Why, of course this would be optional, I really thought that went without saying!
Both replies above thus make me wonder if perhaps my intended suggestion is being vastly misunderstood (I thought referencing facebook made it clear enough?), so let me see if I can elaborate:

I've come across threads in where people are referencing me in some way, something I said in my own thread or something, which made me think it might be nice if there was some quick&easy way for the mere usage of the name of another member (like on facebook) would result in an email notice to that member in a "this member mentioned you in a post" kind of way (again this is straight from facebook).
That's where my suggestion came from, although its usage could obviously be more purposeful. So, for another case sample, I could actually point some other member's attention to a specific thread I'm participating in without having to make an additional, specific PM to that person to get that point across. I could thus make a response in that thread where I 'tag' that member's name, which in turn sends him a "this member has tagged you in this post" kind of email notice automatically.
Hope this is clear enough now.

And again, NONE of this would be obligatory!

There's only one thing to do in crisis like this - Sleep on it!
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