docs: function(viewport) {
        var dt = viewport.currentDisplayTransform;
        var containerToTrack = viewport.containerToTrackMap;
        var viewX = dt.xWorldToView(this.xWorld_);
  
        var viewY = -1;
        for (var index in this.yComponents_) {
          var yComponent = this.yComponents_[index];
          var track = containerToTrack.getTrackByStableId(yComponent.stableId);
          if (track !== undefined) {
            var boundRect = track.getBoundingClientRect();
            viewY = yComponent.yPercentOffset * boundRect.height + boundRect.top;
            break;
          }
        }
  
        return {
          viewX: viewX,
          viewY: viewY
        };
      }