Ability to @mention only those who've taken part in the discussion of a channel

It would be good to be able to only mention people who have taken part in the discussion on a channel. The mention would only work when posted in that channel.

Best-case scenario, admins could choose in their server settings the length of time it's been for this mention to work. Do they want it to work for anyone who's ever posted in the channel, or only for people who have posted there in the last week. Even better best-case scenario, admins could choose how this mention works per channel, and not just one choice for the entire server.

Side note: I came up with this after looking up what @here covered. @here would be the perfect word for this mention. @here should be the word for this, and @online or @active should be the word for people who are currently available.

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