docs: function groupSeriesByAxis(ecModel) {
      var result = [];
      var axisList = [];
  
      ecModel.eachSeriesByType('boxplot', function (seriesModel) {
          var baseAxis = seriesModel.getBaseAxis();
          var idx = zrUtil.indexOf(axisList, baseAxis);
  
          if (idx < 0) {
              idx = axisList.length;
              axisList[idx] = baseAxis;
              result[idx] = {axis: baseAxis, seriesModels: []};
          }
  
          result[idx].seriesModels.push(seriesModel);
      });
  
      return result;
  }