Xml的具体流程

  XmlDocument xmlDoc = new XmlDocument();
            xmlDoc.Load(Server.MapPath("bookstore.xml"));
            XmlNodeList xnl = xmlDoc.SelectSingleNode("bookstore").ChildNodes;
            foreach (XmlNode xn in xnl)
            {
                XmlElement xe = (XmlElement)xn;
                if (xe.GetAttribute("genre") == "fantasy")
                {
                    xe.RemoveAttribute("genre");
                }
                else if (xe.GetAttribute("genre") == "update李赞红")
                {
                    xe.RemoveAll();
                }
            }
            xmlDoc.Save(Server.MapPath("bookstore.xml"));

这行代码的流程是什么，重点是foreach里的代码，请详细说明一下，谢谢