System.Xml.XmlDocument doc = new System.Xml.XmlDocument();
System.Xml.XmlElement el = new System.Xml.XmlElement("p");
el.AppendToDocument(doc);

System.Xml.XmlDocument doc = System.Xml.XmlDocument.Create();
System.Xml.XmlElement el = System.Xml.XmlElement.Create("p");
doc.AppendChild(el);