/**
  * Returns an instance of the self.
  * 
  * @remark      To support PHP 5.2, this method needs to be defined in each extended class 
  * as in static methods, it is not possible to retrieve the extended class name in a base class in PHP 5.2.x.
  * @return      object
  */
 public static function getInstance($sOptionKey = '')
 {
     if (isset(self::$oSelf)) {
         return self::$oSelf;
     }
     $sOptionKey = $sOptionKey ? $sOptionKey : AmazonAutoLinks_Registry::$aOptionKeys['template'];
     $_sClassName = __CLASS__;
     self::$oSelf = new $_sClassName($sOptionKey);
     return self::$oSelf;
 }