Swift_Message::attachSigner PHP Метод

    public function attachSigner(Swift_Signer $signer)
    {
        if ($signer instanceof Swift_Signers_HeaderSigner) {
            $this->headerSigners[] = $signer;
        } elseif ($signer instanceof Swift_Signers_BodySigner) {
            $this->bodySigners[] = $signer;
        }
        return $this;
    }

 public function testCloningWithSigners()
 {
     $message1 = new Swift_Message('subj', 'body', 'ctype');
     $signer = new Swift_Signers_DKIMSigner(dirname(dirname(__DIR__)) . '/_samples/dkim/dkim.test.priv', 'test.example', 'example');
     $message1->attachSigner($signer);
     $message2 = new Swift_Message('subj', 'body', 'ctype');
     $signer = new Swift_Signers_DKIMSigner(dirname(dirname(__DIR__)) . '/_samples/dkim/dkim.test.priv', 'test.example', 'example');
     $message2->attachSigner($signer);
     $message1_clone = clone $message1;
     $this->_recursiveObjectCloningCheck($message1, $message2, $message1_clone);
 }