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

[lx]

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.
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