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.childNodes.length).toBe(3);
          expectTextNode(e.childNodes[0], 'foo');
        }
      });
      itRenders('only null and false children as blank', async render => {
        const e = await render(<div>{false}{null}{null}{false}</div>);
        expect(e.childNodes.length).toBe(0);
      });
    });
    describe('elements with implicit namespaces', function() {
      itRenders('an svg element', async render => {
        const e = await render(<svg />);
        expect(e.childNodes.length).toBe(0);
        expect(e.tagName).toBe('svg');
        expect(e.namespaceURI).toBe('http:www.w3.org/2000/svg');
      });
      itRenders('svg child element with an attribute', async render => {
        let e = await render(<svg viewBox="0 0 0 0" />);
        expect(e.childNodes.length).toBe(0);
        expect(e.tagName).toBe('svg');
        expect(e.namespaceURI).toBe('http:www.w3.org/2000/svg');
        expect(e.getAttribute('viewBox')).toBe('0 0 0 0');
      });
      itRenders(
        'svg child element with a namespace attribute',
        async render => {
          let e = await render(
            <svg><image xlinkHref="http:i.imgur.com/w7GCRPb.png" /></svg>,
          );
          e = e.firstChild;