code: function buildContainerGroups() {
              let container = svg
                .append('g')
                  .classed('container-group', true);
  
              container
                .append('g')
                  .classed('chart-group', true);
              container
                .append('g')
                  .classed('legend-group', true);
          }
docs: Builds containers for the chart, the legend and a wrapper for all of them
  @private