[Samba] What does idmap_ldb:use rfc2307 = yes do exactly?

[Brady, Mike]

I see that on the page 
https://wiki.samba.org/index.php/Using_RFC2307_on_a_Samba_DC#Check_if_RFC2307_is_used_by_your_Domain_Controllers 
that

  idmap_ldb:use rfc2307 = yes

is required on all DC when wanting to use RFC2307, but I can not find 
any mention of this parameter in the man pages or any explanation of 
exactly what it does anywhere else.

I am using RFC2307 in my set up and do have this in all my server 
configuratiosn (both DC and member) and I think that everything is 
working, so just wanting understand what this actually does rather than 
having a problem.

Regards

Mike