• When a user subscribes to a publish-subscribe node (presumably via some higher-level abstraction), other online devices are aware of the new subscription immediately, and can choose to reflect the new subscription in their UI.
• Not all devices may be capable of handling the particular payload and/or service, and therefore should signal which payload and/or service types they support.
• The same capability as point 1 should be possible for unsubscribing.

• When a user brings a new device online, it should be able to quickly learn all the user's current subscriptions and present them to the user in its UI.

• When the device is offline for an extended period (beyond XEP-0198 resumption capability), it needs to be able to obtain all the events it missed, including when the events occured.
• It should be able to tell which of these the user is unlikely to have seen on other devices.
• Further, it needs to be able to tell if new subscriptions have been added, or old ones removed.

• A one-way subscription to a user should still allow PEP.
• PEP should work the same way as now - users see filtered notifications about the things they care about.

Clients need to include a capability in Disco. Probably.

Servers need to advertise capability against account.

Clients use a modified XEP-0060 Subscribe with a newly added "jid" attribute? Presumably this may need to be in a distinct namespace.

It is tempted to suggest that all pubsub operations might be contained within a new namespace with the additional jid attribute, as they can be forwarded verbatim as required.

Servers use traditional XEP-0060 subscribes, but sent from the bare jid of the account.

Servers MUST send a Thing to indicate the new subscription to all clients capable of this protocol.

As above.

XEP-0237 FTW. Needs a new construct, since the subscriptions element in XEP-0060§5.6 will only list the user's local subscriptions (ie, to their PEP nodes). Maybe just the new namespace defaults to everything instead? But we'd still need the XEP-0237 model.

Servers need to subscribe to remote PEP services explicitly those nodes which are of interest. Interest needs to be detirmined by the client issuing a request; but this implies that servers would gradually acrue any node type which the user has had a capable client at any time.

Perhaps timing out node types which have not been requested for over a certain period?

Clients can use +notify to handle auto-subscriptions between clients and their server.

Servers receiving +notify from accounts known to support this protocol ignore them.

Clients filter subscriptions using a specific stanza (iq, probably), containing a list of node names. This can be used instead of the odler +notify (which is broadcast).

We probably want to say that events are now archived by MAM, but this may imply that clients need to filter out such events (or explicitly include them). Maybe the mask above affects MAM queries?