Direct host SMB - Ports

It's well known that SMB uses port 445, and that NetBIOS uses ports 137-139. However, according to all official MS documentation (https://support.microsoft.com/en-us/kb/204279), SMB uses both TCP and UDP.

Based on my tests it works even if only TCP is enabled, so what is actually done over port 445 UDP as far as SMB is conceed?

Or, is it that the official documentation refers to and older version of SMB and versions 3+ only use TCP?

Can anyone clarify what exactly 445 UDP is used for?