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.

<div>
          <div key="one">
            <div key="A">A</div><div key="B">B</div>
          </div>
          <div key="two">
            <div key="C">C</div><div key="D">D</div>
          </div>
        </div>,
        container,
      );
      
      ReactDOM.render(
        <div>
          <div key="one">
            <div key="B">B</div><div key="A">A</div>
          </div>
          <div key="two">
            <div key="D">D</div><div key="C">C</div>
          </div>
        </div>,
        container,
      );
      expect(container.textContent).toBe('BADC');
    });
  });
  describe('createOpenTagMarkup', () => {
    function quoteRegexp(str) {
      return (str + '').replace(/([.?*+\^$\[\]\\(){}|-])/g, '\\$1');
    }
    function toHaveAttribute(actual, expected) {