According to the man page, if I run this command:
tmux source-file ~/.tmux.conf
tmux is going to execute the commands in ~/.tmux.conf. However if, for example, I add a key binding to tmux.conf, and later remove it, the key binding stays, even if I source the file (which is logical, since there's no actual command to execute for that binding).
So I'm wondering, before sourcing the config, if there a way to somehow clear tmux's internal state (all binding, settings, etc.) so that it starts with the default one?