anchor.diff:  
     void writeTo(StringBuffer buffer) {
       if (prefix != null) {
  -      buffer.add(prefix).add(':');
  +      buffer.add(prefix);
  +      buffer.add(':');
       }
       buffer.add(local);
     }
  
positive.code:   XmlDoctype(String data) : super(data);
  
    void writeTo(StringBuffer buffer) {
      buffer.add('<!DOCTYPE').add(data).add('>');
    }
  
  }
  
negative.code:   String get target => _target;
  
    void writeTo(StringBuffer buffer) {
      buffer.add('<?');
      buffer.add(target);
      buffer.add(data);
      buffer.add('?>');
    }
  
  }
  