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.

return str && str.replace(/\(at .+?:\d+\)/g, '(at **)');
  }
  beforeEach(() => {
    jest.resetModules();
    React = require('react');
    ReactDOM = require('react-dom');
    ReactDOMFeatureFlags = require('ReactDOMFeatureFlags');
    ReactDOMServer = require('react-dom/server');
    ReactTestUtils = require('ReactTestUtils');
    inputValueTracking = require('inputValueTracking');
  });
  describe('updateDOM', () => {
    it('should handle className', () => {
      var container = document.createElement('div');
      ReactDOM.render(<div style={{}} />, container);
      ReactDOM.render(<div className={'foo'} />, container);