Macro send_prefix 

macro_rules! send_prefix {
    (@cmd ($cmd:expr) -2, $($tail:tt)*) => { ... };
    (@cmd ($cmd:expr) -t $target:expr, $($tail:tt)*) => { ... };
    (@cmd ($cmd:expr)) => { ... };
    () => { ... };
    (($cmd:expr), $($tail:tt)*) => { ... };
    ($($tail:tt)*) => { ... };
}

Send the prefix key

Manual

tmux >=1.6:

send-prefix [-2] [-t target-pane]

tmux >=1.5:

send-prefix [-t target-pane]

tmux >=0.8:

send-prefix [-t target-window]