zendframework $this->view->baseUrl = $this->_request->getBaseUrl();

Question

<?php
class IndexController extends Zend_Controller_Action
{function init()
{
$this->registry = Zend_Registry::getInstance();
$this->view = $this->registry['view'];
$this->view->baseUrl = $this->_request->getBaseUrl();// 
 
}$this->registry = Zend_Registry::getInstance();
$this->view = $this->registry['view'];
$this->view->baseUrl = $this->_request->getBaseUrl();
能把这3句解释下吗，尤其是第3句， _request的类型为Zend_Controller_Request_Abstract，
而 Zend_Controller_Request_Abstract类中没有getBaseUrl()方法，
getBaseUrl()方法在类Zend_Controller_Front中，求解！！！