code: function (itemOptions) {
              var chart = this.chart,
                chartOptions = chart.options,
                plotOptions = chartOptions.plotOptions,
                userOptions = chart.userOptions || {},
                userPlotOptions = userOptions.plotOptions || {},
                typeOptions = plotOptions[this.type],
                options;
  
              this.userOptions = itemOptions;
  
              options = merge(
                typeOptions,
                plotOptions.series,
                itemOptions
              );
  
              // The tooltip options are merged between global and series specific options
              this.tooltipOptions = merge(
                defaultOptions.tooltip,
                defaultOptions.plotOptions[this.type].tooltip,
                userOptions.tooltip,
                userPlotOptions.series && userPlotOptions.series.tooltip,
                userPlotOptions[this.type] && userPlotOptions[this.type].tooltip,
                itemOptions.tooltip
              );
  
              // Delete marker object if not allowed (#1125)
              if (typeOptions.marker === null) {
                  delete options.marker;
              }
  
              return options;
  
          }
docs: Set the series options by merging from the options tree
  @param {Object} itemOptions