Add a regex validator to a form element in the Zen

I created a Form class in zend Framework.

class Application_Form_UserSignup extends Zend_Form {

public function init()
{
    // Set the method for the display form to POST
    $this->setMethod('post');

    // Add an Firstname element
    $this->addElement('text', 'firstname', array(
                              'label'      => 'Your first name:',
                              'required'   => true,
                  'validators' => array('regex', false, array(
                'pattern'   => '/[^<>]/i',
                'messages'  =>  'Your first name cannot contain those characters : < >'))
    ));
    }

}

I would like to validate it with my own regex using the Zend_Validate_Regex validator.

There must be an error in the syntax because I get this error but I cannot figure it out.

The error is :

Message: Invalid validator passed to addValidators() Stack trace:

0 /usr/share/php/libzend-framework-php/Zend/Form/Element.php(1217): Zend_Form_Element->addValidators(Array)
1 /usr/share/php/libzend-framework-php/Zend/Form/Element.php(363): Zend_Form_Element->setValidators(Array)
2 /usr/share/php/libzend-framework-php/Zend/Form/Element.php(253): Zend_Form_Element->setOptions(Array)
3 /usr/share/php/libzend-framework-php/Zend/Form.php(1108): Zend_Form_Element->__construct('firstname', Array)
4 /usr/share/php/libzend-framework-php/Zend/Form.php(1039): Zend_Form->createElement('text', 'firstname', Array)
5 /home/damiens/workspace/manu/application/forms/UserSignup.php(18): Zend_Form->addElement('text', 'firstname', Array)
6 /usr/share/php/libzend-framework-php/Zend/Form.php(240): Application_Form_UserSignup->init()
7 /home/damiens/workspace/manu/application/controllers/UsersController.php(35): Zend_Form->__construct()
8 /usr/share/php/libzend-framework-php/Zend/Controller/Action.php(513): UsersController->signupAction()
9 /usr/share/php/libzend-framework-php/Zend/Controller/Dispatcher/Standard.php(295): Zend_Controller_Action->dispatch('signupAction')
10 /usr/share/php/libzend-framework-php/Zend/Controller/Front.php(954): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
11 /usr/share/php/libzend-framework-php/Zend/Application/Bootstrap/Bootstrap.php(97): Zend_Controller_Front->dispatch()
12 /usr/share/php/libzend-framework-php/Zend/Application.php(366): Zend_Application_Bootstrap_Bootstrap->run()
13 /home/damiens/workspace/manu/public/index.php(26): Zend_Application->run()
14 {main}

Any Help would be appreciated !

Its addValidatorS (multiple validators):

$this->addElement('text', 'firstname', array(
                          'label'      => 'Your first name:',
                          'required'   => true,
              'validators' => array(
                  array('regex', false, array(
                  'pattern'   => '/[^<>]/i',
                  'messages'  =>  'Your first name cannot contain those characters : < >'))
              )
));