$mw->bind( '<Control-KeyPress-a>',   [sub {print "Button a has been pressed\n"}] );
$mw->bind( '<Control-KeyRelease-a>', [sub {print "Button a has been released\n"}] );

##</code><code>##

$mw->bind( '<Control-KeyPress-a>',   sub {print "Button a has been pressed\n"} );
$mw->bind( '<Control-KeyRelease-a>', sub {print "Button a has been released\n"} );

##</code><code>##

$mw->bind( '<Control-KeyPress-a>',   [ \&say_button_pressed,  "a" ]);
$mw->bind( '<Control-KeyRelease-a>', [ \&say_button_released, "a" ]);

# Unlikely to do it this way unless the following subroutines are
# longer, or likely to be called from multiple places...
#
sub say_button_pressed {
    printf "Button %s has been pressed\n", $_[0];
}
sub say_button_released {
    printf "Button %s has been released\n", $_[0];
}