return Qnil;

      return NOKOGIRI_STR_NEW2(uri);
    }