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.

expectDev(console.error.calls.count()).toBe(2);
      expectDev(console.error.calls.argsFor(0)[0]).toBe(
        'Warning: Unknown DOM property for. Did you mean htmlFor?\n    in label',
      );
      expectDev(console.error.calls.argsFor(1)[0]).toBe(
        'Warning: Unknown DOM property autofocus. Did you mean autoFocus?\n    in input',
      );
    });
  });
  describe('whitespace', () => {
    it('renders innerHTML and preserves whitespace', () => {
      const container = document.createElement('div');
      const html = '\n  \t  <span>  \n  testContent  \t  </span>  \n  \t';
      const elem = <div dangerouslySetInnerHTML={{__html: html}} />;
      ReactDOM.render(elem, container);
      expect(container.firstChild.innerHTML).toBe(html);
    });
    it('render and then updates innerHTML and preserves whitespace', () => {
      const container = document.createElement('div');
      const html = '\n  \t  <span>  \n  testContent1  \t  </span>  \n  \t';
      const elem = <div dangerouslySetInnerHTML={{__html: html}} />;
      ReactDOM.render(elem, container);
      const html2 = '\n  \t  <div>  \n  testContent2  \t  </div>  \n  \t';
      const elem2 = <div dangerouslySetInnerHTML={{__html: html2}} />;
      ReactDOM.render(elem2, container);
      expect(container.firstChild.innerHTML).toBe(html2);
    });
  });
});