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. 
async render => {
          const e = await render(<div is="custom-element" foo="bar" />);
          expect(e.getAttribute('foo')).toBe('bar');
        },
      );
      itRenders(
        'no unknown attributes for custom elements using is with null value',
        async render => {
          const e = await render(<div is="custom-element" foo={null} />);
          expect(e.hasAttribute('foo')).toBe(false);
        },
      );
      itRenders('SVG tags with dashes in them', async render => {
        const e = await render(<svg><font-face accentHeight={10} /></svg>);
        expect(e.firstChild.hasAttribute('accentHeight')).toBe(false);
        expect(e.firstChild.getAttribute('accent-height')).toBe('10');
      });
      itRenders('cased custom attributes', async render => {
        const e = await render(<div fooBar="test" />, 1);
        expect(e.getAttribute('foobar')).toBe('test');
      });
    });
    itRenders('no HTML events', async render => {
      const e = await render(<div onClick={() => {}} />);
      expect(e.getAttribute('onClick')).toBe(null);
      expect(e.getAttribute('onClick')).toBe(null);
      expect(e.getAttribute('click')).toBe(null);
    });
    itRenders('no unknown events', async render => {
      const e = await render(