code: func SelectorFromValidatedSet(ls Set) Selector {
  	if ls == nil || len(ls) == 0 {
  		return internalSelector{}
  	}
  	var requirements internalSelector
  	for label, value := range ls {
  		requirements = append(requirements, Requirement{key: label, operator: selection.Equals, strValues: []string{value}})
  	}
  	// sort to have deterministic string representation
  	sort.Sort(ByKey(requirements))
  	return requirements
  }
docs: // SelectorFromValidatedSet returns a Selector which will match exactly the given Set.
  // A nil and empty Sets are considered equivalent to Everything().
  // It assumes that Set is already validated and doesn't do any validation.