public function attachEvent($event, $handler, $priority = 0)
    {
        $this->eventDispatcher->addListener($event, $handler, $priority);
        return $this;
    }
public function attachEvent($event, $handler, $priority = 0)
    {
        $this->eventDispatcher->addListener($event, $handler, $priority);
        return $this;
    }
public function attachEvent ( $ event , $ handler , $ priority = 0 ) { $ this -> eventDispatcher -> addListener ( $ event , $ handler , $ priority ) ; return $ this ; }
Attach event handler
@param string $event event name
@param callable|array|string $handler event handler
@return \Sokil\Mongo\Document
Attach event handler