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.log.calls.count()).toBe(2);
      expectDev(console.log.calls.argsFor(0)[0]).toContain('onError called');
      expectDev(console.log.calls.argsFor(1)[0]).toContain('onLoad called');
    });
  });
  describe('updateComponent', () => {
    var container;
    beforeEach(() => {
      container = document.createElement('div');
    });
    it('should warn against children for void elements', () => {
      ReactDOM.render(<input />, container);
      expect(function() {
        ReactDOM.render(<input>children</input>, container);
      }).toThrowError(
        'input is a void element tag and must neither have `children` nor use ' +
          '`dangerouslySetInnerHTML`.',
      );
    });
    it('should warn against dangerouslySetInnerHTML for void elements', () => {
      ReactDOM.render(<input />, container);
      expect(function() {
        ReactDOM.render(
          <input dangerouslySetInnerHTML={{__html: 'content'}} />,
          container,
        );
      }).toThrowError(
        'input is a void element tag and must neither have `children` nor use ' +
          '`dangerouslySetInnerHTML`.',
      );