channels may start with not just # and & but also + and !

[timo]

Randomly stumbled upon this while reading the source. This is the first line that uses # and & to check if a message is going to a channel, or if it's meant to be a private message to just the user:

IRC-Client/lib/IRC/Client.rakumod

Line 270 in bd4bef4

$channel.starts-with('#') || $channel.starts-with('&')

There are a few more mentions.

Here's a section in the RFC2811 that names the allowed prefixes for channels:

https://datatracker.ietf.org/doc/html/rfc2811#section-3

In regard to the lifetime of a channel, there are typically two
groups of channels: standard channels which prefix is either '&', '#'
or '+', and "safe channels" which prefix is '!'.