code: func (c *Client) Userlist(channel string) ([]string, error) {
  	c.channelUserlistMutex.RLock()
  	defer c.channelUserlistMutex.RUnlock()
  	usermap, ok := c.channelUserlist[channel]
  	if !ok || usermap == nil {
  		return nil, fmt.Errorf("Could not find userlist for channel '%s' in client", channel)
  	}
  	userlist := make([]string, len(usermap))
  
  	i := 0
  	for key := range usermap {
  		userlist[i] = key
  		i++
  	}
  
  	return userlist, nil
  }
docs: // Userlist returns the userlist for a given channel