It seems problematic to allow arbitary non-lowercase attribute on HTML nodes. Because the server has no ability to keep them case sensitive (HTML isn't). So they will end up different on the client.

We should probably warn if the attribute is not a known one *and* is not lowercase.
expect(e.value).toBe('foo');
      });
      itRenders('a textarea with a value and readOnly', async render => {
        const e = await render(<textarea value="foo" readOnly={true} />);
        
        
        expect(e.getAttribute('value')).toBe(null);
        expect(e.value).toBe('foo');
      });
      itRenders(
        'a textarea with a value and no onChange/readOnly',
        async render => {
          
          
          const e = await render(<textarea value="foo" />, 1);
          expect(e.getAttribute('value')).toBe(null);
          expect(e.value).toBe('foo');
        },
      );
      itRenders('a textarea with a defaultValue', async render => {
        const e = await render(<textarea defaultValue="foo" />);
        expect(e.getAttribute('value')).toBe(null);
        expect(e.getAttribute('defaultValue')).toBe(null);
        expect(e.value).toBe('foo');
      });
      itRenders('a textarea value overriding defaultValue', async render => {
        const e = await render(
          <textarea value="foo" defaultValue="bar" readOnly={true} />,
          1,
        );