What db objects can only be created with superuser?

I noticed that in the CREATE EXTENSION code, the permission is elevated to the superuser who creates and owns all of the extension objects.

I was wondering why this elevation is done.

I understand that the C-based functions can only be created by a superuser. Are there any other db objects that require superuser? Or is C-based functions the only one?

I am hacking around the extension code (locally for my own purpose), and seeking information on this. Thank you.