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(3)[0]).toContain(
        ReactDOMFeatureFlags.useFiber
          ? 'The tag <hasOwnProperty> is unrecognized in this browser'
          : 'The tag <hasownproperty> is unrecognized in this browser',
      );
    });
    it('should warn against children for void elements', () => {
      var container = document.createElement('div');
      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', () => {
      var container = document.createElement('div');
      expect(function() {
        ReactDOM.render(
          <input dangerouslySetInnerHTML={{__html: 'content'}} />,
          container,
        );
      }).toThrowError(
        'input is a void element tag and must neither have `children` nor use ' +
          '`dangerouslySetInnerHTML`.',
      );
    });
    it('should include owner rather than parent in warnings', () => {
      var container = document.createElement('div');
      function Parent(props) {