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.

mountComponent({dangerouslySetInnerHTML: {__html: null}});
      }).not.toThrow();
    });
    it('should warn about contentEditable and children', () => {
      spyOn(console, 'error');
      mountComponent({contentEditable: true, children: ''});
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(console.error.calls.argsFor(0)[0]).toContain('contentEditable');
    });
    it('should respect suppressContentEditableWarning', () => {
      spyOn(console, 'error');
      mountComponent({
        contentEditable: true,
        children: '',
        suppressContentEditableWarning: true,
      });
      expectDev(console.error.calls.count()).toBe(0);
    });
    it('should validate against invalid styles', () => {
      expect(function() {
        mountComponent({style: 'display: none'});
      }).toThrowError(
        'The `style` prop expects a mapping from style properties to values, ' +
          "not a string. For example, style={{marginRight: spacing + 'em'}} " +
          'when using JSX.',
      );
    });
    it('should track input values', () => {
      var container = document.createElement('div');
      var inst = ReactDOM.render(