anchor.diff:    void enteredView() {
   
       super.enteredView();
  -    this.displayValue = notifyPropertyChange(#value, this.displayValue, this.unit.value);
  -
  +    this.displayValue = notifyPropertyChange(#value, this.displayValue, this.unit.value.toString());
       PathObserver observer = new PathObserver(this.unit, 'value');
       observer.changes.listen((_) {
         print(this.unit.toString() + ' ' + this.editing.toString() + ' ' + this.unit.value.toString());
  
positive.code: library my_polymer_my_unit_element;
  
  import 'package:polymer/polymer.dart';
  
  import 'main_element.dart';
  
negative.code:   }
  
    void set value(String value) {
      try {
        print('set ' + value + ' ' + double.parse(value).toString());
        this.editing = true;
        this.unit.value = double.parse(value);
        this.displayValue = notifyPropertyChange(#value, displayValue, value);
      } on FormatException {}
    }
  
    MyUnitElement.created() : super.created();
  