The error event on `<source>` elements doesn't work. Looking at #4370, it seems like there is an `onError` for `<video>` but I can't tell if that's supposed to work for `<source>` too.

The error event is useful so I can deduce which format the browser is using.

var returnedValue = ReactDOMServer.renderToString(<Container/>);
      expect(returnedValue).not.toContain('</BR>');
    });
    it('should warn against children for void elements', function() {
      var container = document.createElement('div');
      expect(function() {
        ReactDOM.render(<input>children</input>, container);
      }).toThrowError(
        'input is a void element tag and must not have `children` or ' +
        'use `props.dangerouslySetInnerHTML`.'
      );
    });
    it('should warn against dangerouslySetInnerHTML for void elements', function() {
      var container = document.createElement('div');
      expect(function() {
        ReactDOM.render(
          <input dangerouslySetInnerHTML={{__html: 'content'}} />,
          container
        );
      }).toThrowError(
        'input is a void element tag and must not have `children` or use ' +
        '`props.dangerouslySetInnerHTML`.'
      );
    });
    it('should treat menuitem as a void element but still create the closing tag', function() {
      var container = document.createElement('div');
      var returnedValue = ReactDOMServer.renderToString(<menu><menuitem /></menu>);
      expect(returnedValue).toContain('</menuitem>');
      expect(function() {
        ReactDOM.render(<menu><menuitem>children</menuitem></menu>, container);