checkLength example

    public function checkLength($value)
    {
        if (strlen($value) != 8) {
            $this->setCheck(false);
        } else {
            $this->setCheck(true);
        }

        return parent::checkLength($value);
    }
}

    public function checkLength($value)
    {
        if (strlen($value) == 7) {
            $this->setCheck(false);
        } else {
            $this->setCheck(true);
        }

        return parent::checkLength($value);
    }
}

    public function isValid($value)
    {
        if (!is_string($value)) {
            $this->_error(self::INVALID);
            return false;
        }

        $this->_setValue($value);
        $adapter       = $this->getAdapter();
        $this->_length = $adapter->getLength();
        $result        = $adapter->checkLength($value);
        if (!$result) {
            if (is_array($this->_length)) {
                $temp = $this->_length;
                $this->_length = "";
                foreach($temp as $length) {
                    $this->_length .= "/";
                    $this->_length .= $length;
                }

                $this->_length = substr($this->_length, 1);
            }