MODE <channel> <+|-><modes> [parameters]
+? designates that the cmode is provided by an extension
+and may not be present on this server.
+
CHANNELMODE - DESCRIPTION
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NO PARAMETERS:
messages is stripped.
+g - Free invite. Everyone may invite users. Significantly
weakens +i control.
+ ? +u - Unfiltered. Receive messages that would otherwise be filtered
+ server side based on content.
+z - Op moderated. Messages blocked by +m, +b and +q are instead
sent to ops.
+L - Large ban list. Increase maximum number of +beIq entries.
(however, new forwards can still be set subject to +F).
+C - Disable CTCP. All CTCP messages to the channel, except ACTION,
are disallowed.
+ ? +O - IRC Operator only channel.
+ ? +A - IRC server administrator only channel.
+ ? +T - No NOTICEs allowed in the channel.
+ ? +S - Only users connected via SSL/TLS may join the channel while this
+ mode is set. Users already in the channel are not affected.
WITH PARAMETERS:
+f - Forward. Forwards users who cannot join because of +i,