For this specification, ‘target’ MUST be a valid nick as determined by the IRC daemon.
Existing server implementations choose to either ignore invalid nicks, or send MONOFFLINE then ignore it.
This implementation sends ERRONEOUSNICKNAME instead because I believe it makes more sense, but that's debatable.
https://ircv3.net/specs/extensions/monitor
The spec requires:
Existing server implementations choose to either ignore invalid nicks, or send MONOFFLINE then ignore it. This implementation sends ERRONEOUSNICKNAME instead because I believe it makes more sense, but that's debatable.