BUG: Namespace "xml" is not reserved when using System.Xml (317503)

XmlDocument x = new XmlDocument();
XmlElement c = x.CreateElement("test");
c.SetAttribute("xml:lang", "en-US");
x.AppendChild(c);
Console.Out.WriteLine( "'" + x.DocumentElement.Attributes[0].NamespaceURI + "'" );
Console.Out.WriteLine( "'" + x.DocumentElement.Attributes[0].Prefix + "'"); 
				

''
'xml'
				

'http://www.w3.org/XML/1998/namespace'
'xml'
				

MORE INFORMATION

According to the World Wide Web Consortium (W3C) specification (http://www.w3.org/TR/REC-xml-names/#xmlReserved), namespace prefixes beginning with the three-letter sequence x, m, l, in any case combination, are reserved for use by XML and XML-related specifications.

It is illegal to use "xml" as a prefix to create random elements or attributes other than xml:lang or xml:space. For example, it is illegal to create an attribute xml:this on the element "that" as follows:

<that xml:this="bob" />
				

Steps to Reproduce Behavior

1. Create a Microsoft C# console project.
2. Replace the code inside Class1.cs with the following:

   using System;
   using System.Xml;
   
   namespace XMLTest1
   {
   	/// <summary>
   	/// Summary description for Class1.
   	/// </summary>
   	class Class1
   	{
   		static void Main(string[] args)
   		{
   			XmlDocument x = new XmlDocument();
   			XmlElement c = x.CreateElement("test");
   			c.SetAttribute("xml:lang", "en-us");
   			x.AppendChild(c);			
   			
   			Console.Out.WriteLine( "'" + x.DocumentElement.Attributes[0].NamespaceURI + "'" );
   			Console.Out.WriteLine( "'" + x.DocumentElement.Attributes[0].Prefix + "'");  
   
   			Console.Out.WriteLine("output from XmlDocument: " + x.InnerXml);
   			
   			Console.Out.WriteLine("\noutput from XmlTextWriter: "); 
   			XmlTextWriter writer = new XmlTextWriter(Console.Out);
   			writer.Formatting = Formatting.Indented;
   			x.WriteTo( writer );
   			writer.Flush();
   			Console.WriteLine();
   
   			return;
   		}
   	}
   }
   					

3. Compile and then run the project. The output is as follows:

   ''
   'xml'
   output from XmlDocument: <test lang="en-us" />
   
   output from XmlTextWriter:
   <test xml:lang="en-us" />
   						

   The XmlTextWriter writes the correct XML data.