code: def validate(cls, keystr):
          
          if "#{" in keystr:
              # it's a template with keys vars
              keys = cls.from_template(keystr)
              for k in keys:
                  cls.validate_one(cls.extract(k))
          else:
              # plain keys str
              cls.validate_one(keystr)
docs: raises cls.Bad if keys has errors