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.

render() {
          return <span />;
        }
        componentWillUnmount() {
          
          expect(ReactDOM.findDOMNode(this).nodeName).toBe('SPAN');
        }
      }
      var container = document.createElement('div');
      ReactDOM.render(<div><Inner /></div>, container);
      ReactDOM.unmountComponentAtNode(container);
    });
  });
  describe('tag sanitization', () => {
    it('should throw when an invalid tag name is used server-side', () => {
      var hackzor = React.createElement('script tag');
      expect(() => ReactDOMServer.renderToString(hackzor)).toThrowError(
        'Invalid tag: script tag',
      );
    });
    it('should throw when an attack vector is used server-side', () => {
      var hackzor = React.createElement('div><img /><div');
      expect(() => ReactDOMServer.renderToString(hackzor)).toThrowError(
        'Invalid tag: div><img /><div',
      );
    });
    it('should throw when an invalid tag name is used', () => {
      var hackzor = React.createElement('script tag');
      expect(() => ReactTestUtils.renderIntoDocument(hackzor)).toThrow();
    });