template/scratch.go
func (s *Scratch) Key(k string) bool {
	s.RLock()
	defer s.RUnlock()
	_, ok := s.values[k]
	return ok
}
func (s *Scratch) Key(k string) bool {
	s.RLock()
	defer s.RUnlock()
	_, ok := s.values[k]
	return ok
}
// Key returns a boolean indicating whether the given key exists in the map.