code: func (b *eventListenerSupport) addListener(substr string, listener chan string) {
  	b.Lock()
  	defer b.Unlock()
  	if listeners, ok := b.listeners[substr]; ok {
  		b.listeners[substr] = append(listeners, listener)
  	} else {
  		b.listeners[substr] = []chan string{listener}
  	}
  }
docs: // addListener adds a listener to the list of listeners for the specified substring