If quoting a post, quote doesn't count towards msg length?

[N9ne]

That's not what I need.

I need to know how to use some sort of referrer function, to find out where the user is coming from to post the post, and if it's a quote, the quote will already be in the message field, so it should strip the char count of the text that is already there from the total.

Or simpler, just set char count to 0 for the entire post (if that's easier to do, i'm willing so sacrifice).