code: function createLinkedTimelines() {
      const tl1 = createTimeline();
      const tl2 = createTimeline();
      tl1.setNeighbouringTimeline(tl2, EventTimeline.FORWARDS);
      tl2.setNeighbouringTimeline(tl1, EventTimeline.BACKWARDS);
      return [tl1, tl2];
  }
docs: /*
  create a pair of linked timelines