See the original report in https://github.com/facebook/react/issues/10772#issuecomment-333242375.

The problem is that SVG is case sensitive, and so naïvely setting `tabIndex` and relying on insensitivity won't work with it.

The good news is it seems like `tabindex` is the only valid [SVG attribute](https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute) with this problem. We just missed it because it applies both to HTML and SVG.

I think the fix is to add it back to the whitelist. 
const e = await render(<div><br /></div>);
      expect(e.childNodes.length).toBe(1);
      expect(e.firstChild.tagName).toBe('BR');
    });
    itRenders('a string', async render => {
      let e = await render('Hello');
      expect(e.nodeType).toBe(3);
      expect(e.nodeValue).toMatch('Hello');
    });
    itRenders('a number', async render => {
      let e = await render(42);
      expect(e.nodeType).toBe(3);
      expect(e.nodeValue).toMatch('42');
    });
    itRenders('an array with one child', async render => {
      let e = await render([<div key={1}>text1</div>]);
      let parent = e.parentNode;
      expect(parent.childNodes[0].tagName).toBe('DIV');
    });
    itRenders('an array with several children', async render => {
      let Header = props => {
        return <p>header</p>;
      };
      let Footer = props => {
        return [<h2 key={1}>footer</h2>, <h3 key={2}>about</h3>];
      };
      let e = await render([
        <div key={1}>text1</div>,
        <span key={2}>text2</span>,
        <Header key={3} />,