anchor.diff:      .remove();
   
     /* ------- PREVIEW (NO DATA) -------*/
  -  if (preview) {
  -    svg.append("rect")
  +  mask = svg.select(".preview");
  +  children = mask.selectAll("*");
  +  if (preview && children.empty()) {
  +    mask.append("rect")
         .attr("x", -width / 2)
         .attr("y", -height / 2)
         .attr("width", width)
  
positive.code:   return 0;
  }
  
  function update_data() {
    hide_percent();
    total_amount = 0;
  
negative.code:       .attr("fill", "white")
        .attr("opacity", 0.75);
  
      mask.append("text")
        .text("Preview")
        .attr("dy", ".4em")
        .style("text-anchor", "middle")
        .style("font-size", "1.9em");
    }
    else if (!preview) {
      children.remove();
    }
  
  };
  