anchor.diff:  VTextInput textInput({
     Object key,
     String value,
  +  String placeholder,
  +  bool autofocus,
     String id,
     Map<String, String> attributes,
     List<String> classes,
  
positive.code:     if (_value != null) {
        ref.value = _value;
      }
    }
  
    void update(VTextInput other, Context context) {
  
negative.code:     if (other._value != null && ref.value != other._value) {
        ref.value = other._value;
      }
      if (other.placeholder != placeholder) {
        ref.placeholder = other.placeholder;
      }
      // no need to update autofocus when element is already created.
    }
  }
  