docs: def get_for(self, dynamic_part):
          """
          Return a variation of the current dynamic field based on the given
          dynamic part. Use the "format" attribute to create the final name
          """
          if not hasattr(self, '_instance'):
              raise ImplementationError('"get_for" can be used only on a bound field')
          name = self.get_name_for(dynamic_part)
          return self._instance.get_field(name)