It seems problematic to allow arbitary non-lowercase attribute on HTML nodes. Because the server has no ability to keep them case sensitive (HTML isn't). So they will end up different on the client.

We should probably warn if the attribute is not a known one *and* is not lowercase.
expect(stubStyle.fontFamily).toBe('');
      expect(stubStyle.lineHeight).toBe('');
    });
    it('should throw when mutating style objects', () => {
      var style = {border: '1px solid black'};
      class App extends React.Component {
        state = {style: style};
        render() {
          return <div style={this.state.style}>asd</div>;
        }
      }
      ReactTestUtils.renderIntoDocument(<App />);
      expectDev(() => (style.position = 'absolute')).toThrow();
    });
    it('should warn for unknown prop', () => {
      spyOn(console, 'error');
      var container = document.createElement('div');
      ReactDOM.render(<div foo={() => {}} />, container);
      expectDev(console.error.calls.count(0)).toBe(1);
      expectDev(normalizeCodeLocInfo(console.error.calls.argsFor(0)[0])).toBe(
        'Warning: Invalid prop `foo` on <div> tag. Either remove this prop ' +
          'from the element, or pass a string or number value to keep ' +
          'it in the DOM. For details, see https://fb.me/react-unknown-prop' +
          '\n    in div (at **)',
      );
    });
    it('should group multiple unknown prop warnings together', () => {
      spyOn(console, 'error');
      var container = document.createElement('div');
      ReactDOM.render(<div foo={() => {}} baz={() => {}} />, container);