public static function addAdditionalNodeIDPerObject( $contentObjectID, $additionalNodeID )
    {
        if ( !isset( self::$additionalNodeIDsPerObject[$contentObjectID] ) )
        {
            self::$additionalNodeIDsPerObject[$contentObjectID] = array();
        }

        self::$additionalNodeIDsPerObject[$contentObjectID][] = $additionalNodeID;
    }