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.
'&#x27;&quot;&lt;&gt;&amp;' +
          '</div>',
      );
    });
  });
  describe('unmountComponent', () => {
    
    if (!ReactDOMFeatureFlags.useFiber) {
      it('should clean up input value tracking', () => {
        var container = document.createElement('div');
        var node = ReactDOM.render(
          <input type="text" defaultValue="foo" />,
          container,
        );
        var tracker = inputValueTracking._getTrackerFromNode(node);
        spyOn(tracker, 'stopTracking');
        ReactDOM.unmountComponentAtNode(container);
        expect(tracker.stopTracking.calls.count()).toBe(1);
      });
      it('should clean up input textarea tracking', () => {
        var container = document.createElement('div');
        var node = ReactDOM.render(<textarea defaultValue="foo" />, container);
        var tracker = inputValueTracking._getTrackerFromNode(node);
        spyOn(tracker, 'stopTracking');
        ReactDOM.unmountComponentAtNode(container);
        expect(tracker.stopTracking.calls.count()).toBe(1);
      });
    }
    it('unmounts children before unsetting DOM node info', () => {
      class Inner extends React.Component {