<kml:kml xmlns:kml="http://www.opengis.net/kml/2.2">
  <kml:NetworkLinkControl>
     <kml:message>This is a pop-up message. You will only see this once</kml:message>
     <kml:cookie>cookie=sometext</kml:cookie>
     <kml:linkName>New KML features</kml:linkName>
     <kml:linkDescription><![CDATA[KML now has new features
                         available!]]></kml:linkDescription>
  </kml:NetworkLinkControl>
</kml:kml>