def filtered_keys
      values.keys.reject { |k| k == :title || !attr_def[k] || (attr_def[k][:behaviour] == :namevar && @namevars.size == 1) }
    end
def filtered_keys
      values.keys.reject { |k| k == :title || !attr_def[k] || (attr_def[k][:behaviour] == :namevar && @namevars.size == 1) }
    end
attribute names that are not title or namevars