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. 
expectMarkupMatch(<div>{2}</div>, <div>2</div>));
      it('should error reconnecting different numbers', () =>
        expectMarkupMismatch(<div>{2}</div>, <div>{3}</div>));
      it('should error reconnecting different number from text', () =>
        expectMarkupMismatch(<div>{2}</div>, <div>3</div>));
      it('should error reconnecting different text in two code blocks', () =>
        expectMarkupMismatch(
          <div>{'Text1'}{'Text2'}</div>,
          <div>{'Text1'}{'Text3'}</div>,
        ));
    });
    describe('element trees and children', function() {
      it('should error reconnecting missing children', () =>
        expectMarkupMismatch(<div><div /></div>, <div />));
      it('should error reconnecting added children', () =>
        expectMarkupMismatch(<div />, <div><div /></div>));
      it('should error reconnecting more children', () =>
        expectMarkupMismatch(<div><div /></div>, <div><div /><div /></div>));
      it('should error reconnecting fewer children', () =>
        expectMarkupMismatch(<div><div /><div /></div>, <div><div /></div>));
      it('should error reconnecting reordered children', () =>
        expectMarkupMismatch(
          <div><div /><span /></div>,
          <div><span /><div /></div>,
        ));
      it('should error reconnecting a div with children separated by whitespace on the client', () =>
        expectMarkupMismatch(
          <div id="parent"><div id="child1" /><div id="child2" /></div>,
          
          <div id="parent"><div id="child1" />      <div id="child2" /></div>,