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.

expect(container.firstChild.hasAttribute('dangerouslySetInnerHTML')).toBe(
        false,
      );
      ReactDOM.render(
        <my-component dangerouslySetInnerHTML={{__html: 'bye'}} />,
        container,
      );
      expect(container.firstChild.hasAttribute('dangerouslySetInnerHTML')).toBe(
        false,
      );
    });
    it('should render null and undefined as empty but print other falsy values', () => {
      var container = document.createElement('div');
      ReactDOM.render(
        <div dangerouslySetInnerHTML={{__html: 'textContent'}} />,
        container,
      );
      expect(container.textContent).toEqual('textContent');
      ReactDOM.render(<div dangerouslySetInnerHTML={{__html: 0}} />, container);
      expect(container.textContent).toEqual('0');
      ReactDOM.render(
        <div dangerouslySetInnerHTML={{__html: false}} />,
        container,
      );
      expect(container.textContent).toEqual('false');
      ReactDOM.render(
        <div dangerouslySetInnerHTML={{__html: ''}} />,
        container,
      );
      expect(container.textContent).toEqual('');