pfbc checkbox all options required

I am using a PFBC checkbox, and I want to make all options to have attribute required, for HTML5 validation.

This code is sent to PFBC for rendering, but it does't add the 'required' attribute:

array (
                'name' => 'agreements',
                'label' => '',
                'type' => 'Checkbox',
                'options' => array('over_18'=>'I am over 18 years of',
                            'understand_risks'=>'I understand the risks',
                'properties'=> array (
                        'required' => array('over_18','understand_risks')
                )
        ),