问保存XmlDocument时，它会忽略XmlDeclaration (UTF8)中的编码并使用UTF16

EN

var doc = new XmlDocument();

XmlDeclaration xmlDeclaration = doc.CreateXmlDeclaration("1.0", "UTF-8", null);
doc.AppendChild(xmlDeclaration);

XmlElement root = doc.CreateElement("myRoot");
doc.AppendChild(root);
root.InnerText = "myInnerText";

StringWriter sw = new StringWriter();
doc.Save(sw);
Console.WriteLine(sw.ToString());

Console.WriteLine();

MemoryStream ms = new MemoryStream();
doc.Save(ms);
Console.WriteLine(Encoding.ASCII.GetString(ms.ToArray()));

<?xml version="1.0" encoding="utf-16"?>
<myRoot>myInnerText</myRoot>

???<?xml version="1.0" encoding="UTF-8"?>
<myRoot>myInnerText</myRoot>