How these three callback functions work?

Hi there,

i am learning the Arducopter’s code, i get a problem with one kind callback funtion.
In file Copter.h, code as follow:

// Mission library
    AP_Mission mission{ahrs,
            FUNCTOR_BIND_MEMBER(&Copter::start_command, bool, const AP_Mission::Mission_Command &),
            FUNCTOR_BIND_MEMBER(&Copter::verify_command_callback, bool, const AP_Mission::Mission_Command &),
            FUNCTOR_BIND_MEMBER(&Copter::exit_mission, void)};

    bool start_command(const AP_Mission::Mission_Command& cmd) {
        return mode_auto.start_command(cmd);
    bool verify_command_callback(const AP_Mission::Mission_Command& cmd) {
        return mode_auto.verify_command_callback(cmd);
    void exit_mission() {

In the code, the funtions: start_command, verify_command_callback, exit_mission, seems like are callback funtions, and are called from some where.

Here is my problem: where these three functions be called? i seek for a long time, but get no answer so far.
Any one can give me some clue? thanks.

Opening the project in Microsoft VisualStudioExpress or something similar will give you a fast answer.