code: void addData(double xOffset, double yOffset, String xValue, String yValue) {
  
      String label = getLabel(xValue, yValue);
  
      addData(xOffset, yOffset, label);
    }
docs: Adds a data (xValue, yValue) with coordinates (xOffset, yOffset). This point will be
  highlighted with a circle centering (xOffset, yOffset)