How do I implement Feature report? HID class

[Richard Závodný]

I'm trying to implement Feature reports on my device. I'm using hid_mouse example application and I came by this part of code in main.cpp:

int8_t app_set_report_callback(uint8_t interface, uint8_t report_type,
                               uint8_t report_id)
{
	/* To handle Set_Report, call usb_start_receive_ep0_data_stage()
	 * here. See the documentation for HID_SET_REPORT_CALLBACK() in
	 * usb_hid.h. For this device though, there are no output or
	 * feature reports. */
	return -1;
}

but I'm not sure how to correctly implement it even with the commented sections. Could someone help me?