ActivityPub/Primer/Streams

The streams property of ActivityPub actors is defined as A list of supplementary Collections which may be of interest.

This property is not widely implemented. There is not a clear way to filter the list of Collections according to what a client application may need. For example, a client application that wants to show contact lists to the user would not have an easy way to find only contact lists in streams. A client application that wants to show photo albums to the user would not have an easy way to find only photo albums in streams.

Servers

Servers should use extension properties of the actor to provide specific collections like albums, contact lists, or filtered inbox or outbox streams.

Publishers can also include those collections in the streams list, to allow users to review the streams even if their client software does not support the extension.

Clients

Clients should use extension properties of the actor to query specific collections like albums, contact lists, or filtered inbox or outbox streams.

Clients can also show collections in the streams list to users, to let them manually browse the collections.

Clients may use streams to query specific collections by heuristics -- for example, the name property, or the type property of items in the collections. However, this will be inexact, and is less preferable than using well-defined extensions.