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.

expectDev(console.log.calls.count()).toBe(2);
      expectDev(console.log.calls.argsFor(0)[0]).toContain('onError called');
      expectDev(console.log.calls.argsFor(1)[0]).toContain('onLoad called');
    });
  });
  describe('updateComponent', () => {
    var container;
    beforeEach(() => {
      container = document.createElement('div');
    });
    it('should warn against children for void elements', () => {
      ReactDOM.render(<input />, container);
      expect(function() {
        ReactDOM.render(<input>children</input>, container);
      }).toThrowError(
        'input is a void element tag and must neither have `children` nor use ' +
          '`dangerouslySetInnerHTML`.',
      );
    });
    it('should warn against dangerouslySetInnerHTML for void elements', () => {
      ReactDOM.render(<input />, container);
      expect(function() {
        ReactDOM.render(
          <input dangerouslySetInnerHTML={{__html: 'content'}} />,
          container,
        );
      }).toThrowError(
        'input is a void element tag and must neither have `children` nor use ' +
          '`dangerouslySetInnerHTML`.',
      );