docs: 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)