docs: function SliceGroup(parentContainer, opt_sliceConstructor, opt_name) {
      tr.model.EventContainer.call(this);
  
      this.parentContainer_ = parentContainer;
  
      var sliceConstructor = opt_sliceConstructor || Slice;
      this.sliceConstructor = sliceConstructor;
  
      this.openPartialSlices_ = [];
  
      this.slices = [];
      this.topLevelSlices = [];
      this.haveTopLevelSlicesBeenBuilt = false;
      this.name_ = opt_name;
  
      if (this.model === undefined)
        throw new Error('SliceGroup must have model defined.');
    }