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(node.removeAttribute.mock.calls.length).toBe(2);
    });
    it('should not incur unnecessary DOM mutations for string properties', () => {
      var container = document.createElement('div');
      ReactDOM.render(<div value="" />, container);
      var node = container.firstChild;
      var nodeValueSetter = jest.genMockFn();
      var oldSetAttribute = node.setAttribute.bind(node);
      node.setAttribute = function(key, value) {
        oldSetAttribute(key, value);
        nodeValueSetter(key, value);
      };
      ReactDOM.render(<div value="foo" />, container);
      expect(nodeValueSetter.mock.calls.length).toBe(1);
      ReactDOM.render(<div value="foo" />, container);
      expect(nodeValueSetter.mock.calls.length).toBe(1);
      ReactDOM.render(<div />, container);
      expect(nodeValueSetter.mock.calls.length).toBe(1);
      ReactDOM.render(<div value={null} />, container);
      expect(nodeValueSetter.mock.calls.length).toBe(1);
      ReactDOM.render(<div value="" />, container);
      expect(nodeValueSetter.mock.calls.length).toBe(2);
      ReactDOM.render(<div />, container);
      expect(nodeValueSetter.mock.calls.length).toBe(2);
    });
    it('should not incur unnecessary DOM mutations for boolean properties', () => {
      var container = document.createElement('div');
      ReactDOM.render(<div checked={true} />, container);
      var node = container.firstChild;
      var nodeValue = true;