delete the key from all replicas.
The binary protocol is required and any other command is unaffected.
+
+### TLS/SSL
+
+libmemcached does not support TLS/SSL, yet.
+See [github issue #37](https://github.com/awesomized/libmemcached/issues/37).
+
+
+### Coroutines and event loops
+
+libmemcached does not support explicit asynchronous usage, yet.
+See [github issue #54](https://github.com/awesomized/libmemcached/issues/54).
+
+
+### META protocol
+
+libmemcached deos not support memcached's META protocol, yet.
+See [github issue #121](https://github.com/awesomized/libmemcached/issues/121).