Doubts about how to enable Subscriptions
I'm trying ('cause I know very little about JS, node, etc.) to enable subscriptions for my [Postgraphile Docker](https://hub.docker.com/r/graphile/postgraphile/) container, I'm following the example provided by the [doc](https://www.graphile.org/postgraphile/subscriptions/#custom-subscriptions). The info over there is lacking for details for beginners, IMHO. There are several things that I am unsure of, so I need an orientation.

This is what i have done so far:

### docker-compose.yaml
```
  graphql:
    build: 
      context: ./graphql
    container_name: my-gql
    restart: unless-stopped
    env_file: 
      - ./graphql/.env
    depends_on: 
      - db
    networks: 
      my-net:
        ipv4_address: 172.27.0.3
    ports: 
      - 5000:5000
    command: [
      "--connection", "postgres://${NAME_ROLE}:${PWD_ROLE}@172.27.0.2:5432/${DB_NAME}", 
      "--owner-connection", "postgres://${NAME_ADMIN}:${PWD_ADMIN}@172.27.0.2:5432/${DB_NAME}", 
      "--watch", 
      "--schema", "${DEFAULT_SCHEMA}", 
      "--default-role", "${DEFAULT_ROLE}",
      "--jwt-secret", "${JWT_SECRET}", 
      "--jwt-token-identifier", "${JWT_TOKEN_ID}",
      "--dynamic-json",
      "--plugins", "@graphile/pg-pubsub",
      "--subscriptions",
      "--no-setof-functions-contain-nulls",
      "--no-ignore-rbac",
      "--no-ignore-indexes",
      "--show-error-stack", "json",
      "--extended-errors", "hint,detail,errcode",
      "--enable-query-batching",
      "--legacy-relations", "omit",
      "--export-schema-graphql", "my_schema.graphql",
      "--append-plugins", "@graphile-contrib/pg-simplify-inflector,/postgraphile/custom_plugins/MySubscriptionPlugin.js",
      "--simple-collections", "only",
      "--enhance-graphiql"
    ]
    volumes: 
      - ./graphql/custom_plugins:/postgraphile/custom_plugins
```

### graphql/Dockerfile
```
FROM graphile/postgraphile:latest
RUN yarn add @graphile-contrib/pg-simplify-inflector
RUN yarn add @graphile/pg-pubsub
```

### graphql/custom_plugins/MySubscriptionPlugin.js
The same content that doc's [example](https://www.graphile.org/postgraphile/subscriptions/#writing-the-plugin).

### PostgreSQL's UDT 
```
CREATE TYPE my_schema.jwt_token AS (
  role text, 
  user_id uuid,
  exp integer
);
```

### PostgreSQL's objects being used for subscriptions:
```
my_schema.my_complex_proc1(any_value text)
my_schema.my_complex_proc2(any_value int)
my_schema.my_complex_view
```


## My questions:

- Based on the example provided, it seems that subscriptions only work with tables, is it? 
- My goal is to use a complex query result from a procedure or from a view. Is this possible? If so, what changes should I do into `MySubscriptionPlugin.js`? Sincerely, there several parts of that script that it is cryptic to understand for me, so I don't know what to modify.
- Using procedures/views for subscriptions, how does it affects `app_public.graphql_subscription()` function in its content and usage? 
- Should `context.jwtClaims.user_id` be changed to this `context.jwt.claims.user_id`? or it is invariant no matter what. This is because I use in my PostgreSQL scripts `jwt.claims.user_id`.
- Should the schema used in that example be the same schema exposed in Postgraphile's parameters?
- If I wanna have more than one subscription, should I create more scripts similar to `MySubscriptionPlugin.js`? or what should changes be added to that script to reflect that purpose?

Thanks.