DFS-R between 2008 R2 and 2012 R2

I found this thread here:

http://social.technet.microsoft.com/Forums/windowsserver/en-US/8b660aa6-1577-4799-93f2-28411eea42da/compatibilityinteroperability-between-windows-server-2012-dfs?forum=winserverfiles

And the answer refers to updating the schema:

Update the Active Directory Domain Services (AD DS) schema to include Windows Server 2012, Windows Server 2008 R2, Windows Server 2008, or Windows Server 2003 R2 schema additions. (If you install a domain controller running Windows Server 2012 the schema is automatically updated.) You cannot use read-only replicated folders with the Windows Server 2003 R2 or older schema additions.

I cannot find a Microsoft document that mentions that.  Will there be problems if the schema is NOT updated?  Is there a Microsoft document that specifies this as a requirement?