tmux in your tmux
If you are running tmux locally and you shell into another machine to access tmux remotely, you will suddenly find yourself in tmux inception. You will have a tmux instance running within your local tmux instance. If you have the same prefix key set for both, then you may be wondering how you can send a tmux command to the inner tmux instance.
If you press your prefix twice (e.g. <C-a> <C-a>), then the second prefix
will be sent to the inner tmux instance which will then be listening for
the rest of your command. So, to open a new window within the inner tmux
instance, you can hit <C-a> <C-a> c.