Today I found myself in a complex codebase and my ticket was: this JS on this old page makes the monkey dance, can you make it dance on the new page? Well, my JS knowledge is... limited but I have a really mean right click. So I right clicked and looked around the source Chrome showed me. There was a div with a class
slideshow-node-embed-processed. Now that's important:
-processed is added by the jQuery once plugin that Drupal 7 happens to ships with. It's much easier to recognize the handiwork of the plugin than actually use it -- this is true for many similar reverse engineering scenarios.