In Attributes inspector there is an option Installed. I am unsure of it's meaning. Does it mean that the element will be present in any size class?
It is for adding that specific view to the corresponding size class. If the installed is checked it will be added to the view hierarchy of that size class, else it won't be added. You can check more about this option in Enable And Disable Views.
来源：https://stackoverflow.com/questions/33975427/installed-option-in-attributes-inspector