umask does not have -S option

I'm trying to use umask -S to show the current mask in symbolic form (per man umask on my system, which gives me the page BASH_BUILTINS(1)). But umask doesn't seem to behave as the manpage claims:

user$ umask
22
user$ umask -S
umask: Improper mask.
user$ umask -p
umask: Improper mask.
user$ which umask
umask: shell built-in command.

I'm running this in csh on RHEL 6.9. Something like umask 022 works fine. Why would the behavior differ from the manpage?