Man pages matching name memcached_cas_by_key in section 3:

memcached_cas_by_key.3.en	debian 10 / libmemcached-dev
memcached_cas_by_key.3.en	debian 11 / libmemcached-dev
memcached_cas_by_key.3.en	debian 12 / libmemcached-dev