Clarify whether "Actor Objects" properties are Functional

[cjslep]

The additional properties added to the ActivityStream types in the Actor Objects section does not explicitly mark any of them as functional. There is also no indication whether this is intentional.

The default guidance from the ActivityStreams properties section is:

Properties marked as being "Functional" can have only one value. Items not marked as "Functional" can have multiple values.

This affects the following properties:

• inbox
• outbox
• following
• followers
• liked
• streams
• preferredUsername
• endpoints
• proxyUrl
• oauthAuthorizationEndpoint
• oauthTokenEndpoint
• provideClientKey
• signClientKey
• sharedInbox

[gobengo]

I interpret any property not explicitly labeled functional as not being functional

[evanp]

We reviewed this ticket. I've updated the Primer on the W3C wiki to cover best practices for publishers and consumers to deal with array values in these properties.

https://www.w3.org/wiki/ActivityPub/Primer/Cardinality_of_properties

With that documentation, I think this issue is closed.

[snarfed]

+1, thanks for this:

A guideline for implementers:

• Publishers should not include array values for these properties, since there is no way for a consumer to decide which value to choose.
• Consumers should be able to process a property with an array value, and should choose an array element to process, or process all. Note that this is poorly-defined behaviour!

Notably, AP logic and behavior depends on some of these values in nontrivial ways, eg inbox and especially sharedInbox. We could maybe infer reasonable behavior for some, eg deliver to all inboxes as @gobengo mentioned verbally, but multiple sharedInbox values is less clear.

[melvincarvalho]

Publishers should not include array values for these properties

@evanp Could you clarify what is meant by "these properties"? Which properties specifically?

[snarfed]

@melvincarvalho I expect he meant all of the Actor properties mentioned in the original issue description ^.