Dynamic TVML shelf & collectionlist event?

There are many examples of updating shelf and collectionlist’s objects, but I can’t find anything about knowing when to do so. Let me will explain…

As an example, a TVML document with three shelves, each with five lockups visible at any time. When the user navigates to the document, I request ten shows per shelf. As the user starts sliding the focus to the right, I’d like to be able to request more data from the service and dynamically add these items. I know how to actually add the items, I do it now with search. What I don’t know is which shelf the user is sliding around on, and where they are on that shelf to be able to issue the correct service request.

Are there any focus events, or display events that I can listen for to create service requests? I’m trying to avoid requests for anything the user isn’t looking at.

I figured it out. There is an event generated called “highlight” which includes the currently focused element.