Zend Form Element Multicheckboxes unordered list tag ul

Multicheckboxes.php

<?php 

class My_Form_Template extends My_Form
{
	public function init()
	{
		parent::init();
		
		$this->addElements(array(
		    $this->createElement(self::TYPE_MULTICHECKBOX, 'checks', array(
				'label' => 'Unordered Listed Checkboxes',  
				'title' => 'myboxes',
				'validators' => array(),
				'required' => true,
				'separator' => '</li><li>',
				'decorators' => array(
				    'viewHelper',
				    'Errors',
				    array(array('uno' => 'HtmlTag'), array('tag' => 'li')),
				    array(array('due' => 'HtmlTag'), array('tag' => 'ul','class' => 'check')),
				),
				'multioptions' => array(
				    'test2', 'prova2'
				),
		    )),
		)); 
	}
}