如何使用XmlWriter将编码属性放到utm-16的xml中？

var settings = new XmlWriterSettings
{
    Encoding = Encoding.UTF8,
    Indent = true
};

using (var writer = XmlWriter.Create("output.xml", settings))
{
    // 编写XML文档
}

writer.WriteStartDocument();
writer.WriteStartElement("utm-16");

writer.WriteAttributeString("encoding", "UTF-8");

writer.WriteEndElement();
writer.WriteEndDocument();

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

class Program
{
    static void Main(string[] args)
    {
        var settings = new XmlWriterSettings
        {
            Encoding = Encoding.UTF8,
            Indent = true
        };

        using (var writer = XmlWriter.Create("output.xml", settings))
        {
            writer.WriteStartDocument();
            writer.WriteStartElement("utm-16");

            writer.WriteAttributeString("encoding", "UTF-8");

            writer.WriteEndElement();
            writer.WriteEndDocument();
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<utm-16 encoding="UTF-8" />