docs: function crosshair(g) {
        var group = g.selectAll('g.data.top').data([change], function(d) { return d; }),
            groupEnter = group.enter(),
            dataEnter = groupEnter.append('g').attr('class', 'data top').style('display', 'none');
  
        group.exit().remove();
  
        dataEnter.append('path').attr('class', 'horizontal wire');
        dataEnter.append('path').attr('class', 'vertical wire');
  
        plot.annotation.append(dataEnter, xAnnotation, 'x');
        plot.annotation.append(dataEnter, yAnnotation, 'y');
  
        g.selectAll('rect').data([0]).enter().append('rect').style({ fill: 'none', 'pointer-events': 'all' });
  
        crosshair.refresh(g);
      }