anchor.diff:      let html = '';
       let wasIndex = 0;
       html += '<table><tr valign="top">';
  -    html += makeTd(makeIndexLeft());
  -    html += makeTd(makeIndexRight());
       $.each(param.events, (_n, event) => {
         const colour = event.colour;
         if (colour !== '') {
  
positive.code:     });
      html += '</tr></table>';
      return html;
    };
  
    // - - - - - - - - - - - - - - - - - - - - - - - -
  
    const makeIndexLeft = () => {
      return '' +
        '<button class="triangle button" id="prev-index">' +
          '<img src="/images/triangle_prev.gif" alt="move to previous diff"/>' +
        '</button>';
    };
  
    // - - - - - - - - - - - - - - - - - - - - - - - -
  
    const makeIndexRight = () => {
      return '' +
        '<button class="triangle button" id="next-index">' +
          '<img src="/images/triangle_next.gif" alt="move to next diff"/>' +
        '</button>';
    };
  
    // - - - - - - - - - - - - - - - - - - - - - - - -
  
negative.code:       <div id="download-button-container"></div>
        <div id="diff-filenames"></div>
      </td>
      <td colspan="3">
        <div id="diff-content"></div>
      </td>
    </tr>
  