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All native drivers, both generic and family, must export a single data symbol that characterizes the driver's functionality and origin. This symbol, called TheDriverDescription, must be exported as a CFM symbol. It is documented in Driver Description Structure.
The driver description information helps match drivers with devices. This includes letting the Device Manager or device Family Expert pick the best driver among multiple candidates. The Device Manager uses the information in the driver description to determine whether a disk-based device driver is a better match for a device than a device driver that is in the Mac OS ROM. For example, a USB class driver in the Mac OS ROM for the mouse may be a valid match for some generic aspects of a third-party mouse device. However, the driver description for the third-party device driver installed on the disk should provide vendor ID, product ID, and other data to ensure the USB Manager/Family Expert replaces the Mac OS ROM driver when the third-party mouse is detected.