"sub-routine" in procmailrc

This may be naive but I have not found how to - in procmailrc is it =

possible to have a sub-set of rules that can be re-used under certain =

conditions?  I thought of using separate 'rc' files to "go to" from the =

main rc (/etc/procmailrc or ~/.procmailrc); not sure how to implement the =

scheme. E.g. Is "incldue" a right way?  Will appreciated any suggestions.

Thanks,
Zhiliang