/**
  * header
  *
  * @param string  $string
  * @param bool    $replace
  * @param integer $code
  *
  * @return  static
  */
 public function header($string, $replace = true, $code = null)
 {
     if (strpos($string, ':') !== false) {
         list($header, $value) = explode(': ', $string, 2);
         if ($replace) {
             $this->message = $this->message->withHeader($header, $value);
         } else {
             $this->message = $this->message->withAddedHeader($header, $value);
         }
     } elseif (strpos($string, 'HTTP') === 0) {
         $this->status = $string;
     } else {
         $this->others[] = $string;
     }
     return $this;
 }