User blog comment:DaNASCAT/Going Up To Speed On Wikia's Performance Initiative/@comment-1114229-20131107213307/@comment--20131107214732

If you're referring to regular collapsible elements, those do load all content on page load, so lazy loading is not in place there. Having an item in a collapsible box, to the best of my knowledge, makes no direct difference on overall page load speed versus having all that same information in a "regular" table.