ents_();
    },

    set selection(selection) {
      if (selection.length <= 1) {
        throw new Error('Only supports multiple items');
      }
      this.setSelectionWithoutErrorChecks(selection);
    },

    get selection() {
      return this.currentSelection_;
    },

    setSelectionWithoutErrorChecks(selection) {
      this.currentSelection_ = selection;
      if (this.isAttached) this.updateContents_();
    },

    get eventsHaveDuration() {
      return this.eventsHaveDuration_;
    },

    set 