Follow up from https://github.com/facebook/react/pull/11616.

Here's one I found. These two invariants:

https://github.com/facebook/react/blob/7e7127387ba64f57299eaff8656542cea6fb3a2d/packages/react-reconciler/src/ReactFiberClassComponent.js#L330-L343

are in a function that's behind a DEV block:

https://github.com/facebook/react/blob/7e7127387ba64f57299eaff8656542cea6fb3a2d/packages/react-reconciler/src/ReactFiberClassComponent.js#L447-L449

I don't think this is intentional, but need to verify.

There may be more. I'll use this issue to track while https://github.com/facebook/react/pull/11616 preserves existing behavior.
}
        this.stack.push(frame);
        return '';
      } else {
        
        var nextElement = ((nextChild: any): ReactElement);
        return this.renderDOM(nextElement, context, parentNamespace);
      }
    }
  }
  renderDOM(
    element: ReactElement,
    context: Object,
    parentNamespace: string,
  ): string {
    var tag = element.type.toLowerCase();
    let namespace = parentNamespace;
    if (parentNamespace === Namespaces.html) {
      namespace = getIntrinsicNamespace(tag);
    }
    if (__DEV__) {
      if (namespace === Namespaces.html) {
        
        
        warning(
          tag === element.type,
          '<%s /> is using uppercase HTML. Always use lowercase HTML tags ' +
            'in React.',
          element.type,
        );