Callbacks with ContextSwitch Action Helper

Hello,

Can someone please show me an example of how to use callbacks with the ContextSwitch action helper? I have read the documentation at http://framework.zend.com/manual/en/zend.controller.actionhelpers.html#zend.controller.actionhelpers.contextswitch.custom but there are no examples.

I have specified bogus callbacks in my $spec array hoping to throw a descriptive exception but none was thrown. Here is my test code:

    // From within an action controller
    public function init()
    {
        $contextSwitch = $this->_helper->getHelper('contextSwitch');
       
        $context = 'text';
        $spec = array(
            'suffix'        => 'text',
            'headers'       => array(
                'Content-type' => 'text/plain'
            ),
            'callbacks'     => array(
                'init'          => 'testinit'
                'post'          => 'testpost'
            )
        );
       
        $contextSwitch->addContext($context, $spec);
        $contextSwitch->addActionContext('view', 'text')
                      ->initContext();
    }

If the above code looks correct, where should I be defining my callbacks? Are they global functions, or methods of the current action controller, or methods of the ContextSwitch helper? Thanks!

-Hector