http://i3xi5qxvbrngh3g6o7czwjfxwjzigook7zxzjmgwg5b7xnjcn5hzciad.onion/control-spec/index.html
(Version 0 is used by Tor
versions 0.1.0.x; the protocol in this document only works with Tor
versions in the 0.1.1.x series and later.) The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
RFC 2119.