public function help($event_name, $callback)
    {
        if (!isset($this->event_helpers[$event_name]))
        {
            $this->event_helpers[$event_name] = $callback;
        }
    }
public function help($event_name, $callback)
    {
        if (!isset($this->event_helpers[$event_name]))
        {
            $this->event_helpers[$event_name] = $callback;
        }
    }
public function help ( $ event_name , $ callback ) { if ( ! isset ( $ this -> event_helpers [ $ event_name ] ) ) { $ this -> event_helpers [ $ event_name ] = $ callback ; } }
add a helper callback to an event
add a helper callback to an event