docs: def directive(apply_globally=False, api=None):
      """A decorator that registers a single hug directive"""
      def decorator(directive_method):
          if apply_globally:
              hug.defaults.directives[underscore(directive_method.__name__)] = directive_method
          else:
              apply_to_api = hug.API(api) if api else hug.api.from_object(directive_method)
              apply_to_api.add_directive(directive_method)
          directive_method.directive = True
          return directive_method
      return decorator