added failing test for #468.

test/xml/test_builder.rb

@@ -199,6 +199,17 @@ def test_raw_append_with_instance_eval
         assert_equal 'hello', builder.doc.at('/root').content
       end
 
+      def test_raw_xml_append
+        builder = Nokogiri::XML::Builder.new do |xml|
+          xml.root do
+            xml << '<aaa><bbb/><ccc/></aaa>'
+          end
+        end
+
+        assert_equal ["aaa"],       builder.doc.at_css("root").children.collect(&:name)
+        assert_equal ["bbb","ccc"], builder.doc.at_css("aaa").children.collect(&:name)
+      end
+
       def test_cdata
         builder = Nokogiri::XML::Builder.new do
           root {