"!" in front of a variable?

Hey all, I've got some code from someone else I've inherited and need to sort out some problems with. The programmer that wrote it originally was much better than I and programmed a little over my head to say the least. One function that I've come across that has 5 variables as input: function($var1,$var2,!$var2,$var3->cc,$var3->bcc); The question I have is on the 3rd input variable, what does the "!" in front of $var2 do to that variable? Jeff