在C#中正确使用XmlNode.SelectSingleNode(string xpath)是什么？

using System;
using System.Xml;

class Program {
    static void Main() {
        string xmlString = "<root><person name='John' age='30'/></root>";
        XmlDocument xmlDoc = new XmlDocument();
        xmlDoc.LoadXml(xmlString);

        XmlNode personNode = xmlDoc.SelectSingleNode("/root/person");
        if (personNode != null) {
            Console.WriteLine("Name: " + personNode.Attributes["name"].Value);
            Console.WriteLine("Age: " + personNode.Attributes["age"].Value);
        }
    }
}