C2S (7): send, join, part, nick, topic, mode, ping
S2C (12): message, dm, notice, join, part, quit, nick, topic, mode, system, error, pong
S2S (6): relay, link, unlink, sync, ping, pong
Each message type has its own schema file under schema/{c2s,s2c,s2s}/.
schema/README.md provides an index of all types with descriptions.
