How can the method below to work?

```
$this->getRequest()->getPost();

```

There is no method `getPost()` in class `Zend_Controller_Request_Abstract`, but how can it work? In OOP principle, the method `getPost()` should appear in `Zend_Controller_Request_Abstract`.

How can the Zend pull `getPost()` in class `Zend_Controller_Request_Http` if there is no direct instance?

Thank you.