This usually means that the user mixed up our lowercase/uppercase naming convention; see https://github.com/facebook/react/pull/3429#issuecomment-85166440.

We could add a message like

> Warning: The tag <commentBox> is unrecognized in this browser. If you meant to render a React component, start its name with an uppercase letter.

We'd check this only once per tag and only in development mode.

node.removeAttribute.mockImplementation(nodeRemoveAttribute);
      ReactDOM.render(<div id="" />, container);
      expect(node.setAttribute.mock.calls.length).toBe(0);
      expect(node.removeAttribute.mock.calls.length).toBe(0);
      ReactDOM.render(<div id="foo" />, container);
      expect(node.setAttribute.mock.calls.length).toBe(1);
      expect(node.removeAttribute.mock.calls.length).toBe(0);
      ReactDOM.render(<div id="foo" />, container);
      expect(node.setAttribute.mock.calls.length).toBe(1);
      expect(node.removeAttribute.mock.calls.length).toBe(0);
      ReactDOM.render(<div />, container);
      expect(node.setAttribute.mock.calls.length).toBe(1);
      expect(node.removeAttribute.mock.calls.length).toBe(1);
      ReactDOM.render(<div id="" />, container);
      expect(node.setAttribute.mock.calls.length).toBe(2);
      expect(node.removeAttribute.mock.calls.length).toBe(1);
      ReactDOM.render(<div />, container);
      expect(node.setAttribute.mock.calls.length).toBe(2);
      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);
      };