2
setDescription method works only for individual form elements
Example for text type input:
$page_banner = new XoopsFormText( _AM_SYSTEM_BANNERS_CONTNAMET, 'banners', 5, 5, $this->getVar( 'banners', 'e' ) );
$page_banner->setDescription( _AM_SYSTEM_BANNERS_CONTNAMET_DESC );
$form->addElement( $page_banner );