Expiration time is still defined as optional in section 1. #177
Description
From the definition of Subscription in section 1:
Subscriptions may (at the hub's decision) have expiration times akin to DHCP leases which must be periodically renewed.
This contradicts the rest of the specification.
hub.lease_seconds
Hubs MUST supply this parameter when hub.mode is set to "subscribe".
Hubs MUST enforce lease expirations, and MUST NOT issue perpetual lease durations.