C#XMLElement.OuterXML在一行而不是格式

<root>
 <child>
    <subchild>Hello, world!</subchild>
  </child>
</root>

  <subchild>Hello, world!</subchild>
</child>

using System;
using System.IO;
using System.Xml;

class Program
{
    static void Main(string[] args)
    {
        string xml = "<root><child><subchild>Hello, world!</subchild></child></root>";
        XmlDocument doc = new XmlDocument();
        doc.LoadXml(xml);

        XmlWriterSettings settings = new XmlWriterSettings();
        settings.OmitXmlDeclaration = true;
        settings.Indent = false;
        settings.NewLineHandling = NewLineHandling.None;

        XmlElement childElement = (XmlElement)doc.SelectSingleNode("//child");
        string formattedXml = FormatXmlElement(childElement, settings);

        Console.WriteLine(formattedXml);
    }

    static string FormatXmlElement(XmlElement element, XmlWriterSettings settings)
    {
        using (StringWriter sw = new StringWriter())
        {
            using (XmlWriter xw = XmlWriter.Create(sw, settings))
            {
                element.WriteTo(xw);
                xw.Flush();
            }
            return sw.ToString();
        }
    }
}