code: function mouseover(d) {
  
    var percentage = (100 * d.value / totalSize).toPrecision(3);
    var percentageString = percentage + "%";
    if (percentage < 0.1) {
      percentageString = "< 0.1%";
    }
  
    d3.select("#percentage")
        .text(percentageString);
  
    d3.select("#explanation")
        .style("visibility", "");
  
    var sequenceArray = getAncestors(d);
    updateBreadcrumbs(sequenceArray, percentageString);
  
    // Fade all the segments.
    d3.selectAll("path")
        .style("opacity", 0.3);
  
    // Then highlight only those that are an ancestor of the current segment.
    vis.selectAll("path")
        .filter(function(node) {
                  return (sequenceArray.indexOf(node) >= 0);
                })
        .style("opacity", 1);
  }
docs: Fade all but the current sequence, and show it in the breadcrumb trail.