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.
'Can only set one of `children` or `props.dangerouslySetInnerHTML`.',
      );
    });
    it('should validate against use of innerHTML', () => {
      spyOn(console, 'error');
      mountComponent({innerHTML: '<span>Hi Jim!</span>'});
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(console.error.calls.argsFor(0)[0]).toContain(
        'Directly setting property `innerHTML` is not permitted. ',
      );
    });
    it('should validate against use of innerHTML without case sensitivity', () => {
      spyOn(console, 'error');
      mountComponent({innerhtml: '<span>Hi Jim!</span>'});
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(console.error.calls.argsFor(0)[0]).toContain(
        'Directly setting property `innerHTML` is not permitted. ',
      );
    });
    it('should validate use of dangerouslySetInnerHTML', () => {
      expect(function() {
        mountComponent({dangerouslySetInnerHTML: '<span>Hi Jim!</span>'});
      }).toThrowError(
        '`props.dangerouslySetInnerHTML` must be in the form `{__html: ...}`. ' +
          'Please visit https://fb.me/react-invariant-dangerously-set-inner-html for more information.',
      );
    });
    it('should validate use of dangerouslySetInnerHTML', () => {
      expect(function() {
        mountComponent({dangerouslySetInnerHTML: {foo: 'bar'}});