This usually means that the user mixed up our lowercase/uppercase naming convention; see https://github.com/facebook/react/pull/3429#issuecomment-85166440.

We could add a message like

> Warning: The tag <commentBox> is unrecognized in this browser. If you meant to render a React component, start its name with an uppercase letter.

We'd check this only once per tag and only in development mode.

<input type="text" defaultValue="foo" />,
        container,
      );
      var tracker = inputValueTracking._getTrackerFromNode(inst);
      expect(tracker.getValue()).toEqual('foo');
    });
    it('should track textarea values', () => {
      var container = document.createElement('div');
      var inst = ReactDOM.render(<textarea defaultValue="foo" />, container);
      var tracker = inputValueTracking._getTrackerFromNode(inst);
      expect(tracker.getValue()).toEqual('foo');
    });
    it('should warn for children on void elements', () => {
      class X extends React.Component {
        render() {
          return <input>moo</input>;
        }
      }
      var container = document.createElement('div');
      expect(function() {
        ReactDOM.render(<X />, container);
      }).toThrowError(
        'input is a void element tag and must neither have `children` ' +
          'nor use `dangerouslySetInnerHTML`.\n\nThis DOM node was rendered by `X`.',
      );
    });
    it('should support custom elements which extend native elements', () => {
      if (ReactDOMFeatureFlags.useCreateElement) {
        var container = document.createElement('div');
        spyOn(document, 'createElement').and.callThrough();