In my add-on, I would like to add a property that is not scene-specific but unique for the entire project file so I can call it from any scene and always get a unique value.

I know how to add a Scene-specific property by adding a line like this in the register function:

bpy.types.Scene.my_prop = IntProperty(something-something)

But what about a Project File property? Is that even a thing?

In my add-on, I would like to add a property that is not scene-specific but unique for the entire project file so I can call it from any scene and always get the same value.

In case you need to know, in my situation it would be a PointerProperty that points to a list of properties of different types.

I know how to add a Scene-specific property by adding a line like this in the register function:

bpy.types.Scene.my_prop = PointerProperty(type=my_list_of_properties)

But what about a Project File property? Is that even a thing?