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.
"not a string. For example, style={{marginRight: spacing + 'em'}} " +
          'when using JSX.',
      );
    });
    it('should track input values', () => {
      var container = document.createElement('div');
      var inst = ReactDOM.render(
        <input type="text" defaultValue="foo" />,
        container,
      );
      var tracker = inputValueTracking._getTrackerFromNode(inst);
      expect(tracker.getValue()).toEqual('foo');
    });
    it('should track textarea values', () => {
      var container = document.createElement('div');
      var inst = ReactDOM.render(<textarea defaultValue="foo" />, container);
      var tracker = inputValueTracking._getTrackerFromNode(inst);
      expect(tracker.getValue()).toEqual('foo');
    });
    it('should warn for children on void elements', () => {
      class X extends React.Component {
        render() {
          return <input>moo</input>;
        }
      }
      var container = document.createElement('div');
      expect(function() {
        ReactDOM.render(<X />, container);
      }).toThrowError(
        'input is a void element tag and must neither have `children` ' +