White space is preserved only if XmlDocument.PreserveWhitespace is set to true.

The encoding on the XmlWriter determines the encoding that is written out (The encoding of the XmlDeclaration node is replaced by the encoding of the XmlWriter). If there was no encoding specified on the XmlWriter, the XmlDocument is saved without an encoding attribute.

When the document is saved, xmlns attributes are generated to persist the node identity (LocalName + NamespaceURI) correctly. For example, the following C# code

 XmlDocument doc = new XmlDocument();
 doc.AppendChild(doc.CreateElement("item","urn:1"));
 doc.Save(Console.Out);

generates this xmls attribute:

<item
    xmls="urn:1"/>

This method is a Microsoft extension to the Document Object Model (DOM).

Note that only the XmlDocument.Save(string) method enforces a well-formed XML document. All other Save overloads only guarantee a well-formed fragment.