/*
 * call-seq:
 *   namespace_uri
 *
 * Get the URI defining the namespace associated with the node
 */
static VALUE namespace_uri(VALUE self)
{
  xmlTextReaderPtr reader;
  Data_Get_Struct(self, xmlTextReader, reader);
  const char * uri = (const char *)xmlTextReaderConstNamespaceUri(reader);
  if(uri == NULL) return Qnil;

  return NOKOGIRI_STR_NEW2(uri);
}