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. 
expectTextNode(e.childNodes[0], 'foo');
          expectTextNode(e.childNodes[2], 'bar');
        } else {
          expect(e.childNodes.length).toBe(2);
          expectTextNode(e.childNodes[0], 'foo');
          expectTextNode(e.childNodes[1], 'bar');
        }
      });
    });
    describe('number children', function() {
      itRenders('a number as single child', async render => {
        const e = await render(<div>{3}</div>);
        expect(e.textContent).toBe('3');
      });
      
      itRenders('zero as single child', async render => {
        const e = await render(<div>{0}</div>);
        expect(e.textContent).toBe('0');
      });
      itRenders('an element with number and text children', async render => {
        const e = await render(<div>{'foo'}{40}</div>);
        
        if (
          render === serverRender ||
          render === clientRenderOnServerString ||
          render === streamRender
        ) {
          
          expect(e.childNodes.length).toBe(3);
          expectTextNode(e.childNodes[0], 'foo');