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(node.hasAttribute('foo')).toBe(false);
      expect(node.getAttribute('bar')).toBe('buzz');
    });
    it('should clear a single style prop when changing `style`', () => {
      var styles = {display: 'none', color: 'red'};
      var container = document.createElement('div');
      ReactDOM.render(<div style={styles} />, container);
      var stubStyle = container.firstChild.style;
      styles = {color: 'green'};
      ReactDOM.render(<div style={styles} />, container);
      expect(stubStyle.display).toEqual('');
      expect(stubStyle.color).toEqual('green');
    });
    it('should reject attribute key injection attack on markup', () => {
      spyOn(console, 'error');
      for (var i = 0; i < 3; i++) {
        var container = document.createElement('div');
        var element = React.createElement(
          'x-foo-component',
          {'blah" onclick="beevil" noise="hi': 'selected'},
          null,
        );
        ReactDOM.render(element, container);
      }
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(console.error.calls.argsFor(0)[0]).toEqual(
        'Warning: Invalid attribute name: `blah" onclick="beevil" noise="hi`',
      );
    });
    it('should reject attribute key injection attack on update', () => {