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.

if (__DEV__) {
    var ownerName = getCurrentFiberOwnerName();
    if (ownerName) {
      
      return '\n\nThis DOM node was rendered by `' + ownerName + '`.';
    }
  }
  return '';
}
function assertValidProps(tag: string, props: ?Object) {