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.

var container = document.createElement('div');
      ReactDOM.render(
        <my-component
          children={['foo']}
          suppressContentEditableWarning={true}
        />,
        container,
      );
      expect(container.firstChild.hasAttribute('children')).toBe(false);
      expect(
        container.firstChild.hasAttribute('suppressContentEditableWarning'),
      ).toBe(false);
      ReactDOM.render(
        <my-component
          children={['bar']}
          suppressContentEditableWarning={false}
        />,
        container,
      );
      expect(container.firstChild.hasAttribute('children')).toBe(false);
      expect(
        container.firstChild.hasAttribute('suppressContentEditableWarning'),
      ).toBe(false);
    });
    it('should skip dangerouslySetInnerHTML on web components', () => {
      var container = document.createElement('div');
      ReactDOM.render(
        <my-component dangerouslySetInnerHTML={{__html: 'hi'}} />,
        container,
      );