anchor.diff:  library my_polymer_my_unit_element;
   
  +import 'dart:html';
   import 'package:polymer/polymer.dart';
   
   import 'main_element.dart';
  
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:   }
  
    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();
  