def node_routing( routing )
      routing.each_pair do | node_class_name, node_class_routing |
        constraints node_class_routing[:constraints] do
          for_node_class(node_class_name.constantize) do
            yield
          end
        end
      end
    end
def node_routing( routing )
      routing.each_pair do | node_class_name, node_class_routing |
        constraints node_class_routing[:constraints] do
          for_node_class(node_class_name.constantize) do
            yield
          end
        end
      end
    end
expects Releaf::Content.routing hash or a subset of it as an argument