anchor.diff:        if (colour !== '') {
           const nowIndex = event.index;
           const barGap = (param.nowIndex === nowIndex) ? 'bar' : 'gap';
  -        html +=
  -          "<td><div class='diff-traffic-light'" +
  -                " data-tip='ajax:traffic_light'" +
  -                ` data-id='${param.id}'` +
  -                ` data-avatar-name='${param.avatarName}'` +
  -                ` data-colour='${colour}'` +
  -                ` data-was-tag='${wasIndex}'` +
  -                ` data-now-tag='${nowIndex}'>` +
  -            `<img class='with-bar-gap' src='/images/bulb_${colour}_${barGap}.png'/>` +
  -          '</div></td>';
  +        html += makeTd([
  +          "<div class='diff-traffic-light'",
  +              " data-tip='ajax:traffic_light'",
  +              ` data-id='${param.id}'`,
  +              ` data-avatar-name='${param.avatarName}'`,
  +              ` data-colour='${colour}'`,
  +              ` data-was-tag='${wasIndex}'`,
  +              ` data-now-tag='${nowIndex}'>`,
  +              `<img class='with-bar-gap' src='/images/bulb_${colour}_${barGap}.png'/>`,
  +          '</div>'
  +        ].join(''));
           wasIndex = nowIndex;
           lastColour = event.colour;
           trafficLightCount++;
         }
       });
   
  -    html += '<td>';
  -    html += `<div class='traffic-light-count ${lastColour}'>`;
  -    html += trafficLightCount;
  -    html += '</div>';
  -    html += '</td>';
  +    html += makeTd([
  +      `<div class='traffic-light-count ${lastColour}'>`,
  +      trafficLightCount,
  +      '</div>'
  +    ].join(''));
  +
       html += '</tr></table>';
   
       return html;
  
positive.code:   // - - - - - - - - - - - - - - - - - - - - - - - -
  
    const makeTrafficLightsHtml = (events) => {
      // Displays all the events that it receives from the differ/diff
      // JSON call and sets up was/now index for each event with the
      // was-index simply being the previous event index.
      // Note that event.indexs will not be contiguous if events
      // contains non-test events.
      let html = '';
      let wasIndex = 0;
      let lastColour = '';
  
negative.code:   //-----------------------------------------
    // refresh [<] event [>]
    //-----------------------------------------
    // [<] is enabled if there is an event to the lhs of param.nowIndex
    // [>] is enabled if there is an event to the rhs of param.nowIndex
    //-----------------------------------------
  
    const refreshEventControls = () => {
  