Introduction and question

[Rebecca Meyer]

Greetings,
New subscriber here. I'm a lecturer in linguistics at San Diego State
University, where I teach an upper division survey course (Linguistics and
English). I'm always searching for new dialect examples/sightings and
resources (website, books, videos, etc.), and this looks like it might be
"the place".

I also have a question. Although it's not strictly dialect question, I'm
really at a loss as to where else to ask it. I did ask in alt.usage.english,
but that ng can be a bit of a freakshow, and I'm not counting on getting any
usable feedback. Here is the question as it appeared in AEU:

I'm de-lurking here to make an inquiry on behalf of a colleague who is
researching grammar/punctuation/spelling flames on Usenet.
In the course of her research, my friend encountered an exchange where
one party (A) was exhorting another poster (B) to "learn how to
punctuate". The sentence under attack was structured exactly like a
tag question, but without the question mark (e.g., "You're a real
moron, aren't you.").  Party B defended his/her punctuation by stating
that the sentence was an "assurance" and not a question.
My friend brought it to my attention and asked me if it was a bona
fide sentence type. Unfortunately, I've never encountered this term
(assurance) before. Is it new? Is it legitimate? I've looked in Fowler
and several other usage texts, but can find no mention of it.
Am I simply an old fuddy-duddy who needs to "get with it"?

Soo...have I missed the inception of a new and exciting sentence type, or is
"assurance" a purely contrived label?

Thanks!

Rebecca Meyer