Hi,
It appears that 16.0 improved some of the checks in ALTER ROLE. Previously, it was possible to do the following (assuming current_user is a bootstrap user):
```
ALTER ROLE current_user NOSUPERUSER
```
As of 16.0, this produces an error:
```
ERROR: permission denied to alter role
DETAIL: The bootstrap user must have the SUPERUSER attribute.
```
The attached patch documents this behavior by providing a bit more clarification to the following statement:
"Database superusers can change any of these settings for any role."
--