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.

ReactDOM.render(
        <div dangerouslySetInnerHTML={{__html: null}} />,
        container,
      );
      expect(container.textContent).toEqual('');
      ReactDOM.render(
        <div dangerouslySetInnerHTML={{__html: undefined}} />,
        container,
      );
      expect(container.textContent).toEqual('');
    });
    it('should remove attributes', () => {
      var container = document.createElement('div');
      ReactDOM.render(<img height="17" />, container);
      expect(container.firstChild.hasAttribute('height')).toBe(true);
      ReactDOM.render(<img />, container);
      expect(container.firstChild.hasAttribute('height')).toBe(false);
    });
    it('should remove properties', () => {
      var container = document.createElement('div');
      ReactDOM.render(<div className="monkey" />, container);
      expect(container.firstChild.className).toEqual('monkey');
      ReactDOM.render(<div />, container);
      expect(container.firstChild.className).toEqual('');
    });
    it('should properly update custom attributes on custom elements', () => {
      var container = document.createElement('div');
      ReactDOM.render(<some-custom-element foo="bar" />, container);
      ReactDOM.render(<some-custom-element bar="buzz" />, container);
      var node = container.firstChild;