original_string: public function setSubject($subject)
      {
          if ($this->_subject === null) {
              $subject = $this->_filterOther($subject);
              $this->_subject = $this->_encodeHeader($subject);
              $this->_storeHeader('Subject', $this->_subject);
          } else {
              /**
               * @see Zend_Mail_Exception
               */
              // require_once 'Zend/Mail/Exception.php';
              throw new Zend_Mail_Exception('Subject set twice');
          }
          return $this;
      }
code: public function setSubject($subject)
      {
          if ($this->_subject === null) {
              $subject = $this->_filterOther($subject);
              $this->_subject = $this->_encodeHeader($subject);
              $this->_storeHeader('Subject', $this->_subject);
          } else {
              /**
               * @see Zend_Mail_Exception
               */
              // require_once 'Zend/Mail/Exception.php';
              throw new Zend_Mail_Exception('Subject set twice');
          }
          return $this;
      }
code_tokens: public function setSubject ( $ subject ) { if ( $ this -> _subject === null ) { $ subject = $ this -> _filterOther ( $ subject ) ; $ this -> _subject = $ this -> _encodeHeader ( $ subject ) ; $ this -> _storeHeader ( 'Subject' , $ this -> _subject ) ; } else { /**
               * @see Zend_Mail_Exception
               */ // require_once 'Zend/Mail/Exception.php'; throw new Zend_Mail_Exception ( 'Subject set twice' ) ; } return $ this ; }
docstring: Sets the subject of the message
  
  @param   string    $subject
  @return  Zend_Mail Provides fluent interface
  @throws  Zend_Mail_Exception
docstring_tokens: Sets the subject of the message