It works...but why?

[openldap-g@bary1.org]

I'm new to LDAP and have set up OpenLDAP on my home network to hopefully get
some experience I can transfer to
my office environment. After a day of messing about with OpenLDAP I have it
functioning, but after looking at my setup
I really don't understand why it is working. For example, I have
successfully added some entries with ldapadd using the
following ldif format:

dn: cn=Paul Bary, o=Bary-Home, c=US
objectclass: inetOrgPerson
cn: Paul Bary
sn: Bary
title: Administrator
mail: paul@bary.net

I'm confused in that the inetOrgPerson objectclass (I found this designation
in some article I found on the 'net) isn't listed
in the slapd.oc.conf nor is the mail attribute listed in the slapd.at.conf.
My (mis) understanding is that these two files provide
the framework for the various data requirements, so I am at a loss to
understand why this entry is working, and how does slapd
know how to deal with this data

I apologize in advance for this elementary query...I obviously am missing
something very basic...

Paul