FW: pam_passwdqc

Can someone explain the min= n0,N1,N2,N3,N4 parameters of pam_passwdqc?
I set them to be 
pam_passwdqc min=disabled,24,24,8,8 passphrase=0 and expected that to be
interpreted as:
passwords cannot be only 1 class,
passphrases or not to be used,
if 2 classes are used they must be 24 characters,
if 3 classes are used they must be 8 characters
if 4 classes are used they must be 8 characters.

When I test it, it allows me to use a password like "abcdefgh".

How are these Nn parameters used?

Thanks,
David