@nschonni - in the code this become a post ajax trigger that the menu will hook into for some special function. In the menu's case it is simply removing the classes in the element. This is used to Fight the FOUC. The menu system in wet has a different state in mobile than in desktop. For leaner CSS it is easier to leverage the TB visible-lg visible-md, etc classes control the default view. This cause of a bit of flicker when you get down to mobile since you are have to manually override the aforementioned default classes once the content is on. It is easier and better to have the menu know that is has to alter certain classes once the content is in so that the content does not flicker between one state to another.