Help: chat-keep-days
Bounty program for improvements to Tcl and certain Tcl packages.

The "chat-keep-days" setting:

The /chat subsystem will try to discard messages that are older then chat-keep-days. The value of chat-keep-days can be a floating point number. So, for example, if you only want to keep chat messages for 12 hours, set this value to 0.5.

A value of 0.0 or less means that messages are retained forever.