[Dovecot] system_groups_user syntax especially in LDAP

so if possible, I'd like an example of how to include system_groups_user in the userdb setup.

I'm using ldap, but I could revert to using pam on ldap. There is a ldap query (gleaned from smbldap-tools) that will return a list of groups for a user

(&(objectclass=posixGroup)(memberuid=%u)) but I don't know if the ldap driver will handle it but above all I can't figure out how it fits into the dovecot configuration!

I'm trying to get Dovecot 2.1.7 on debian wheezy to recognize shared folders that have group ownership.