function setMaxFileSize($bytes = 0)
    {
        if ($bytes > 0) {
            $this->_maxFileSize = $bytes;
        }
        if (!$this->elementExists('MAX_FILE_SIZE')) {
            $this->addElement('hidden', 'MAX_FILE_SIZE', $this->_maxFileSize);
        } else {
            $el =& $this->getElement('MAX_FILE_SIZE');
            $el->updateAttributes(array('value' => $this->_maxFileSize));
        }
    }