When dragging an item from library under a Loader and some other types, you are presented with various invalid properties to which the item should be bound to

E.g. drag a Rectangle under a Loader node. You'll be presented with the following dialog:

Data and resources are default properties that should never be bound to in qml code, and item is a read-only property of Loader. ContainmentMask is a technically valid property to bind to, but I'm not sure it should be presented here, either, as it's rather rare you will want to do that.

Some other types also present these invalid options, such as Loader3D and View3D. View3D offers these properties: