code: def __select_subfeatures (parent_property, features):
      
      if __debug__:
          from .property import Property
          assert isinstance(parent_property, Property)
          assert is_iterable_typed(features, Feature)
      return [f for f in features if is_subfeature_of (parent_property, f)]
docs: Given a property, return the subset of features consisting of all
          ordinary subfeatures of the property's feature, and all specific
          subfeatures of the property's feature which are conditional on the
          property's value.