I’m getting a lot out of these ruminations you’re doing about links as
notifications. For me, I think I’m going to include a ‘cc’ bit of post metadata,
much like I already have ‘via’ metadata, to advertise the original source for a
bit of hypertext. Cool idea.
The idea of a ‘bcc’ is even more interesting—it isn’t possible to have secret
recipients listed in the HTML. They would need to be encrypted or something.
E-mail actually removes the ‘Bcc’ header for recipients. I put this in the same
category as encrypted private posts—very tricky to fit into the Indieweb and
possibly just wrong for it.

So, I think person-tagging encompasses all of the normal e-mail send actions:

Direct reply. The text is meant for that individual to read. It’s important to
show the person-tag, because it is important context.

Cc. The text is relevant to the individual and it’s relevant to show the
person-tag to all readers.

Bcc. The text is relevant to the individual, but their connect to it is meant
to be private.

And there seem to be other connections beyond these:

Mentions. The individual is a subject of the text. While they might be
notified of this, it is more important that readers see the connection.

Unlinked mentions…? What if you had an individual who was the subject of the
text, but you didn’t want to notify them? You may want to include an unlinked
@boffosocko, to refer to someone without summoning them. But—what if you
wanted to link readers to the person without notifying them?

Group syndication. All of the above actions could be used for a group URL
(such as IndieNews or Indieweb.xyz) as an alias for a group of individuals.
This is similar to a mailing list e-mail address.

It feels like there might be much more than this.

I do see the purpose of these “@” and “#” prefixes—as a type of miniature
language for simplifying linking. However, there is no distinction between
‘reply’, ‘cc’ and ‘bcc’ with the “@” prefix. (Micro.blog has a problem—or, at
least it did a few months ago—if you send a Webmention to a micro.blog
username, it prefixes the post with an @-mention, even if you’re only mentioning
them in the post. This is confusing, because the post may not be a direct reply,
but it ends up looking like it.)
I do think Indieweb blog software could
improve on these by letting you type shortcut prefixes for ‘reply’, ‘cc’,
‘mention’, etc. types of person-tagging—and then turning them into just normal
links or post metadata, rather than keeping the prefixes in there. (I think
Facebook does this.)