docs: def select_fields(self, *fields):
          """set multiple fields to be selected"""
          if fields:
              if not isinstance(fields[0], basestring): 
                  fields = list(fields[0]) + list(fields)[1:]
  
          for field_name in fields:
              field_name = self._normalize_field_name(field_name)
              self.select_field(field_name)
          return self