anchor.diff:      $.each($('.diff-traffic-light'), (_, light) => {
         const $light = $(light);
         const nowTag = $light.data('now-tag');
  -      $light.click(() => { show(nowTag); });
  +      $light.click(() => show(nowTag));
       });
       cd.setupHoverTips($('[data-tip]')); // lights + other tips
     };
  
positive.code:     // preserve diff on/off state
      if (diffCheckBox().is(':checked')) {
        const prev = getPrevTag()
        param.wasTag = (prev != null) ? prev : 0;
      } else {
        param.wasTag = tag;
      }
  
negative.code:     diffCheckBox()
        .attr('checked', inDiffMode())
        .unbind('click')
        .bind('click', () => show(param.nowTag));
    };
  
    const diffCheckBox = () => $('#diff-checkbox');
  
    const inDiffMode = () => param.wasTag != param.nowTag;
  
    //-----------------------------------------
    // refresh traffic-lights
  