code: func (list ErrorList) Filter(fns ...utilerrors.Matcher) ErrorList {
  	err := utilerrors.FilterOut(list.ToAggregate(), fns...)
  	if err == nil {
  		return nil
  	}
  	// FilterOut takes an Aggregate and returns an Aggregate
  	return fromAggregate(err.(utilerrors.Aggregate))
  }
docs: // Filter removes items from the ErrorList that match the provided fns.