code: function drawVerticalMarker() {
              // Not ideal, we need to figure out how to call exit for nested elements
              if (verticalMarkerContainer) {
                  svg.selectAll('.vertical-marker-container').remove();
              }
  
              verticalMarkerContainer = svg.select('.metadata-group')
                .append('g')
                  .attr('class', 'vertical-marker-container')
                  .attr('transform', 'translate(9999, 0)');
  
              verticalMarkerLine = verticalMarkerContainer.selectAll('path')
                  .data([{
                      x1: 0,
                      y1: 0,
                      x2: 0,
                      y2: 0
                  }])
                  .enter()
                    .append('line')
                      .classed('vertical-marker', true)
                      .attr('x1', 0)
                      .attr('y1', chartHeight)
                      .attr('x2', 0)
                      .attr('y2', 0);
          }
docs: Creates the vertical marker
  @return void