Example of attaching "expand" listener of collapsible?

Example of attaching "expand" listener of collapsible?

Can someone provide a working sample of attaching an event listening for the "expand" event on a Collapsible object?  I'm sure my issue is just "where and when" to attach the event

this is where I am getting the code:


this is the code I put together as an example


I can't *quite* show exactly what I am doing, as I am making an AJAX call to get the page for a particular item, but if someone could get that event to fire in the example code that will be enough to go on

Thanks in advance