Bittorrent MDHT responses

What does the 'v' key value correspond to in Bittorrent Mainline DHT (MDHT) responses?

Here's an example buncoded 开发者_运维技巧response:

{'y': b'r', 
 'r': {'id': b'\x9d\x97\xb5\x8cJ\x8c#\xf4PF\xe3|\xf3\t\xbb#\xdaj\\\xdc'},
 't': b'7/',
 'v': b'UT[\xf9'}

I can't find this key documented anywhere.

Here are my current sources on the protocol:

• BEP 5: DHT Protocol
• Kademlia: A Design Specification

'v' indicates the client name and version (according to this)

UT: uTorrent
LT: libtorrent
MO: Mono Torrent
...etc

A more complete list of client identifiers can be found here