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

[Greg KH]

On Mon, Sep 08, 2014 at 11:31:32AM +0800, lx wrote:
> 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"?

Think SCSI, HID, Serial, or any other type of usb device that is just
using the USB connection as a physical transport of a specific type of
data.

Does that help?

greg k-h