anchor.diff:  
     get valid => _valid;
     set valid(value) {
  -    _invalid = false;
       _valid = true;
  -
       _animate.addClass(element, NG_VALID_CLASS);
       _animate.removeClass(element, NG_INVALID_CLASS);
     }
   
  -  get invalid => _invalid;
  +  get invalid => !_valid;
     set invalid(value) {
       _valid = false;
  -    _invalid = true;
  -
       _animate.addClass(element, NG_INVALID_CLASS);
       _animate.removeClass(element, NG_VALID_CLASS);
     }
  
positive.code:     _parentControl.touched = true;
    }
  
    get untouched => _untouched;
    set untouched(value) {
      _touched = false;
      _untouched = true;
  
      _animate.addClass(element, NG_UNTOUCHED_CLASS);
      _animate.removeClass(element, NG_TOUCHED_CLASS);
    }
  
negative.code:   get dirty => _dirty;
    set dirty(value) {
      _dirty = true;
      _animate.addClass(element, NG_DIRTY_CLASS);
      _animate.removeClass(element, NG_PRISTINE_CLASS);
  
  