anchor.diff:    assertTextInvariants(xml);
     assertIteratorInvariants(xml);
     assertCopyInvariants(xml);
  +  assertTransformerInvariants(xml);
     assertPrintingInvariants(xml);
   }
   
  
positive.code:   assertTextInvariants(xml);
    assertIteratorInvariants(xml);
    assertCopyInvariants(xml);
  }
  
  void assertDocumentInvariants(XmlNode xml) {
  
negative.code: 
  void assertCopyInvariants(XmlNode xml) {
    final copy = xml.copy();
    assertParentInvariants(copy);
    assertNameInvariants(copy);
    assertCompareInvariants(xml, copy);
  }
  
  void assertTransformerInvariants(XmlNode xml) {
    final copy = XmlTransformer().visit(xml);
    assertParentInvariants(copy);
    assertNameInvariants(copy);
    assertCompareInvariants(xml, copy);
  }
  