optgroup

<?php
$fields = array(
    'countries' => array(
        'type'   => 'select',
        'groups' => array(
            array(
        		'name'    => 'Europe'
        		'options' => array(
        			'no' => 'Norge',
        			'sv' => 'Sverige'
        		)
        	),
        	array(
        		'name'    => 'asia',
        		'options' => array(
        			'jp' => 'Japan',
        			'ch' => 'China',
        		)
        	)
        )
    )
);