code: func SelectorFromSet(ls Set) Selector {
  	if ls == nil {
  		return Everything()
  	}
  	items := make([]Selector, 0, len(ls))
  	for field, value := range ls {
  		items = append(items, &hasTerm{field: field, value: value})
  	}
  	if len(items) == 1 {
  		return items[0]
  	}
  	return andTerm(items)
  }
docs: // SelectorFromSet returns a Selector which will match exactly the given Set. A
  // nil Set is considered equivalent to Everything().