How to filter subscriptions presence endpoints by user IDs ?

[abda11ah]

greetings to all,
I recently tested the mercure topics subscription and it works.

The idea is that each user subscribes to his user_id as a starting topic as in :

url.searchParams.append('topic', users/${this.userId});

then he subscribes to the topic presence api with a list of predefined ids (the people I've liked).
I think it's more optimized to not to ask for all the users in the topic ./well-known/mercure/subscriptions, as it could be too cumbersome if there are thousands of users.

That's why I only want to ask for certain user_ids, but that's where I'm stuck.

The AI suggests me the template :
/.well-known/mercure/subscriptions/users/{id=(4|8|52)}
to request only user_id=4 or user_id=8 or user_id=52

but this is not a valid URI. I've started reading RFC6570 but I can't find which mask matches this request.