public function setFormat($format)
    {
        if (empty($format) || !is_string($format)) {

            throw new Zend_Validate_Exception("A postcode-format string has to be given for validation");
        }

        if ($format[0] !== '/') {
            $format = '/^' . $format;
        }

        if ($format[strlen($format) - 1] !== '/') {
            $format .= '$/';
        }

        $this->_format = $format;
        return $this;
    }