Add this to your `~/.tmux.conf`` file to let tmux work with the mouse:
setw -g mouse on
Start a new session, make a new split with either `LEADER-%`` or `LEADER-"`` then drag when divider to resize the panes.
I didn't think this worked at first because the mouse icon didn't change when I hovered over the divider line in iTerm2. The click and drag still worked as expected.
Hit the leader key (which defaults to CTRLb) then hold the OPTION key and press the ARROW of the direction to push the window
If you're on a mac make sure to use the CTRL key and not Command
At one point I was setup to use ESC instead of CTRL based of some setting in iTerm2, but that's no longer the case. Not sure what changed. I think it had something to do with a remapping I did for Emacs maybe,