def _key_chain
      handler = self
      key_chain = []

      begin
        key_chain = handler.keys + key_chain
        handler = handler.parent
      end while handler

      key_chain
    end
def _key_chain
      handler = self
      key_chain = []

      begin
        key_chain = handler.keys + key_chain
        handler = handler.parent
      end while handler

      key_chain
    end
Returns a key chain which includes all parent's keys and self keys