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. 
return null;
        }
      };
    });
    describe('elements', function() {
      describe('reconnecting different component implementations', function() {
        let ES6ClassComponent, PureComponent, bareElement;
        beforeEach(() => {
          
          ES6ClassComponent = class extends React.Component {
            render() {