无法使用HTML Agility Pack抓取所有HTML代码

我有以下使用HTMLAgilityPack分析某些示例HTML的C＃控制台应用程序代码：

static void Main(string[] args)
{
  string input = @"
<span style=""font-style: italic"">This is the title</span>.
This is the introductory text:
<ol>
  <li>List Item One</li>
  <li>List Item Two</li>
  <li>List Item Three</li>
  <li>This list item is nested:
      <ol>
        <li>List Item Four A.</li>
        <li>List Item Four B.</li>
      </ol>
      Yes it is.
  </li>
  <li>List Item Five</li>
</ol>
This is the footer text. Last updated: July 20, 2014

";

  HtmlDocument doc = new HtmlDocument();

  try
  {
    doc.LoadHtml(input);
  }
  catch (Exception e)
  {
    LogIt("ERROR: " + e.Message);
    return;
  }

  HtmlNode get_title = doc.DocumentNode.SelectSingleNode("//span");
  if (get_title != null)
  {
    LogIt("Title: '" + get_title.InnerHtml + "'");
  }

  HtmlNodeCollection get_outer_lists = doc.DocumentNode.SelectNodes("//ol//li");

  if (get_outer_lists != null)
  {
    foreach (HtmlNode hn_outer in get_outer_lists) 
    {
      LogIt("Begin outer for");
      LogIt("outer HTML: '" + hn_outer.OuterHtml + "'");

      // Now fetch inner list, the text above the inner list, and the 
      // text below the inner list.

      HtmlNodeCollection get_inner_lists = doc.DocumentNode.SelectNodes("//ol//li//ol//li");

      if (get_inner_lists != null)
      {
        foreach (HtmlNode hn_inner in get_inner_lists)
        {
          LogIt("\tinner HTML: '" + hn_inner.OuterHtml + "'");
        }
      }
      else
      {
        LogIt("ERROR: Could not get inner list");
      }
    }
  }
  else
  {
    LogIt("ERROR: Could not select //ol//li");
    Console.Read();
    return;
  }

  Console.Read();
  return;
}

private static void LogIt(string str)
{
  Console.WriteLine(str);

  return;
}

...这是输出：

Title: 'This is the title'
Begin outer for
outer HTML: '<li>List Item One</li>'
        inner HTML: '<li>List Item Four A.</li>'
        inner HTML: '<li>List Item Four B.</li>'
Begin outer for
outer HTML: '<li>List Item Two</li>'
        inner HTML: '<li>List Item Four A.</li>'
        inner HTML: '<li>List Item Four B.</li>'
Begin outer for
outer HTML: '<li>List Item Three</li>'
        inner HTML: '<li>List Item Four A.</li>'
        inner HTML: '<li>List Item Four B.</li>'
Begin outer for
outer HTML: '<li>This list item is nested:
      <ol>
        <li>List Item Four A.</li>
        <li>List Item Four B.</li>
      </ol>
      Yes it is.
  </li>'
        inner HTML: '<li>List Item Four A.</li>'
        inner HTML: '<li>List Item Four B.</li>'
Begin outer for
outer HTML: '<li>List Item Four A.</li>'
        inner HTML: '<li>List Item Four A.</li>'
        inner HTML: '<li>List Item Four B.</li>'
Begin outer for
outer HTML: '<li>List Item Four B.</li>'
        inner HTML: '<li>List Item Four A.</li>'
        inner HTML: '<li>List Item Four B.</li>'
Begin outer for
outer HTML: '<li>List Item Five</li>'
        inner HTML: '<li>List Item Four A.</li>'
        inner HTML: '<li>List Item Four B.</li>'

1. 我可以很好地获得标题文本，但是如何获得介绍性文本或页脚？它们不属于我可以选择的HTML元素。
2. 外部foreach循环遍历外部和内部有序列表。如何更改XPath字符串，以便外部for循环仅迭代外部列表？内部for循环应注意内部列表。