code: func (r *EtcdRegistry) UnitStates() (states []*unit.UnitState, err error) {
  	var mus map[MUSKey]*unit.UnitState
  	mus, err = r.statesByMUSKey()
  	if err != nil {
  		return
  	}
  
  	var sorted MUSKeys
  	for key, _ := range mus {
  		sorted = append(sorted, key)
  	}
  	sort.Sort(sorted)
  
  	for _, key := range sorted {
  		states = append(states, mus[key])
  	}
  
  	return
  }
docs: // UnitStates returns a list of all UnitStates stored in the registry, sorted
  // by unit name and then machine ID.