anchor.diff:  
   import 'xml_examples.dart';
   
  -void validate(String input) {
  +void assetParseInvariants(String input) {
     var tree = parse(input);
     assertTreeInvariants(tree);
     var copy = parse(tree.toXmlString());
  
positive.code:         builder.attribute('lang', 'en', namespace: uri);
          builder.element('element', namespace: uri);
        }, namespace: uri);
        var actual = builder.build().toString();
        var expected =
            '<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" xsd:lang="en">'
              '<xsd:element />'
  
negative.code: void assertNameInvariant(XmlNode xml) {
    for (var node in xml.descendants) {
      if (node is XmlElement) {
        assertQualifiedInvariant(node.name);
      } else if (node is XmlAttribute) {
        assertQualifiedInvariant(node.name);
      }
    }
  }
  