code: def holtWintersConfidenceArea(requestContext, seriesList, delta=3):
      
      bands = holtWintersConfidenceBands(requestContext, seriesList, delta)
      results = areaBetween(requestContext, bands)
      for series in results:
          series.name = series.name.replace('areaBetween',
                                            'holtWintersConfidenceArea')
      return results
docs: Performs a Holt-Winters forecast using the series as input data and plots
      the area between the upper and lower bands of the predicted forecast
      deviations.