code: def _parse(cls, scope):
      
      if not scope:
        return ('default',)
      if isinstance(scope, string_types):
        scope = scope.split(' ')
      scope = {str(s).lower() for s in scope if s}
      return scope or ('default',)
docs: Parses the input scope into a normalized set of strings.
  
      :param scope: A string or tuple containing zero or more scope names.
      :return: A set of scope name strings, or a tuple with the default scope name.
      :rtype: set