When "is_library_indirect" property of ID's could be set to True? Every ID datablock in Blender has an is_library_indirect property (
https://docs.blender.org/api/2.79/bpy.types.ID.html#bpy.types.ID.is_library_indirect)

I wanna know after what user actions it could be set to True.
I have figured that out. It is set to true for objects that located in linked groups.