[exim] only numbers

Hi all

I have a router as such

account_bookings:
debug_print = "R: real_local for $local_part@$domain"
driver = accept
domains = +local_domains
local_parts = bookings
local_part_prefix = *-
check_local_user
transport = LOCAL_DELIVERY

Would there be anyway to have the wildcard to be only numbers.

I dont want foreign characters etc.

If anyone has any advices tips etc, it would be great fully be appreciated.

Kind Regards
Brent Clark