anchor.diff:      diffCheckBox()
         .attr('checked', inDiffMode())
         .unbind('click')
  -      .bind('click', () => { show(param.nowTag); });
  -  };
  -
  -  const diffCheckBox = () => {
  -    return $('#diff-checkbox');
  -  };
  -
  -  const inDiffMode = () => {
  -    return param.wasTag != param.nowTag;
  -  }
  +      .bind('click', () => show(param.nowTag));
  +  };
  +
  +  const diffCheckBox = () => $('#diff-checkbox');
  +
  +  const inDiffMode = () => param.wasTag != param.nowTag;
   
     //-----------------------------------------
     // refresh traffic-lights
  
positive.code:           const halfSecond = 500;
            diffSheet.animate({
              scrollTop: '+=' + (section.offset().top - downFromTop) + 'px'
              }, halfSecond);
            sectionIndex += 1;
            sectionIndex %= sectionCount;
          }
  
negative.code:     // For some reason the hover-tip gets displayed behind
      // the file-diff.
      html += '<td>';
      html += `<div class='traffic-light-count ${lastColour}'>`;
      html += trafficLightCount;
      html += '</div>';
      html += '</td>';
  