6.2.8 Bus drivers that produce at most one child in Start()

Some bus drivers are for bus controllers that have only a single port, so they have at most one child handle. If RemainingDevicePath is NULL, then that one child handle should be produced. If RemainingDevicePath is not NULL, then the RemainingDevicePath should be parsed to see if it matches a device path node that the bus driver knows how to produce.
For example, a serial port can have only one device attached to it. This device may be a terminal, a mouse, or a drill press, for example. The driver that consumes the Serial I/O Protocol from a handle must create a child handle with the produced protocol that uses the services of the Serial I/O Protocol.