code: func (w *Writer) Handle(h Handler) {
  	w.mutex.Lock()
  	defer w.mutex.Unlock()
  
  	if h != nil {
  		w.handlers = append(w.handlers, h)
  	}
  }
docs: // Handle registers a handler that will be called for every logging
  // event. The function receives a message, which is a structured
  // representation of the log message text.
  //
  // This function is useful for registering handlers that send log
  // information to external sources.