code: private static DecoratorMap concat(DecoratorMap... d_maps) {
          return (Stream<Consumer<MutableContext>> in, Context ctx) -> {
              for (DecoratorMap d_map : d_maps) {
                  in = d_map.map(in, ctx);
              }
              return in;
          };
      }
docs: Create a decorator map, by chaining zero or more decorator maps.