How to understand "using interfaces layered over USB" in this article?

hi all: I read this article, but I can't understand this section： ############################################################ Most USB device drivers should pass these tables to the USB subsystem as well as to the module management subsystem. Not all, though: *some driver frameworks connect using interfaces layered over USB, and so they won't need such a "struct usb_driver".* ############################################################ From: https://www.kernel.org/doc/Documentation/usb/hotplug.txt How to understand "using interfaces layered over USB"? Thank you.