Follow up from https://github.com/facebook/react/pull/11616.

Here's one I found. These two invariants:

https://github.com/facebook/react/blob/7e7127387ba64f57299eaff8656542cea6fb3a2d/packages/react-reconciler/src/ReactFiberClassComponent.js#L330-L343

are in a function that's behind a DEV block:

https://github.com/facebook/react/blob/7e7127387ba64f57299eaff8656542cea6fb3a2d/packages/react-reconciler/src/ReactFiberClassComponent.js#L447-L449

I don't think this is intentional, but need to verify.

There may be more. I'll use this issue to track while https://github.com/facebook/react/pull/11616 preserves existing behavior.
);
        expect(e.getAttribute('xlinkhref')).toBe(
          'http:i.imgur.com/w7GCRPb.png',
        );
      });
      itRenders('svg element with a tabIndex attribute', async render => {
        let e = await render(<svg tabIndex="1" />);
        expect(e.tabIndex).toBe(1);
      });
      itRenders(
        'svg element with a badly cased tabIndex attribute',
        async render => {
          let e = await render(<svg tabindex="1" />, 1);
          expect(e.tabIndex).toBe(1);
        },
      );
      itRenders('svg element with a mixed case name', async render => {
        let e = await render(
          <svg>
            <filter>
              <feMorphology />
            </filter>
          </svg>,
        );
        e = e.firstChild.firstChild;
        expect(e.childNodes.length).toBe(0);
        expect(e.tagName).toBe('feMorphology');
        expect(e.namespaceURI).toBe('http:www.w3.org/2000/svg');
      });
      itRenders('a math element', async render => {