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. 
getChildContext() {
          return {text: this.props.text};
        }
        render() {
          return this.props.children;
        }
      }
      Parent.childContextTypes = {text: PropTypes.string};
      PurpleContext = props => <Parent text="purple">{props.children}</Parent>;
      RedContext = props => <Parent text="red">{props.children}</Parent>;
    });
    itRenders('class child with context', async render => {
      class ClassChildWithContext extends React.Component {