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.className).toEqual('foo');
      ReactDOM.render(<div className={'bar'} />, container);
      expect(container.firstChild.className).toEqual('bar');
      ReactDOM.render(<div className={null} />, container);
      expect(container.firstChild.className).toEqual('');
    });
    it('should gracefully handle various style value types', () => {
      var container = document.createElement('div');
      ReactDOM.render(<div style={{}} />, container);
      var stubStyle = container.firstChild.style;
      
      var setup = {display: 'block', left: '1px', top: 2, fontFamily: 'Arial'};
      ReactDOM.render(<div style={setup} />, container);
      expect(stubStyle.display).toEqual('block');
      expect(stubStyle.left).toEqual('1px');
      expect(stubStyle.fontFamily).toEqual('Arial');
      
      var reset = {display: '', left: null, top: false, fontFamily: true};
      ReactDOM.render(<div style={reset} />, container);
      expect(stubStyle.display).toEqual('');
      expect(stubStyle.left).toEqual('');
      expect(stubStyle.top).toEqual('');
      expect(stubStyle.fontFamily).toEqual('');
    });
    it('should not update styles when mutating a proxy style object', () => {
      var styleStore = {display: 'none', fontFamily: 'Arial', lineHeight: 1.2};
      
      
      var styles = {
        get display() {