Kohana: how they did it?

<?php

class Controller_Index extends Controller_Template {
  public $template = 'v_index';

  public function action_index()
  {
    $this->template->title = "Internet shop";
    $this->template->content = "Home page";
  }
}

I wonder, how did they achieve it? to assign some new variables to string var $template? I know smth about Reflection, but still have no versions