code: func mouseCallbacks(xu *xgbutil.XUtil,
  	key xgbutil.MouseKey) []xgbutil.CallbackMouse {
  
  	xu.MousebindsLck.RLock()
  	defer xu.MousebindsLck.RUnlock()
  
  	cbs := make([]xgbutil.CallbackMouse, len(xu.Mousebinds[key]))
  	copy(cbs, xu.Mousebinds[key])
  	return cbs
  }
docs: // mouseBindCallbacks returns a slice of callbacks for a particular key.