code: function drawHoverOverlay() {
              // Not ideal, we need to figure out how to call exit for nested elements
              if (overlay) {
                  svg.selectAll('.overlay').remove();
              }
  
              overlay = svg.select('.metadata-group')
                .append('rect')
                  .attr('class', 'overlay')
                  .attr('y1', 0)
                  .attr('y2', chartHeight)
                  .attr('height', chartHeight)
                  .attr('width', chartWidth)
                  .attr('fill', overlayColor)
                  .style('display', 'none');
          }
docs: Draws an overlay element over the graph
  @private