>> 1) Typical semantics of "mentioning" someone on a social network are
>> that the posted object is distributed to the person mentioned as well
>> as the author's followers. So, a Twitter post like "@jsnell hello"
>> would go to user @jsnell as well as all followers.

>> Does this secondary audience need to be made explicit? If so, how? If
>> not explicit, I think it would be coded like...

>>    {"to": [{objectType: "person", id: "acct:jsn...@example.com"}]}

>> If explicit, maybe something like:

>>    {"to": [{objectType: "person", id: "acct:jsn...@example.com"}],
>>     "cc": [{objectType: "group", id: "followers-of-evan"}]
>>    }

> In this case, I think targeting the secondary audience would be
> optional but yes, that's how it would be done.

>> ? Some networks also make a "public" stream for the site available, so
>> something like:

>>    {"to": [{objectType: "person", id: "acct:jsn...@example.com"}],
>>     "cc": [{objectType: "group", id: "followers-of-evan"},
>>              {objectType: "group", id: "everyone-on-this-site"}]
>>    }

>> ... or even:

>>    {"to": [{objectType: "person", id: "acct:jsn...@example.com"}],
>>     "cc": [{objectType: "group", id: "followers-of-evan"},
>>              {objectType: "group", id: "everyone-on-this-site"}],
>>              {objectType: "group", id: "everyone-in-the-world"}]
>>    }
> Yes. I would recommend using the "alias" extension property instead of
> id tho. The "alias" is something that was discussed on list a couple
> of months ago. I just remembered this morning that I needed to add it
> to the spec... I've done so now.. It would look like...

>     {"to": [{objectType: "person", id: "acct:jsn...@example.com"}],
>      "cc": [{objectType: "group", id: "followers-of-evan"},
>               {objectType: "group", alias: "@all"}],
>               {objectType: "group", alias: "@world"}]
>    }

> Or something along those lines.. the value of the alias is some fairly
> system specific alias for the object in lieu of using an explicit ID.

>> Another option is to explicitly list all followers, which might be
>> tractable for small numbers of followers but falls down with 1M+
>> follower accounts on some popular systems.
> Using groups would be ideal, yes.

>> 2) If audiences are explicit, there's an implicit ACL in the targeting
>> -- by analogy with email, where it's unusual to allow a user to view a
>> message that was not addressed to them. (Auditing and administration
>> being the main exception here -- email list archives being a secondary
>> one.)

>> It would be useful to either call this out ("Processors SHOULD NOT
>> show activities to people who aren't in the audience"), or explicitly
>> disclaim it ("Audience != ACL").
> Disclaiming it would be good. The targeting information is meant to
> express the intent of the sender not necessarily control what the
> recipient does with it (with clear exception of bto and bcc handling).

>> 3) It's not clear what to do with an activity that has no audience
>> specification. It could mean either a) this isn't targeted to anyone
>> b) it's targeted to some system default (followers, the whole site,
>> the public), or c) the processor doesn't support targeting.

>> It may be useful to call out a default secondary audience when no
>> targeting is specified, e.g. "my followers".
> I would rather leave this up to the implementation. Like I said, the
> targeting information is meant only to express the intent of the
> sender. It's up to the implementation to figure out how to actually
> handle the activity, including selection  of the default audience.

>> Thanks,

>> -Evan

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