The note about notifying the hub is somewhat misleading.
Hubs and publishers which would like to agree on a standard mechanism to communicate might consider employing an existing delivery mechanism, namely Linked Data Notifications or Webmention.
In practice, the current deployed hubs do have a somewhat standardized method for notifying the hub, which looks like a similar request to subscribing to the hub.
I would suggest removing this note since it's misleading in terms of what has been deployed in practice. Perhaps replacing it with a note that this may be standardized in the future as an extension.
The note about notifying the hub is somewhat misleading.
In practice, the current deployed hubs do have a somewhat standardized method for notifying the hub, which looks like a similar request to subscribing to the hub.
See: Superfeedr, Google, and Switchboard
The requests use the following parameters for the publisher to notify the hub the topic URL was updated:
hub.mode=publish&hub.url=__________hub.mode=publish&hub.url=__________hub.mode=publish&hub.topic=__________I would suggest removing this note since it's misleading in terms of what has been deployed in practice. Perhaps replacing it with a note that this may be standardized in the future as an extension.