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.
return props.children;
      }
      function Owner() {
        
        
        
        return (
          <Parent>
            <input dangerouslySetInnerHTML={{__html: 'content'}} />
          </Parent>
        );
      }
      expect(function() {
        ReactDOM.render(<Owner />, container);
      }).toThrowError('\n\nThis DOM node was rendered by `Owner`.');
    });
    it('should emit a warning once for a named custom component using shady DOM', () => {
      spyOn(console, 'error');
      var defaultCreateElement = document.createElement.bind(document);
      try {
        document.createElement = element => {
          var container = defaultCreateElement(element);
          container.shadyRoot = {};
          return container;
        };
        class ShadyComponent extends React.Component {