docs: static boolean isNode(Object v) {
          // Note: A value is a subject if all of these hold true:
          // 1. It is an Object.
          // 2. It is not a @value, @set, or @list.
          // 3. It has more than 1 key OR any existing key is not @id.
          if (v instanceof Map && !(((Map) v).containsKey("@value") || ((Map) v).containsKey("@set")
                  || ((Map) v).containsKey("@list"))) {
              return ((Map<String, Object>) v).size() > 1 || !((Map) v).containsKey("@id");
          }
          return false;
      }