extends — какой код будет запускаться перед созданием в php？

<?php
# Generated by the protocol buffer compiler.  DO NOT EDIT!
# source: order.proto

namespace Order;

use Google\Protobuf\Internal\GPBUtil;

class Test extends \Google\Protobuf\Internal\Message
{
private $student_id = '';

public function __construct($data = NULL)
{
echo 'test message';
exit;
\GPBMetadata\Order::initOnce();
parent::__construct($data);
}

/**
* Generated from protobuf field <code>string student_id = 1;</code>
*
* @return string
*/
public function getStudentId()
{
return $this->student_id;
}

/**
* Generated from protobuf field <code>string student_id = 1;</code>
*
* @param string $var
* @return $this
*/
public function setStudentId($var)
{
GPBUtil::checkString($var, True);
$this->student_id = $var;

return $this;
}

}