When the chanchange option is set, the mud will tell you whenever
your default channel changes.  It displays the follwing text:

New default channel: xxx

Where 'xxx' is the name of the channel, or '(none)' if you no
longer have a default channel.  This @option is most useful with
MUD clients that can be programmed to display useful information.
Ask around for macros for the 'tf' client that use this option.