Returns the drag data associated with this data set.  This will be 
        used when the user attempts to drag & drop a data set from the
        chart somewhere.  If no key is supplied, then the full data dictionary
        is returned.
        
        :param      key     | <str> || None
                    default | <variant>
        
        :return     (<variant> drag value, <dict> where values)

def dragData(self, key=None, default=None):
        """
        Returns the drag data associated with this data set.  This will be 
        used when the user attempts to drag & drop a data set from the
        chart somewhere.  If no key is supplied, then the full data dictionary
        is returned.
        
        :param      key     | <str> || None
                    default | <variant>
        
        :return     (<variant> drag value, <dict> where values)
        """
        if key is None:
            return self._dragData
        
        return self._dragData.get(nativestring(key), default)