[Samba] Samba 3.0 config option "domain controller = xxx"

[Joseph Phillips]

A new option has appeared in the default smb.conf from samba 3.0.0 beta3.  

Here it is:

# Use only if you have an NT server on your network that has been
# configured at install time to be a primary domain controller.
   domain controller = xxx

My question is, what does this do exactly?  The old man pages for samba 2.x
obviously don't include any reference to this new feature.  And on samba.org
website, there are no new man pages for samba 3.0.

So would anyone please care to discuss what this features does?  Thanks.