anchor.diff:        </table>
       </td>
       <td>
  -      <div id="review-navigator"></div>
  +      <button id="prev-index" class="triangle button">
  +        <img src="/images/triangle_prev.gif" alt="move to previous diff"/>
  +      </button>
  +    </td>
  +    <td>
  +      <button id="next-index" class="triangle button">
  +        <img src="/images/triangle_next.gif" alt="move to next diff"/>
  +      </button>
  +    </td>
  +    <td>
         <div id="review-traffic-lights"></div>
       </td>
     </tr>
  
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:     let html = '';
      let wasIndex = 0;
      html += '<table><tr valign="top">';
      $.each(param.events, (_n, event) => {
        const colour = event.colour;
        if (colour !== '') {
  