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.
expectDev(console.error.calls.argsFor(0)[0]).toBe(
        'Warning: Invalid DOM property `for`. Did you mean `htmlFor`?\n    in label',
      );
      expectDev(console.error.calls.argsFor(1)[0]).toBe(
        'Warning: Invalid DOM property `autofocus`. Did you mean `autoFocus`?\n    in input',
      );
    });
    it('should suggest property name if available (ssr)', () => {
      spyOn(console, 'error');
      ReactDOMServer.renderToString(
        React.createElement('label', {for: 'test'}),
      );
      ReactDOMServer.renderToString(
        React.createElement('input', {type: 'text', autofocus: true}),
      );
      expectDev(console.error.calls.count()).toBe(2);
      expectDev(console.error.calls.argsFor(0)[0]).toBe(
        'Warning: Invalid DOM property `for`. Did you mean `htmlFor`?\n    in label',
      );
      expectDev(console.error.calls.argsFor(1)[0]).toBe(
        'Warning: Invalid DOM property `autofocus`. Did you mean `autoFocus`?\n    in input',
      );
    });
  });
  describe('whitespace', () => {
    it('renders innerHTML and preserves whitespace', () => {
      const container = document.createElement('div');
      const html = '\n  \t  <span>  \n  testContent  \t  </span>  \n  \t';
      const elem = <div dangerouslySetInnerHTML={{__html: html}} />;
      ReactDOM.render(elem, container);