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