C# xpath表达式在HtmlAlityPack上工作不正常

我正在尝试使用xpath表达式搜索html节点。
目标是将具有2个子节点的所有

tr

节点与属性

class=“shiftHolder”

匹配（示例中的秒数

tr

）

我不知道HtmlAgilityPack有什么不同吗

<table>
       <tr class="staffRow">
          <td class="staff" data-staffid="2" data-primaryrole="1">
             <div class="sn">Leyla-claire Collins</div>
          </td>
          <td class="shiftHolder">
          </td>
          <td class="shiftHolder unavailable">
             Holiday
          </td>
       </tr>
       <tr class="staffRow">
          <td class="staff" data-staffid="11" data-primaryrole="4">
             <div class="sn">Natale Dersley</div>
          </td>
          <td class="shiftHolder">
          </td>
          <td class="shiftHolder">
          </td>
       </tr>
    </table>

//tr[@class='staffRow'][count(td[@class='shiftHolder'])=2][td[@class='staff' and @data-staffid and @data-primaryrole][div[@class='sn']]]

//tr[@class='staffRow' and count(td[@class='shiftHolder'])=2 and td[@class='staff' and @data-staffid and @data-primaryrole and div[@class='sn']]]