PhpThumb::isValidImplementation PHP Method

    public function isValidImplementation($implementation)
    {
        if ($implementation == 'n/a') {
            return true;
        }
        if ($implementation == 'all') {
            foreach ($this->_implementations as $imp => $value) {
                if ($value == false) {
                    return false;
                }
            }
            return true;
        }
        if (array_key_exists($implementation, $this->_implementations)) {
            return $this->_implementations[$implementation];
        }
        return false;
    }