When configuring a route for Enterprise Voice, you want to match long distance numbers but you do not want to match high-risk numbers, such as 900 and 976.
How do you do that in a regular expression?
It looks like this...
This expression is allowing +411 or +1 XXX YYY ZZZZ, but not any number where XXX is 900, or 976, or 242 ... you get the idea.
Incidentally, the XXX set above is a comprehensive list you can use in your dial plans as a best practice.
So the basic syntax for "except" is ?!(). Anything in the brackets will be excluded in the match processing.