anchor.diff:        <table class="controls">
           <tr>
             <td><%= render partial: 'review/resume_button' %></td>
  -          <td><%= render partial: 'review/checkbox' %></td>
  +          <td><%= render partial: 'review/diff_checkbox' %></td>
             <td><%= render partial: 'review/fork_button' %></td>
  -          <td><div id="checkout-button-box"></div></td>
  +          <td><%= render partial: 'review/checkout_button' %></td>
           </tr>
         </table>
         <table>
  
positive.code:          wasIndex:wasIndex,
           nowIndex:nowIndex
      };
      fadeIntoReviewPage();
      review.setupButton('checkout', () => review.fadeIntoKataPage(() => { // [1]
        cd.checkout({ src_id:review.params.id, src_index:review.params.nowIndex });
      }));
      setCheckoutButtonTip();
      review.refresh();
    };
  
    // - - - - - - - - - - - - - - - - - - - - - - - -
    const fadeIntoReviewPage = () => {
      $kataPage.fadeOut('fast', () => {
        review.page.fadeIn('fast');
      });
  
negative.code:   };
  
    // - - - - - - - - - - - - - - - - - - - - - - - -
    review.setupButton = (name, handler) => {
      const button = `<button id="${name}-button" type="button"></button>`;
      $(`#${name}-button-box`).html(button);
  