//[NotWorking ("default namespace seems null, not String.Empty")]
        public void DefaultXmlnsAttributeLookup()
        {
            string xml = @"<!DOCTYPE X [
			<!ELEMENT X (Y)+>
			<!ENTITY baz 'urn:baz'>
			<!ATTLIST X
				xmlns CDATA 'urn:foo'
				xmlns:bar CDATA 'urn:bar'
				xmlns:baz CDATA #IMPLIED
				dummy CDATA 'dummy'
				baz:dummy CDATA 'dummy'>
			<!ELEMENT Y (#PCDATA)*>
			<!ATTLIST Y
				xmlns CDATA #IMPLIED
				xmlns:bar CDATA #IMPLIED>
			]>
			<X xmlns:baz='&baz;'><Y/><Y>text.</Y><Y xmlns='' xmlns:bar='urn:hoge'>text.</Y></X>"            ;
            XmlValidatingReader xvr = new XmlValidatingReader(
                xml, XmlNodeType.Document, null);

            xvr.Read();              // DTD
            xvr.Read();              // whitespace
            xvr.Read();
            Assert.AreEqual("urn:foo", xvr.LookupNamespace(String.Empty), "#1-1");
            Assert.AreEqual("urn:bar", xvr.LookupNamespace("bar"), "#1-2");

            Assert.AreEqual("urn:baz", xvr.LookupNamespace("baz"), "#1-a");
            Assert.IsTrue(xvr.MoveToAttribute("baz:dummy"), "#1-b");
            Assert.AreEqual("urn:baz", xvr.NamespaceURI, "#1-c");

            Assert.IsTrue(xvr.MoveToAttribute("dummy"), "#1-d");
            Assert.AreEqual(String.Empty, xvr.NamespaceURI, "#1-e");

            xvr.Read();              // first Y, empty element
            Assert.AreEqual("urn:foo", xvr.LookupNamespace(String.Empty), "#2-1");
            Assert.AreEqual("urn:bar", xvr.LookupNamespace("bar"), "#2-2");
            xvr.Read();              // second Y, start element
            Assert.AreEqual("urn:foo", xvr.LookupNamespace(String.Empty), "#3-1");
            Assert.AreEqual("urn:bar", xvr.LookupNamespace("bar"), "#3-2");
            xvr.Read();              // inside normal Y. Check inheritance
            Assert.AreEqual("urn:foo", xvr.LookupNamespace(String.Empty), "#4-1");
            Assert.AreEqual("urn:bar", xvr.LookupNamespace("bar"), "#4-2");
            xvr.Read();              // second Y, end element
            Assert.AreEqual("urn:foo", xvr.LookupNamespace(String.Empty), "#5-1");
            Assert.AreEqual("urn:bar", xvr.LookupNamespace("bar"), "#5-2");
            xvr.Read();              // third Y, suppresses default namespaces
            Assert.AreEqual(null, xvr.LookupNamespace(String.Empty), "#6-1");
            Assert.AreEqual("urn:hoge", xvr.LookupNamespace("bar"), "#6-2");
            xvr.Read();              // inside suppressing Y. Check inheritance
            Assert.AreEqual(null, xvr.LookupNamespace(String.Empty), "#7-1");
            Assert.AreEqual("urn:hoge", xvr.LookupNamespace("bar"), "#7-2");
            xvr.Read();              // end of suppressing element
            Assert.AreEqual(null, xvr.LookupNamespace(String.Empty), "#8-1");
            Assert.AreEqual("urn:hoge", xvr.LookupNamespace("bar"), "#8-2");
        }