How to make a checkbox required, how to tell checker?

Hi,

I am looking for a way to have a required checkbox field. I have the code for the form but don't know how to tell the checker function.

'text' => array(
'type' => 'checkbox',
'name' => 'text',
'caption' => _t('_check_2'),
'required' => true,
'checker' => ?????????,
'db' => array (
'pass' => 'Xss',
),
),

anyone a hint please

sighs, no idea or its so easy that I don't see the solution?