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.
});
    });
    describe('htmlFor property', function() {
      itRenders('htmlFor with string value', async render => {
        const e = await render(<div htmlFor="myFor" />);
        expect(e.getAttribute('for')).toBe('myFor');
      });
      itRenders('no badly cased htmlfor', async render => {
        const e = await render(<div htmlfor="myFor" />, 1);
        expect(e.hasAttribute('for')).toBe(false);
        expect(e.getAttribute('htmlfor')).toBe('myFor');
      });
      itRenders('htmlFor with an empty string', async render => {
        const e = await render(<div htmlFor="" />);
        expect(e.getAttribute('for')).toBe('');
      });
      itRenders('no htmlFor prop with true value', async render => {
        const e = await render(<div htmlFor={true} />, 1);
        expect(e.hasAttribute('for')).toBe(false);
      });
      itRenders('no htmlFor prop with false value', async render => {
        const e = await render(<div htmlFor={false} />, 1);
        expect(e.hasAttribute('for')).toBe(false);
      });
      itRenders('no htmlFor prop with null value', async render => {
        const e = await render(<div htmlFor={null} />);
        expect(e.hasAttribute('htmlFor')).toBe(false);
      });
      itRenders('htmlFor attribute on custom elements', async render => {
        const e = await render(<div is="custom-element" htmlFor="test" />);