/**
  * Register a handler for a specific client-request action
  *
  * The callback will be executed upon a request like /?_task=mail&_action=plugin.myaction
  *
  * @param string $action  Action name (should be unique)
  * @param mixed $callback Callback function as string or array with object reference and method name
  */
 public function register_action($action, $callback)
 {
     $this->api->register_action($action, $this->ID, $callback, $this->mytask);
 }