code: function mouseleave(d) {
  
    // Hide the breadcrumb trail
    d3.select("#trail")
        .style("visibility", "hidden");
  
    // Deactivate all segments during transition.
    d3.selectAll("path").on("mouseover", null);
  
    // Transition each segment to full opacity and then reactivate it.
    d3.selectAll("path")
        .transition()
        .duration(250)
        .style("opacity", 1)
        .each("end", function() {
                d3.select(this).on("mouseover", mouseover);
              });
  
    d3.select("#explanation")
        .style("visibility", "hidden");
  }
docs: Restore everything to full opacity when moving off the visualization.