Man pages matching name memcached_append_by_key in section 3:

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