[exim] Host list files

Hi,

It's been _far_ too long since I've delved into the depths of Exim for
myself, and was wondering how I specify a list of IP addresses and/or
subnets within a file for use with a !hosts ACL. For example do I use:

!hosts = /etc/file
!hosts = lsearch;/etc/file
!hosts = partial-lsearch;/etc/file

Regards,

    Martyn