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.
});
      itRenders('unknown attributes for custom elements', async render => {
        const e = await render(<custom-element foo="bar" />);
        expect(e.getAttribute('foo')).toBe('bar');
      });
      itRenders(
        'no unknown attributes for custom elements with null value',
        async render => {
          const e = await render(<custom-element foo={null} />);
          expect(e.hasAttribute('foo')).toBe(false);
        },
      );
      itRenders(
        'unknown attributes for custom elements using is',
        async render => {
          const e = await render(<div is="custom-element" foo="bar" />);
          expect(e.getAttribute('foo')).toBe('bar');
        },
      );
      itRenders(
        'no unknown attributes for custom elements using is with null value',
        async render => {
          const e = await render(<div is="custom-element" foo={null} />);
          expect(e.hasAttribute('foo')).toBe(false);
        },
      );
      itRenders('SVG tags with dashes in them', async render => {
        const e = await render(
          <svg>
            <font-face accentHeight={10} />