code: func runMouseBindCallbacks(xu *xgbutil.XUtil, event interface{}, evtype int,
  	win xproto.Window, mods uint16, button xproto.Button) {
  
  	key := xgbutil.MouseKey{evtype, win, mods, button}
  	for _, cb := range mouseCallbacks(xu, key) {
  		cb.Run(xu, event)
  	}
  }
docs: // runMouseBindCallbacks executes every callback corresponding to a
  // particular event/window/mod/button tuple.