code: func (ps *Plugins) Registered() []string {
  	ps.lock.Lock()
  	defer ps.lock.Unlock()
  	keys := []string{}
  	for k := range ps.registry {
  		keys = append(keys, k)
  	}
  	sort.Strings(keys)
  	return keys
  }
docs: // Registered enumerates the names of all registered plugins.