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. 
expect(e.childNodes.length).toBe(3);
          expectTextNode(e.childNodes[0], ' ');
          expectTextNode(e.childNodes[1], ' ');
          expectTextNode(e.childNodes[2], ' ');
        }
      });
      itRenders('a div with text sibling to a node', async render => {
        const e = await render(<div>Text<span>More Text</span></div>);
        let spanNode;
        expect(e.childNodes.length).toBe(2);
        spanNode = e.childNodes[1];
        expectTextNode(e.childNodes[0], 'Text');
        expect(spanNode.tagName).toBe('SPAN');
        expect(spanNode.childNodes.length).toBe(1);
        expectNode(spanNode.firstChild, TEXT_NODE_TYPE, 'More Text');
      });
      itRenders('a non-standard element with text', async render => {
        const e = await render(<nonstandard>Text</nonstandard>);
        expect(e.tagName).toBe('NONSTANDARD');
        expect(e.childNodes.length).toBe(1);
        expectNode(e.firstChild, TEXT_NODE_TYPE, 'Text');
      });
      itRenders('a custom element with text', async render => {
        const e = await render(<custom-element>Text</custom-element>);
        expect(e.tagName).toBe('CUSTOM-ELEMENT');
        expect(e.childNodes.length).toBe(1);
        expectNode(e.firstChild, TEXT_NODE_TYPE, 'Text');
      });
      itRenders('a leading blank child with a text sibling', async render => {
        const e = await render(<div>{''}foo</div>);