dn.exact vs dn.base

[Nick Milas <nick@eurobjects.com>]

I was wondering whether there is any difference between dn.exact and 
dn.base constructs.

For example, theoretically (according to the documentation) we can use 
either:

access to dn.base="ou=system,dc=example,dc=com"
   by dn.exact="uid=userx,ou=people,dc=example,dc=com" write

or:

access to dn.exact="ou=system,dc=example,dc=com"
   by dn.base="uid=userx,ou=people,dc=example,dc=com" write

It seems to me that the two forms are interchangeable (as used, e.g. 
here: http://www.openldap.org/faq/data/cache/1140.html)

Can you please clarify?

Thanks,
Nick