anchor.diff:      expect(quxNewed.outerHtml, quxOuterHtml);
       expect(quxNewed is Qux, isTrue);
       expect(quxNewed is InputElement, isTrue);
  -    expect(isFormElement(quxNewed), isTrue);
  +    expect(isFormControl(quxNewed), isTrue);
   
       // new Element.tag
   
  
positive.code:   var testForm = new FormElement()..id = 'testForm';
    document.body.append(testForm);
  
    var isFormElement = (element) {
      testForm.append(element);
      return element.form == testForm;
    };
  
negative.code:     expect(barNewed.outerHtml, barOuterHtml);
      expect(barNewed is Bar, isTrue);
      expect(barNewed is InputElement, isTrue);
      expect(isFormControl(barNewed), isTrue);
  
      var bazNewed = new Baz();
      var bazOuterHtml = "<x-baz></x-baz>";
  