Tapping into dynamic lists

How do I determine from a script/module the item selected on a dynamically populated list?

For example a movie is selected in MyVideoNav and I want to display some info in a control that depends on the selected movie – I am going to feed the control from my script.

How do I determine fe. genres available for the currently displayed set of movies (that is for example path library://video/movies/supermovies.xml created with Library Node Editor)?